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Geology of the polymetallic volcanogenic Buttle Lake Camp, with emphasis on the Price Hillside, central… Juras, Stephen Joseph 1987

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GEOLOGY OF THE POLYMETALLIC VOLCANOGENIC BUTTLE LAKE CAMP, WITH EMPHASIS ON THE PRICE HILLSIDE, CENTRAL VANCOUVER ISLAND, BRITISH COLUMBIA, CANADA by STEPHEN JOSEPH JURAS B. Sc. (Honours) University of Manitoba, 1978 M. Sc. University of New Brunswick, 1981 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES Department of Geological Sciences We accept this thesis as conforming to the required standard THE UNVERSITY OF BRITISH COLUMBIA October 1987 © Stephen Joseph Juras, 1987 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia 1956 Main Mall Vancouver) Canada V6T 1Y3 \ Date Q C T H . LIES DE-6(3/81) Frontispiece: Price Hillside (looking northwest or mine west), Buttle Lake Camp, central Vancouver-Island, British Columbia. Road leads to Price adits: Price showing is in gully immediately to the right of the end of the upper road. ii ABSTRACT The Buttle Lake Camp is a major Paleozoic volcanogenic massive sulphide district in which the relationships between massive sulphide mineralization and associated volcanism are best explained if the ore deposits and associated lithologic units formed in a rift basin generated by rifting in an island arc system. This setting accounts for the marked linear distribution of the massive sulphide bodies, and the presence and distribution of volcanic products from four distinct source areas: a volcanic arc region, a back-arc (or intra-arc) rifting region, and two seamount areas. These interpretations were achieved largely through detailed mapping (1: 2400) of the Price Hillside and the relogging of pertinent drill core. Geology of the Buttle Lake Camp consists of newly proposed, four lowermost formations of the Paleozoic Sicker Group in the Buttle Lake uplift (in order of decreasing age): (1) the Price Formation, a thick sequence of basaltic andesite flows and related breccias; (2) the massive sulphide-bearing Myra Formation, consisting of mainly volcanic and volcaniclastic units; (3) theThelwood Formations bedded sequence of siliceous tuffaceous sediments, subaqueous pyroclastic deposits and mafic sills; and (4) the Flower Ridge Formation, largely comprising coarse mafic pyroclastic deposits. Significant units within the Myra Formation are the lowermost, largely felsic H-W Horizon which hosts the large H-W deposit; the Lynx-Myra-Price Horizon, which contains two massive sulphide mineralized felsic volcanic units; the ultramafic G-Flow unit; and the uppermost, basaltic Upper Mafic unit. Zircon U-Pb dating yielded a Late Devonian age of 370 Ma for the Myra Formation. Volcanic units in the Price and Myra Formations are grouped into five volcanic series: two mafic to intermediate volcanic series, two felsic volcanic series, and an ultramafic to mafic volcanic series. These volcanic series are the result of at least three distinct and partly contemporaneous magmatic lineages. Source region for the ultramafic to intermediate parental magmas was an upper mantle peridotite variably enriched in large ion lithophile elements but depleted in high field strength elements (relative to N-type MORB). The felsic volcanic series were generated from two distinct iii sources. One series is from evolved andesitic magma whereas the other is from magma formed by partial melting of lower crustal material.' The Price and Myra Formations represent a general sequence of repeated events comprising: mafic to intermediate arc volcanism; rifting and sulphide mineralization; felsic arc.volcanism; ultramafic to mafic rift volcanism; and volcanogenic sedimentation. The sequence was repeated twice and formed two mineralized horizons (H-W and Lynx-Myra-Price). The Thelwood and Flower Ridge Formations indicate a major change in depositional style and environment from the two underlying units. The Thelwood Formation is a sediment-sill complex underlying mafic volcanic rocks of the Flower Ridge Formation. iv TABLE OF CONTENTS Page Abstract :.• iii List of Tables x List of Figures xiii Foreward xviii Acknowledgements xix CHAPTER 1. INTRODUCTION 1 CHAPTER 2. THE PALEOZOIC SICKER GROUP, BUTTLE LAKE UPLIFT: A REVISED STRATIGRAPHY ....4 2.1 INTRODUCTION .". 4 2.2 REVIEW OF SICKER GROUP STRATIGRAPHIC NOMENCLATURE 4 2.3 REVISED SICKER GROUP STRATIGRAPHY, BUTTLE LAKE UPLIFT 8 2.3.1 Price Formation 10 2.3.2 Myra Formation 11 2.3.3 Thelwood Formation 12 2.3.4 Flower Ridge Formation 12 2.3.5 Buttle Lake Formation 13 2.3.6 Henshaw Formation 13 2.4 CORRELATION WITH THE COWICHAN - HORNE LAKE UPLIFT 14 2.5 CONCLUSIONS 18 CHAPTER Z. GEOLOGY OF BUTTLE LAKE VOLCANOGENIC MASSIVE SULPHIDE CAMP 19 3.1 INTRODUCTION 19 3.2 MINE PROPERTY LITHOLOGY AND STRATIGRAPHY 26 3.2.1 Price Formation (Footwall H-W Andes i te) [DCp] 26 3.2.2 Myra Formation (Mine Sequence) [DCm] 30 3.2.2.1 H-W Horizon [DCm 1] 30 v 3.2.2.2 Hanging Wall H-W Andesite [DCm2] 37 3.2.2.3 Ore Clast Breccia Unit [DCm3] 38 3.2.2.4 Lower Mixed Volcaniclastics [OCm4] 44 3.2.2.5 Upper Dacite [DCm5] / 5E Andesite / North Dacite 48 3.2.2.6 Lynx-Myra-Price Horizon [0Cm6] 54 3.2.2.7 G-FlowUnit[DCm7] 56 3.2.2.8 Upper Mixed Volcaniclastics [DCm8] 58 3.2.2.9 Upper Rhyolite Unit [DCm9] 61 3.2.2.10 Upper Mafic Unit [DCm 10] 65 3.2.2.11 Volcanic Source Regions 67 3.2.3 Thelwood Formation (Sharp Banded Tuff) [DCt] :. ...10 3.2.4 Flower Ridge Formation [DCfr] 79 3.2.5 Intrusive Rocks [Jg.TRb] 85 3.3 STRUCTURAL GEOLOGY 86 • 3.3.1 Introduction 86 3.3.2 Price Hillside Structure 86 3.3.3 Deformational History of the Mine-Area 90 3.3.4 Mine-Area Faults 91 3.3.5 Myra Formation (Mine Sequence) - Thelwood Formation Contact 92 3.4 ALTERATION AND METAMORPHISM 93 3.4.1 Price and Myra Formations 94 3.4.2 Thelwood and Flower Ridge Formations 98 3.5 GEOCHRONOMETRY 99 3.5.1 Introduction 99 3.5.2 Analytical Techniques 99 3.5.3 Results and Discussion 100 3.5.3.1 U-Pb 100 3.5.3.2 Rb-Sr 104 vi 3.5.3.3 K - A r 107 3.5.4 Conclusions 109 CHAPTER 4. GEOCHEMISTRY AND PETROGENESIS 110 4.1 INTRODUCTION 1 10 4.2 ANALYTICAL PROCEDURE 111 4.3 RESULTS 112 4.3.1 Element Mobility 112 4.3.2 Price and Myra Formations 113 4.3.3 Thelwood and Flower Ridge Formations 134 4.4 PETROGENESIS OF THE PRICE AND MYRA FORMATIONS 138 4.4.1 Delineation of Magmatic Lineages 138 4.4.2 Early Arc (EARC)-Price Seamount (PSMT) Lineage 143 4.4.3 Volcanic Arc (VARC) Lineage 144 4.4.4 Back-Arc Rifting (ARFT) Lineage 146 4.5 PETROGENESIS OF THE THELWOOD AND FLOWER RIDGE FORMATIONS 150 4.6 CONCLUSIONS 151 CHAPTER 5. DEPOSITIONAL HISTORY 153 5.1 INTRODUCTION 153 5.2 DEPOSITIONAL HISTORY OF THE PRICE AND MYRA FORMATIONS ,.154 5.2.1 Price-H-W Cycle 155 5.2.2 Inter zone Cycle 166 5.2.3. L-M-P Cycle 168 5.2.4 Upper Cycle 170 5.2.5 Genesis of the Buttle Lake Deposits 171 5.3 DEPOSITIONAL HISTORY OF THE THELWOOD AND FLOWER RIDGE FORMATIONS 173 5.3.1 Thelwood Formation 173 5.3.2 Flower Ridge Formation 175 vii 5.4 CONCLUSIONS 176 CHAPTER 6. SUMMARY AND CONCLUSIONS 178 REFERENCES ; 186 APPENDIX A: SAMPLE LOCATIONS AND DESCRIPTIONS 197 A.1 GUIDE TO SAMPLE LOCATION AND DESCRIPTION TABLES 197 A. 2 DETAILED DESCRIPTIONS OF VOLCANI CLASTIC CLAST TYPES AND PYROCLASTIC DEPOSITS, MYRA FORMATION 204 A.2.1 H-W Horizon, Pyroclastic and Volcaniclastic Member 204 A.2.2 Ore Clast Breccia Unit, Volcaniclastic Breccia Members 204 A.2.3 Lower Mixed Volcaniclastics, Subaqueous Pyroclastic Flow Deposits. 205 A.2.4 Upper Rhyolite Unit, Pyroclastic Deposit Member 205 A.2.5 Upper Mafic Unit, Hydroclastic and Pyroclastic Deposits 208 APPENDIX B: SUBAQUEOUS PYROCLASTIC DEPOSITS 209 B. I INTRODUCTION 209 B.2 NOMENCLATURE AND TERMINOLOGY 210 B.3 'HOT' SUBAQUEOUS PYROCLASTIC FLOW DEPOSITS, BUTTLE LAKE CAMP -FACT OR FICTION 21 1 B. 4 EXAMPLES OF TEXTURAL EVIDENCE FOR WELDED SUBAQUEOUS PYROCLASTIC FLOW DEPOSITS, BUTTLE LAKE CAMP, VANCOUVER ISLAND 216 APPENDIX C. ANALYTICAL PROCEDURES 222 C. I SAMPLE SELECTION AND PREPARATION 222 C.2 X-RAY FLUORESCENCE 223 C.2.1 Pellet Formation 225 C.2.2 Accuracy, Precision and Detection Limil 225 C.3 ATOMIC ABSORPTION PROCEDURE FOR THE DETERMINATION OF RARE EARTH ELEMENTS 235 C.3.1 Introduction 235 viii C.3.2 Methods 238 C.3.3 Results and Discussion 239 C.3.4 Conclusions .-, 243 C.4 DETERMINATION OF WATER AND CARBON DIOXIDE 244 C.S ELECTRON MICROPROBE ANALYSIS 244 APPENDIX D: ANALYTICAL DATA 245 ix LIST OF TABLES Page TABLE 2.1: Stratigraphic sequence at the west fork of Shaw Creek, Vancouver Island In the Cowichan - Home Lake uplift, and proposed correlations with new stratigraphy in both the Cowichan - Home Lake uplift and Buttle Lake uplift 17 TABLE 3.1: Average whole rock chemical compositions for Sicker Group metavolcanic rocks, Buttle Lake Camp, Vancouver Island, B.C 27 TABLE 3.2: Litho-stratigraphic units found in the four volcanic series of the Myra Formation, Buttle Lake Camp, Vancouver Island, B.C 69 TABLE 3.3: Common metamorphic mineral assemblages in Sicker Group rock units, Price Hillside, Buttle Lake Camp, Vancouver Island, B.C 95 TABLE 3.4: U-Pb analytical data on zircon separates from the Buttle Lake Camp, Vancouver Island, B.C 102 TABLE 3.5: Analytical data for Rb, Sr, and 8 7 Sr / 8 6 Sr from metavolcanic rocks in the Myra Formation, Buttle Lake Camp, Vancouver Island, B.C 105 TABLE 3.6: Analytical data for K-Ar dates from whole rock and mineral concentrates from metavolcanic rocks in the Price and Myra Formations, Buttle Lake Camp, Vancouver Island, B.C 108 TABLE 4.1: Summary of litho-stratigraphic units and flow types found in the five volcanic series of the Price and Myra Formations, Buttle Lake Camp, Vancouver Island, B.C : 114 TABLE 4.2: Chemical analyses of Early Arc (EARC) series (Price Formation) volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C 117 TABLE 4.3: Chemical analyses of Volcanic Arc (VARC) series (H-W Horizon units) volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C .119 TABLE 4.4: Chemical analyses of Volcanic Arc (VARC) series (North Dacite) and Lynx-Myra-Price Horizon volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C 120 TABLE 4,5: Chemical analyses of Price Seamount (PSMT) series volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C 123 TABLE 4.6: Chemical analyses of West G Seamount (WSMT) series (H-W Hanging Wall Andesite) volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C 124 TABLE 4.7: Chemical analyses of West G Seamount (WSMT) series (5E Andesite and Upper Dacite, upper member) volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C. . 125 TABLE 4.8: Chemical analyses of Arc Rifting (ARFT) series volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C 128 x TABLE 4.9: Representative electron microprobe analyses of clinopyroxene phenocrysts in Arc Rifting (ARFT) series volcanic rocks, Thelwood Formation mafic sills, and Flower Ridge Formation basalts 131 TABLE 4.10: Representative electron microprobe analyses of chromite microphenocrysts in G-Flow komatiitic basalts 132 TABLE 4.11: Chemical analyses of Thelwood Formation volcanic and magmatic rocks, Buttle Lake Camp, Vancouver Island, B.C 135 TABLE 4.12: Chemical analyses of Flower Ridge Formation volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C 136 TABLE 5.1: Summary of volcanogenic products and emplacement processes in the Buttle Lake Camp basin 156 TABLE 5.2: Litho-stratigraphic units and associated volcanic series present in each of the four volcanic/volcanogenic sedimentation cycles (Price -H-W, Interzone, L-M-P, and Upper cycles) in the Buttle Lake Camp basin 157 TABLE A. 1 •. Sample location and description table for Price Hillside samples ?. 198 TABLE A.2: Sample location and description table for Price section drillcore samples 201 TABLE A.3: Sample location and description table for West G, Lynx, and H-W-Myra sections drillcore samp les 202 TABLE A.4-. Longitude and latitude locations for isotopically analyzed samples described in Tables A. 1 to A.3 203 TABLE B. 1: Granulometric classification of pyroclastic deposits (modified after Schmid, 1981) 211 TABLE B.2: Terms for mixed pyroclastic- epiclastic rocks (after Schmid, 1981) 214 TABLE C. 1: X-ray fluorescence spectrometry machine parameters for major and trace element analyses 224 TABLE C.2: Major element calibration 226 TABLE C.3: Trace element regression analyses i.228 TABLE C.4: Results of sixteen replicate sample analyses 233 TABLE C.5: Results of mixed sample analysis 236 TABLE C.6: Operating conditions for the determination by graphite furnace atomic absorption of Sm, Eu, Dy, Er and Yb using the Perkin Elmer® 603 with an HGA® -2200 graphite furnace 240 TABLE C.7: Determination of Sm, Eu, Dy, Er and Yb in international standard rocks (all values in ppm) 241 xi TABLE D. 1: Duplicate and miscellaneous XRF whole rock chemical analyses, Buttle Lake Camp, Vancouver Island, B.C 246 TABLE D.2: XRF whole rock chemical analyses on mine property samples from XRF data file of Westmin Resources Ltd., Buttle Lake Camp, Vancouver Island, B..C 250 TABLE D.3: Electron microprobe analyses of clinopyroxene phenocrysts from a komatiitic basalt sample (R136-1), G-Flow unit, Myra Formation 257 TABLE D.4: Electron microprobe analyses of clinopyroxene phenocrysts from a komatiitic basalt sample (R136-2), G-Flow unit, Myra Formation 260 TABLE D.5: Electron microprobe analyses of clinopyroxene phenocrysts from a komatiitic basalt sample (PR/124B), mafic flow member, H-W Horizon, Myra Formation. ..263 TABLE D.6: Electron microprobe analyses of clinopyroxene phenocrysts from a basaltic flow clast sample (PR42), Upper Mafic unit, Myra Formation 266 TABLE D.7: Electron microprobe analyses of clinopyroxene phenocrysts from a mafic sill sample (P206), Thelwood Formation 270 TABLE D.8: Electron microprobe analyses of clinopyroxene phenocrysts from a basaltic flow clast sample (P243), Flower Ridge Formation 272 TABLE D.9: Electron microprobe analyses of chromite microphenocrysts from komatiitic basalt samples (R136-1 and Rl 36-2), G-Flow unit, Myra Formation 276 TABLE D. 10: Electron microprobe analyses of amphibole alteration of pyroxene phenocrysts and groundmass phases in volcanic flow units from the Price Formation, Myra Formation, and Flower Ridge Formation, Buttle Lake Camp, Vancouver Island, B.C 278 TABLE D. 11: N-type MORB multi-element and chondrite rare earth element normalization values used in various figures in Chapter 4 279 xii LIST OF FIGURES Page Figure 2.1: Sicker Group uplifts (stippled pattern) in Southern Vancouver Island (after Brandon et al., 1986) 5 Figure 2.2: Stratigraphy of the Sicker Group in the Buttle Lake uplift, central Vancouver Island, B.C 9 Figure 3.1: Geology map of the Price Hillside, Buttle Lake Camp, Vancouver Island, B.C back pocket Figure 3.2: Orientation diagram for geological descriptions, Buttle Lake Camp, Vancouver Island, B.C 20 Figure 3.3: Detailed composite geology along main Price section (183+00 E), Buttle Lake Camp, Vancouver Island, B.C back pocket Figure 3.4: Generalized composite geology along Price section (183+00 E), Buttle Lake Camp, Vancouver Island, B.C :. 21 Figure3.5: Composite geology along H-W-Myra section (124+00 E: after Walker, 1985), Buttle Lake Camp, Vancouver Island, B.C 23 Figure 3.6: Composite geology along Lynx section (60+00 E: after Walker, 1985), Buttle Lake Camp, Vancouver Island, B.C 24 Figure3.7: Composite geology along West G section (5+00 E: after Walker, 1985), Buttle Lake Camp, Vancouver Island, B.C 25 Figure 3.8: Cut drillcore slab examples of typical Price Formation lithologic units 28 Figure 3.9: Photomicrograph showing characteristic apatite and opaque oxide (magnetite?) microphenocryst association, Price Formation. 28 Figure 3.10: Cut drillcore slab examples of typical H-W Horizon quartz + feldspar porphyritic rhyolite 32 Figure 3.11: Photomicrographs of quartz + feldspar porphyritic rhyolite, H-W Horizon 34 Figure 3.12: Peperite within the mafic flow member, H-W Horizon, Price Hillside 36 Figure 3.13: Feldspar porhyritic andesite flow breccia, Hanging Wall H-W Andesite, Price Hillside 39 Figure 3.14: Volcaniclastic breccia member deposits, Ore Clast Breccia unit, Price Hillside: rhyolite-rich member (top) and rhyolite-poor member (bottom) 41 Figure 3.15: Rusty weathered, pyrite mineralized quartz crystal rhyolite coarse tuff 'raft', Ore Clast Breccia unit, Price Hillside .42 xiii Figure 3.16: Andesite dominant volcaniclastic breccia deposit, Lower Mixed Volcaniclastics, Price Hillside 45 Figure 3.17: Examples of different types of pale volcanic flow clasts, Lower Mixed . Volcaniclastics - Ore Clast Breccia contact area, Price Hillside:- 47 Figure 3.18: Felsic pseudo-pillow and hyaloclastite, Upper Dacite lower member, Price Hillside 49 Figure 3.19: Graded and well bedded, feldspar crystal-vitric felsic coarse to fine tuff, Upper Dacite lower member, Price Hillside 51 Figure 3.20: Photomicrographs of spherulitic felsic vitric clast, Upper Dacite lower member. ....52 Figure 3.21: Felsic flow clasts in a dark green, strongly feldspar porphyritic mafic to intermediate volcanic flow, Upper Dacite upper member, Price Hillside 53 Figure 3.22: Amygdaloidal komatiitic basalt flow with jasper filling probable pillow interstices, G-Flow unit, Price Hillside 57 Figure 3.23: Photomicrograph of an interstitial jasper sample (from a komatiitic basalt flow) showing characteristic spherulitic texture, G-Flow unit, Price Hillside 57 Figure 3.24: Mafic lapilli—tuff, Upper Mixed Volcaniclastics, Price Hillside 60 Figure 3.25: Cut slab samples of main rock types in the pyroclastic member, Upper Rhyolite unit. Price Hillside 62 Figure 3.26: Well bedded, normally graded, quartz + feldspar crystal-lithlc-vitric rhyolite coarse tuff and lapilli—tuff, Upper Rhyolite unit, Price Hillside 64 Figure 3.27: Pyroxene + feldspar porphyritic basaltic coarse lapilli-tuff, hydroclastic and pyroclastic deposit, Upper Mafic unit, Price Hillside 66 Figure 3.28: Strongly hematite and carbonate altered ultramafic hyaloclastite, Upper Mafic unit, Price Hillside 68 Figure 3.29: Tuffaceous sediment unit, Thelwood Formation, Price Hillside 71 Figure 3.30: Measured stratigraphic section of a tuffaceous sediment unit, Thelwood Formation, Buttle Lake Camp, Vancouver Island, B.C 72 Figure 3.31: Normally graded, very thinly laminated, vitric-crystal fine tuff, tuffaceous sediment unit, Thelwood Formation, Price Hillside 73 Figure 3.32: Pyroclastic deposit unit, Thelwood Formation, Price Hillside 75 Figure 3.33: Measured stratigraphic section of a pyroclastic deposit unit, Thelwood Formation, Buttle Lake Camp, Vancouver Island, B.C 76 Figure 3.34: Photomicrographs showing vitric constituents in a pyroclastic deposit unit, Thelwood Formation, Price Hillside 77 xiv Figure 3.35: Mafic sill, Thelwood Formation, Price Hillside 78 Figure 3.36: Mafic sill - tuffaceous sediment contact, Thelwood Formation, Price Hillside 80 Figure 3.37: Strongly amygdaloidal basaltic tuff-breccia, Flower Ridge Formation, Price Hillside 81 Figure 3.38: Photomicrographs of matrix components, basaltic pyroclastlc (agglutinate) deposits, Flower Ridge Formation 84 Figure 3.39: Location of stuctural subareas within the Myra Formation, Price Hillside, Buttle Lake Camp, Vancouver Island, B.C 88 Figure 3.40: Detailed structural data for the Price Hillside, Buttle Lake Camp, Vancouver Island, B.C back pocket Figure 3.41: Equal-area stereonet diagrams for Price Hillside structural data 89 Figure 3.42: Geological cross sections at a) 170+00 E, b) 173+00 E, c) 178+00 E and d) 180+00 E, Price Hillside, Buttle Lake Camp, Vancouver Island, B.C. 7...back pocket Figure 3.43: U-Pb concordia diagram for zircons form Upper Rhyolite sample, Myra Formation, Buttle Lake Camp, Vancouver Island, B.C 103 Figure 3.44: Rb—Sr errorchron diagram for units from the Myra Formation, Buttle Lake Camp, Vancouver Island, B.C : 106 Figure 3.45: Rb—Sr isochron diagram for lower Myra Formation units, Buttle Lake Camp, Vancouver Island, B.C 106 Figure 4.1: N-type MORB normalized multi-element patterns for mafic volcanic rocks from modern island arc systems: a) Mariana system, and b) Hokuroko district, Japan, and New Britain system, Papua New Guinea ...116 Figure 4.2: Normalized trace element patterns for EARC-PSMT series units; a) chondrite normalized REE patterns, b) N-type MORB normalized multi-element patterns. ..118 Figure 4.3: Chondrite normalized REE patterns for VARC series units 122 Figure 4.4: Normalized trace element patterns for WSMT series units; a) chondrite normalized REE patterns, b) N-type MORB normalized multi-element patterns. .127 Figure 4.5: Normalized trace element patterns for ARFT series units; a) chondrite normalized REE patterns, b) N-type MORB normalized multi-element patterns. .. 130 Figure4.6: Mg/(Mg+Fe2+) vs. Cr/(Cr+Al) diagram for ARFT komatiitic basalt chromite microphenocrysts. 133 Figure 4.7: Normalized trace element patterns for Thelwood and Flower Ridge Formation units; a) chondrite normalized REE patterns, b) N-type MORB normalized multi-element patterns 137 xv Figure 4.8: Ti/Zr vs. Y/Zr Pearce element-ratio diagram comparing PSMT and VARC series samples with each other, and with EARC series samples 139 Figure 4.9: Yb/Zr vs. Y/Zr Pearce element-ratio diagram comparing EARC series samples to PSMT and VARC series samples 141 Figure 4.10: Cep, vs. (Ce/Sm)n trace element process identification diagram for EARC-PSMT series and VARC series units 141 Figure 4.11: Yb/Zr vs. Y/Zr Pearce element-ratio diagram comparing WSMT series samples to EARC series samples 142 Figure 4.12: Ti/Zr vs. Y/Zr Pearce element-ratio diagram comparing WSMT series samples to PSMT and VARC series samples 142 Figure 4.13: Zr vs. Ti covariation diagram for EARC—PSMT series samples 145 Figure 4.14: Zr vs. Ti covariation diagram for VARC series samples (H-W Horizon only). 147 Figure 4.15: Zr vs. Ti covariation diagram for ARFT series samples 149 Figure 5.1: Generalized geologic cross section reconstructions (to predeformation state) of the a) Price section and b) West G section, Buttle Lake Camp, Vancouver Island 158 Figure 5.2: Idealized longitudinal section reconstruction to predeformation state of the Myra Formation (Mine Sequence), Buttle Lake Camp, Vancouver Island, showing the Buttle Lake massive sulphide deposits 160 Figure 5.3: Evolution of the Buttle Lake rift basin (BBSIM): a) the Price-H-W Cycle, b) the Inter zone and L-M-P Cycles, and c) the Upper Cycle 161 Figure 5.4: Schematic representations of the oppositional setting for the Thelwood and Flower Ridge Formations 174 Figure A. 1: Locations of samples examined and analyzed in detail, Price Hillside, Buttle Lake Camp, Vancouver Island, B.C back pocket Figure A.2: Feldspar ± pyroxene porphyritic andesite flow clast dominant sample, rhyolite-poor volcaniclastic breccia member, Ore Clast Breccia unit, Price Hillside 206 Figure A.3: Feldspar porphyritic andesite cognate lithic clast dominant sample, rhyolite-poor volcaniclastic breccia member, Ore Clast Breccia unit, Price Hillside 206 Figure A.4: Mafic volcanic clast dominant sample, rhyolite-rich volcaniclastic breccia member, Ore Clast Breccia unit, Price Hillside 207 Figure B. 1: Mixture terms and end-member rock terms for pyroclastic fragments (after Fisher, 1966) •. , 213 Figure B.2: Welded, quartz + feldspar crystal rhyolite subaqueous pyroclastic flow deposit, . H-W Horizon, Myra Formation, Price section 217 xvi Figure B.3: Photomicrograph of welded sample in Figure B.2 217 Figure B.4: Photomicrograph of a welded feldspar crystal subaqueous pyroclastic flow deposit, Lower Mixed Volcaniclastics, Myra Formation, Price section 218 Figure B.5: Tuffaceous mudstone rip-up clasts in (a) an unwelded subaqueous pyroclastic flow deposit, and (b) a welded subaqueous pyroclastic flow deposit, pyroclastic deposit unit, Thelwood Formation, Price Hillside 219 Figure B.6: Welded subaqueous pyroclastic flow deposit, pyroclastic deposit unit, Thelwood Formation, Price Hillside 220 Figure B.7: Photomicrographs of welded sample in Figure B.6 221 Figure C. 1: Chondrite normalized REE patterns for a Quaternary-aged alkali olivine basalt from Well's Gray Park, B.C., and a Devonian-aged meta-andesite from central Vancouver Island, B.C 242 Figure D. 1: AFM diagrams for: a) EARC-PSMT volcanic series, b) WSMT volcanic series, c) ARFT volcanic series, and d) mafic volcanic units in the Thelwood and Flower Ridge Formations, Buttle Lake Camp, Vancouver Island, B.C _ 254 Figure D.2: Tholeiitic versus calc-alkaline determination based on the SiOo. vs. FeO*/MgO diagram after Miyashiro (1974) for all mafic and intermediate volcanic units in the Buttle Lake Camp; a) Price and Myra Formations, b)The1woodand Flower Ridge Formations 255 Figure D.3: MnO/TiC /^^ Os minor element discriminant diagrams (after Mullen, 1983) for mafic (basaltic and basaltic andesite compositions) volcanic units in the Buttle Lake Camp: a) EARC series, b) WSMT series, c) ARFT series, and Thelwood and Flower Ridge Formations 256 Figure D.4: Pyroxene quadrilateral diagrams for compositions of clinopyroxene phenocrysts from G-Flow komatiitic basalts - (b) and (d), H-W Horizon ultramafic flow unit (c), Upper Mafic basalt (a), Thelwood Formation mafic sill (e), and Flower Ridge Formation basalt (f), Buttle Lake Camp, Vancouver Island, B.C 273 xvii FQREWARD Major and trace element chemical analyses on samples from the Buttle Lake Camp were carried out in conjunction with similar work by C J. Hickson on the Quaternary basaltic rocks of the Wells Gray - Clearwater area in east-central British Columbia. A joint investigation of sample contamination stemmed from this analytical work and has been published in Canadian Mineralogist (Hickson and Juras, 1986). A second joint study was undertaken into the analysis of rare earth elements by graphite furnace atomic absorption techniques, and is being published in Chemical Geology (Juras, Hickson, Horsky, Godwin and Mathews, 1987). Funding for this work came jointly from C. I. Godwin (Energy, Mines and Resources Research Agreement) and W. H. Mathews (NSERC grant A1107). A modification of this paper appears as part of Appendix C. xviii ACKNOWLEDGEMENTS Fieldwork for this project was carried out during the summers of 1983,1984 and 1985 while the author was temporarily employed by Westmin Resources Ltd. Their support for this study is gratefully appreciated. I would particularly like to thank R. R. Walker, G. MacVeigh and B. Jeffery for their cooperation and assistance. Their enthusiasm for the geology in the Buttle Lake Camp helped immeasurably in the development of many of the interpretations presented in this study. 1 would like to gratefully acknowledge my thesis supervisor, Dr. Colin 1. Godwin, who, after summing up the thesis problem in one rather short sentence, forgot to tell me that it would take over 4 years to answer it. His patient corrections of numerous drafts of this manuscript and many suggestions for its improvement are deeply appreciated. I would also like to thank Dr. Kelly Russell for his willingness to listen and discuss some of my more 'radical' volcanological observations, even though they occur in so-called 'green' rocks. His critical reviews of parts of this manuscript and suggestions for their improvement are very much appreciated. Critical reviews and suggestions by Dr. R. L. Armstrong are also much appreciated. I would like to acknowledge the help of a number of people, whose assistance and discussions during many facets of this project were very beneficial: P. van der Heyden and J. K. Mortensen for their patience and guidance during the trials and tribulations of zircon U-Pb geochronometry, S. Horsky for enlightening me in the powers of XRF and graphite furnace AA analysts, J. Knight who not only helped with the operation of the SEM but allowed me to earn my microprobe veterans license, and C. J. Hickson for her eagerness to jointly plunge into the wonderful worlds of column chemistry, contamination, and error analysis. M. Mills (1985) and P. Fischl (1984) provided capable and amiable assistance in the field. Finally, I would especially like to thank my lovely wife, Mary Ann, for her infinite reservoir of patience and support throughout the course of this project. xix CHAPTER 1  INTRODUCTION The Buttle Lake Camp, a volcanogenic massive sulphide district with Paleozoic host rocks and ore, is 85 km southwest of Campbell River at the south end of Buttle Lake within Strathcona Provincial Park, central Vancouver Island, British Columbia (Fig. 2.1). The ore deposits are currently being mined by Westmin Resources Ltd. through the operation of two underground mines, the H-W and Lynx. Proven and indicated ore reserves as of January 1,1987 (Westmin Resources Ltd., Annual Report 1986) were 374,900 tonnes at 2.67 gAu/t, 77.5 gAg/t, 1.088 Cu, 0.908 Pb, and 7.778 Zn for the Lynx Mine, and 13,294,000 tonnes at 2.39 gAo/t, 37.4 g Ag/t, 2.418 Cu, 0.328 Pb, and 5.448 Zn for the H-W Mine. Production to the end of 1986 comprised 6,933,563 tonnes (approximately 85 percent of which was Lynx and Myra ore) at 2.13 gAu/t, 97.5 gAg/t 1.648 Cu, 1.328 Pb, and 7.188 Zn. These numbers Indicate that the Buttle Lake Camp already represents a world class volcanogenic district. The H-W deposit is within the upper decile (in both tonnage and grade) of similar volcanogenic massive sulphide deposits in Canada (Boldy, 1977; Sangster, 1977) and Australia (Large etal, 1987) whereas the Lynx-Myra-Price deposits fall well within the general size and grade range of the same volcanogenic deposits. The first claims in the Buttle Lake Camp region were staked in 1917 when Strathcona Park was opened for prospecting. Three showings were staked: the Lynx, Price and Paw (Myra) claims. Sporadic work continued on the ground until 1925. The property then remained dormant until 1946 when renewed interest brought about various examinations by individuals and companies. In 1959 the claims were acquired by the Reynolds Syndicate who in turn negotiated an option-purchase agreement with Western Mines in 1961. Western Mines concentrated their exploration in the Lynx claim group which had the best showings within the camp. By mid-1964, after potential ore zones consisting of 1.5 million tonnes were defined on five levels, a decision was made to begin production. Production, largely open pit, began in early 1967. From 1969 to the end of 1974 the Lynx open pit was gradually phased out in favour of underground ore. The total tonnage produced from the Lynx open 2 pit was 1.6 million tonnes. The Myra deposit (formerly the Paw group) was evaluated in 1970 and put into production as a separate mine by 1972. Mining at the Myra Mine terminated in late 1985 due to depletion of reserves. The Price showings received serious attention during the period from 1979 to 1981, which resulted in the discovery of the Upper Price zone. Reserves of 209,457 tonnes at 1.23 gAu/t, 53.1 gAg/t, 1.108 Cu, 1.078 Pb, and 8.318 Zn were blocked out but a production decision for this deposit has been put on hold indefinitely. The large H-W deposit was discovered in late 1979 with the decision to mine it being made shortly after in early 1980. The H-W Mine officially come on stream in September of 1985. Also during this time period (in 1981), Western Mines changed their corporate name to Westmin Resources Ltd. Published accounts of the geology of the Buttle Lake Camp are limited and consist of government reports (Gunning, 1931; Jeffery, 1965, 1970; Muller and Carson, 1969; Muller, 1980), a paper by Seraphim (1980) with an associated discussion by Walker (1980), and field trip guides by Walker (1983, 1985). The geology of the camp was also the focus of a Ph.D. thesis by Carvalho (1979). The government reports focussed on the mineralization and immediate host rocks of Lynx, Myra and Price ore zones, and only generally discussed the 1 ithologies within the hosting stratigraphic zone (called the Mine Sequence). The contributions by Seraphim and Carvalho discuss the Mine Sequence lithologies in somewhat more detail but lack information on the middle to lower parts of the Mine Sequence (i.e. the H-W ore zone); consequently the usefulness of their structural interpretations and proposed facies descriptions is limited. The field trip guides by Walker present the first recognition of correctable litho-stratigraphic zones throughout the Buttle Lake Camp. They also include documentation of the effects of Mesozoic and later deformation on units of the Mine Sequence. The Buttle Lake Camp affords a good opportunity to establish a volcanological regime in which massive sulphide deposits formed. In order to investigate this, a more detailed and unifying Mine Sequence stratigraphy had to be determined. Work in this study concentrated on the Price Hillside (Fig. 3.2) because it has the only exposure of a complete section of the Mine Sequence in the Buttle Lake Camp. This section, excellently exposed in the steep facing hill slope of the Price Hillside, 3 approximates a cross-sectional view of the structure and stratigraphy in the Camp. Fieldwork consisted of detailed mapping (at a scale of 1: 2400: Fig. 3.1) and relogging of surface and underground diamond drill core (more than 35,000 feet). Data from the Price region were augmented by detailed geologic sections (from underground drilling) through the H-W, Lynx, and West 6 ore zones. The field data were supplemented by over 110 chemical analyses of the main volcanic flow types found in the Buttle Lake Camp. In addition to establishing a volcanological regime for the Mine Sequence (Chapter 3), other objectives were also real ized. These include: 1. A chance to propose revisions to the Paleozoic Sicker Group stratigraphy in the Buttle Lake uplift (Chapter 2); 2. The determination of volcanic and magmatic events associated with intra-arc or back-arc rifting in an ancient island arc system (Chapter 4); 3. An opportunity to document volcanogenic sedimentation and sulphide mineralization in a rift basin setting within an island arc system (Chapter 5); and 4. The examination of subaqueous volcaniclastic deposits (especially subaqueous pyroclastic deposits), and their generation and emplacement processes (Chapters 3 and 5, Appendix B). 4 CHAPTER 2 THE PALEOZOIC SICKER GROUP. BUTTLE LAKE UPLIFT: A REVISED STRATIGRAPHY 2.1 INTRODUCTION The Sicker Group, composed of all stratified Paleozoic rocks and oogenetic intrusions on Vancouver Island (Fy les, 1955; Yole, 1969; Muller, 1980), represents the oldest rocks of Wrangellia (Insular Belt of Muller, 1977a),which is an allocthonous terrane that underlies most of Vancouver Island (Jones etal, 1977). The Sicker Group is exposed in structural culminations (Fig. 2.1). The most important to this study are the Buttle Lake uplift and the Cowichan - Home Lake uplift. A major problem in understanding theiSicker Group geology has been the difficulty in establishing a consistent formal stratigraphy for correlation within and among these uplifts. This is due in part to the paucity of detailed studies in the various uplifts, the structurally complex nature of the rocks, and the presence of rapid facies variations within many of the lithologic units in the Sicker Group. Revision of Sicker Group stratigraphy at Buttle Lake proposed here expands on earlier recommendations by Yole (1969), Jeffery (1970) and Muller (1980). Nomenclature for upper formations are left intact whereas the controversial lower divisions are redefined. This new description of the stratigraphy results from a detailed study of the geology of lower Sicker Group rock units located in the Buttle Lake Camp (i.e. around Westmin Resources Ltd.'s Myra Falls mine site) at the south end of Buttle Lake (Fig. 2.1). 2.2 REVIEW OF SICKER GROUP STRATIGRAPHIC NOMENCLATURE Sicker Group, first called the Sicker Series (Clapp, 1912), was defined as the deformed metavolcanic and metasedimentary rocks in the vicinity of Mount Sicker on southern Vancouver Island. However, its stratigraphic position (thus age) was incorrectly stated as overlying the Triassic Vancouver Group. The correct relationship between the two groups was indirectly recognized by 5 Figure 2.1: Sicker Group uplifts (stippled pattern) in Southern Vancouver Island (after Brandon et al, 1986; cf. duller, 1977b). Uplift symbols are: A = Buttle Lake, B = Cowichan — Home Lake, C = Nanoose. D and E are not named. Location of the Buttle Lake Camp within the Buttle Lake uplift is also shown. 6 Gunning (1931) in his reconnaissance stuay of the Buttle Lake area. He was the first to report Upper Paleozoic fossils from limestone horizons [hat were overlain conformably by the Vancouver Group. He declined to formally name the older strata suggesting only that the name Buttle Lake Group or Formation for all or part of the sequence be used. Fyles (1955), working in the Cowichan Lake area, proposed that the Sicker Series be renamed Sicker Group, and include rocks that are lithologically similar to or associated with the lithologies described by Clapp (1912), and Clapp and Cooke (1917) in the Duncan area. Fyles also suggested that the name Sicker Group be applied to similar regions elsewhere on Vancouver Island. Although he did not formally divide the group, Fyles recognized a.marker horizon (informally named the 'chert unit') composed of approximately 200 m of thinly bedded cherty tuff, chert and tuffaceous greywacke. This horizon is underlain by massive green volcanic breccia and minor flows, and overlain by interbedded sequences of tuffaceous sediments, argillaceous and feldspathic tuffs, volcanic breccia, and amygdaloidal basaltic flows and flow breccias. Fyles also established that the limestone sequence was the uppermost formation of the Sicker Group and that its top marked the base of the Vancouver Group. The first formal stratigraphy for the Sicker Group was proposed by Yole (1965, 1969). He divided it into two formal and one informal units: (1) the Youbou Formation that comprises all stratified rocks beneath the Buttle Lake Formation (below), and that is dominated by volcanic and volcaniclastic rocks with subordinate, largely non-calcareous sedimentary rocks (type section for this unit is the sequence measured by Fyles (1955) at the west fork of Shaw Creek in the Cowichan Lake area); (2) the Buttle Lake Formation, consisting mainly of crinoidal limestone and lesser clastic rocks and chert (type section is at Azure Lake, south of Mount McBride in the Buttle Lake area); and (3) an uppermost, unnamed formation consisting of thin bedded clastic rocks. Detailed examination of the Sicker Group - Vancouver Group contact by Jeffery (1970) lead to definition of the Henshaw Formation. This unit unconformably overlies the Buttle Lake Formation and is composed of conglomerate, clastic sediments, reworked volcanics, and pyroclastic deposits. The 7 Henshaw Formation is overlain by the Karmutsen Formation of the Vancouver Group. The type area for the Henshaw Formation is near the mouth "of Henshaw Creek on the east side of the south end of Buttle Lake. Muller (1980) replaced the Youbou Formation with three new divisions based on a mapping program which involved all Paleozoic stratigraphy on Vancouver Island (Muller and Carson, 1969; Muller etal, 1974; Muller, 1980). The divisions, in order of decreasing 8ge, are the: (1) Nitinat Formation composed of conspicuously pyroxene-phyric mafic flows and assrciated breccias and minor tuff (type areas are exposed in the valleys of the upper branches of the Nitinat River in the Cowichan - Home Lake uplift); (2) Myra Formation consisting of basic to rhyodacitic banded tuff, breccia and flows, and bedded to massive argillite, siltstone and chert (type area is the Myra Creek area within Westmin Resources Ltd.'s Myra Falls mine site in the Buttle Lake uplift); and (3) Sediment-Sill unit (informal name) composed of bedded to massive argillite, siltstone and chert with interlayered diabase sills. The first phase of the LITHOPROBE project on southern Vancouver Island (Sutherland Brown andYorath, 1985; Yorath etal., 1985) determined that the subdivisions proposed by Muller were of limited use due to poor correlation of the relative position and continuity of units in the Cowichan -Home Lake and Nanoose uplifts. Consequently, local informal units were established pending more detailed mapping, and new paleontological and isotopic data. Most recently Brandon etal. (1986) in their study summarizing fossil and isotopic data for the Sicker Group suggest that the divisions proposed by Yole (1969) should be retained, but that those proposed by Muller (1980) should be considered informal units within the Youbou Formation. Results of recently completed geological mapping in the Cowichan - Home Lake uplift by the Geological Survey of Canada in support of the LITHOPROBE 1 Project (Sutherland Brown etal, 1986; Sutherland Brown, in preparation) have established a formal stratigraphy within this uplift. The Sicker Group is divided into two subgroups, the Youbou Subgroup and the Buttle Lake Subgroup, this subdivision is proposed for all Sicker Group units on Vancouver Island. The establishment of 8 formations within each uplift, however, is to be done separately (at least until more detailed studies are completed). In the Cowichan - Home lake uplift, the Youbou Subgroup comprises two formations: (1) Nitinat Formation, comprising pyroxene-phyric mafic volcanic agglomerate, tuff-breccias and tuffs with lesser pillowed or massive flows, and intercalated volcanic sediments; and (2) McLauglin Ridge Formation, consisting of an epiclastic facies of dominantly massive to bedded volcanic sandstone with lesser pebbly sandstone, volcanic conglomerate, siltstone, and chert, and an effusive facies composed of mafic to intermediate volcanic, pillowed to massive flows. The Buttle Lake Subgroup consists of the: CO Cameron River Formation, a highly variable, thinly bedded unit consisting of siliceous argillite and shale, black chert, grey bioclastic limestone, green volcanic sandstone, red and green ribbon chert, and chert breccia or conglomerate in a volcanic sandstone matrix; (2) Mt. Mark Formation (previously the Buttle Lake Formation), composed of mainly thick bioclastic limestone; and (3) St. Mary's Lake Formation, composed of thinly bedded sandstone and shale. 2.3 REVISED SICKER GROUP STRATIGRAPHY. BUTTLE LAKE UPLIFT The following formal division of the Sicker Group in the Buttle Lake uplift is proposed. Formations, in order of decreasing age, are (thicknesses and age relationships are in Fig. 2.2): (1) Price Formation (new name): feldspar ± pyroxene porphyritic andesite flows and flow breccias (both variably pillowed), and lesser volcaniclastic deposits; (2) Myra Formation: basaltic to rhyolitic flows and volcaniclastic rocks, lesser epiclastic sediments, argillites and cherts, and massive sulphide mineralization; (3) Thelwood Formation (new name): siliceous tuffaceous sediments, subaqueous volcaniclastic debris flows and pyroclastic deposits, and intercalated mafic sills; (4) Flower Ridge Formation (new name): moderately to strongly amygdaloidal basaltic . lapilli tuff and volcanic breccia, tuffaceous siltstone and wacke, minor basaltic flows and tuffs, and minor tuffaceous mudstone and argillaceous sediments; 9 Ear lif H » m h * * P r r m u n ( ' ) F o r m a t i o n Early P t r m u n B u t t l e Lake to F o r m a t i o n P e n n s u l v a n i a n Pennsylvania!! Flower or Ridge Mississippian Formation Early Thelwood Mississippian Formation (?) Late Devonian M y r a Formation Late Devonian or older Pr ice Formation iiiiiiiiuniiiiiiiimn - - O O O O O O O O O < o O O O o.o 5 -IOO 300 m 6 5 0 * m 270 -500 m 310 -440 m 300 • m C o n g l o m e r a t e . e p i c l a s t i c d e p o s i t s . v i t r i e t u f f N C r i n o i d a l l i m e s t o n e , m i n o r c h e r t Moderately to strongly amygdaloidal mafic l ap i l l i - tu f f , t u f f - b r e c c i a , minor tuff and f lows Subaqueous pyroc last ic deposi ts , si l iceous tuffaceous sediments, mafic s i l l s (A) Intermediate^-) to felsic(«.) volcanics, v o l c a n i c l a s t i c s ( ° ) , minor sediments, massive sulphide mineral izat ion^*) Feldspar-pyroxene porphyr i t ic andesite f lows, flow brecc ias , minor pyroclast ic deposits Figure 2.2: Stratigraphy of the Sicker Group in the Buttle Lake uplift, central Vancouver Island, B.C. 10 (5) Buttle Lake Formation: partly silicified crinoidal limestone, and lesser chert and argillite; and (6) Henshaw Formation: conglomerate with volcanic and limestone boulders, pyroclastic tuff and breccias, and epiclastic sediments. 2.3.1 PRICE FORMATION The Price Formation represents the basal unit of the Sicker Group in the Buttle Lake uplift. This unit occurs in outcrop in a small area southwest of the mouth of Thelwood Creek, and north of the confluence of Price and Thelwood creeks. It also has been intersected in drillcore at the Myra Falls mine site. Rocks of the Price Formation consist of feldspar ± pyroxene porphyritic basaltic andesite flows, flow breccias and coarse volcaniclastic deposits. Rocks from this unit are usually moderately to strongly altered to chlorite + epidote + albitic plagioclase ± actinolite assemblages. A conspicuous feature of this formation is the presence of medium to very coarse grained, black to dark green pyroxene phenocrysts invariably pseudomorphed by actinolite. The presence of pyroxene grains alone, however, is not diagnostic of the Price Formation because pyroxene phenocrysts and crystals also occur in units within overlying formations (see below). The top of the Price Formation is defined as the lower contact of the first, widespread appearance of rhyolitic volcanic rocks (either flows or tuffs, the latter commonly interbedded with argillite), which also marks the start of the Myra Formation. The thickness of the Price Formation can only be given as >300 m as the base of this unit is not exposed in the Buttle Lake area. The age of the Price Formation is not known except that it is Late Devonian or older because it lies below the isotopically dated Late Devonian Myra Formation (Chapter 3). The Price Formation possibly represents an early phase of island arc volcanism in a marginal basin or volcanic arc setting (Chapters 4 and 5). 2.3.2 MYRA FORMATION The Myra Formation, originally proposed by Muller (1980), has been redefined here as a volcanic and volcaniclastic unit consisting of basaltic to rhyolitic volcanic rocks and lesser sedimentary units. The volcanic rocks, predominantly intermediate in composition, consist of flows and flow breccias, and subaqueous pyroclastic deposits (emplaced by sediment gravity flow processes; Chapter 3). Sedimentary units include heterolithic volcaniclastic breccias and lesser sandstones to siltstones, argillites, cherts and sulphide mineralization. The Myra Formation, exposed mainly at the southwest end of Buttle Lake (where it overlies the Price Formation and is overlain by the Thelwood Formation), varies in thickness from 310 to 440 m. Its age is Late Devonian as determined by zircon U-Pb dating (Chapter 3). A complete section of the Myra Formation is exposed approximately 1 km northeast of Mt. Myra at the southwest end of Buttle Lake and is designated as the type section for this formation (Fig. 3.1). The Myra Formation represents a phase of island arc rifting and basin development as reflected by three general geologic settings (Chapter 5): a volcanic arc setting consisting of andesitic to rhyolitic flows and pyroclastic deposits; a rift basin setting comprising volcanogenic sediments (pyroclastic and epiclastic), pelagic deposits, hydrothermal mineralization, and intermediate volcanic flows; and an intra-arc or back-arc rift setting consisting of mafic flows and volcaniclastic deposits. Some characteristics of the Myra Formation are similar to those of the Price Formation. Specifically the uppermost unit (5 to >200 m thick) of the Myra Formation consists of pyroxene + feldspar porphyritic basaltic flow breccia and hydroclastic tuff deposits, and clasts and local lenses of jasper and chert. This unit is similar to feldspar + pyroxene porphyritic basaltic andesite flows in the Price Formation. However the Myra Formation unit can be distinguished by the presence of relict pyroxenes (with chlorite » actinolite alteration), presence of jasper and chert clasts and lenses, its stratigraphic position overlying rhyolitic members of the Myra Formation, and its more mafic whole rock composition (Chapter 3). 12 2.3.3 THELWOOD FORMATION The Myra Formation in the Buttle Lake uplift is overlain, in places unconformably, by a bedded unit consisting of fine-grained siliceous tuffaceous sediments, subaqueous pyroclastic and volcaniclastic debris flows, and penecontemporaneous mafic sills (Guaymas basin-type: Einsele, 1985; see section 3.2.3). The name Thelwood Formation is proposed for this unit and is taken from the site where excellent exposures of these rocks occur on the west side of the mouth of Thelwood Creek at the southwest end of Buttle Lake. The Thelwood Formation varies in thickness from 270 to 500 m. No age determinations have been made of this unit in the Buttle Lake uplift, but microfossil ages from possibly equivalent rock types in the Cowichan - Home Lake uplift indicate an Early Mississippian age(Muller, 1980; Brandon etal, 1986). The Thelwood Formation represents a sediment-sill complex in an island arc environment (Chapter 5). 2.3.4 FLOWER RIDGE FORMATION The unit lying above the Thelwood Formation in the Buttle Lake uplift is named, here, the Flower Ridge Formation. This is a redefinition from the Youbou Formation in the original proposal by Yole (1969), which was to represent all stratified rocks below the Buttle Lake Formation. The name for this formation is taken from good exposures of the unit on the west side of Flower Ridge, located immediately southeast of the south end of Buttle Lake. The Flower Ridge Formation consists of moderately to strongly amygdaloidal, feldspar ± pyroxene porphyritic basaltic lapilli-tuff and pyroclastic breccia, tuffaceous siltstone and wacke, and minor flows, tuffs and bedded tuffaceous mudstone and argillaceous sediments. A diagnostic feature of this unit is the markedly amygdaloidal nature of the volcanic clasts, both in the pyrxlastic horizons and in the tuffaceous sediments. Also, unlike the lower Myra and Price Formations, no penetrative fabric was observed. Pyroxene crystals, when present, are only weakly to moderately altered to actinolite or chlorite. A complete section was not measured in the Buttle Lake uplift but a minimum thickness of 650 m was determined at the Myra Falls mine site. The underlying contact with the Thelwood Formation is conformable and is characterized by the first appearance of abundant scoriaceous volcanic clasts in either tuffs or epiclastic deposits. The age of this formation is not known at Buttle Lake except that it is bracketed by the Late Devonian Myra Formation and the Pennsylvanian Buttle Lake Formation. The Flower Ridge Formation marks the resumption of voluminous shallow marine mafic volcanism in the area. 2.3.5 BUTTLE LAKE FORMATION The striking, cliff-forming limestone horizon in the Buttle Lake uplift was designated as the Buttle Lake Formation by Yole (1969). The Buttle Lake Formation is exposed throughout the Buttle Lake uplift with the most extensive exposures being around the headwaters of Marblerock Creek (the location of the type section described by Yole at Azure Lake). The unit comprises massive and bedded crinoidal limestone, lesser chert and, in places, thin interbeds of mudstone and siltstone. The Buttle Lake Formation conformably overlies the Flower Ridge Formation (Yole, 1969) and ranges in thickness from 10O to 500 m. The age of this formation (based on biostratigraphic dating) at Buttle Lake ranges from Pennsylvanian (W. R. Danner, personal communication, 1987) to Early Permian (Yole, 1969; Brandon etal., 1986). This unit, similar in nature to modern carbonate shelf deposits, was deposited in relatively shallow water (Yole, 1969). 2.3.6 HENSHAW FORMATION Jeffery (1970), in a summary of his work in the Buttle Lake uplift, proposed a new formation called the Henshaw Formation to represent a heterogeneous and irregularly distributed group of rocks that appear to overlie or take the place of Buttle Lake Formation (probably equivalent to the unnamed uppermost unit of Yole, 1969). The type locality for the Henshaw Formation is near the mouth of Henshaw Creek in the southern part of Buttle Lake. It consists of conglomerate, variably purple-coloured epiclastic deposits, and purple to grey vitric tuff beds (Jeffery, 1970). This formation apparently is characterized by the presence of cririiodal limestone clasts and boulders, and the variable but ubiquitous purple to red alteration of its volcanic members. The thickness of this 14 unit varies from 5 to 1 OO m, and it is overlain by pillowed lavas or thin argillaceous sediments of the Karmutsen Formation of the Triassic Vancouver Group. It is probably Permian in age (Jeffery, 1970) and represents shallow marine to subaeriai sedimentation and the final Paleozoic magmatic episode in the Buttle Lake uplift. 2.4 CORRELATION WITH THE COWICHAN — HORNE LAKE UPLIFT Past stratigraphic nomenclature proposals for the Sicker Group attempted to define a sequence applicable to all Sicker Group exposures on Vancouver Island. This approach was only partially successful. The upper, limestone-bearing Buttle Lake Formation is a distinctive and relatively easily identifiable unit, but this is not the case for the lower lithologies. Any detailed subdivision of the lower units encountered problems due to the presence of many different types of rock units and marked facies variations. Consequently recent workers (e.g. Brandon etal, 1986) favoured a general definition for the lower sequences that lump all rock units below the Buttle Lake Formation. This has proven to be unsatisfactory to workers conducting detailed studies in the lower members. This is especially true for exploration geologists searching for massive sulphide mineralization in both the Cowichan - Horhe Lake and Buttle Lake uplifts. Current work for the LITHOPROBE 1 Project proposes subdivision of the Sicker Group into the Youbou Subgroup and Buttle Lake Subgroup (Sutherland Brown, in preparation). The former represents the dominantly volcanic lower sequences of the Sicker Group, whereas the latter represents the dominantly sedimentary upper units. The subgroups would then be broken down into formations within each uplift. The following discussion focusses on comparisons between the revised Buttle Lake stratigraphy (lower units only: Price, Myra, Thelwood and Flower Ridge Formations) and descriptions of possible similar units in the Cowichan - Home Lake uplift. The basal formation of the Sicker Group, thought to be present only in the Cowichan-Horne Lake uplift, was named the Nitinat Formation (Muller, 1980). It is defined as a unit comprising pyroxene ± feldspar porphyritic basaltic to andesitic massive to pillowed flows, flow breccias and coarse volcaniclastic rocks and minor tuff (Muller, 1980; Brandon etal, 1986) and is most widely 15 exposed northwest of Cowichan Lake in the Nitinat River headwater region. Good descriptions of Nitinat-like units are found in Clapp and Cooke (1917), Fyles (1955) and Muller (1980). The recognition of pyroxene-phyric mafic volcanic rocks alone is not sufficient to classify the unit in question as the basal formation of the Sicker Group. Documentation of pyroxene-bearing rxk types in all four lowermost formations in the Buttle Lake uplift precludes this as the only criteria. The lowermost unit in the Buttle Lake uplift, the Price Formation, may be correlative to the Nitinat Formation in the Cowichan - Home Lake uplift. However, further detailed work, especially isotopic age determinations, is needed in order to show if both mafic volcanic units indeed represent the same formation. Presence of Myra Formation-equivalent units in the Cowichan - Home Lake uplift has recently been under dispute (Sutherland Brown and Yorath, 1985; Brandon etal, 1986). The problem is due in part to the overly generalized definition of the unit by Muller (1980) and the significant facies variations of the lithologic units. The occurrence of felsic volcanic rocks and sulphide mineralization in the Mount Sicker area (e.g. the old Twin J mine and the Lara property near Duncan) suggest that Myra Formation-equivalent units are present in the Cowichan — Home Lake uplift. This is implied further by similarity in galena Pb isotopes from volcanogenic massive sulphide deposits between the two uplifts (Andrew, 1987). Ongoing mapping by the Geological Survey Branch of the B. C. Ministry of Energy, Mines and Petroleum Resources (BCMEMPR) under the Canada/ British Columbia Mineral Development Agreement (Massey and Friday, 1987; N. W. D. Massey, personal communication, 1987) may define Myra Formation-equivalent units as part of the new McLauglin Ridge Formation (see above) or as a discontinuous unit in the uppermost part of the Nitinat Formation within the Cowichan - Home Lake uplift. The nature of oogenetic Paleozoic felsic intrusive rocks, namely the Saltspring Intrusions in the Cowichan - Home Lake uplift, within the Myra Formation is still unclear. No such units are found in the Buttle Lake uplift. Recent isotopic age determinations gave an Early Devonian age for the Saltspring Intrusions (Brandon etal, 1986). This is distinctly older than the Late Devonian Myra Formation at Buttle Lake thus contradicts suggestions that the Myra Formation felsic members may be 16 extrusive equivalents to these intrusive units. The Saltspring Intrusions therefore are either part of an older Myra Formation-equivalent unit'in the Cowichan - Home Lake uplift or a separate event wholly contained within the basal Nitinat Formation. Equivalent units to the Thelwood and Flower Ridge Formations in the Cowichan — Home Lake uplift are probably represented in the measured stratigraphic sequence at the west fork of Shaw Creek (Table 2.1). Fyles (1955) suggested that the contact between the 'chert unit' and the underlying 5 to 10 m thick, coarse green volcanic breccia unit be considered a marker horizon. Muller (1980) proposed that this interval represented the contact between the Nitinat and Myra Formations in the Cowichan Lake area. However Brandon etal (1986) dispute the correlation of the 'chert unit' to Myra Formation-equivalent units because the cherty sediments are inferred to be younger than the Myra Formation (the top of the unit is clearly younger but the age of the bottom sediments has not yet been determined). Based on present work in the Cowichan - Home Lake uplift, the "chert unit" and overlying volcaniclastic sequences are correlated to the Cameron River Formation (Sutherland Brown, in preparation). Relative to the Buttle Lake stratigraphy, the 'chert unit' could correlate to the Thelwood Formation whereas the overlying tuffaceous sediments and amygdaloidal basalt flows and breccias may correspond to the Flower Ridge Formation. The underlying volcanic breccia horizon (Nitinat Formation) might represent equivalent units to either the Price Formation or the uppermost mafic units in the Myra Formation. Correlation of the Flower Ridge Formation to the amygdaloidal basalt and tuffaceous sediment sequence at Shaw Creek in the Cowichan - Home Lake uplift could help to constrain the age of the unit in the Buttle Lake uplift. The Flower Ridge Formation is defined as lying between the Thelwood and Buttle Lake Formations. Based on fossil ages from the top of the 'chert unit' and the bottom of Buttle Lake Formation-equivalent units in the Cowichan area (Brandon etal, 1986) a possible age for the Flower Ridge Formation is post-Early Mississippian (Kinderhookian) and pre-Middle Pennsylvanian. .17 TABLE 2.1 Stratigraphic sequence at the west fork of Shaw Creek, Vancouver Island in the Cowichan Home Lake uplift, and proposed correlations with new stratigraphy in both the Cowichan - Home Lake uplift and the Buttle Lake upl ift. Approximate thickness (m) Shaw Creek (after Fyles, 1955) Cowichan - Home Lake Buttle Lake (Sutherland Brown, in prep.) (proposed here) Top not exposed Purplish volcanic breccia Green tuffaceous greywacke Amygdaloidal basalt Thin and thick beds of tuffaceous greywacke Black feldspathic and argillaceous tuff, thin limestone lenses Chert unit Thin bedded cherty tuff, radiolarian ribbon chert 60-90 400 80 310 240 180 1400+ —unconformity?— Nitinat tuff Massive green breccia Cameron River Formation Nitinat Formation Flower Ridge Formation Thelwood Formation Myra Formation Price Formation 18 2.5 CONCLUSIONS Detailed work on lower Sicker Group rock units has resulted in the revised subdivision of the Paleozoic stratigraphy in the Buttle Lake uplift. The revised units, in order of decreasing age, are: Price Formation, Myra Formation, Thelwood Formation, Flower Ridge Formation, Buttle Lake Formation, and Henshaw Formation. Comparison with the Sicker Group in the Cowichan -Home Lake uplift shows that similar units to those defined in the Buttle Lake uplift are present. However their exact interrelationships and extent are not well known at this time. Generally the two lowermost formations, Price and Myra, correlate to the Youbou Subgroup of Sutherland Brown (in preparation) and the uppermost two formations, Henshaw and Buttle Lake, correspond to the Buttle Lake Subgroup. The Thelwood and Flower Ridge Formations could correlate with either the McLauglin Ridge Formation (Youbou Subgroup) or the Cameron River Formation (Buttle Lake Subgroup). Continuing BCMEMPR. work in the Cowichan - Home Lake uplift may clarify relationships between the two uplifts. 19 CHAPTER 3 GEOLOGY OF THE BUTTLE LAKE VOLCANOGEN1C MASSIVE SULPHIDE CAMP 3.1 INTRODUCTION Buttle Lake Camp ore deposits consist of many individual massive sulphide lenses grouped into several major zones within two main felsic volcanic stratigraphic intervals in the Paleozoic Sicker Group within the Buttle Lake uplift. The Sicker Group is represented in the Buttle Lake Camp by four formations: the Late Devonian or older Price Formation, the sulphide deposit-bearing Late Devonian Myra Formation, the Early Mississippian(?) Thelwood Formation, and the Mississippian(?) Flower Ridge Formation. The first three formations are also referred to as the Footwall H-W Andesite, the Mine Sequence, and the Sharp Banded Tuff unit. Each of the four formations is described below with particular emphasis on the Myra Formation (Mine Sequence). The geology map of the Price Hillside (Fig. 3,1 in back pocket: mapped at a scale of 1: 2400), and four composite geologic cross sections form the basis of the lithologic and facies variation descriptions. The cross sections span the length of the mine property (Fig. 3.2) at the following mine coordinates: 183+00 E (Fig. 3.3 in back pxket; Fig. 3.4), 124+00 E (Fig. 3.5), 60+00 E (Fig. 3.6) and 5+00 E (Fig. 3.7). Unit symbols used in the geology map and composite cross sections are shown in square brackets in the descriptions below. Description of the mine-area geology (especially the Myra Formation), complicated by abrupt and major facies changes, is facilitated by reference to its setting as a rift basin within an island arc system (Chapter 5). The long axis of the basin is defined by the northwestern trend of the ore zones: therefore variations along this direction are discussed in terms of the Price (183+00 E), H-W-Myra (124+00 E), Lynx (60+00 E), and West G (5 + 00 E) sections (Fig. 3.2). Lateral facies variations perpendicular to the basin axis are described by designating the areas around the ore zones as the central region, the area towards Buttle Lake lo Ihe northeast as the volcanic arc (VARC) region, and the area towards Mt. Myra to the southwest as the arc rift (ARFT) region (Fig. 3.2). The names of the latter two regions, intended for use in this chapter as directions only, reflect interpreted Figure 3.2: Orientation diagram for geological descriptions, Buttle Lake Camp, Vancouver Island, B.C. Descriptions in text are made relative to the northwestern trend of the massive sulphide ore zones (shown In plan.projections as solid patterns: Waker, 1985). The area around the ore zones between the dashed-dot lines is defined as the central region. The area to the northeast towards Buttle Lake is referred to as the volcanic arc (VARC) region whereas the area towards Mount Myra to the southwest is designated the arc r i f t (ARFT) region. Lengths of section lines represent area covered in the respective cross sections: Price (Figs. 3.3 and 3.4), H-W-Myra(Fig. 3.5), Lynx (Fig. 3.6), and West G (Fig. 3.7). Area outlined by dots defines the Price Hillside 21 Figure 3.4: Generalized composite geology along Price section (183+00 E), Buttle Lake Camp, Vancouver Island, B.C. Data are from Figure 3.3. Rock unit symbols are: DCp = Price Formation; 1 = H-W Horizon; 1d = H-W Horizon, dacite; If = H-W Horizon, feldspar porphyritic rhyolite; Im = H-W Horizon, mafic flow member; 1q = H-W Horizon, quartz + feldspar porphyritic rhyolite; 2 = Hanging Wall H-W Andesite; 3 = Ore Clast Breccia unit; 3z = Ore Clast Breccia unH, Interzone Rhyolite; 4 = Lower Mixed Yolcaniclastics; 5L = Upper Dacite, lower member; 5u = Upper Dacite, upper member; 5N = North Dacite; 6 = Lynx-Myra-Price Horizon, G-Zone; 6H = Lynx-Myra-Price Horizon, G-Hanging Wall Zone; 7 = G-Flow unit; 8 = Upper Mixed Volcaniclastlcs; 9 = Upper Rhyolite unit; 10 = Upper Mafic unit; and DCt = Thelwood Formation. Figure 3.5: Composite geology along H-W—Myra section (124+00 E: after Walker, ,1985), Buttle Lake Camp, Vancouver Island, B.C. Rock unit symbols are the same as for Figure 3.4 except: IA = H-W Horizon, argillite member; 4d = Lower Mixed Volcaniclastics, dacite; 5E = 5E Andesite; i = undifferentiated Myra Formation interzone units (Ore Clast Breccia unit, Lower Mixed Volcaniclastics, Upper Dacite lower member); and U = undifferentiated Myra Formation upper units (Upper Dacite upper member, 5E Andesite, Upper Mixed Volcaniclastics, Upper Rhyolite unit, Upper Mafic unit). Solid patterns represent massive sulphide bodies and wavy pattern represents hydrothermal alteration associated with feeder zone of sulphide mineralization. Letter "c" denotes chert. Figure 3.6: Composite geology along Lynx section (60 + 00 E: after Walker, 1985), Buttle Lake Camp, Vancouver Island, B.C. Rock unit symbols are the same as for Figure 3.4 except: 1 A = H-W Horizon, argillite member; 5E = 5E Andesite; ^undifferentiated Myra Formation interzone units (Ore Clast Breccia unit, Lower Mixed Volcaniclastics, 5E Andesite); and U = undifferentiated Myra Formation upper units (Upper Mixed Volcaniclastics, Upper Rhyolite unit, Upper Mafic unit); Solid patterns represent massive sulphide bodies and wavy pattern represents hydrothermal alteration associated with feeder zone of sulphide mineralization. SW + 1000 ft Sea Figure3.7: Composite geology along West 6 section (5+00 E: after Walker, 1985), Buttle Lake Camp, Vancouver Island, B.C. Rock unit symbols are the same as for Figure 3.4 except: 5E = 5E Andesite, and U = undifferentiated Myra Formation upper units (Upper Mixed Volcaniclastics, Upper Rhyolite unit, Upper Mafic unit). Solid patterns represent massive sulphide bodies and wavy pattern represents hydrothermal alteration associated with feeder zone of sulphide mineralization. island arc environments that are discussed in Chapters 4 and 5. Most Sicker Group rock units on the mine property are composed of subaqueous volcaniclastic deposits. The terminology used for describing such deposits is based largely on that developed for the subaerial environment (Wright etal, 1980; Schmid, 1981). However, modifications are required due to the subaqueous environment of deposition, in particular for pyroclastic-rich deposits formed by sediment gravity flow processes. No formal nomenclature has been established for such deposits. The working terminology used in this study is derived from recent studies on subaqueous pyroclastic-rich deposits (e.g. Fisher, 1984; Gosson, 1986) and the author's personal experience. The nomenclature used is in Appendix B. Average whole rock chemical compositions for the main volcanic members in the mine-area are in Table 3.1 to generally characterize the volcanic units. Discussion of chemical variations within and among the units, and overall pedogenesis are in Chapter 4. 3.2 MINE PROPERTY LITHQLOGY AND STRATIGRAPHY 3.2.1 PRICE FORMATION (FOOTWALL H-W ANDESITE) [DCp] . The lowermost unit exposed in the mine-area and in the Buttle Lake uplift is a thick sequence (> 300 m) of massive to pillowed basaltic andesite flows and flow breccias, and minor associated fine to coarse pyroclastic rocks. The Price Formation has been intersected in drillcore throughout the property but is exposed at surface only in a small region southwest of the mouth of Thelwood Creek (Fig. 3.1). The base of this formation is not known. Price Formation is characterized by alternating, 30 to 150 m thick sequences of feldspar--phyric and pyroxene + feldspar porphyritic flow units (Fig. 3.8). Most flows are characterized by trace to 7 percent, 0.1 to 0.3 mm, ovoid to elongate amygdules. The feldspar-phyric flows consist of 15 percent, 0.6 to 5.0 mm long plagioclase, and trace to 0.5 percent, 0.5 to 2.5 mm long, euhedral clinopyroxene phenocrysts. The fine-grained groundmass is hyalopilitic to pilotaxitic. The pyroxene TABLE 3.1. Average whole reck chemical compositions for Sicker Group metavolcanic rocks, Buttle Lake Camp, Vancouver Isiand, B.C Data from Tables 4.2, 4.3. 4.4, 4.5, 4.6, 4.7, 4.8, 4.1 : and 4.12. F e 2 0 3 is expressed as total i rcn. LOI represents loss on ignition. Symbol " < '* denotes less than detection limit. Unit 1 Price Fm H-W H-W H-W HW-A UD 5E LriP G-Flow UM Thl.pr Thl.ms FR •• Rock Type 2 b-ande QFP FP dac ance dac b-ande rhy-T hmb bas ande b-ande bas No. of analyses (5) (3) (13 (4) (4) (3) (1) (3) (3) (2) (3) (4) (2) S i0 2 (w t . %) 54.3 71.0 80.1 58.0 57.6 70.1 54.1 72.1 48.2 51.2 68.6 53.8 52.0 T i 0 2 0.80 0.23 0.17 0.60 0.77 0.52 0.92 0.48 0.62 0.83 0.71 1.38 1.26 A l 2 03 '6 .7 15.8 10.5 15.8 15.9 13.7 16.6 16.4 13.1 16.3 12.9 14.8 16.3 Fe 203 10.2 3.07 1.14 4.42 10.7 3.60 10.5 3.37 10.9 11.4 7.47 14.0 13.6 MnO 0.16 0.04 0.01 0.06 0.16 0.05 0.15 0.05 0.21 0.27 0.16 0.26 0.23 hgO 6.12 1.00 0.02 1.07 4.77 0.79 6.37 1.96 15.7 7.92 2.15 4.68 5.67 CaO 7.12 2.05 0.40 2.94 6.85 2.64 7.88 1.94 9.22 8.18 3.32 6.59 7.08 Na 20 4.34 3.45 5.85 5.75 2.82 5.14 3.00 0.44 1.85 3.66 2.68 3.80 3.52 K 2 0 0.18 3.13 1.75 1.14 0.18 0.36 0.15 3.54 0.12 0.14 1.29 0.06 0.16 P 2 0 5 0.28 0.07 0.04 0.25 0.20 0.20 0.40 0.15 0.18 0.26 0.19 0 38 0.22 LOi 4.35 2.47 0.77 2.21. 3.87 1.27 4.1 1 4.25 5.30 3.71 2.55 4.05 3.92 Ba (ppm) 164 1360 475 490 135 209 134 2350 181 156 620 69 134 Rb < 4 40 15 14 < 4 6 < 4 39 < 4 4 17 < 4 5 Sr 424 176 53 291 53? 304 530 88 218 388 338 198 212 rib 2 5 4 3 2 3 4 5 2 3 4 3 4 Y 25 18 18 36 25 33 34 28 17 20 44 34 28 Zr 69 133 1 16 108 72 96 88 115 43 61 167 93 7 7 ' Cr 95 5 19 8 23 11 30 15 1280 58 21 19 52 Ni 35 5 13 12 17 14 8 17 325 18 15 18 16 Cu 68 14 < 7 13 44 < 7 63 12 97 26 15 24 74 Zn 100 32 31 98 117 44 95 154 ' 80 89 100 98 80 V 260 18 1 7 21 1 48 206 107 270 229 66 353 320 1. Unit abbreviations are: H-W = H-W Horizon, HW-A = Hanging Wall H-W Andesite, UD •= Upper Dacite, 5E = 5E Andesite, LMP = Lynx -Myra -Price Horizon, UM = Upper Mafic unit, Thl = Thelwood Fm, pr = pyroclastic deposit units, ms = mafic s i l l , and FR =* Flower Ridge Fm. 2. Rock type abbreviations are: b-ande = basaltic andesite, QFP = quartz+feldspar porphyrit ic rhyol i te, FP « feldspar porphyrit ic rhyolite, hmb = high hgO basalt, ande = andesite, dac = dacite, rhyT = rhyolite tuff, and bas •= basalt. 28 lllimHIIIIIItlHUIIIIItimMIIIIUUIill 1:!;!,! n 1 9l 1 ICH 1 ill , { I 2 r ' 131 1 Ml f 6 Figure 3.8: Cut drillcore slab examples of typical Price Formation lithologies. Top left sample is a feldspar-phyric basaltic andesite, and the top right sample is an amygdaloidal, pyroxene + feldspar porphyritic basaltic andesite. The bottom sample represents possible pillow breccia with relict quenched margins and associated, strongly epidotized hyaloclastite. Scale divisions are in mm and cm. Figure 3.9: Photomicrograph showing characteristic apatite (A) and opaque oxide (magnetite?) microphenocryst association, Price Formation. Fieldof view is 0.75 mm x 1 mm. + feldspar porphyritic flows contain 5 percent, 1 to 10 mm long, euhedrai clinopyroxene and 3 percent, 0.8 to 2.5 mm long plagioclase'phenocrysts. The groundmass is generally pilotaxitic. Plagioclase phenocrysts in both flow types occur as single grains or glomerocrysts whereas pyroxene phenocrysts are present mainly as single crystals. Accessory m inerals in both flow types consist of microphenocrysts of apatite, almost always associated with oxide aggregates (Fig. 3.9), and opaque oxides (magnetite?). Flow units in the Price Formation have been pervasively altered (see section 3.4). Plagioclase phenocrysts are moderately to strongly altered to a more albitic plagioclase (An2y), epidote±clinozoisite and lesser calcite, sericite and chlorite. The intensity of this alteration is reflected in the character of the feldspar grains in hand sample; weakly altered grains are grayish and translucent whereas strongly altered crystals are white and opaque. Pyroxene phenocrysts are pseudomorphed by actinolite and variable but lesser amounts of chlorite, epidote and calcite. Opaque oxide microphenocrysts are altered to hematite and leucoxene. The groundmass is moderately to strongly altered to epidote, chlorite and albite. The amygdules are filled with quartz, chlorite, epidoteiclinozoisite and calcite. Alteration also has accentuated former vitric phases in the clastic lithologies of the Price Formation. Flow breccias consist of variably epidotized porphyritic flow clasts in a darker, chloritized volcanic flow host. Some of these clasts display chloritic, dark green, fine-grained aphyric rims, probably reflecting relict quenched margins of isolated pillows or pillow breccias (Fig. 3.8). In places, clastic horizons are characterized by strongly epidotized, angular to sub-angular, weakly to moderately porphyritic clasts set in a distinctly less-epidotized, crystal bearing matrix. These are interpreted to represent hyaloclastite with the epidote marking altered vitric phases. Coarse pyroclastic deposits contain clasts similar to those in the flow breccias but with a distinctive matrix of yellowish-green, epidotized, fine-grained tuffaceous sediment or strongly altered vitric tuff. The Price Formation locally contains areas of hydrothermal alteration associated with sulphide mineralization (i.e. the H-W feeder zone), and gray to purplish, albite porphyritic felsite intervals (up to 15 m wide) consisting mostly of albite microlites with subordinate quartz and minor chlorite. Origin of these alteration types are discussed in section 3.4. Price Formation represents a major period of andesitic volcanism. This flow dominant sequence implies almost continuous effusive volcanism prior to the deposition of the largely volcaniclastic Myra Formation. 3.2.2 MYRA FORMATION (MINE SEQUENCE) [DCm] The Myra Formation consists of a 310 to 440 m thick sequence of complex volcanic -dominant stratigraphy. Myra Formation lithologic units exhibit remarkable linear continuity (>7 km) along the northwestern trend of the ore zones, but abrupt lateral northeast to southwest facies changes. The Myra Formation is divided into ten general litho-stratigraphic units (in decreasing relative age): H-W Horizon, Hanging Wall H-W Andesite, Ore Clast Breccia unit, Lower Mixed Volcaniclastics, Upper Dacite / 5E Andesite / North Dacite, Lynx-Myra-Price Horizon, G-Flow unit, Upper Mixed Volcaniclastics, Upper Rhyolite unit, and Upper Mafic unit. Distinctions within and among the volcaniclastic dominant units are made chiefly on the presence or absence of certain clast types (critical types can be as minor as one volume percent). Therefore descriptions of those units are quite detailed with some of the more lengthy parts confined to Appendix A. 3.2.2.1 H-W Horizon [DCml] The lowermost Myra Formation unit is the predominantly rhyolitic H-W Horizon. This horizon varies in thickness from approximately 15 m to 200 m and occurs throughout the mine-area. It consists of dacitic to rhyolitic flows and domes, pyroclastic deposits, argillite, and sulphide mineralization. H-W Horizon units vary laterally from bedded argillite and felsic tuffs towards the ARFT region to complex felsic domal and flow assemblages towards the VARC area (Figs. 3.4 and 3.5). It can be divided into five parts: ( Dan argillite member, (2) a felsic flow member, 31 (3) a pyroclastic and volcaniclastic member, (4) a mafic flow member, and (5) a massive sulphide member. The argillite member [ 1 A] is a 1.5 to 45 m thick, more or less continuous unit consisting of massive to thinly laminated beds of black siliceous argillite; normally graded, thinly bedded, fine to coarse rhyolite tuff; beds made up of varying mixtures of argillite and tuff (tuffaceous argillite to argillaceous tuffs); and minor chert. The argillites are composed of quartz, lesser feldspar, and variable but minor chlorite and carbonaceous matter. The tuff beds comprise quartz and feldspar crystals and a former vitric-rich host. The latter has relict shards which are difficult to discern due to strong alteration to sericite and quartz. Sedimentary structures observed include scour marks, load casts and rip-up clasts; no cross laminated structures were observed. The bedded sequences within this member reflect A-E and A-B-E turbidite deposits. Minor but ubiquitous sulphide mineralization consists of thin laminae or lenses of pyrite, or less commonly pyrrhotite, in the "argillite beds, and pyrite or pyrrhotite disseminations and pebble-size clasts in some tuffaceous units. The felsic flow member can be divided into three types: a quartz + feldspar porphyritic (QFP) rhyolite [1q], an aphyric to feldspar porphyritic (FP) rhyolite [ If], and a feldspar porphyritic dacite [Id]. Chemically, the first two are rhyolites whereas the dacite spans the dacite—rhyolite division (Table 3.1; Chapter 4). The FP and QFP rhyolite flow units occur throughout the H-W Horizon in the VARC region and parts of the central region, but disappear towards the ARFT area. The feldspar porphyritic dacite flow units are present only in the central region and appear to have a different source area than the rhyolites (see section 3.2.2.11 and Chapter 5). The dacite flows thicken southeastward towards the Price section and not the VARC area - unlike the distribution of the rhyolites. The felsic flow units consist of autobrecciated to massive flows; massive phases are predominant in the FP rhyolite and dacite flow types, and brecciated phases are more common in the QFP rhyolite flow types. QFP rhyolites occur in domal to linear ridge-like bodies (up to 1.5 km long x 250 m widex 200 m high) and comprise two main phases: a pale gray to pale green-gray, massive to variably flow-banded phase, and a medium to dark green, flow laminated vitrophyric phase (Fig. 3.10). Both 32 Figure 3.10: Cut drillcore slab examples of typical H-W Horizon quartz + feldspar porphyritic rhyolite. The right and middle samples contain the two main flow phases: a pale green-grey, massive to flow banded phase, and a darker green vitrophyric phase. The sample to the left represents a phase gradational between the two main types. Scale divisions are in mm and cm. can occur together with the vitrophyre phase commonly hosting clasts of the light-coloured type. Fragment sizes, typically less than 15 cm', range from 0.5 cm to > 30 cm. Both QFP flow types contain 3 to 10 percent, 0.5 to 3 mm long, euhedral plagioclase, and 1 to 5 percent, 0.2 to 2 mm in diameter, subhedral to euhedral .variably embayed quartz phenocrysts (Fig. 3.11). Somevitrophyric rhyolite horizons display very coarse-grained (3 to 8 mm) quartz + feldspar phenocryst-bearing intervals. No alkali feldspar phenocrysts were observed. Accessory minerals include microphenocrysts of apatite, zircon and opaque oxide. The quartz crystals usually contain inclusions of very fine-grained chlorite and lesser serlcite aggregates (former silica liquid inclusions). Occasionally these inclusions display perl itic cracks. Plagioclase phenocrysts are commonly weakly to moderately clouded by fine-grained hematite( ?) and serlcite. Some grains show minor sieve texture. The groundmass in the pale QFP rhyolites comprises fine-grained, irregular to perl itic-textured aggregates of quartz and feldspar, and lesser sericite and chlorite (Fig. 3.11). Sodium cobaltinitrate staining indicated that in some samples both albite and potassium feldspar are present in the groundmass. Flow banding, where present, is outlined by subtle variations in sericite ± chlorite content in thin section. The groundmass in the vitrophyric QFP phase consists of fine-grained sericite and subordinate feldspar and quartz. Flow laminations are outl ined by fine trails of leucoxene in the sericite-rich zones. FP rhyolites are aphyric to weakly phyric containing up to 7 percent, 0.5 to 2 mm long plagioclase phenocrysts. The phenocrysts commonly contain trace apatite inclusions, and are weakly altered with fine-grained sericite and epidote. The hyalophitic to pilotaxitic groundmass consists of anhedral to microlitic feldspar, quartz and sericite. Some flows have up to 5 percent fine-grained opaque oxide (magnetite or hematite) disseminations in their groundmass resulting in a dark purple-gray colour. Feldspar porphyritic dacites occur as linear bodies up to 1.5 km long x 250 m wide x 150 m high. They are typically medium to dark olive-green and comprise trace quartz, chlorite or epidote amygdules, and 2 to 10 percent, 0.2 to 1.0 mm long plagioclase glomerocrysts to phenocysts. Some samples contain rare pyroxene phenocrysts. Accessory phases include apatite and relict opaque 34 Figure 3.11: Photomicrographs of quartz + feldspar porphyritic rhyol ite, H-W Horizon. Quartz phenocrysts are embayed and contain inclusions composed of very fine-grained chlorite and sericite aggregates. Groundmass consists of irregular (top photogragh) to perl itic-textured (bottom photogragh) aggregates of quartz, feldspar, and lesser sericite and chlorite. Rectangular phenocrysts are plagioclase. Sample in the bottom photogragh was stained by sodium cobaltinitrate. Field of view in both photographs is3mmx4mm. oxide aggregates and microphenocrysts. The groundmass displays good pilotaxitic texture consisting of felted to flow aligned plagioclase microlites. The dacites are moderately altered with the feldspars altered to epidote and sericite, and the pyroxene grains pseudomorphed by chlorite and epidote. The pyroclastic and volcaniclastic member [ 1 r] makes up most of the H-W Horizon in the central region. The rock units consist mainly of medium to thin bedded, fairly well sorted, normally graded sequences of quartz + feldspar crystal-lithic-vitric lapilli - tuff, and coarse to fine tuff. They occur throughout the H-W Horizon becoming generally finer grained towards the ARFT region. A detailed description of this unit is given in Appendix A. Other units in this member include unwelded to welded, subaqueous pyroclastic Mow deposits (see Appendix B for documentation of welded deposits); heterolithic, rhyolite-dominant debris flow deposits; and rare, unsorted and ungraded tuff-breccia deposits. The pyroclastic flow deposits extend to all regions. The debris flow deposits are constrained laterally, occurring only in the central region. Some basal debris flow deposits are characterized by up to 25 percent Price Formation andesite clasts. The coarser felsic lapilli-tuffs and tuff-breccias predominate around and between the various felsic flow units in the VARC region. The mafic flow member [ 1 m] in the H-W Horizon consists of a pyroxene-phyric high MgO basalt (Table 4.8) flow and hyaloclastite unit. Only a single flow unit was recognized. It occurs immediately above or within the argillite member in the middle area of the H-W Horizon, Price section (Figs. 3.3 and 3.4), where it is > 370 m long by approximately 240 m wide, and 11 m thick at its center but thinning to 2 m at its edges. The flow contains 5 percent clinopyroxene phenocrysts and glomerocrysts in a very fine-grained groundmass comprising feldspar, actinolite (after-pyroxene) and minor calcite and epidote. Trace to 3 percent, 0.1 to 0.8 mm, elongate to ovoid, calcite ± chlorite amygdules are also observed. The flow overl ies a 1.5 to 6 m thick hyaloclastite zone which is characterized by feathery shard-like vitric mafic clasts (generally 1 to4cm longby0.5to 1.5cm wide) mixed with up to 40 percent fine to coarse felsic tuff, felsic tuff clasts, feldspar and quartz crystals, argillaceous material, and the occasional massive sulphide fragment (Fig. 3.12). The matrix is fine-grained and has been silicified. This apparently chaotic deposit probably represents a peperite formed by the interaction of the rapidly extruded, hot lava with the underlying, water-saturated and 36 Figure 3.12: Peperite within the mafic flow member, H-W Horizon, Price Hillside. Green clasts are aphyric to clinopyroxene porphyritic ultramafic hyaloclastite. The felsic matrix is silicified and contains feldspar and quartz crystals. S = massive sulphide clast. Scale divisions are in mm and cm. unlithified sediments (Williams and McBirney, 1979: p. 148). Other mafic volcanic eruptive cycles occurred post-argillite deposition. They are present as hyaloclastite and debris flow deposits at the H-W Horizon and Ore Clast Breccia unit boundary towards the ARFT region (see below). The massive sulphide member [solid pattern] consists of a number of massive sulphide deposits - collectively known as the H-W deposit (Fig. 3.5). This unit is one of the earliest deposited lithologic units in the Myra Formation in the Buttle Lake Camp. The H-W deposit will not be discussed in detail as that is beyond the scope of this study. The following is largely from Walker (1985). The H-W massive sulphide bodies are mainly pyritic with subordinate sphalerite, chalcopyrite, galena and barite, and minor tennantite and bornite. Trace native gold and arsenopyrite are recognized. The sulphides in the H-W deposit exhibit a strong lateral zoning from a thick massive pyrite central portion having chalcopyrite and sphalerite-rich zones, and relatively thin, pyrite-poor, sphalerite and barite-rich phases. The latter also contain significant galena and silver mineralization. Gold generally is distributed uniformly. The H-W Horizon represents the first felsic volcanic cycle in the Myra Formation. Felsic volcanic activity was largely concentrated in the VARC region with the deposition of flows and related elastics. An exception to this is the dacite flow unit which originated from a different source southeast of the Price section. Rift basin development produced sites for volcaniclastic and massive sulphide deposition; concomitant volcanic activity was confined to the occasional pyroclastic flow or suspension fallout deposit from the VARC region. Hemipelagic sedimentation (argillite member) was the main depositional process towards the ARFT area. 3.2.2.2 Hanging Wall H-W Andesite [DCm2] Hanging Wall H-W Andesite [2] is an up to 100 m thick unit mainly consisting of basaltic andesite to andesite flows and related breccias. The proportion of pyroclastic deposits relative to the flows and related breccias varies from 20:80 in the central regions of all sections, but approximately 60:40 in the VARC region of the Price section (Fig. 3.4). In the H-W-Myra and Price sections, the H-W Horizon felsic flow member has influenced the distribution of Hanging Wall H-W Andesite rock units. The discontinuity of the Hanging Wall H-W Andesite in the Price section (Fig. 3.4) is caused by the formation of a paleo- barrier by the H-*W dacite. However, in the H-W-Myra section (Fig. 3.5), the H-W dacite is quite thin and consequently has not affected the distribution of the overlying andesite flows. Instead, in that section, the andesite flows encountered another paleo-barrier built by a series of H-W quartz + feldspar porphyritic rhyolite flows. Basaltic andesite to andesite flows consist of 20 percent (up to 35 percent) plagioclase glomerocrysts, rare to 1 percent pyroxene phenocrysts, and trace microphenocrysts of apatite and opaque oxide (unlike andesites of the Price Formation, the apatite and oxide grains do not occur together). The pyroxene phenocryst content increases in the upper, relatively younger flow units. The groundmass is hyalopilitic comprising feldspar microl ites and interstitial epidote and chlorite. Most samples have up to 3 percent, irregularly shaped to lenticular, chlorite + epidote ± quartz-filled amygdules. Individual flows are often mantled on one or both sides by coarse angular breccias which are interpreted to be flow related (Fig. 3.13). The less common pyroclastic deposits are made up of massive, monolithic, matrix-poor lapilli-tuff, tuff-breccia, and bedded, feldspar crystal, fine to coarse tuff. The tuffs and lapilli—tuffs are usually moderately to well sorted, and display good normal grading of constituents. Tuff -breccia deposits are poorly sorted and only crudely graded. Units in the Hanging Wall H-W Andesite have been moderately to strongly altered resulting in sausseritized plagioclase crystals, chlorite pseudomorphs after pyroxene phenocrysts, and leucoxene and hematite pseudomorphs after opaque oxide microphenocrysts. In areas within the flow breccia deposits, some fragments have been completely altered to epidote resulting in a mottled appearance to drillcore or outcrop. 3.2.2.3 Ore-Clast Breccia Unit [DCm3] The Ore Clast Breccia unit [ 3] represents a series of volcaniclastic submarine debris flow deposits and lesser pyroclastic deposits. The unique feature of this unit is the presence of massive 39 Figure 3.13: Feldspar porhyritic andesite flow breccia, Hanging Wall H-W Andesite, Price Hillside. Scale bars are each 1 cm long. 40 sulphide clasts and lenses or "rafts' (olistoliths) of pyrite-mineralized rhyolite coarse tuff to lapilli-tuff. The unit is up to 90 m thick and is found thoughout the mine-area, being best developed in the central region in the Price end (Figs. 3.1 and 3.4). Excellent exposures are present on the Price Hillside. The Ore Clast Breccia unit can be divided into three mappable members: (1) a^hyolite-rich volcaniclastic breccia [3R] having from 10 to 50 percent non-andesite or mafic volcanic constituents (average is 25 percent); (2) a rhyolite-poor volcaniclastic breccia [3] with less than 10 percent non-andesite or mafic volcanic constituents; and (3) the Interzone Rhyolite [3Z], a rhyolite pyroclastic horizon. Generally, the rhyolite-rich member occurs in the lower to middle parts of the unit whereas the rhyolite-poor member is found in the middle to upper portions. The Interzone Rhyolite generally is found in the middle to upper portions of the Ore Clast Breccia unirtut it can occur at any level within the Ore Clast Breccia unit because It marks a paleosurface present at the time of its emplacement. The two volcaniclastic breccia members (Fig. 3.14) consist mainly of debris flow deposits. Less common types represented include slump/slide deposits (olistostromes) and subaqueous pyroclastic flow deposits. The latter occurs immediately above or below the Interzone Rhyolite (see below). These members are distinguished on the basis of clast type, size and distribution. Clast types present in the volcaniclastic breccia members can be highly variable. Detailed descriptions of the clast types observed are in Appendix A. Generally, the clast types comprise feldspar porphyritic andesite clasts; amygdaloidal, aphyric to weakly pyroxene-phyric mafic volcanic clasts; dacite flow clasts; quartz + feldspar porphyritic rhyolite clasts; massive sulphide (largely pyrite) clasts; rhyolite fine tuff and chert rip-up clasts; and argillite clasts. Rhyolite 'rafts' (Fig. 3.15) consist of rusty weathering, quartz ± feldspar crystal-vitric rhyolite coarse tuff to lapilli-tuff. They are usually mineralized by 1 to 10 percent disseminated pyrite with some lenses containing semi-massive to massive sulphide + barite + quartz pods (e.g. Lower Price showing, Fig. 3.1). The clasts and 'rafts' are matrix supported in a yellow to pale green matrix composed mainly of fine grained to aphanitic epidote and variable but minor quartz and feldspar. Little, if any phyllosilicate component is present. Other matrix constituents, less than 4 mm in size, include trace 41 Figure 3.14: Volcaniclastic breccia member deposits, Ore Clast Breccia unit, Price Hillside: rhyolite-rich member (top) and rhyolite-poor member (bottom). Rusty patches in the rhyolite-rich member (top) represent weathered massive sulphide clasts. Pale, blocky clasts in both members consist of both feldspar porphyritic dacite and quartz + feldspar porphyritic rhyolite. Dacite clasts are more abundant than rhyolite in the bottom rhyolite-poor member. Scale card in the top photo is 6 cm long. 42 Figure 3.15: Rusty weathered, pyrite mineralized quartz crystal rhyolite coarse tuff 'raft', Ore Clast Breccia unit, Price Hillside. to 2 percent quartz + feldspar crystals, 2 to 7 percent wispy to angular fragments of andesite cognate lithic clasts, and up to 5 percent, intensely altered volcanic( ?) clasts. Clast sizes in the breccia members are highly variable ranging from 1 cm to 1.5 m with rhyolite 'rafts' obtaining dimensions of up to 50 m long by 15 m wide. The rhyolite 'rafts' and most of the coarsest clast components occur in the Price area. Towards the H-W-Myra and Lynx sections the Ore Clast Breccia unit contains a distinctly smaller sized coarse fraction; the rhyolite 'raft' component is rare or absent. Clast-type distribution within the two volcaniclastic breccia members exhibits a consistent pattern. Deposits in the lower portions of the Ore Clast Breccia unit in the central to ARFT regions are mafic volcanic clast dominant, whereas towards the VARC area they are andesite clast dominant. Generally the deposits in the middle and upper parts of the unit are andesite dominant and comprise andesite accessory lithic clast dominant debris flow deposits and andesite cognate lithic clast "pyroclastic flow deposits. Most deposits in this region have varying amounts of both andesite components. The remainder of the clast types do not follow any zonations within their respective members. Dacite clasts occur approximately equally in both breccia members, varying from 2 to 10 percent. Massive sulphide and argillite fragments, found mainly in the rhyolite-rich member, comprise trace to 2 percent. The non-'raft' rhyolite components occur in both breccia members but are more common within the rhyolite-rich one, averaging 5 percent. The Interzone Rhyolite member is up to 20 m thick, and consists of bedded felsic tuff, lapilli-tuff and tuff-breccia. This member is thickest in the central region where it consists of quartz + feldspar porphyritic (QFP) rhyolite clasts in moderately well sorted, normally graded, feldspar + quartz crystal, vitric lapilli-tuff to coarse tuff deposits. The zone extends towards the ARFT area and largely comprises nicely bedded, normally graded, coarse to fine crystal vitric tuffs and rare green to black, radiolaria-bearing chert and argillaceous mudstone. Equivalent felsic tuff units are also present in the VARC region (Figs. 3.3 and 3.4). In general, the pyroclastic constituents consist of 7 percent plagioclase crystals, 3 percent quartz crystals, 5 to 25 percent angular to 'feathery-shaped', feldspar porphyritic, accessory to cognate lithic felsic volcanic accessory clasts, and 10 lo 50 percent subangular to subrounded, occasionally feldspar-phyric, variably perl itic-textured, sericite altered felsic cognate lithic clasts. Accidental components can be observed in areas comprising up to 10 percent rhyolite fine tuff rip-ups, massive pyrite + sphalerite + epidote clasts, QFP rhyolite flow clasts, and granophyric quartz + feldspar clasts. Granophyric texture is uncommon but ubiquitous occurring either in clasts or as overgrowths on quartz crystals. The matrix component is fine-grained consisting of quartz, epidote( ?) and lesser chlorite and feldspar. Ore Clast Breccia unit represents a proximal submarine fan facies where the coarse clastic horizons outline possible feeder channels. The rhyolite 'rafts' represent ollstoliths from H-W Horizon( ?) units deposited on a relatively unstable volcanic slope area. The Interzone Rhyolite member represents a temporary break in the slide and debris flow sedimentation characterized by numerous felsic volcanic explosive (phreatomagmatic, see Chapter 5) eruptions. These eruptions formed subaqueous pyroclastic deposits, pyroclastic flow deposits, and ni inor suspension fallout deposits. 3.2.2.4 Lower Mixed Volcaniclastics [DCm4] The Lower Mixed Volcaniclastics [4 ] represent andesite dominant volcaniclastic deposits. The unit is up to 90 m thick and occurs throughout the property. It contains volcaniclastic breccias (Fig. 3.16), tuff-breccia, bedded lapilli-tuff and coarse to fine tuff, and minor subaqueous pyroclastic flow deposits. Rare, thin feldspar porphyritic andesite flows are also present locally. The coarse clastic deposits occur mainly in the central region in the Price end and the West G end of the mine-area, whereas the Lynx and H-W-Myra sections contain relatively greater sequences of finer grained, bedded deposits. The subaqueous pyroclastic flow deposits are most prevalent in the VARC region. Generally the Lower Mixed Volcaniclastics thicken from the Price area to the H-W-Myra section, before gradually thinning towards the Lynx and West G sections. Towards the ARFT region this horizon 'merges* with the Hanging Wall H-W Andesite and Ore Clast Breccia units resulting in an andesite-rich volcaniclastic unit with minor dacite and trace rhyolite components. The Lower Mixed Volcaniclastics in the VARC area directly overly the Hanging Wall H-W Andesite (Fig. 3.4). 45 Figure 3.16: Andesite dominant volcaniclastic breccia deposit, Lower Mixed Volcaniclastics, Price Hillside. Pale green to white clasts are dacite. Lens cap is 5 cm in diameter. Characterization of the various constituent types in the Lower Mixed Volcaniclastics are best dealt with by describing them in terms of the bedded clastic sequences and the coarse clastic deposits. Descriptions of the subaqueous pyroclastic flow deposits are in Appendices A and B. The bedded clastic sequences are largely (> 50 percent) made up of aphyric to plagioclase-phyric, subrounded, chloritized relict andesite cognate lithic fragments. These clasts contain a very fine-grained groundmass with only rare microlite development. Other constituents include: 5 to 20 percent, broken to euhedral, plagioclase crystals; trace subangular to subrounded quartz crystals; up to 15 percent, subangular to subrounded, aphyric, occasionally spherulitic andesite(?) cognate lithic clasts; and trace to 1 percent variably amygdaloidal, chloritic andesite accessory lithic clasts. Towards the VARC region both clast and crystal components contain ubiquitous pyroxene grains (replaced by chlorite or lesser epidote). The matrix component in the coarse tuff to lapilli—tuff beds consists of fine-grained epidote and subordinate chlorite and feldspar. Coarse clastic deposits are made up of generally subangular, prolate to equant andesite and subrounded equant dacite flow clasts. The clast sizes (long axes) vary from 1 to 60 cm, averaging around 10 cm. The andesite component is by far the most common and occurs as two types. The first and more common type comprises chloritized and/or epidotized, perl itic-textured, variably feldspar-phyric (up to 15 percent) cognate lithic clasts. The groundmass displays a hyalophitic texture. Amygdules are uncommon (about 1 percent, rarely as high as 10 percent) and are usually filled with chlorite or epidote. The second andesite clast type is strongly feldspar glomeroporphyr itic (25 percent) and contains approximately 1 percent pyroxene phenocrysts (altered to amphibole and chlorite). The groundmass is strongly altered to epidote and leucoxene. This second clast type probably is accidental, originating from the underlying Hanging Wall H-W Andesite unit. The pale yellow to green 'dacite' flow clasts (Fig. 3.17) can actually represent one of three rock types: dacite blocks from the H-W Horizon dacite body, silicified and albitized andesite clasts, or massive dacite flow clasts from flows or domes lying southeast of the Price section. 47 Figure 3.17; Examples of different types of pale volcanic flow clasts, Lower Mixed Volcaniclastics -Ore Clast Breccia contact area, Price Hillside. A = silicified and albitized, pyroxene + feldspar porphyritic andesite. D = feldspar porphyritic dacite. R = quartz + feldspar porphyritic rhyolite. Scale divisions are in mm and cm. Lower Mixed Volcaniclastics represent the continuation of volcaniclastic sedimentation started in the Ore Clast Breccia unit; it is distinctive by not having rhyolite or massive sulphide components. Deposition primarily occurred as subaqueous debris flows redistributing andesite pyroclastic and flow material as well as reworked( ?) dacite clasts from previously erupted units. Associated turbidity currents were responsible for the emplacement of parts of the bedded sequences. 3.2.2.5 Upper Dacite (DCm5)/5E Andesite / North Dacite The Upper Dacite [5] / 5E Andesite [5E] / North Dacite [5N] units represent three approximately contemporaneous yet different eruptive events which occurred in non-overlapping relationships throughout the mine property. The Upper Dacite unit is present in the Prtce section . (Fig. 3.4) and comprises massive to bedded deposits of dacite to rhyolite hyaloclastite, flow breccia -and subaqueous pyroclastic deposits. The 5E Andesite is best developed at the West 6 end (Fig. 3.7) and consists of up to a 250 m thick sequence of massive to pillowed, feldspar porphyritic basaltic andesite to andesite flows and lesser flow breccia deposits. Both the Upper Dacite and the 5E Andesite units are thickest in their respective central regions; they thin markedly towards the middle sections (Lynx and H-W- Myra) of the mine-area. The Upper Dacite unit probably extends towards the ARFT region but its extent is not known. The 5E Andesite is not known in the ARFT region, but this is based on limited data. Both units are absent in the VARC region. The North Dacite, a feldspar porphyritic felsic flow unit, is only present in the VARC area where it occupies the same general stratigraphic position as the other two litho-stratigraphic units (Fig. 3.4). Only the Upper Dacite unit is discussed in detail below as data for the other two units are limited (differences related to magmatic sources are expanded in Chapter 4). The Upper Dacite unit consists of two general parts: (1) the Upper Dacite lower member, and (2) the Upper Dacite upper member. The contact zone between the two members is represented in some areas by the Lynx-Myra-Price Horizon (Fig. 3.4). The Upper Dacite lower member f 5L1. up to 60 m thick, is composed of resedimented but only slightly reworked hyaloclastite and pillow breccia deposits (Fig. 3.18), and subaqueous 49 Figure 3.18: Felsic pillow and hyaloclastite, Upper Dacite lower member, Price Hillside. Top photograph shows two round felsic pillows lying in a hyaloclastite and pillow breccia host. Bottom photograph is of a cut slab sample from the hosting hyaloclastite. Symbols in the bottom photograph are: v = felsic vitric clasts, pb = variably flow layered pillow fragments, f = feldspar porphyritic flow clasts. Lens cap (top) is 5 cm in diameter. Scale divisions (bottom) are in mm and cm. pyroclastic deposits (Fig. 3.19). The deposits contain two clast populations comprising feldspar porphyritic flow clasts and aphyric to weakly porphyritic altered vitric clasts (Fig. 3.18). The former is characterized by 10 to 25 percent, variably glomeroporphyritic, sieve-textured plagioclase phenocrysts, trace apatite microphenocrysts, and rare pyroxene phenocrysts. The groundmass is fine-grained with occasional relict spherulitic areas. Some of the clasts display a relict flow-layering pattern outlined by concentrations of opaque m inerals. The vitric clasts vary from subrounded to subangular shapes. They consist of 0 to 5 percent plagioclase phenocrysts and trace apatite and opaque (magnetite?) m icrophenocrysts. The groundmass is very fine-grained and contains relict vitric textures which include fine spherulitic intergrowths of feldspar and sericite (recrystallized in places to a microgranular aggregate of quartz and feldspar: Fig. 3.20); it has a crudely developed perlitic texture. The groundmass can also be microlite-bear ing with a hyalopilitic to hyalophitic texture. Most lower member deposits also contain up to 10 percent, variably broken, plagioclase, and rare to trace pyroxene and quartz crystals (coarse to fine tuff layers can contain up to 25 percent feldspar crystals). The matrix component of these elastics is made up of an altered mesostasis of chlorite, feldspar and quartz. Groundmass components of the above clast types have been altered to feldspar, chlorite, quartz and opaques (Fe-Ti oxides). Pyroxene crystals, where present, are pseudomorphed by epidote. The Upper Dacite upper member [ 5U] consists of intermediate flows containing yellow-green to dark grey to purple, subrounded to rounded, feldspar porphyritic felsic flow clasts (Fig. 3.21), and subaqueous pyroclastic deposits. The flow phase is medium to dark green and strongly feldspar porphyritic." It consists of 25 percent plagioclase phenocrysts which form two equally distributed populations: a 1. to 2.5 mm long, glomerocrystic type, and a 0.2 to 0.8 mm long, single grain set. Apatite and opaque oxide phases (magnetite?) occur together as microphenocrysts. The groundmass is made up of very fine-grained chlorite, feldspar and minor epidote. Entrapped felsic clasts consist of 15 percent, 0.5 to 3 mm long, variably glomerocrystic and sieve textured plagioclase phenocrysts, 0.5 percent pyroxene phenocrysts, and trace microphenocrysts of apatite and opaque oxide. The groundmass comprises feldspar, quartz and disseminated hematite. The opaque grains commonly 51 Figure 3.19: Graded and well bedded, feldspar crystal-vitric felsic coarse to fine tuff, Upper Dacite lower member .Price Hillside. Note disrupted and ripped up fine tuff layers near lens cap. Disruption was caused by the emplacement (by subaqueous sediment gravity flow processes) of the overlying coarse tuff to fine lapilli-tuff. Lens cap is 5 cm in diameter. 52 Figure 3.20: Photomicrographs of a spherulitic felsic vitric clast in a felsic hyaloclastite from the Upper Dacite lower member. Spherulites are recrystallized to microgranular aggregates of quartz and feldspar. Opaque clast to the left represents intense alteration by very fine grained Fe-Ti oxide minerals of a former felsic vitric clast. Top photograph is in plane polarized light; bottom photograph is under crossed polars. Field of view is 3 mm x 4 mm. Figure 3.21: Felsic flow clasts in a dark green, strongly feldspar porphyritic mafic to intermediate volcanic flow, Upper Dacite upper member, Price Hillside. Felsic clasts are white to pale green. Lens cap is 5 cm in diameter. display flow-related patterns especially around phenocrysts. Feldspar microlites are rare. The pyroclastic deposits consist of bedded fine to coarse tuff and lapilli-tuff, composed of similar constituents as in the lower member deposits. The main difference is in the low amounts of hyaloclastite or pillow fragments in the upper member. Upper Dacite unit represents a resumption of felsic volcanism from some source southeast of the Price section (same region as the H-W Horizon dacite). Felsic lava extruded onto the sea floor and formed extensive hyaloclastite debris as well as pillow breccia and isolated pillows. This debris periodically slumped from the volcanic apron into the adjacent rift basin. The Upper Dacite eruptive event ended with the emplacement of domes or flows. Evidence for this is in the upper member where the onset of intermediate lava flows into the rift basin characteristically contain altered and rounded felsic flow clasts. In many areas these clasts are quite large, indicating a nearby source. The lava apparently extruded along and through earlier erupted felsic flows and domes. 3.2.2.6 Lynx-Myra-Price Horizon [DCm6] The upper massive sulphide mineralized felsic volcanic units in the mine-area comprise the Lynx-Myra-Price Horizon [6], This horizon consists of two spatially distinct units: (1) the 6-Zone member [6], and (2) the G-Hanging Wall Zone member [6H]. The two are separated by units from upper parts of the 5E Andesite in the West G and Lynx sections, and by the Upper Dacite upper member in the Price section and possibly the H-W-Myra section. In the West G and Lynx areas the separation is 30 to 150 m whereas in the Price end, it is 10 to 60 m. Both G-Zone and G-Hanging Wall Zone members can be traced throughout the mine property. The difference between the two lies in their lateral extent. The stratigraphically lower G-Zone member can be traced for at least 300 m in the West G section, over 825 m in the Lynx section, and only 300 m in the H-W-Myra and Price sections. The overlying G-Hanging Wall Zone member is at least 1000 m wide in both West G and Price sections. No estimates can be made for the Lynx and H-W-Myra areas because of limited data, though extrapolating between the West G and Price sections suggest similar widths throughout the mine-area. Both zones vary in thickness from 1 to 45 m, but generally the 6-Zone member- is thicker than the G- Hangi ng Wal 1 Zone mem ber. Both Lynx-Myra-Price Horizon members consist mainly of massive to bedded, fine to coarse quartz - feldspar crystal vitric rhyolite tuff and lapilli—tuff, and massive sulphide mineralization and associated hydrothermal ly altered assemblages around fossil discharge sites. The rhyolite tuffs commonly occur as normally graded, moderately to well sorted, thin to thick beds. They contain 10 to 25 percent, variably broken plagioclase crystals, 5 to 15 percent, angular to subangular quartz crystals, 5 percent disseminated pyrite grains, and trace apatite crystals. Most samples also contain 10 to 25 percent gray rhyolite accessory lithic clasts, and 5 percent, dark green to black, wispy, sericitic rhyolite cognate lithic clasts. The matrix is composed of sericite and quartz. Plagioclase crystals are commonly altered to quartz or sericite. Massive sulphide deposits [solid pattern] are largely located on or near the uppermost contact of the respective member with no underlying feeder zones (i.e. distal). They are composed of banded sphalerite, chalcopyrite, pyrite, galena and barite. Minor tennantite is also present. These deposits are relatively pyrite-poor when compared to the H-W deposit. Massive sulphide lenses found within or along the bottom contact are usually proximal to fossil hydrothermal discharge areas (Fig. 3.6). The feeder zones, located in the Lynx section for the G-Zone member and West G section for the G-Hanging Wall Zone member, are characterized by schistose, sericite + quartz + pyrite assemblages almost always within the underlying andesitic units. In the G-Zone member, hydrothermal fluids probably percolated along strike into the Myra and Price rhyolites variably altering them (intensely in places). The lapilli-tuff deposits appear to have been the most altered. The G-Hanging Wall Zone member contains two additional lithologic units. They are a vitrophyric rhyolite coarse tuff to fine lapilli-tuff unit, and a chert unit. The vitrophyric tuffs consist of 10 percent euhedral feldspar crystals, and 2 percent euhedral to subhedral, embayed quartz crystals in a devitrified, relict vitrophyric host. The latter displays a characteristic fluidal texture composed of sericite-rich strands in a chlorite + quartz rnesostasis. These tuffs locally are associated with bedded tuffaceous siltstone and mudstone deposits. The latter contain sparse radiolarian 'ghosts'. Total thickness of this unit is usually less than 3 m. The chert unit [6Hc] occurs in the central regions in the Price and H-W-Myra sections. It is composed of thin to medium laminated beds of white to light green chert, jasper, and, less commonly, black argillaceous chert. No radiolaria were observed in samples of any of the three chert types. Thickness of this unit varies from 1 to 3 m. Lynx-Myra-Price Horizon represents cycles of rhyolite pyroclastic volcanism. The felsic volcanic material was deposited mainly as turbidity currents (slumping off the volcanic slope or, from pyroclastic flows originating in or entering the marine environment), and suspension fallout deposits. 3.2.2.7 G-Flow Unit [DCm7] The G-Flow unit [ 7] represents a number of thin (2 to 15m thick) but widespread ultramafic (komatiitic basalts: Chapter 4) flows and flow breccia and hyaloclastite deposits overlying the two members of the Lynx-Myra-Price Horizon (Figs. 3.6 and 3.7). At the Price end, this unit consists of medium to dark green, pyroxene porphyritic, amygdaloidal, massive to pillowed flows (Fig. 3.22), and lesser lapilli-tuff and coarse tuff deposits. In the H-W-Myra, Lynx and West G sections, the G-Flow unit is characterized by distinctly purple zones. These zones mainly consist of hyaloclastite and flow breccia and are moderately to intensely altered by carbonate and hematite. Associated massive to pillowed flows are less affected by this alteration and remain medium to dark green. The unit, thickest in the West G and Lynx areas, becomes steadily thinner towards the Price section. Laterally, it disappears towards the VARC region but thickens towards the ARFT area. Least altered flow units consist of 5 percent, augite glomerocrysts, trace chromite microphenocrysts, and trace to rare olivine( ?) phenocrysts. The groundmass is fine-grained and composed of felted actinolite, lesser chlorite, minor plagioclase and relict granular clinopyroxene. The pyroxene crystals in these units are variably altered to actinolite and chlorite whereas the olivine( ?) phenocrysts are pseudomorphed by chlorite, actinolite and epidote. The flows are always 57 Figure 3.23: Photomicrograph of an interstitial jasper sample (from a komatiitic basalt flow: see Fig. 3.22) showing characteristic spherulitic texture, G-Flow unit, Price Hillside. Opaque mineral is magnetite, which is variably altered to hematite. Field of view is 3 mm x 4 mm amygdaloidal with generally 3 percent (up to 15 percent) lenticular to irregularly-shaped, 0.5 to 3.0 mm long, chlorite + epidote amygdules. Some flows also contain trace to 1 percent, ovoid amygdules filled with radiating calcite. Flow units in the Lynx and West 6 sections have distinctly more calcite and less chlorite amygdules. Pillowed flows contain magnetite-rich (Price area) or hematite-rich (West G section), fine-grained relict selvages, and spherulitic jasper in pillow interstices (Figs. 3.22 and 3.23). The purple-altered hyaloclastite and flow breccia units maintain well preserved macroscopic original textures, but the same does not apply for microscopic features which are poorly preserved at best. Clasts from these members commonly have finer grained, darker purple rims reflecting relict devitrified glassy rinds. They are also moderately to strongly (5 to 25 percent) amygdaloidal with white to pink calcite and minor chlorite amygdules. The clasts appear to be aphyric having a fine-grained altered groundmass consisting of chlorite, calcite, sericite and hematite. Jasper can also occur as fragments in some of the clastic layers. The alteration of these units probably occurred during their emplacement as alteration phases do not transcend into overlying or underlying lithologies. G-Flow unit represents the first major phase of ultramafic volcanism recognizable in the region. The ultramafic character is indicative of an upper mantle source (Chapter 4) and would also be responsible for the extensive areal extent of the flows relative to their thickness. The high MgO basaltic lavas would have had a relatively low viscosity that enabled them to spread quickly and widely from vents. 3.2.2.8 Upper Mixed Volcaniclastics [DCm8] The Upper Mixed Volcaniclastics [8] represents a mafic to intermediate volcanic dominant volcaniclastic unit consisting of bedded fine to coarse tuff and lapilli-tuff sequences, and massive coarse lapilli-tuff to tuff-breccia deposits. Purplish hematite alteration is present irregularly in both types. The unit is up to 50 m thick and occurs throughout the mine property, being best developed in the central regions of all four sections. 59 Bedded tuff sequences are thinly to medium bedded, moderately well sorted and normally graded, and consist largely of feldspar crystal intermediate to mafic tuffs. In places, maroon fine tuff beds mark the tops of the graded deposits. Tuffs in these sequences are composed of 25 to 40 percent, usually broken plagioclase crystals; trace to 1 percent subhedral pyroxene crystals; trace broken quartz crystals; 35 percent, subangular to subrounded, aphyric to occasionally plagioclase porphyritic mafic volcanic vitric clasts; and 5 percent, subrounded, aphyric felsic clasts. Massive lapilli-tuff and tuff-breccia deposits (Fig, 3.24) contain 5 to 15 percent euhedral (whole > broken) plagioclase crystals, trace pyroxene crystals, and a wide variety of vitric and flow clasts. The matrix is fine-grained and composed of epidote, albite and chlorite. The clast types (in decreasing order of relative abundance) comprise crudely perl itic-textured, weakly plagioclase porphyritic mafic to intermediate volcanic cognate lithic clasts; variably perlitlc-textured and spherulitic, subrounded, aphyric to plagioclase-phyric, felsic cognate lithic clasts; subangular to irregularly-shaped, crudely perl itic-textured, plagioclase + pyroxene porphyritic basaltic cognate to accessory lithic clasts; and bleached, pale yellowish, strongly epidotized, feldspar ± pyroxene porphyritic andesite accidental clasts. The last clast type can resemble the felsic clasts in hand samples and drillcore. Minor clast types (< 5 percent) comprise: massive to flow-banded, weakly plagioclase-phyric rhyolite; rip-up clasts of tuffaceous siltstone and mudstone; and angular to subrounded, white to black chert. Rare clasts of massive pyrite are also present. A lateral compositional variation of the clast types is recognized. Intermediate and felsic volcanic constituents are uncommon towards the ARFT region but become increasingly more abundant towards the VARC area. The mafic volcanic clast distribution generally follows the reverse of the above pattern. Rock types on the Upper Mixed Volcaniclastics are moderately chloritized and epidotized. Feldspar crystals are moderately to strongly altered to epidote, sericite, albitic plagioclase and disseminated hematite. Pyroxene grains are altered to chlorite or epidote. Upper Mixed Volcaniclastics represent the resumption of rift basin-filling volcanogenic sedimentation. The clast type population appears to have been controlled by encroaching volcanic activity from the ARFT region and continued volcanic arc volcanism (VARC region). Minor but 60 Figure 3.24: Mafic lapilli-tuff, Upper Mixed Volcaniclastics, Price Hillside. Samples consist of aphyric to weakly feldspar-phyric mafic volcanic cognate lithic clasts (dark green) and aphyric felsic volcanic cognate lithic clasts (pale green to white). Sample on the left contains a variably bleached, andesite accidental clast (A). Epidote-rich patches (yellow green) in the sample to the right represent strongly altered volcanic clasts or sediment rip-up fragments. Scale divisions are in mm and cm. 61 significant erosion of material from the underlying Upper Dacite unit and, to a lesser degree, Lynx-Myra-Price Horizon, by sediment gravity flow processes also took place. 3.2.2.9 Upper Rhyolite Unit [DCm9] The Upper Rhyolite unit [9] is the stratigraphicaily highest rhyolite horizon in the Mine Sequence. Distribution of rock types in the Upper Rhyolite unit consists of two general parts: ( D a pyroclastic deposit-rich member; and (2) a siliceous argillite-chert dominant member. In most areas the siliceous argillite - chert member underlies the pyroclastic member. The pyroclastic deposit member [ 9] is up to 50 m thick and made up of thin to medium bedded, normally graded, crystal-lithic-vitric coarse tuff to lapilli-tuff, and lesser fine tuff and tuff-breccia deposits (Fig. 3.25). This member displays a distinct lateral facies variation from the VARC region to the ARFT area. It is thickest towards the VARC region, being approximately 50 m in thickness, where it consists mainly of lapilli-tuff deposits with subordinate coarse tuff and tuff-breccia beds. The sequence is generally coarsening-upward with the individual deposits remaining fining upward. The member in the central region (in all sections) is composed of moderately well sorted, fine to coarse tuff and fine lapilli-tuff, and a heterolithic tuffaceous breccia deposit (still contains at least 70 percent rhyolite constituents) which can form up to 25 percent of the sequence. Non-rhyolite constituents comprise lapilli-size clasts of andesite or dacite, chert, jasper, sulphide mineralized (pyrite, sphalerite, chalcopyrite) felsic tuff, massive sulphide (pyrite), and argillite (Fig. 3.25). The pyroclastic deposits in the central region are variably but distinctly purple due to pervasive hematite alteration. Associated fine tuff layers are either dark purple or maroon (Fig. 3.25). Pyroclastic deposits associated with siliceous argillite and chert (see below) are uncommonly affected by this type of alteration. The pyroclastic member in the ARFT region is finer grained and markedly thinner (approximately 10 m) where it eventually disappears. 62 Figure 3.25: Cut slab samples of main rock types in the pyroclastic member, Upper Rhyolite unit, Price Hillside. Sample on the right is a quartz + feldspar crystal-vitric coarse tuff to fine lapilli-tuff. Upper left sample represents a heterolithic tuffaceous breccia deposit. Fragments present include: quartz + feldspar porphyritic rhyolite (Q), quartz * feldspar porphyritic vitrophyre (V), argillite (a), and massive pyrite (s). Bottom left sample is a normally graded, quartz + feldspar crystal-vitric coarse to fine tuff (maroon). Scale divisions are in mm and cm. The most common rock types in the pyroclastic member are coarse tuff to lapilli-tuff deposits (Fig. 3.26). A detailed description of this rock type is in Appendix A. Generally, the coarse tuff to lapilli-tuff deposits consist of 15 to 30 percent crystals comprising plagioclase, minor quartz, trace amphibole, and accessory zircon and apatite. Main clast types present are: quartz + feldspar porphyritic rhyolite accessory clasts; mica-poor, weakly porphyritic felsic cognate lithic clasts; quartz + feldspar porphyritic, sericite-rich felsic cognate lithic clasts; and mafic volcanic accidental clasts. The siliceous argillite - chert member f 9a.c.il consists of thin to medium laminated beds of grey to black siliceous argillite, white to pale green chert, green to gray rhyolite fine tuff, and minor jasper. This member ranges from 1 to 15 m in thickness and is largely confined to the central regions of all sections. Siliceous argillites are the most common rock type in this member and consist of up to 20 percent, angular to subrounded, feldspar and quartz crystals. The argillaceous material is represented by chlorite. Stylolites can be present. Round, relatively unflattened radiolarian 'ghosts' (i 0.1 mm in diameter) also are occasionally observed. The cherts and jaspers commonly contain no recognizable tuffaceous constituents or radiolaria. tn one area in the Price area, thin layers of semi-massive pyrite are intercalated with siliceous argillite and fine tuff. Upper Rhyolite unit represents a lull in volcanism and related volcanogenic sedimentation from the ARFT area. Instead volcanic activity initally consisted of intermittant rhyolitic pyroclastic eruptions from the VARC area that deposited thin suspension and pyroclastic flow deposits. During periods of no volcanic activity, sedimentation consisted of hemipelagic (siliceous argillite) and hydrothermal (chert) deposition. Rhyolitic volcanism gradually intensified in the VARC area resulting in greater amounts of material being deposited on the volcanic aprons. This material, in turn, was resedimented by sediment gravity flow processes into the well-bedded pyroclastic deposit member. 64 Figure 3.26: Well bedded, normally graded, quartz + feldspar crystal-lithic-vitric rhyolite coarse tuff and lapilli-tuff, Upper Rhyolite unit, Price Hillside. Scale bars are each 1 cm long. 65 3.2.2.10 Upper Mafic Unit [DCm 10] The Upper Mafic unit [ 10] is the uppermost litho-stratigraphic unit in the Myra Formation. It is present throughout the property being thickest (> 200 m )'in the ARFT region and thinning to approximately 5 to 20 m towards the VARC area. As the Myra Formation - Thelwood Formation contact possibly represents an unconformity (see section 3.3), this unit is missing in areas and notably thin in others. The main rock types present are basaltic in composition (Table 3.1) and occur mainly as hydroclastic and pyroclastic deposits. Flow and flow breccia, and mixed sedimentary and pyroclastic units are less common. Hydroclastic and pyroclastic deposits are the most abundant lithology in the Upper Mafic unit (Fig. 3.27). The deposits are poorly to moderately sorted and form generally coarsening-upward sequences. Lower parts consist of normally graded coarse tuff to lapilli-tuff deposits. Up section the main deposits become composed of lapilli-tuff and tuff-breccia horizons. Clast sizes vary from 1 mm to 50 cm but more commonly range from 2 to 15 cm. The main clast type is a strongly pyroxene + feldspar porphyritic basaltic flow clast (Fig. 3.27: detailed description in Appendix A). Other, less common volcanic clast types in this member consist of aphyric, fine-grained to medium-grained basalt accessory lithic clasts, and subrounded to rounded, perlitic-textured, aphyric to weakly feldspar + amphibo1e(?) porphyritic felsic accessory lithic clasts. Non-volcanic clasts form i 5 percent of a deposit and include variably sized clasts of spherulitic jasper ± magnetite, pale green to gray chert, bedded mafic fine tuff, and yellow-green, fine-grained epidote-rich sediment. The sediment and, to a lesser degree, tuff clasts were only partially lithified prior to brecciation as the clast margins display penetration textures caused by adjacent crystals and flow clasts (Fig. 3.27). The matrix component in these deposits comprises 15 percent of a deposit and is made up of fine-grained to aphanitic, epidote + quartz containing up to 2 percent feldspar and pyroxene crystals. These clastic deposits were thus formed by post-emplacement brecciation of original deposits. The principal evidence, cited above, includes non-volcanic clast components and margins on basaltic clasts that transect both phenocrysts and microlite patterns. Figure 3.27: Pyroxene + feldspar porphyritic basaltic coarse lapilli-tuff from a hydroclastic and pyroclastic deposit, Upper Mafic unit, Price Hillside. Bottom photograph is of a cut slab sample from the outcrop shown in the top photograph. Yellowish clasts represent rip-up fragments of very fine grained sediment. These clasts display penetration textures caused by adjacent crystal and flow clasts indicating that they were only partly lithified prior to brecciation. Scale bars in top photograph are each 1 cm long; scale divisions in the bottom photograph are in mm and cm. Flow and flow breccia deposits occur as 3 to 15 m thick flow units in the middle to upper parts of the Upper Mafic unit. This rock type is pyroxene + plagioclase porphyritic, variably calcite + chlorite amygdaloidal, and usually contains up to 7 percent epidote vein lets. The uppermost parts of this member in the ARFT region contain moderately to strongly purple, hematite + carbonate ± sericite altered hyaloclastite (Fig. 3.28). Clasts in the hyaloclastite are rimmed, aphyric to weakly phyric, and contain 10 percent (up to 40 percent), 2 to 15 mm in diameter, calcite + hematite amygdules. Many have subrounded to rounded, fluidal-like shapes, due in part to the ultramafic affinity of parts of this phase (Chapter 4). Mixed sedimentary and pyroclastic deposits are found in the middle to lower parts of the Upper Mafic unit. They are only sporadically present in the ARFT region, but are equal to or greater in abundance than to the above two deposit types towards the VARC area. The deposits are 2 to 7 m thick and consists of thinly bedded, massive to laminated cherty tuff, jasper and chert, and epidote-rich mudstone beds. Fine to coarse tuff and fine lapilli-tuff deposits are also present. Primary sedimentary structures, such as scours and flames, are common. The hydroclastic nature of many parts of the Upper Mafic unit reflects phreatic and/or phreatomagmatic explosive activity in the source area. The debris was sloughed off into the rift basin by means of debris flows. Effusive phases eventually began to cover parts of the mine-area. If additional members of the Upper Mafic unit were deposited before cessation of this volcanic event, they would have been eroded at the unconformity between the Mine Sequence and Thelwood Formation. 3.2.2.11 Volcanic Source Regions Field relationships, particularly thickening and thinning, proximal to distal characteristics, permit definition of four volcanic source regions for Myra Formation lithologies. These are defined and examined in more detail later (Chapters 4 and 5). To facilitate orientation and description, they are named here (Table 3.2; see Fig. 3.2 for orientation): (I) the volcanic arc (VARC) series from the volcanic arc region, (2) the Price seamount (PSMT) series from southeast of the Price area, 68 • I 1* ... . 1 . 1 9 1 , 1 , _ T IUI ' i n 121 1 , I2 1 . 1 , 1 ,r, Figure 3.28; Strongly hematite- and carbonate-altered ultramafic hyaloclastite, Upper Mafic unit, Price Hillside. Fragments are aphyric and chlorite and calcite amygdaloidal. White grains in the matrix are carbonate. Scale divisions are in mm and cm. TABLE 3.2 Litho-stratigraphic units found in the four volcanic series of the Myra Formation, Buttle Lake Camp, Vancouver Island, B.C. See Figure 3.2 for orientation. Source Region Volcanic Series Litho-stratigraphic Units Volcanic arc region VARC H-W Horizon (felsic flow member) Ore Clast Breccia unit (Interzone Rhyolite) North Dacite Lynx-Myr a-P r ice Hor izon Upper Rhyolite unit Southeast of the Price area PSMT H-W Horizon (dacite flow unit) Upper Dacite (lower member) Northwest of the West G area WSMT Hanging Wall H-W Andesite 5E Andesite Upper Dacite (upper member) Arc rift region ARFT H-W Horizon (mafic flow member) G-Flow unit Upper Mafic unit (3) the West G seamount (WSMT) series from northwest of the West G area, and (4) the arc rifting (ARFT) series from the arc rift region. The relative positioning of these series in the Myra Formation (Mine Sequence) are shown in two generalized cross sections in Figure 5.1 and an idealized longitudinal section reconstruction in Figure 5.2 (both figures are in Chapter 5). 3.2.3 THELWOOD FORMATION (SHARP BANDED TUFF) [DCt] The Thelwood Formation [DCt] is a 270 to 500 m thick bedded sequence of siliceous tuffaceous sediments, subaqueous pyroclastic flow deposits and penecontemporaneous mafic sills. This unit is present throughout the mine property but the best exposures occur on the west side of the mouth of Thelwood Creek and around Myra Falls. The rock units can be grouped into three general, repetitive lithologies: (1) tuffaceous sediment units, (2) pyroclastic deposit units, and (3) mafic sills. Components of all three occur within each generalized member. Tuffaceous sediment units range from 5 to 30 m in thickness and consist of massive to thinly bedded, very thinly to thinly laminated tuffaceous mudstone and siltstone, mudstone, and vitric ± crystal fine tuff (Figs. 3.29 and 3.30). Minor chert layers are also present. Also present are up to 20 percent coarse grained subaqueous pyroclastic deposits. Bedding and laminations are mostly straight to wavy parallel with only rare cross laminae. The beds are normally graded to massive in the mudstone deposits. Rare beds display convolute laminae and fluid escape structures. The mudstone deposits (Fig. 3.29) are composed of relatively phyllosilicate-free, quartz + feldspar aggregates with variable amounts of epidote and/or clinozoisite. The si Itstone and fine tuff deposits (Fig. 3.31) consist of 1 to 15 percent, broken plagioclase crystals; trace to 1 percent broken quartz grains; and rare to 5 percent accessory intermediate flow clasts. The matrix is shard-rich containing platy and slivered shards (Fig. 3.31). The tuffaceous sediment units probably represent sedimentation by suspension fallout and minor turbidity currents. Figure 3.29: Tuffaceous sediment unit, Thelwood Formation, Price Hillside. Pale beds in top photograph are thinly bedded tuffaceous mudstone and siltstone. Massive dark beds are crystal-lithic fine to coarse tuff. Cut slab sample in bottom photograph represents thinly bedded tuffaceous mudstone and siltstone. Scale divisions in bottom photograph are in mm and cm. 72 TOP s / "> \ / \ / - / rubbla nibble rubbK BOTTOM Figure 3.30: Measured stratigraphic section of a tuffaceous sediment unit, Thelwood Formation, Price Hillside. Location of the section, in terms of mine coordinates, is 171 +25 E and 120+ 50 N. Lithology patterns are: blank = tuffaceous mudstone and siltstone (< 0.1 mm), dots = tuff (0.1 to 2 mm), small circles = lapilli (> 2 to 64 mm), irregular to rectangular shapes = tuffaceous mudstone rip-up clasts, lines = thinly bedded sequences, and random dashes = mafic sill. Abbreviations are: Pyr = subaqueous pyroclastc flow deposit, and s = scoured base. Figure 3.31: Normally graded, very thinly laminated, vitr ic-crystal fine tuff, tuffaceous sediment unit, Thelwood Formation, Price Hillside. Photograph to the left is of a cut slab sample (scale divisions are in mm and cm). Photomicrograph to the right shows platy and slivered snard-rich nature of the fine tuff Field of view is 3 mm x 4 mm. Pyroclastic deposit units range from 4 to 25 m in thickness and consist of vitric-lithic, fine lapilli-tuff to coarse tuff beds intercalated with up to 50 percent tuffaceous sediment deposits (Figs. 3.32 and 3.33). The pyroclastic deposits are moderately well sorted and massive to crudely parallel stratified; scoured bases are common. Clast sizes rarely exceed 1 cm, but rectangular tuffaceous mudstone rip-up clasts are up to 40 cm by 10 cm. The deposits are non-graded to normally graded although reverse grading of lithic clasts was observed locally. Upper parts of some deposits contain thinly bedded, coarse to fine tuff which displays a fining-upward sequence that grades into tuffaceous siltstone or mudstone beds. (This feature has been called a doubly graded sequence by Fiske and Matsuda (1964) in subaqueous pyroclastic flow deposits.) Many deposits in this member also show a pronounced, non-tectonic, primary orientation of constituents. Welded zones in some subaqueous pyroclastic flow deposits also have been recognized in places (Juras, 1986; Appendix B). The pyroclastic deposits are intermediate in composition (Table 3.1) and composed of 2 to 10 percent, usually broken plagioclase crystals; trace broken quartz grains; 10 percent, aphyric to weakly plagioclase porphyritic, hyalophitic to hyalopilitic intermediate accessory lithic clasts; trace to 15 percent, vitric tuff accessory lithic clasts (from older pyroclastic deposits); and 10 to 25 percent, subrounded to rounded, variably perlitic-textured, aphyric, mica-poor felsic cognate lithic clasts (Fig. 3.34). Tuffaceous mudstone rip-up clasts are common and generally are concentrated in the lower portions of a deposit (Fig. 3.32). A few massive pyroclastic deposits have plastically-deformed chert clasts or lenses in their uppermost parts. The matrix component consists of relict platy shards and fine-grained vitric(?) debris now altered to chlorite and lesser epidote (Fig. 3.34). The pyroclastic deposits represent subaqueous pyroclastic flows and resedimented deposits emplaced by debris flows and turbidity currents from oversteepened, pyroclastic debris-rich volcanic slopes. Mafic sills consist of 1 to 90 m thick, massive basaltic to basaltic andesite (Table 3.1) sills. They are found throughout the Thelwood Formation but are generally more common in the lower portions. Theyalsoseem to be associated with the tuffaceous sediment units (Fig. 3.35). Someof thickest sills are found at the Myra Formation - Thelwood Formation contact. The sills tend to follow bedding planes but correlation of individual units between drillholes is difficult. This may be due to Figure 3.32: Pyroclastic deposit unit, Thelwood Formation, Price Hillside. Massive brown bed in left photograph represents a subaqueous pyroclastic flow deposit that has cut into the underlying tuffaceous mudstone beds. Note the mudstone rip-up clasts (R) in the pyroclastic bed Cut slab sample in the right photograph represents contact between a subaqueous pyroclastic flow deposit and siliceous tuffaceous sediment beds. Constituents in the flow deposit consist of cognate lithic clasts (v) , relict pumice clasts, accessory lithic clasts (L), and plagioclase crystals and relict shards. Scale divisions are in mm and cm. 76 T O P rubbl* Pyr Pyr Pyr Pyr Pyr B O T T O M Figure 3.33: Measured stratigraphic section of a pyroclastic deposit unit, Thelwood Formation, Price Hillside. Location of the section, in terms of mine coordinates, is 176+30 E and 121+00 N. Lithology patterns and abbreviations are as defined in Figure 3.30. Discontinuous lined pattern ' represents discontinuous or poorly defined layering. Figure 3.34: Photomicrographs showing vitric constituents in subaqueous pyroclastic deposits, pyroclastic deposit unit, Thelwood Formation, Price Hillside. Top photomicrograph contains platy shards and relict pumice clasts. Symbols are: p = pumice clast, c = plagioclase crystals, and L = accessory andesite flow clasts. Bottom photomicrograph shows perlitic-textured cognate lithic clasts (v). Field of view in both photomicrographs is 3 mm x 4 mm. Figure 3.35: Mafic si l l , Thelwood Formation, Price Hillside. Top photograph shows typical mafic sill (massive, dark green layer) - tuffaceous sediment (pale unit) association. Sill is approximately 6 m thick. Bottom photograph is a close-up on the upper contact which displays flame-like protrusions of tuffaceous mudstone into the sill. This feature was caused by the intrusion of the sill into wet, unlithified sediment. 'step-and-stair' transgression (Francis, 1982). Contacts of sills can be finer grained than the interiors and reflect chilled margins (Fig. 3.36). In some samples the contacts consist of a 2 to 10 mm wide relict shard-bearing margin (Fig. 3.36). Sills are dark green, characteristically 2 percent epidote veined, generally medium-grained, aphyric, and composed of approximately 60 percent subhedral to euhedrai plagioclase ; 5 percent subhedral magnetite; trace to 7 percent, anhedral quartz; and trace chlorite amygdules. The groundmass displays an intersertal texture with the interstitial mesostasis altered to chlorite and minor epidote. Some of the thicker sills contain zones of coarser grained, weakly porphyritic phases. These phases consist of up to 3 percent, 1 to 3 mm long plagioclase glomerocrysts, and trace to 2 percent, 1 to 3 mm long clinopyroxene phenocrysts in a pyroxene-bear ing, intergranular groundmass. Sills apparently were intruded into wet, unlithified sediment. This is indicated by the presence of hyaloclastitic contacts, flame-like protrusions of tuffaceous sediment into the sill (Fig. 3.35), and the pervasive epidote alteration of the injected portions of the sediment. These interaction features are similar to other documented examples of interaction between wet sediment and magma (Kokelaar, 1982). Thelwood Formation is a basaltic sill-sediment complex somewhat like the Guaymas Basin (Einsele, 1985). The lack of coarse clastic deposits and the presence of numerous intercalated fine-grained, siliceous tuffaceous sediment beds implies a distal location of the basin relative to active volcanoes. 3.2.4 FLOWER RIDGE FORMATION [DCfr] The Flower Ridge Formation [DCfr] is the uppermost Paleozoic unit exposed in the mine-area. The unit is basaltic in composition (Table 3.1) and consists mainly of moderately to strongly . amygdaloidal feldspar ± pyroxene porphyritic basaltic lapilli-tuff, tuff-breccia and pyroclastic breccia (Fig. 3.37). Other rock types of this formation are fine to coarse tuffs, basalt flows and flow breccias, and bedded tuffaceous mudstone and argillaceous sediments. The top of the Flower Ridge 80 Figure 3.36: Mafic sill - tuffaceous sediment contact, Thelwood Formation, Price Hillside. Cut slab sample in top photograph shows the sill contact to have a chilled margin (darkest areas). In thin section (photomicrograph in bottom) the margin is seen to be composed of relict shards (indicativeof interaction with water) and plagioclase crystals. The sediment is pervasively altered with epidote due to hydrothermal alteration caused by the intrusion. Scale divisions in the top photograph are in mm and cm. Field of view in the photomicrograph is 3 mm x 4 mm. 6! Figure 3.37: Strongly amygdaloidal basaltic tuff-breccia, Flower Ridge Formation, Price Hillside. White 'grains' in top photograph are a weathering feature of the amygdules in outcrop. The amygdule mineralogy is shown more clearly in a cut slab sample (bottom photograph). Most amygdules consist of chlorite (dark green) with lesser quartz. In the coarser clasts, additional amygdule phases include epidote, quartz and albite. Scale bars in top photograph are each 1 cm; scale divisions in bottom photograph are in mm and cm. Formation is not on the mine property - only the lower 650 m can be observed. Traverses on the west side of Flower Ridge south of the south end of Buttle Lake, however, show that this formation extends to the contact with the overlying Buttle Lake Formation. The contact with the underlying Thelwood Formation is conformable and characterized by the first appearance of abundant scor iaceous volcanic clasts in either pyroclastic or sedimentary beds. In places the contact zone is marked by a 5 to 15 m thick, rhyolite pyroclastic lapilli-tuff to fine tuff sequence. This horizon may also contain interbedded argillite that locally is purplish due to hematite alteration. A lateral facies variation was not recognized. A general change in vertical facies, though, was observed. The lowermost units consist of an approximately 30 m thick sequence of normally graded basaltic lapilli-tuff to coarse tuff deposits. This is followed by a > 30 m thick section of intercalated, white weathering, massive to thinly laminated tuffaceous mudstone to mudstone, feldspar crystal-vitric coarse to fine tuffs, and feldspar porphyritic mafic sills. The remainder (and majority) of the unit is composed largely of basaltic pyroclastic deposits. It generally starts as a coarsening-upward sequence consisting of fining-upward deposits of fine lapilli-tuff to coarse tuff, coarse to fine lapilli-tuff to coarse tuff, and tuff-breccia to lapilli-tuff. Flow breccia and minor flows occur with the coarsest clastic members. The rest of the sequence is essentially a ser ies of normally graded, fine lapilli-tuff to coarse tuff deposits with minor coarser clastic layers and uncommon fine tuff beds. Basaltic pyroclastic deposits (Fig. 3.37) consist of 5 to 15 percent, variably broken plagioclase crystals; trace to 1 percent, euhedral clinopyroxene crystals; 15 to 40 percent, irregularly shaped to subrounded, moderately to strongly amygdaloidal (< 1 mm, usually 0.1 to 0.5 mm in diameter), aphyric to weakly plagioclase glomeroporphyritic, hyalophitic to hyalopilitic essential clasts; 5 to 20 percent, subangular to subrounded, finely (approximately 1mm in diameter) to coarsely (2 to 8 mm in diameter) weakly to moderately amygdaloidal, plagioclase (10 percent) + clinopyroxene (il percent) porphyritic, pilotaxitic accessory to essential clasts; up to 10 percent, green, angular, variably perlitic-textured, fine-grained chlorite-rich cognate lithicdasts; rare to 5 percent, pale yellow to white, hard, aphyric to weakly feldspar-phync, strongly altered (clinozoisite and/or epidote), pilotaxitic accessory or accidental clasts; and rare, subrounded, pyritic siliceous accidental clasts. The amygdaloidal clasts contain a variety of cavity-fill ing minerals. Fine amygdules are generally monomineralic consisting mainly of chlorite and lesser epidote, quartz and albite. Coarse amygdules within clasts are commonly concentrically zoned. The coarsest amygdules always occupy the core of a clast. The amygdule mineral phases comprise quartz, albite, clinozoisitc and/or epidote, and pumpellyite. The first clast type described above appears to represent bombs and broken bombs. The second type could represent bomb fragments or pieces of flow debris. The white clasts and the pyritic fragments could represent hydrothermally altered material liberated by phreatic explosions. The matrix of the basalt pyroclastic deposits has a diagnostic creamy white and medium green, mottled appearance (Fig. 3.37). In thin section, the white component corresponds to irregularly shaped to subrounded clasts( ?) of massive, very fine-grained clinozoisite with minor chlorite and occasional feldspar crystals. The green component consists of relict shards which occur as slivers, globules or platy fragments (Fig. 3.38) that fill all interclast and crystal spaces. Compaction textures of the shards against some clasts and crystals are common (Fig. 3.38). The matrix can contain up to 3 percent amygdules of chlorite, zoisite and/or epidote, commonly concentrated at clast - shard-rich matrix boundaries. These amygdules and compaction textures are indicative of agglutinate deposits (accumulation of basaltic spatter associated with Strombolian- and Hawaiian-type eruptions: Macdonald, 1972). Flower Ridge Formation represents the resumption of effusive basaltic activity from a proximal source. The coarsen ing-upward sequence interval denotes a prograding submarine volcaniclastic apron. The deposits were emplaced by sediment gravity processes coupled with air-fal I tuffs and lapilli-tuffs. The monolithic nature and the lack of pelagic deposits above the lower sections suggest continual eruptive activity. The strongly amygdaloidal nature of many of the clasts, in addition to the dominant lapilli-tuff size of the elastics, implies that the volcanism consisted of shallow marine Strombolian eruptions. Hot emplacement of ejecta is indicated by agglutinate deposits. Figure 3.38: Photomicrographs ot matrix components, basaltic pyroclastic (agglutinate) deposits, Flower Ridge Formation. Top photomicrograph shows relatively undeformed platy to globular shards Bottom photomicrograph contains compacted relict shards against basaltic essential clasts. Field of view in both photomicrographs is 3 mm x 4 mm. 85 3.2.5 INTRUSIVE ROCKS [Jg.TRb] Intrusive phases on the mine property, from oldest to youngest, are: (I) Paleozoic or Triassic diabase dikes, (2) Triassic basaltic sills and dikes related to the Karmutsen Formation, (3) Jurassic feldspar porphyry and quartz diorite dikes related to the Island Intrusions, and (4) Jurassic or younger quartz + feldspar porphyritic rhyolite and hornblende gabbro dikes. These are described below. Paleozoic or Triassic diabase dikes are the second most abundant intrusive unit. They are usually less than I m wide, dark brown, aphyric and always strongly carbonate altered. There are several sets of dikes, but all have been affected by the major Jurassic deformational event, which constrains the age of their intrusion as Paleozoic, Triassic or both. Certain mafic sills and dikes in the Thelwood and Flower Ridge Formations are inferred, on the basis of lithologic similarity, to represent dikes related to the Triassic Karmutsen Formation [TRb]. These basaltic sills and dikes are thick (up to 300 m), coarse to very coarse grained, and contain relatively unaltered pyroxene and plagioclase grains. Jurassic feldspar porphyry [ Jfp] and quartz diorite [ Jqd] dikes are the most abundant intrusive phase on the mine property. The feldspar porphyry dikes are intermediate in composition and contain 10 percent, up to 1 cm long plagioclase phenocrysts in a fine to medium grained, magnetic groundmass. The dikes, up to 25 m wide, crosscut all Sicker Group lithologies and fold-related fabrics in the mine-area. The latest event (Jurassic or younger) is represented by rare quartz + feldspar porphyritic rhyolite dikes, and a coarse to very coarse grained hornblende gabbro dike lJgb]. These dikes crosscut all other intrusive rocks as well as most (but not all) faults. 86 3.3 STRUCTURAL GEOLOGY 3.3.1 INTRODUCTION The structural setting of the mine property and Buttle Lake uplift have been studied by Gunning (1931), Jeffery (1965), Walker (1980, 1983, 1985) and Westmin Resources Ltd. (internal company reports). Previous work in the mine-area focussed around the massive sulphide bodies and the host lithologies. This is especially true for the Lynx-Myra-Price (L-M-P) Horizon with most of the work being done in the Lynx Mine region. This earlier work (Walker, 1983,1985; internal company reports) outlined a subhorizontal, northwest trending (attitudes are relative to true north, which is 45" west of mine north) asymmetric anticline with a steeply dipping southwestern limb and a gentle dipping northeast limb (Fig. 3.6). In the Myra Mine area the L-M-P Horizon is compressed into symmetrical, tight to isoclinal folds. Axial planar foliations in both areas are northwest trending with near-vertical to steeply northeast-dipping surfaces. In places a second, less prominant foliation was observed having similar trends but moderately steep southwest dipping surfaces. Linear elements in these regions have variable bearings and plunges from shallow northwest to shallow southeast. Results of this thesis, below, add to the evolving structural picture of the mine-area. However, a more focussed study is recommended to fully resolve the structural history in both the mine-area and the Buttle Lake uplift. 3.3.2 PRICE HILLSIDE STRUCTURE Structural geology of the Price hillside is discussed b y treating the Thelwood Formation and the Myra and Price Formations separately. Furthermore, to help in the structural evaluation, the Myra Formation was subdivided into three subareas based on the presence of an anticline defined by lithologic units in the overlying Thelwood Formation (Figs. 3.3, 3.39 and 3.42). Rock units comprising the respective limbs of this structure were chosen as separate subareas as well as the hinge region of the anticline. These subareas and the general structural data for the Price Hillside are shown in Figure 3.39. More detailed structural data are shown in Figure 3.40 (in back pocket). The Flower Ridge Formation is omitted from this discussion because of the paucity of structural data. Bedding attitudes (Fig. 3.41) and geologic cross sections of the map-area (Figs. 3.3 and 3.42, both in back pocket) are used to determ ine folds and fold geometries in the Myra and Pr ice Formations. Minor fold structures were rarely observed (outside the Myra Formation - Thelwood Formation contact zone; see below). Bedding attitudes predominantly are low to moderately southwest-dipping and northwest (subarea 1) to west-northwest (subarea 3) trending (Figs. 3.41a and 3.41c). A lesser bedding component displays similar trending but moderately to steeply northeast-dipping attitudes. Bedding in subarea 2 is northwest to north-northwest striking with a range from vertical to moderate northeast and southwest dips (Fig. 3.41 b). Fold geometries in subarea 1 are northeast verging with limb orientations indicating a shallowly southeast plunging axis and a steeply southwest-dipping axial surface. In subarea 2, folding geometries range from tight upright folds and northeast to southwest verging folds with shallow southeasterly plunges. Axial planes generally strike northwest with vertical to steep southwest or northeast dips. Fold style was difficult to ascertain in subarea 3 because of the lack of exposed bedded units and the increased amounts of massive deposits (flows and related breccias). Bedding attitudes around the subarea 2 and 3 boundary region and foliation attitudes suggest upright to southwest verging structures with plunges and trends sim ilar to subarea 1 structures. Bedding in the Thelwood Formation displays gentle southwest- to northeast-dipping and northwest trending attitudes (Fig. 3.4Ig) which outline open, upright folds. Limb orientations indicate horizontal to shallowly northwest plunging axes with nearly vertical, northwest trending axial surfaces (Fig. 3.41 h). Bedding attitudes in this unit change in orientation to east-northeast trending with moderate south dips adjacent to the Jurassic Island Intrusions exposed on Mt. Myra. Penetrative fabrics, developed only within the Myra and Price Formations, consist of axial planar foliations, and mineral and clast elongation lineations on the foliation surfaces. Foliations are best developed in phyllosilicate-rich units (e.g. the Price Rhyolite and the pyrite mineralized rhyolite coarse tuff 'rafts' within the Ore Clast Breccia unit), in most rock types near the boundary Figure 3.39: Location of structural subareas within the Myra Formation, Price hillside, Buttle Lake Camp, Vancouver Island, B.C. Structural subareas, zones 1,2 and 3 (different cross hatching), represent SW limb, hinge area, and NE limb, respectively. Also shown are major structural elements for the Price Hillside (see Fig. 3.40, in back pocket, for detailed structural measurements). Stereonet plots of structural data are in Fig. 3.41). Unit symbols are: DCt = Thelwood Formation and DCm = Myra Formation. Numbers 1, 2 and 3 refer to the structural subareas used to aid in structural analysis. U represents an unconformity. 89 Figure 3.41: Equal-area stereonet diagrams for Price Hillside structural data (see Fig. 3.39 for location of structural subareas). The following are plotted: a) poles to bedding, Myra Formation,- . subarea 1; b) poles to bedding, Myra Formation, subarea 2; c) poles to bedding, Myra Formation, subarea3; d) lineations ( + ) and poles to schistosity, Myra Formation, subarea 1; e) lineations (+ ) and poles to schistosity, Myra Formation, subarea 2; f) lineations (+) and poles to schistosity, Myra Formation, subarea 3; g) poles to bedding, Thelwood Formation; and (h) a contour diagram for the bedding attitudes in (g). Structural data used are plotted in Fig. 3.40 (in back pocket). with the overlying Thelwood Formation, and in subarea 2. They have a northwesterly strike and steep dip throughout the region. Dip directions, however, are variable. In subarea 1 the foliation is vertical to steeply northeast- and steeply southwest-dipping (Fig. 3.4Id). The southwest component becomes less common in subarea 2 and uncommon in subarea 3 (Figs. 3.4 Je and 3.41f). Vertical attitudes also diminish towards subarea 3. The main foliation dip direction in subarea 3 is steeply northeast (Fig. 3.41 f). More than one foliation in an outcrop is rarely observed. The most common linear elements in the Myra and Price Formations consist of bedding and cleavage intersection lineations and clast elongation lineations. Both generally cluster around a gently plunging southeast trending direction in subareas 1 and 3 (Figs. 3.41 d and 3.410. Insubarea2, these lineations remain gently plunging but are characterized by a variation in orientations from east to south-southeast (Fig. 3.41e). Two main joint sets were recognized in the Price area. One set, developed parallel to a-c fold axes (see below), trends northeast with vertical dips. The second set forms a conjugate shear pair. These fractures are mainly north-northeast striking with nearly vertical to steeply east dips, and east-northeast striking with steeply north dips. 3.3.3 DEFORMATIONAL HISTORY OF THE MINE-AREA The main deformational event in the Buttle Lake Camp is Mesozoic in age and affected all pre-Mesozoic stratigraphy in the area. It is expressed in the Thelwood Formation as northwest trending, horizontal to shallowly northwest plunging, upright open folds. No foliations or lineations attributable to this event are recognized in Thelwood Formation lithologies. However, there is a distinct northeast striking, vertical joint set perpendicular to fold axes defined by bedding. Effect of the Mesozoic event on the Myra and Price Formations resulted in the development of second-order or parasitic folds (Hobbs etal, 1976) relative to folds in the Thelwood Formation. The resultant structures, confined largely to the anticlinal cores (defined by folds in the Thelwood Formation), are northwest trending asymmetric open folds with steep southwest- to northeast-dipping axial surfaces, and, less commonly, symmetrical, tight to isoclinal folds with vertical axial planes. This is reflected 91 by the range of steep northeast to steep southwest dips in the predominant foliation on the mine property. Plunges of these structures are shallow and vary in direction from- northwest (Lynx area) to southeast (Price area). Relative to the folding style in the Thelwood Formation, Myra Formation structures can be classified as disharmonic, reflecting contrasting ductilities between the two units (Myra Formation was more ductile). Another interpretation for the contrasting fold styles between the Myra and Thelwood Formations invokes two stages of deformation where the earlier phase is pre-Thelwood. This hypothesis explains the variation in Myra Formation fold symmetries along the same anticlinal core region from the northwest end of the mine property (Lynx and West G) to the southeast end (Price). The main stuctures in the Lynx and West G sections (Figs. 3.6 and 3.7) are southwest verging whereas the the main structures in the Price section (Figs. 3.3 and 3.42) are northeast verging. Associated . ljneations also have opposite orientations. These variances could represent refolding about an almost coaxial fold axis with the Lynx and Price zones being on opposite limbs. This later fold axis would intersect the earlier axis in the Myra area, causing the generally symmetrical nature of the folding in the Myra ore zones (fig. 2 in Walker, 1985). Lithologies in the Buttle Lake Camp also experienced at least two deformational phases after the main Mesozoic episode. The first is characterized by rotation of bedding due to later intrusion of batholiths of the Jurassic Island Intrusions. The second phase might be represented by the north-northeast and east-northeast trending joint sets observed in the mine-area. These joints may have formed as a result of Cretaceous to Tertiary tectonics related to uplifting of the Buttle Lake area. 3.3.4 MINE-AREA FAULTS Most of the numerous mine property faults are high angle, normal faults (e.g. Fig. 3.3); some are strike-slip (Walker, 1985). Though they occur with many different orientations, the main trends are northeast, north, northwest and east-southeast. Many of the more significant faults are associated with schistose zones commonly characterized by gouge, breccia, schistosities parallel to the fault, and abundant kink bands. The kink bands commonly occur singly and deform the last foliation phase. They have axial planes that either strike northeast and dip steeply northwest or strike easterly and dip steeply north, and have fold axes with moderate north plunges and steep southwest or steep east-northeast plunges. Locally bedding, foliations and joints have been rotated near some faults. Fault displacements range from centimeters to hundreds of meters. Most offsets are less than 100 in. The largest measured offset occurs on the Myra-Price fault (see Fig. 3.2) with an estimated net slip of 850 m (Walker, 1985). The majority of the faults are probably post-Mesozoic having formed during uplift in Late Cretaceous time (Yorath etal, 1985) or compression in the Tertiary (Muller, 1980). 3.3.5 MYRA FORMATION (MINE SEQUENCE) - THELWOOD FORMATION CONTACT The contact between the Myra Formation and the overlying Thelwood Formation is a zone of high strain. This zone, 2 to 40 m wide, has been folded by the Mesozoic event, and is characterized by strong to intense schistosity and small scale tight to isoclinal folding of both primary layering and the schistosity. The schistosities are generally parallel to the contact. Relict primary minerals and amygdules have undergone varying degrees of rotation. The majority of this deformational fabric is contained in Myra Formation lithologies. On the Thelwood Formation side, rock units contain no deformational fabrics (the mafic sills) or are only moderately deformed (thinly bedded sediments) characterized by small scale irregular folds without noticeable schistosity. These observations indicate that rock units on either side of the contact behaved as separate blocks of different competency during deformation. Further constraints on the nature of this contact are provided by the distribution of rock units along it. The contact always occurs in the upper stratigraphic units of the Myra Formation, namely the Upper Mafic unit and, to a lesser extent, the Upper Rhyolite unit. The Upper Mafic unit is absent or abnormally thin in places along the contact. This variation does not follow the pattern of fades changes documented in this unit from southwest to northeast on the property. On the Thelwood Formation side, the mafic sills, commonly present along the contact, never are observed below it. The environment of deposition also changes abruptly across the contact. The paleoenvironment indicated 93 ' below the contact is that of encroaching, effusive mafic volcanic activity, whereas above the contact it is that of hemipelagic sedimentation far removed from centers of volcanic activity. These structural and lithologic observations suggest that this contact zone is a possible unconformity which existed in the Late Devonian to Early Mississippian. This unconformity could reflect either a period of erosion or non-deposition prior to the start of deposition of Thelwood Formation units. The Myra - Thelwood contact may have become a site for low angle faults in Late Paleozoic time, or a decollement during Mesozoic deformation due to different deformational behavior above and below the contact. 3.4 ALTERATION AND METAMORPHISM The Sicker Oroup in the Buttle Lake uplift is characterized by low grade regional metamorphism. The emplacement of the Early Jurassic Island Intrusions reset K-Ar and, to a lesser degree, Rb-Sr isotopic dates (see section 3.5). This suggests that the superimposed early Mesozoic metamorphism was primarily dynamothermal (cf. Walker, 1983,1985). However, most parts of the Sicker Group in the mine-area appear to have undergone regional submarine hydrothermal metamorphism, hydrothermal alteration associated with mineralization, and burial metamorphism. The observed metamorphic mineral assemblages are common to those established in studies on sea floor metamorphism (Miyashiro, 1972; Moody, 1979), ophiolite complexes (e.g. Gass and Smew ing, 1973; Coleman, 1977; Moody, 1979; Stern and Elthon, 1979; Evartsand Schiffman, 1983), volcanogenic massive sulphide deposits (e.g. Andrews and Fyfe, 1976; Gibson etal., 1983; Reed, 1983, 1984) and active geothermal systems (e.g. Bargar and Beeson, 1981; Henley and Ellis, 1983; Bird eta/., 1984). Metamorphism in the mine-area is best described by dividing the four formations present into two: (1) Price and Myra Formations, and (2) Thelwood and Flower Ridge Formations. The observed metamorphic mineral assemblages in the mine-area are summarized in Table 3.3. 94 3.4.1 PRICE AND MYRA FORMATIONS . Rock units In the Price and Myra Formations are characterized by lower greenschist mineral assemblages similar to those attributed to regional submarine hydrothermal metamorphism (cf. Reed, 1983, 1984), and locally, hydrothermal alteration associated with sulphide mineralization. The metamorphic mineral assemblages are diverse, reflecting the bulk composition of rock types (ultramafic to rhyolite) in the Myra Formation and whether the unit is flow dominant or clastic dominant. Thus the regional hydrothermal alteration yielded a wide range of mineral assemblages making detailed interpretation of all assemblages present difficult. Description of the alteration and metamorphism in the Price and Myra Formations is best done in terms of ultramafic to intermediate volcanic rocks (high MgO basalts, basalts, basaltic andesites and andesites) and felsic volcanic rocks (feldspar porphyritic felsic volcanics (dacite to rhyolite in composition) and quartz + feldspar porphyritic rhyolites). Metamorphic mineral assemblages of the main lithologic types are in Table 3.3. Alteration of ultramafic to intermediate volcanic flows and clasts generally formed either epidote-dominant or chlorite-dominant assemblages of which the former is more common. Alteration of high MgO basalts yielded actinolite + chlorite + albitic plagioclase ± epidote. Epidote occurs irregularly in the groundmass but is commonly present as veinlets and amygdule phases. Certain high MgO basalt hyaloclastite deposits (e.g. those overlying the Lynx-Myra- Price Horizon in the West G and Lynx sections) experienced moderate to intense alteration to chlorite + calcite + sericite + hematite. Metamorphic mineral assemblages in basaltic units (specifically those in the Upper Mafic unit) consist of chlorite + quartz + albite, chlorite + epidote + albite + quartz ± actinolite ± calcite, and epidote + quartz + albite + calcite ± actinolite. Observed metamorphic mineral assemblage in the basaltic andesites and andesites comprise chlorite + epidote + albite + quartz ± calcite ± actinolite. Actinolite is only common in pyroxene-bearing units, in particular those within the Price Formation. f ABLE 3.3 Common metemorphic mineral assemblages in Sicker Group rock units, Price Hillside, Buttle Lake Camp, Vancouver island, B.C. Formation Rock Type Metamorphic Assemblage(s)1 Price basaltic andesite, andesite chl + ep + ao + q + cc ± act Myra high MgO basalt act + chl + ab + ep chl + cc + ser + hem basalt chl + q + ab chl + ep + ab + q ± act ± cc ep + q + ab + cc ± act basaltic andesite, andesite ep + ab + q ± chl ± cc ± act chl + ab + q ± ep ± cc feldspar porphyritic felsic volcanics ab + q + ep + ser ± chl ± hem quartz+ feldspar porphyritic rhyolite ser + q + ab ± chl Thelwood intermediate tuffs chl + ep (± clz) + q + ab mafic sills chl + ab + ep Flower Ridge basalt chl + ep (± clz) + ab + q + act ± cc ± pp chl + ep (± clz) + ab + q + act ± cc 1. Mineral abbreviations are: ab = albite, act = actinolite, cc = calcite, chl = chlorite, clz = clinozoisite, ep = epidote, hem = hematite, pp = pumpellyite, q = quartz, and ser = sericite. Metamorphic assemblages produced in the ultramafic to intermediate volcanic units are similar to those documented in mid-ocean ridges (cf. Mottl, 1983), or predicted in seawater-basalt reaction experiments (e.g. Bischoff and Dickson, 1975; Mottl and Holland, 1978; Seyfried and Bischoff, 1981) and theoretical studies (e.g. Reed, 1983). Variations in assemblages in the ultramafic to intermediate volcanic rocks generally can be explained by the presence of multiple water/rock ratios in the hydrothermal system (Reed, 1983). The chlorite-dominant assemblages reflect high water/rock ratios, whereas the epidote-rich assemblages indicate low water/rock ratios (Mottl, 1983; Reed, 1983). The marked differences in alteration assemblages in some ultramafic hyaloclastites described above, though, suggest alteration in those units by compositionally different fluid phases rather than by variations in temperatures and water/rock ratios (see Chapter 5). The occurrence of units containing clasts of similar original composition but with different metamorphic mineral assemblages together in the same deposit is interpreted to represent concurrent hydrothermal metamorphism and associated volcanic activity. This is best illustrated in the hydroclastic deposits of the Upper Mafic unit. In these deposits, basaltic clasts representing all three metamorphic mineral assemblages (see above) can occur side by side (i.e. a chlorite + quartz altered clast can occur next to an epidote + albite + quartz altered clast). Clearly alteration formed prior to brecciation and final deposition. The clasts are assumed to have been of similar composition as they are interpreted to be parts of former flows that were brecciated due to phreatic activity after emplacement (section 3.2.2.10). Alteration and metamorphism of felsic volcanic rocks in the Myra Formation formed numerous mineral assemblages. Hydrothermal metamorphism of feldspar porphyritic (FP) felsic volcanic rocks yielded the assemblage albite + quartz + epidote + sericite ± chlorite ± hematite. Chlorite and hematite are present as fine grained disseminations in the Upper Dacite unit and are responsible for the characteristic purple-gray colour of the unit. Various FP felsic flows in the.H-W Horizon and FP felsic volcanic clasts, especially those in the Upper Dacite unit, have also undergone varying degrees of silicification and albitization. Similarly altered and coloured felsic volcanic rocks are documented in subaqueously erupted units from Unalaska Island, Alaska (Snyder and Fraser, 1963) where the alteration was thought to represent hydrothermal processes brought about by the eruption of the flows into unconsolidated, wet hemipelagic sediments. The alteration assemblages in quartz + feldspar porphyritic (QFP) rhyolites involve sericite + quartz + albite ± chlorite. Variations in modal proportions reflect the percentage of former glass in a particular unit. The resultant alteration in both types of felsic volcanic rocks probably was formed by relatively short-lived hydrothermal events controlled largely by the cooling rate of each respective unit. An example supporting this involves the composite vitric rhyolite flow and flow breccia units forming the domal cross section in the H-W Horizon in the H-W-Myra section (Fig. 3.5). Groundmass potassium feldspar (identified by sodium cobaltinitrite staining) is present in the core regions but absent in the outer parts (see section 3.2.2.1). This is also reflected by the difference in the sodium to potassium ratio (see Table 4.3). The core region was spared from alteration by the hydrothermal fluid because the initial alteration first affected more permeable breccia phases along the outer parts relative to the more massive central lavas. The hydrothermal system terminated before the whole unit was affected. The Price and Myra Formations contain two main zones of hydrothermal alteration associated with massive sulphide mineralization. One occurs below the H-W deposit (Fig. 3.5) and a smaller one is found beneath theSouthwall Zone of the L-M-P Horizon in the Lynx Mine (Fig. 3.6). Both feeder zones lie in andesitic volcanic rocks which have been completely altered to assemblages of quartz + sericite + pyrite ± chlorite. Chlorite-bearing rocks appear to be more common in less intensely altered areas, marginal to the central parts of the zones. The H-W alteration zone has an additional flanking zone consisting of moderate to strong albitization and silicification, such that the final assemblage consists of albite + quartz ± sericite ± chlorite. This alteration assemblage also occurs irregularly within the upper Units of the Price Formation outside the feeder zone areas (see Fig. 3.1). Effects of later superimposed burial metamorphism or dynamothermal metamorphism in the Price and Myra Formations are limited. Phyllosilicate phases are recrystallized to coarser grain sizes and there is some pressure shadow development. These effects are most pronounced in the hinge areas of Mesozoic structures and in schist zones related to faulting. 98 3.4.2 THELWOOD AND FLOWER RIDGE FORMATIONS Rock units in the Thelwood and Flower Ridge Formations are characteristically metamorphosed to sub-greenschist and lower greenschist facies. The metamorphic mineral assemblage in the middle to upper parts of the Flower Ridge Formation consists of chlorite + epidote/clinozoisite + albite + quartz + actinolite ± calcite ± pumpellyite. Actinolite occurs only as an alteration product in relict clinopyroxene grains and pumpellyite was only observed in amygdules. This assemblage defines the sub-greenschist pumpellyite—actinolite facies (Liou etal, 1985). In lower to middle parts of the Flower Ridge Formation pumpellyite is absent while the remainder of the assemblage is present. This implies that lower greenschist conditions became prevalent with depth in this unit. The underlying Thelwood Formation contains the lower greenschist metamorphic mineral assemblage of chlorite + clinozoisite/epidote + quartz + albite. Metamorphism and alteration in the Thelwood Formation also resulted from penecontemporaneous intrusions of mafic sills into the tuffaceous sediment units. Sill emplacement may have lead to silicification of the affected sediment deposits (cf. Kastner and Siever, 1983), probably reflected in the overall highly siliceous nature of the fine-grained tuffaceous sediment units in the Thelwood Formation. In addition to possible silicification, pervasive fine-grained epidote mineralization was observed in sediments near some contacts. In the si l l , the hydrothermal activity is represented by characteristically irregular epidote veining (although epidote is uncommon in the groundmass). Epidote indicates that calcium was transferred to the fluid phase during alteration (Maris and Bender, 1982; EvartsandSchiffman, 1983), but eventually was retained in the altered rocks as veins. 99 3.5 GEOCHRONOMETRY 3.5.1 INTRODUCTION Absolute age relationships in the Buttle Lake uplift can only be inferred from similar isotopically or biostratigraphically dated units in the Cowichan-Horne Lake uplift. An exception is the Buttle Lake Formation, which was determined on fossil evidence to be Pennsylvanian (W. R, Danner, personal communication 1987) to Early Permian (Yole, 1963, 1965) in age. During the course of this study an to attempt was made to date the Myra Formation (Nine Sequence) by zircon U-Pb geochronometry. Rb-Sr and K-Ar isotopic systematics also were investigated. All analyses were done in the Geochronometry Laboratory of R. L. Armstrong at The University of British Columbia. 3.5.2 ANALYTICAL TECHNIQUES Zircon was extracted (by the writer) from 25 to 45 kg samples using conventional separation techniques. Fractions of single populations (if large enough) were selected using conventional size (nylon mesh sieve) and magnetic (Frantz isodynamic separator) separations, followed by hand picking to virtual purity. Sample dissolution and chemistry (by P. van der Heyden and J.K. Mortensen) were carried out using a procedure modified from Krogh (1973). U and Pb concentrations were determined using a mixed 2 0 8 Pb / 2 3 5 U spike. Purified U and Pb were loaded on rhenium filaments using the H3PO4 - silica gel technique, Mass spectrometry analysis (by the writer and J.K. Mortensen) was carried out using a VG Isomass 54R solid source mass spectrometer in single collector mode (Faraday cup). Precisions for 207pD/206ph a n (j 208pD/ 206ph were better than 0,1 %, and for 2 0 4 Pb / 2 0 6 Pb they were better than 0.5 %. Total Pb blanks were 0.12 ± 0.5 ng and total U blanks were 0.05 ± 0.02 ng, based on repeated procedural blank runs. U/Pb and Pb/Pb errors for individual zircon fractions were obtained by individually propagating all calibration and analytical uncertainties through the entire date calculation program and summing the individual contributions to the total variance. Ages from discordant fractions were determined by fitting data points to a straight line using 100 a routine based on York (1969), and extrapolating to concordia using the algorithm of Ludwig (1980). Errors on individual dates and on calculated intercept ages are quoted at the 1 sigma level. Rb and Sr concentrations (by the writer) were determined by replicate analysis of pressed powder pellets using X-ray fluorescence. United States Geological Survey rock standards were used for calibration; mass absorption coefficients were obtained from Mo Kct Compton scattering measurements. Rb/Sr ratios have a precision of 2 % (la), and concentrations have a precision of 5 % (la). Sr isotopic composition was measured on unspiked samples prepared using standard ion-exchange techniques (by the writer). Data from the mass spectrometer, VG Isomass 54R, were acquired and processed by a Hewlett- Packard 85 computer. Experimental data have been normalized to an 8 6 Sr / 8 8 Sr ratio of 0.1194 and adjusted so that the National Bureau of Standards'(NBS) standard SrC03 (SRM987) gives an 8 7 Sr / 8 6 Sr ratio of 0.71020 ± 0.00002, and the Elmer and Amend Sr gives a ratio of 0.70800 ± 0,00002. The precision of a single 8 7 Sr / 8 6 Sr ratio is 0.00010 (la) or better. Rb-Sr dates are based on a Rb decay constant of 1.42 x 10 _ 1 1 year-1. The regressions are calculated according to the technique of York (1967). For K-Ar dating, the K analyses were by atomic absorption^  by K.R. Scott), and the Ar analyses were by isotope dilution using conventional procedures (by J. Harakal). The decay constants used are A c + Ac- = 0.581 x 10 ~ 1 0 year1; Ap= 4.962 x 10 " 1 0 year1; and 4 0K/K = 1.167x10~2 atomic percent. 3.5.3 RESULTS AND DISCUSSION 3.5.3.1 U-Pb Five rock units were selected for U-Pb dating: the dacite flow unit in the H-W Horizon, the dacite component in the Upper Dacite unit, the quartz + feldspar crystal-vitric rhyolite lapilli-tuff to coarse tuff deposits in the Upper Rhyolite unit, and two andesitic subaqueous pyroclastic flow deposits from the lower and middle portions of the Thelwood Formation. A lack of zircons precluded analysis for the H-W Horizon dacite and one of the Thelwood Formation units (from the middle portion). Of the 101 other three, the Upper Dacite and the second Thelwood samples yielded only enough zircon to establish minimum Pb—Pb ages. Enough zircons, however, were obtained from the Upper Rhyolite sample to enable fractions to be made. Analytical data for the three samples are given in Table 3.4. Sample locations and descriptions are in Appendix A and Fig. A.1. Zircons from the Upper Dacite unit were clear and colourless with rare fine opaque inclusions in some grains. The sample, analyzed as a bulk fraction, consisted of fine euhedrai grains (approximately 50 %) and broken fragments of larger grains. The analysis is strongly discordant giving a minimum Pb-Pb Late Devonian age of 374 Ma. Zircons from the Upper Rhyolite unit were clear, pink to red and commonly contained fine, prismatic cavities, most common in the coarse fraction. Rare grains with opaque inclusions were avoided. Five fractions, two of which were air abraded, were analyzed. The resulting U-Pb analyses are slightly to moderately discordant, but are not widely dispersed. Nonetheless, they define a good discordia line with an upper intercept Late Devonian age of 370 Ma (Fig. 3.43). The lower intercept is 139 Ma. Similar Late Devonian ages of 365 Ma were recently obtained for a quartz-feldspar porphyritic rhyolite flow in the H-W Horizon of the Mine Sequence (R. Parrish: personal communication 1986). ' The Thelwood Formation sample yielded clear and colourless zircons which were divided into two size fractions by hand picking. They were not split magnetically. Most grains in both fractions were broken, often with no crystal faces (identification of randomly selected grains was checked by scanning electron microscopy with energy dispersive spectrometer). The remainder were stubby, euhedrai grains. Analysis of both fractions are strongly discordant but plot too closely together to allow for the calculation of concordia intercepts. The two m inimum Pb-Pb ages are Late Mississippian, 320 Ma, and Silurian, 419 Ma (with large error), for the coarse and fine fractions respectively; discrepancy between the minimum ages may indicate a mixed zircon population. Since the sample comes from a coherent welded subaqueous pyroclastic flow deposit lying within a tuffaceous sediment sequence, some of the zircons may have come from older volcanic accidental lithic constituents picked up in the vent area or magma chamber during eruption. Zircons probably did not come from the underlying finer grained, siliceous tuffaceous sediment beds. The presence of exotic TABLE 3.4. U-Pb analytical data on zircon separates from the Buttle Lake Camp, Vancouver Island, B.C Sample locations and descriptions are in Appendix A and Figure A . l . Sample/fraction 1 Weight If P b 2 Pb isotopic abundance3 206p b / 204p b Ratios and aces (Ma) 5 (mg) (ppm)' (ppm) 208 207 204 (measured 4) 2 0 6 p b / 238U 20 ,pb/ 235|j 2 0 7 p b / 206p b Upper Dacite, Myra Formation bulk 1.3 (sample name: UD-Zr) 280.3 10.3 13.4791 Dated by: 5.4584 J.K. Mortensen 0.0035 5200 0.03591 ±21 C228±1) 0.2677±17 (241±1) 0.05407±18 (374±7) Upper Rhyolite, Myra Formation (sample name: -200 +325, NM 3.0 462.5 26.10 UR-Zr) 13.9262 Dated by: 5.5026 S.J . Juras and P. van der Heyden 0.0086 7131 0.05479±31 (344±2) 0.4059±32 (346±2) 0.05374±28 (360±12) -200 +325, t i 2.0 546.4 31.36 15.4624 5.6480 0.0184 4300 0.05489±31 (344±2) 0.4071 ±28 (347±2) 0.05379±22 (362±9) -100 +200, NM . 4.2 429.1 24.64 12.2551 5.5203 0.0103 7356 0.05658±32 (355±2) 0.4189±27 (355±2) 0.05370±17 (358±7) -200 +325, NM, Abr 1.3 398.7 23.18 12.9437 5.4321 0.0020 2851 0.05708±33 (358±2) 0.4252±27 (360±2) 0.05403±17 (372±7) -100 +200, M, Abr 3.0 383.2 22.08 10.3314 5.3954 0.0004 13323 0.05788±33 (363±2) 0.4301 ±23 (363±2) 0.05403±11 (367±5) pyroclastic deposit, unit, Thelwood Formation (sample name: +200, bulk 3.9 200 18.3 10.1670 SBT-Zr) 5.3487 , Dated by: 0,0047 J.K. Mortensen 5640 0.03899±21 (244±1) 0.2815±17 (252±1) 0.05280±15 (32C±7) -200 , bulk 0.4 224 10.5 20.7374 6.2018 0.0470 331 0.04266±53 (269±3) 0.3245±63 (285±5) 0.05516±81 (419±33) 1. Abbreviations are: M = magnetic, NM = non-magnetic, and Abr = abraded. Numbers (e.g. -200 +325) refer to mesh sizes. 2. Concentrations include both radiogenic + initial common Pb. 3. Calculated by setting Pb 206 = 100. Values include both radiogenic + initial common Pb, corrected for 0.15 % per atomic mass unit (AMU) fractionation and for I20±50 pg Pb blank with isotopic composition of 208: 207: 206: 204 - 37.30: 15.50: 17.75: 1. 4. Ratios are corrected for 0.15 % per AMU fractionation. 5. Decay constants used are: A 2 3 e = 0.155125 x 1 0 ' 9 / y r . A 2 3 5 = 0.98485 x 1 0 ' V y r , 2 3 8 U / 2 3 5 U = 137.88. Ratios are corrected for U and Pb fractionation, blank Pb, Pb contribution from spike, and for initial common Pb (using the Stacey and Kramer (1975) growth curve and 355 Ma). Uncertainties in isotopic ratios refer to last two significant figures; errors are 1c. 103 0.39 0.40 0.41 0.42 0.43 0.44 0.45 207 Pb / 235 U Figure 3.43: U—Pb concordia diagram for zircons from Upper Rhyol ite sample, Myra Formation, Buttle Lake Camp, Vancouver Island, B.C. Data plotted are from Table 3.4. U-Pb analyses define a good discordia line with an upper intercept Late Devonian age of 370 Ma. Error box in bottom right corner applies to all fractions. Sample fraction abbreviations are as in Table 3.4. volcanic lithics as a potential source for a separate zircon fraction may be implied by the occurrence of small amounts of euhedrai chromite crystals and pyrochlore grains in the heavy mineral separates. Re-sampling of the unit to obtain more zircons might resolve the age of the unit and the existence of an older detrital population. 3.5.3.2 Rb-Sr Twelve Myra Formation (Mine Sequence) samples were analyzed for whole rock Rb-Sr isotopic data. The samples were selected from volcanic flow units throughout the stratigraphic sequence. Sample descriptions and locations are in Appendix A. Analytical data for these-samples are in Table 3.5. The Rb-Sr data are dispersed broadly on an isochron diagram (Fig. 3.44) indicating that the calculated age of 212 Ma is geologically meaningless because various geologic factors have modified these rocks. However, if the data are grouped into their respective litho-stratigraphic units and evalulated separately, the H-W Horizon and Hanging Wall H-W Andesite samples define an isochron giving a Late Devonian age of 365 ± 26 Ma, and an initial 8 7 Sr / 8 6 Sr ratio of 0.7042 (Fig. 3.45). This isochron age agrees closely with the 370 Ma zircon U-Pb date for the Myra Formation (Mine Sequence). The value for the intial ratio is supported by similar values of 8 7 Sr / 8 t )Sr in samples having very low Rb concentrations (Table 3.5). Furthermore, the Sr initial ratio value is only slightly higher than the range for modern-day island arc volcanics (0.7030 - 0.7040: Gill, 1981). Calculated Sr initial ratios for the samples, using a reference age of 370 Ma, range from 0.7023 to 0.7047 (Table 3.5). The range may reflect the effects of regional submarine hydrothermal alteration (Reed, 1983) of many of the units by a Devonian seawater-dominant fluid phase ( 8 7 Sr / 8 6 Sr values for Devonian seawater ranged from 0.7078 to 0.7088: Burke etal, 1982). This would have the effect of slightly resetting the initial Sr ratios of the rock units to higher values soon after emplacement. However, the range of initial ratios towards lower values, as well as the scatter of data points, could also be due to partial resetting caused by fluid transport during later metamorphism and intrusion (Parrish and Roddick, 1985). The actual situation may be complex, involving both resetting types. TABLE 3.5 Analytical data for Rb,' Sr, and 8 ? S r / 6 6 S r from metavolcanic rocks in the Myra Formation, Buttle Lake Camp, Vancouver Island, B.C. Sample locations and descriptions are in Appendix A. Sample No. Sample Description 1 Rb Sr 8 7 R b / 9 6 S r 8 7 S r / 8 6 S r 675 r / 86sr2 (ppm) (ppm) (370 Ma ago) P1412A QFP rhyolite, H-W Horizon 38.5 208 0.534? 0.70669 0.7039 SJ-R73 FP rhyolite, H-W Horizon 14.1 50.0 0.3176 0.70855 0.7043 D i l l C A dacite (altered), H-W Horizon 3.8 184 0.0596 0.70497 0.7047 D1265A FP basaltic andesite, HW Andesite 5.2 432 0.0344 0.70444 0.7043 D39903 QFP rhyolite clast, H-W Horizon 11.3 175 0.1863 0.70510 0.7042 SJ-5EA FP andesite, 5E Andesite 25,3 198 0.3697 0.7051 1 0.7032 P44BA dacite, Upper Dacite 1.6 426 0.0107 0 70433 0.7042 PR30A dacite, North Dacite 67.7 194 1.007 0.70754 0.7023 SJ-R90 rhyolite, North Dacite 47.1 105 1.297 0.70932 0.7026 DL498A quartz+albite rock, 5E Andesite 22.3 121 0.5329 0.70606 0.7033 DW140A QFP vitrophyre, H-W Horizon(?) 106 123 2.506 0.71091 * R - l 36 high MgO basalt, G-Flow < 1.0 446 0.0 0.70434 0.7044 < 1. Abbreviations are: QFP = quartz + feldspar porphyritic, FP = feldspar porphyrit ic, and HW Andesite = Hanging Wall H-W Andesite. 2. Calculated initial 8 7 S r / 8 6 S r ratios at 370 Ma. Symbol " * " denotes impossibly low initial S r ratio at 370 Ma. 106 0.704 0.00 0.50 1.00 1.50 2.00 2.50 3.00 87 Rb / 86 Sr Figure 3.44: Rb-Sr errorchron diagram for units from the Myra Formation, Buttle Lake Camp, Vancouver Island, B.C. Data plotted are from Table 3.5. Pattern is broadly dispersed indicating that the calculated age of 212 Ma reflects significant resetting of Sr isotopic systematics in some of the units. Figure 3.45: Rb-Sr isochron diagram for lower Myra Formation units, Buttle Lake Camp, Vancouver Island, B.C. Data plotted are from Table 3.5. Resultant isochron gives a Late Devonian age of 365 ± 26 Ma, and an initial 8 7 Sr / 8 6 Sr ratio of 0.7042. Date is comparable to U-Pb concordia diagram for zircons (Fig. 3.43). 107 3.5.3.3 K-Ar Three samples were dated by the K-Ar method. They consisted of two hydrothermally altered, feeder zone samples from the H-W stringer zone and the Price Rhyolite alteration zone, and a devitrified (very fine grained sericite) quartz+feldspar porphyritic rhyolite vitrophyre (a flow banded, felsic glassy flow rock, now altered and devitrified). The purpose of the dating was to obtain an age for the main deformational event on the mine property. The K-bearing phase in all three samples was sericite. Sulphide phases were removed from the feeder zone samples by heavy liquids leaving essentially quartz and fine to medium grained sericite to be analyzed. The analytical data in Table 3.6 yields K-Ar dates that range from Early Cretaceous to Middle Jurassic (138 to 168 Ma). The 168 Ma age for the vitrophyre sample could reflect resetting due to the late Early to early Middle Jurassic Island Intrusions (Isachsen etal, 1985) in the Buttle Lake uplift region. The two feeder zone samples have younger dates (138 Ma and 153 Ma), possibly having experienced additional resetting conditions than those for the vitrophyre. The youngest age interestingly was obtained from the H-W feeder zone which lies approximately 400 m stratigraphically below the lithologically similar Price unit. In Middle Jurassic time, the two units may have been vertically separated by as much as 1 km, based on current rock unit configuration corrected for Tertiary faulting. Since greenschist facies temperatures (300 to 350° C) may have existed until uplift began sometime in Late Jurassic to Cretaceous time, and since this temperature range is around the closure temperature for muscovite (350° C), resetting conditions for the feeder zone samples could have persisted after the emplacement of the Island Intrusions. The H-W feeder zone gives the younger age because, being deeper, it would not have reached the closure temperature for sericite at the same time as the Price unit. More K-Ar age determinations would have to be conducted in order to confirm this hypothesis. TABLE 3.6 Analytical data for K—Ar dates from whole rock and mineral concentrates from metavolcanic rocks in the Price and Myra Formations, Buttle Lake Camp, Vancouver Island, B.C. Sample locations are in Appendix A. Analyses were carried out by K. R. Scott (K) and J. Harakal (Ar). Sample1 K 4 0 A r r a d 4 0 A r r a d Date Age2 (wt*) ( x IO-'°mo1es/g) (%) (Ma) H-W Feeder Zone: 1.52 hydrothermally altered andesite, quartz+sericite±chlorite cone. P16C (Price Rhyolite): 2.63 hydrothermally altered rhyolite LT, quartz+sericite±chlorite cone. DW140A: 4.22 QFP rhyolite vitrophyre, sericitic whole rock. 3.786 7.304 12.917 88.9 91.2 95.2 38±5 153±5 168±6 Early Cretaceous Late Jurassic Middle Jurassic 1. Abbreviations are: cone. = concentrate, LT = lapilli-tuff, and QFP = quartz + feldspar porphyritic. 2. Age is based on date and time scale of the DNAG 1983 Time Scale (Palmer, 1983). 109 3.5.4 CONCLUSIONS U-Pb dating has established that the Myra Formation in the Buttle Lake uplift is Late Devonian (370 Ma) in age. Whole rock Rb-Sr isotopic analysis of the lower Myra Formation stratigraphy (H-W Horizon and Hanging Wall H-W Andesite) yielded a Late Devonian (365 Ma) isochron age and an initial 8 7 S r / 8 6 S r ratio of 0.7042. Other samples analyzed for Rb-Sr give a dispersed pattern on an isochron diagram resulting from either (or both) partial resetting during later metamorphism and intrusion, or early submarine hydrothermal metamorphism. The K-Ar dates of 138 Ma to 168 Ma probably reflect the emplacement of the Jurassic Island Intrusions and subsequent uplift tectonics. 1 10 CHAPTER 4  GEOCHEMISTRY AND PETROGENFSIS 4.1 INTRODUCTION The Sicker Group of the Buttle Lake volcanogenic massive sulphide camp represents a Paleozoic oceanic island arc system. Detailed fieldwork outlined a volcanogenic stratigraphy for the region (Chapter 3) which indicates a complex multistage magmatic history. This is especially true of volcanic units in the Myra Formation (Mine Sequence), which are interpreted as being deposited in a back-arc or intra-arc rift basin setting (see Chapter 5). The complex nature is believed to be the result of interlayering of volcanic sequences from diverse sources (Arculus and Johnson, 1978; Saunders and Tarney, 1984; Hawkins eta/., 1984). A modern example of the complexity encountered fn unraveling the magmatic history of an island arc system is documented by Gill etal (1984) in Fiji where, after the main arc building magmatic stage, six distinct magmatic events were documented, all proposed to be responses to changes in plate interactions during the course of subduction. Geochemistry of the Buttle Lake Camp volcanic rocks, in conjunction with field relationships, are used to develop a general petrogenetic synthesis for this Paleozoic island arc system. Data consists of whole rock major and trace element analyses, and mineral phase analyses of pyroxenes and spinels (where preserved). In keeping with the organization of Chapters 3 and 5, the four Paleozoic formations on the mine property are divided into two: (1) the Price and Myra Formations, and (2) the Thelwood and Flower Ridge Formations. Each is discussed separately below. 111 -J 4.2 ANALYTICAL PROCEDURES Seventy-eight rock samples were analyzed by pressed powder X-ray fluorescence (XRF) for ten major and minor elements (Si, Ti, Al, Fe, Mg, Mn, Ca, Na, K and P) and eleven trace elements (Ba,Rb,Sr,Nb,Y,Zr,Cr,Ni,Cu,Zn and V). Sixty-four samples were analyzed at The University of British Columbia (UBC); the remainder were analyzed at Midland Earth Science Associates (Nottingham, U.K.). The UBC samples were also analyzed for their rare earth element (REE) content by a combined XRF (La, Ce and Nd) and graphite furnace atomic absorption (Sm, Eu, Dy, Er and Yb) procedure (Juras etal, 1987; Appendix C). H2O and CO2 contents (UBC samples only) were determined using magnesium perchlorate and ascarite in a procedure modified from that of Hutchinson (1974) (Appendix C; cf. Berman, 1979). Estimated analytical errors for the XRF analyses (based on both counting error and calibration error: Appendix C) are less than 5 % for the major elements (Si02, AI2O3, F&2O3, MgO, CaO, N32O and K2O) and Ti02; HO % for MnO; i 25 % forP2C>5; i 5 % forBa.Sr and Zr; i]0% forCr.Ni.V.Y and Zn; and i15* for Ce, Cu, La, Nb, Nd and Rb. For the atomic absorption analyses, the analytical errors are 15 %. Sample selection and preparation procedures, and analytical techniques are described in Appendix C. Locations and descriptions of samples analyzed are in Appendix A. Analyses for all volcanic series are in Tables 4.2 to 4.8, and Tables 4.11 and 4.12; miscellaneous and duplicate analyses are in Appendix D. Complementing this sample suite are thirty-eight whole rock analyses from an XRF data file of Westmin Resources Ltd. on mine property samples. Analyses of their samples for major and minor elements, and Ba, Rb, Sr, Zr, Ni, Cu and Zn are in Appendix D. Relict mineral phases (clinopyroxene and chromite) were analyzed by a wavelength-dispersive microprobe at The University of British Columbia (Appendix C). In total, 130 analyses were obtained. The mineral compositions and structural formulae are in Appendix D. Representative compositions and structural formulae are in Tables 4.9 and 4.10. 112 4.3 RESULTS 4.3.1 ELEMENT MOBILITY Sicker Group rocks at Buttle Lake, in particular those in the Price and Myra Formations, have undergone moderate to strong hydrothermal alteration and low-grade metamorphism (section 3.4). Therefore caution must be exercised when interpreting the whole rock geochemical data. Numerous studies have been done investigating element mobility in altered metavolcanic terrains (e.g. Pearce andCann, 1973; Floyd and Winchester, 1978; Gel inas (/tai, 1982; Ludden etal, 1982; Murphy and Hynes, 1986). Major and minor elements (especially CaO, Na20 and K2O) as well as large ion lithophile trace elements (LIL: Ba,Rb,Sr,La and Ce) can be moderately to strongly mobile, depending on the intensity of alteration. Various trace elements though, are found to be relatively immobile during the same alteration processes. These are the high field strength elements (HFS: Ti, P, Zr,Y and Nb) and heavy rare earth elements (HRE: Dy, Er and Yb). Transition metal (Ni, Cr and V) concentrations and, to a certain degree, FeO*/MgO ratios also are relatively immobile (Humphris and Thompson, 1978; Pearce, 1978); however these and the other immobile elements, above, can be modified in rocks which have suffered significant carbonate alteration (Murphy and Hynes, 1986). Also, apparent differences between distribution patterns of immobile elements can be due to dilution (as a result of volume change by silicification for example) rather than by primary variations (Dostal and Strong, 1983). Ratioing of immobile elements against one another helps lo avoid these effects. Interpretation of the Sicker Group whole rock data emphasizes the use of immobile elements listed above. Where possible, relict clinopyroxene compositions are utilized as a control on the original chemical character of the host unit because these can be assumed to represent primary conditions (see chapter 14 in Hughes, 1982). However this was of only limited use because in many units clinopyroxene was completely altered to chlorite or uralite. Chemical classification schemes for unaltered volcanic rocks are based either on normative mineralogy (Irvine andBaragar, 1972) or Si02 versus alkali (K 2 0 or Na20 + K20) diagrams 113 (Ewart, 1979; Le Bas etal, 1986). These classification schemes may prove to be unreliable for metavolcanic rocks because of element mobility. Floyd and Winchester (1978) proposed using immobile elements to obtain a classification for metavolcanic rocks, and recommended Zr/Ti02 versus Si02, and Nb/Y versus Zr/Ti02. For this study the silica divisions proposed by Le Bas etal (1986) are used where: basalt is < 52 wt.^  Si02, basaltic andesite is 52 to 57 wt.£ Si02, andesite is 52 to63wt.$ Si02, dacite is > 63 to 69 wt.H Si02, and rhyolite is > 69 wt.SB Si02. The alkali divisions proposed by Le Bas etal (1986) are not used because of suspected mobility in Na and K. To test for alkalic versus sub-alkalic nature, the two Floyd and Winchester diagrams were used (not presented). All Sicker Group rocks at Buttle Lake plot in subalkaline fields. Determination of calc-alkaline versus tholeiitic affinity also is potentially affected by element mobility. Therefore to complement the major element based AFM diagram, and Si02 versus FeO*/MgO plot, a Mn0/Ti02/P205 minor element discriminant diagram proposed by Mullen (1983) is used. The m inor element diagram as well as the two major element plots are in Appendix D. 4.3.2 PRICE AND MYRA FORMATIONS Price and Myra Formations are composed of a range of mafic to felsic volcanic rocks. Intermediate compositions are dominant. The following lava types are recognized based on mineral assemblages: pyroxene porphyritic mafic flows, feldspar ± pyroxene porphyritic mafic to intermediate flows (most common type), feldspar porphyritic felsic flows, and quartz + feldspar porphyritic felsic flows. In the Myra Formation, the volcanic products can be grouped into four volcanic series (see section 3.2.2.11): the volcanic arc (VARC) series, the Price seamount (PSMT) series, the West G seamount (WSMT) series, and the arc rifting (ARFT) series. The Price Formation underlies all Myra Formation volcanic series units and therefore is defined as a separate volcanic series, the early arc (EARC) series. Litho-stratigraphic units and flow types in each of these series are summarized in Table 4.1. The geochemical characteristics of the five volcanic series of the Price and Myra Formations are detailed below. TABLE 4.1 Summary of litho-stratigraphic units and flow types found in the five volcanic series of the Price and Myra Formations, Buttle Lake Camp, Vancouver Island, B.C. Volcanic Series Litho-stratigraphic Unit(s) Flow Type(s) 1 EARC Price Formation - fsp ± pyx and pyx + fsp porphyritic basaltic andesite and lesser andesite VARC H-W Horizon (felsic flow member) Ore Clast Breccia unit (Interzone Rhyolite) North Dacite Lynx-Myra-Price Horizon Upper Rhyolite unit - fsp and q + fsp porphyritic rhyolite - q + fsp porphyritic rhyolite - fsp porphyritic rhyolite - q + fsp porphyritic rhyolite - q + fsp + amph porphyrjtic rhyolite PSMT H-W Horizon (dacite flow unit) Upper Dacite (lower member) • fsp porphyritic dacite to rhyolite WSMT Hanging Wall H-W Andesite 5E-Andesite Upper Dacite (upper member) - fsp ± pyx porphyritic basaltic andesite to andesite, lesser basalt and minor dacite ARFT H-W Horizon (mafic flow member) G-Flow unit Upper Mafic unit - cpx porphyritic komatiitic basalt and fsp + cpx porphyritic basalt 1. Abbreviations are: fsp = feldspar, pyx = pyroxene, q = quartz, amph = amphibole, and cpx = clinopyroxene. Normalized rare earth element (REE) diagrams and multi-element plots (for mafic and intermediate compositions only) are used to characterize the geochemical variations within and among the different volcanic series. The REE data are normalized to chondritic values (Appendix D), whereas the multi-element data are normalized to a representative mid-ocean ridge tholeiitic basalt (N-type MORB: Appendix D). The intent is to describe the units relative to the shape of the normalized data curves in addition to the absolute abundances. The former is especially useful in the discussions dealing with petrogenesis below (cf. Saunders and Tarney, 1984). (The same approach also is used with the Thelwood and Flower Ridge Formations.) For comparative purposes, compositions of mafic volcanic rocks from some modern island arc systems (Mariana, New Britain and Japan) are plotted on multi-element diagrams in Figure 4.1. The Earlv Arc (EARC) series is composed of alternating feldspar ± pyroxene porphyritic and pyroxene + feldspar porphyritic mafic to intermediate flow units. The rock types are basaltic andesites to andesites (Table 4.2) The lack of Fe enrichment on an AFM diagram, or on a Si0>2 versus FeO*7MgO plot (Appendix D), suggests a calc-alkaline affinity. This is indicated also on a Mn0/Ti02/P205 minor element diagram (Appendix 0). EARC series samples all have <1 wt.£ HO2 which is typical of orogenic andesites (Oill, 1981.). REE patterns (Fig. 4.2a) are flat to slightly HRE depleted with HRE 10 to 15 times chondritic levels. When compared to N-type MORB composition (Fig. 4.2b), Price Formation lavas show a slight to moderate LIL element enrichment, a depletion in Nb and Ti contents, a distinct enrichment in Nd and P, and variable depletion in Ni and Cr. The pyroxene porphyritic flows generally have slightly lower HFS element contents and higher Ni and Cr concentrations than their feldspar porphyritic counterparts. The Volcanic Arc (VARC) series consists of feldspar and quartz + feldspar porphyritic felsic flows and associated pyroclastics in the H-W Horizon, Ore Clast Breccia unit (Interzone Rhyolite member), North Dacite, and Upper Rhyolite unit. The thickest accumulation of VARC series units occurs in the H-W Horizon; consequently most of the analyses come from this unit. Only limited data are available for the rest, with no analyses for the Interzone Rhyolite member. Based on their mineralogy and silica contents, units in this series are rhyolites (Tables 4.3 and 4.4). Their REE Rock / MORB 0 0 . 0 ia. 10.0 1.0 — N-type MORB "•" Mariana Trough •o- Mariana remnant arc Mariana back-arc basin RD Ba K Sr La Ce Nb Nd P Zr Eu Ti Dy Y Yb Ni £r 1 16 1 0 0 . 0 t 1 0 0 Rock / MORB ib. — N-type MORB Hokuroko, preore -o- Hokuroko, postore -4- New Br i ta in , arc -X- New Er i t a i n , back-arc LIL RD Ba K Sr La Ce Nb Nd P Zr Eu Ti Dy Y Yb Ni Cr Figure 4.1: N-type MORB normalized multi-element patterns for mafic volcanic rocks from modern island arc systems: a) Mariana system; and b) Hokuroko District, Japan, and New Britain system, Papua New Guinea. Dataarefrom: Wood etaf,\ 980 (Mariana remnant arc: 451-1, and Mariana back-arc basin: 450); Wood etal, 1981 (Mariana Trough: 454A-5-4); Basaltic Volcanism Study Project, 1981 (New Britain arc and back-arc: IA-3 and IA-9); and Dudas etal, 1983 (Hokuroko preore and postore: T-87 and HO-59-203). Mariana Trough is a young intra-arc or back-arc-rift basin. Preore and postore samples in the Hokuroko District refer to position of basaltic units relative to the Kuroko massive sulphides. Abbreviations are: LIL = large ion lithophile elements, and HFS = high field strength elements. 117 TABLE 4.2 Chemical analyses of Early Arc (EARC) series (Price Formation) volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C. Samplejocations and descriptions are in Appendix A. Major and minor element analyses are recalculated to 100 percent on a volati le-free basis. Fe203 is expressed as total iron. Symbol" <" denotes below detection limit. Sample Rock Type1 P122D fp px b-ande D2108 fp ande D2114 fp b-ande D2214 px fp b-ande PI 3-26 fp b-ande S1O2 (wt. %) 53.4 57.7 52.7 54.1 53.7 T102 0.81 0.72 0.85 0.71 0.91 AI2O3 16.3 15.8 17.8 15.6 18.1 F e ^ 10.0 9.15 9.94 10.3 11.5 MnO 0.16 0.16 0.18 0.21 0.11 MgO 5.85 4.91 5.56 8.10 6.19 CaO 9.69 7.16 7.09 6.99 4.69 Na20 3.17 4.08 5.56 3.63 4.27 K20 0.16 0.08 0.16 0.23 ~0.26 P2O5 0.34 0.24 0.30 0.21 0.32 H20 3.90 3.20 3.35 3.30 3.81 CO2 0.80 0.65 1.46 0.55 0.71 Ba (ppm) 360 57 106 193 105 Rb < 4 <4 < 4 <4 4 Sr 417 642 480 212 370 Nb 2 <2 2 <2 <2 Y 29 24 24 21 25 Zr 90 61 65 58 71 Cr 90 19 20 323 21 Ni 41 19 19 75 21 Cu 69 61 46 64 98 Zn 108 97 89 89 117 V 302 206 224 240 329 La 14 4 10 8 4 Ce 16 19 16 12 22 Nd 16 11 14 13 14 Sm 4.7 5.6 6.4 4.4- 5.2 Eu 1.1 1.4 1.3 1.2 1.2 Dy 4.9 2.8 3.4 3.0 4.2 Er 2.1 1.2 1.0 1.2 1.7 Yb 2.3 2.0 1.8 1.6 2.0 1. Abbreviations are: fp = feldspar porphyritic, px = pyroxene porphyritic, b-ande = basaltic andesite, and ande = andesite. I 18 100 Rock / Chondrite 10 * - PSMT (Upper Dacite) -Ar PSMT (H-W dacite) •*- EARC (Price Fm) a. La Ce Nd Sm Eu Dy Er Yb 1 0 0 . 0 10.0 Rock / MORB 1.0 i b . — N-type MORB EARC, pyx-phyr lc **- EARC, fsp-phyr ic LIL | HFS I V Rb Ba K Sr La Ce Nb Nd P Zr Eu Ti Dy Y Yb Ni Cr Figure 4.2: Normalized trace element patterns for EARC-PSMT series units: a) chondrite normalized REE patterns, and b) N-type MORB normalized multi-element patterns. Each pattern represents the average (for n 22) for a respective unit. The range of values (for n 22 only) in a particular sample suite is represented by the standard deviation (plotted as vertical bars). Analytical error in the REE plot is shown by an I-shaped bar. Arrows in the multi-element plot denote below detection limit.-Data are from Tables 4.2 and 4.5, and the normalizing values used are in Appendix D. Abbreviations are: H-W = H-W Horizon, pyx = pyroxene, fsp = feldspar, LIL = large ion lithophile elements, and HFS = high field strength elements. 119 TABLE 4.3 Chemical analyses of Volcanic Arc (VARC) series (H-W Horizon units) volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C. Sample locations and descriptions are in Appendix A. Major and minor element analyses are recalculated to 10O percent on a volatile-free basis. Fe203 is expressed as total iron. Symbols" <", " n.d.", " - ", and " * " denote below detection limit, not detected, not analyzed for, and loss on ignition only, respectively. Sample name symbol" •* " indicates analysis by Midland Earth Science Associates, Nottingham, U.K. Sample D1412A D1362 PR75-545* SJ-R78 D39903 PI 18G Rock Type1 qfp rhy qfp rhy qfp rhy fp rhy qfp rhy qfp rhy Si02 (wt. %) 70.3 71.7 72.6 80.1 81.5 78.0 T1O2 0.26 0.23 0.22 0.17 0.12 0.17 A1203 14.2 14.1 16.6 10.5 9.95 12.8 Fe203 4.09 2.48 1.95 1.14 1.32 1.18 MnO 0.05 0.04 0.01 0.01 0.02 0.03 MgO 0.86 0.66 0.28 0.02 0.31 0.44 CaO 1.59 2.90 2.62 0.40 1.65 1.2-7 N32O 4.27 5.96 2.52 5.86 4.22 4.71 K20 4.26 1.90 3.00 1.75 0.84 1.39 P2O5 0.10 0.09 0.05 0.04 0.04 0.05 H20 1.50 1.28 2.49* 0.77 0.75 1.04 C02 0.73 1.66 - n.d. 1.06 0.46 Ba (ppm) 1350 559 814 475 1200 933 Rb 41 43 42 15 • 14 19 Sr 225 350 89 53 190 279 Nb 3 3 5 4 <2 2 Y 16 20 22 18 14 12 Zr 145 135 130 1 16 90 103 Cr 8 11 <4 19 6 8 Ni 10 11 <3 13 11 9 Cu 22 18 <7 < 7 34 < 7 Zn 56 38 20 31 66 59 V 33 21 7 1 20 20 La 14 26 - 17 15 5 Ce 18 21 - 19 24 20 Nd 6 1 1 - 9 8 8 Sm 2.5 2.8 - 3.6 3.7 5.4 Eu 0.4? 0.62 - 0.62 0.92 1.0 Dy 2.0 2.2 - 2.0 2.1 1.7 Er 0.82 1.6 - 1.1 1.4 0.79 Yb 0.69 1.4 - 1.0 1.8 1.3 1. Abbreviations are: qfp = quartz+feldspar porphyritic, fp - feldspar porphyritic, and rhy = rhyolite. 120 TABLE 4.4 Chemical analyses of Volcanic Arc (VARC) series (North Dacite) and Lynx- Myra-Price Horizon volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C. Sample locations and descriptions are in Appendix A. Major and minor element analyses are recalculated to 100 percent on a volatile-free basis. Fe203 is expressed as total iron. Symbols are as defined in Table-4.3. Sample P16C P121 DL1257 DW295 PR30A SJ-R90 Unit1 L-M-P L-M-P L-M-P L-M-P ND ND Rock Type 1 qfxRT qfx v RT qfx RT qfx RT fp rhy fp rhy Si02 (wt. 58) 73.1 71.1 71.0 67.3 71.0 71.2 Ti02 0.49 0.18 0.48 0.48 0.38 0.53 AI2O3 18.0 16.0 15.8 15.5 15.0 14.2 1.83 4.72 3.57 4.72 4.35 3.15 MnO 0.02 0.05 0.06 0.07 0.06 0,05 MgO 0.39 1.97 2.75 2.75 0.85 0.29 CaO 0.80 0.98 1.96 3.05 2.54 1.93 Na20 0.57 2.16 0.30 4.01 2.09 3.8-4 K20 4.67 2.82 3.91 2.04 3.63 4.68 P2O5 0.15 0.04 0.18 0.13 0.10 0.12 H20 2.02 2.92 2.79 2.07 2.10 0.96 CO2 1.33 n.d. 2.30 2.25 1.45 0.96 Ba (ppm) 1900 2150 4190 950 1080 1170 Rb 47 47 43 28 71 48 Sr 66 129 52 146 •210 110 Nb 6 5 5 4 4 10 Y 25 26 29 30 25 36 Zr 134 155 89 122 191 229 Cr 5 8 16 24 10 7 Ni 13 9 17 22 15 11 Cu 12 < 7 540 554 38 9 Zn 154 66 2440 2360 56 62 V 59 32 141 117 61 2 La 31 23 15 5 1 1 28 Ce 55 43 29 28 29 48 Nd 12 1 1 5 13 17 20 Sm 3.5 2.3 4.1 7.4 3.4 5.0 Eu 1.1 0.70 1.4 2.1 0.77 1.4 Dy 0.93 3.5 3.9 3.7 3.8 4.0 Er 0.67 1.5 1.6 1.8 1.6 2,9 Yb 1.5 1.7 2.0 3.8 1.4 2.2 1. Abbreviations are: L-M-P = Lynx-Myra-Price Horizon, ND - North Dacite, qfx -- quartz + • feldspar crystal, RT = rhyolite tuff, v = vitric, fp = feldspar porphyritic, and rhy = rhyolite. 121 patterns (Fig. 4.3) display moderate light rare earth element / LRE: La, Ce and Nd) enrichment, slight to moderate HRE depletion, no Eu anomalies, and relatively low total REE contents (HRE 4 to 10 times chondritic levels). Geochemical differences within the VARC series do occur; feldspar-phyric flow types have greater Na20 to K20 ratios, higher Ti and Zr contents, and generally lower Ba values than the quartz + feldspar porphyritic types. The Lynx-Myra-Price Horizon is composed of mainly felsic pyroclastic tuffs that are rhyolitic in composition, based on their abundant quartz crystal content and silica values (Table 4.4). Their REE patterns (Fig. 4.3) display slightly fractionated trends and have HRE 8 to 12 times chondritic values. Relative to the other VARC series units, Lynx-Myra-Price Horizon tuffs have higher Ba, Cu, Zn and V concentrations. The Price Seamount (PSMT) series consists of feldspar porphyritic felsic lavas in the H-W Horizon (dacite flow unit) and Upper Dacite unit (lower member). The felsic flows range from dacite to rhyolite in composition, based on silica contents (Table 4.5). Geochemical characteristics of these felsic lavas are moderate to high Na20 to K20 ratios, Ti contents just slightly less than more mafic lavas in other volcanic series, and low Zr and Ba contents. REE patterns (Fig. 4.2a) display slightly fractionated trends (LRE enriched, HRE depleted), no Eu anomalies, and moderate total REE contents (15 to 40 times chondritic values). Variations between H-W Horizon dacite and Upper Dacite lavas are minor with the H-W phase having higher Ba, Zn and V contents. Differences between units in the PSMT series and the VARC series can be significant. Relative lo VARC series quartz + feldspar porphyritic lavas, the PSMT flows have lower Ba, Rb and Zr, and higher Ti, P, Sr, Y, FeO*/MgO ratios and total REE. However, differences with VARC series feldspar -phyric lavas can be less distinct; PSMT flows have lower Ba, Rb and Zr, and higher Ti, Sr and P contents. The West G Seamount (WSMT) series comprises feldspar porphyritic mafic to intermediate flows in the Hanging Wall H-W Andesite, 5E Andesite, and Upper Dacite unit (upper member). Volcanic rock types represented are basalts (uncommon), basaltic andesites and andesites, based on silica contents (Tables 4.6 and 4.7). They are probably cole-alkaline according to no Fe enrichment Figure 4.3: Chondrite normalized REE patterns for VARC series units. Each pattern represents the average (for n 12) for a respective unit. The range of values (for n il only) in a particular sample suite is represented by the standard deviation (plotted as vertical bars). Analytical error is shown by an 1-shaped bar. Data are from Tables 4.3 and 4.4, and the normalizing values used are in Appendix D. 123 TABLE 4.5 Chemical analyses of Price Seamount (PSMT) series volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C. Sample locations and descriptions are in Appendix A. Major and minor element analyses are recalculated to 100 percent oh a volatile-free basis. F6203 is expressed as total iron. Symbols are as defined in Table 4.3. Sample PI 3-74 PI 3-20 LD-ZrC P101C D35267 DP1121 P44BA Unit' LD LD LD LD UD,1 UD.l UD,u Rock Type 1 fpdac fpdac fp rhy fp rhy fp rhy fp rhy fp rhy Si02 (wt. %) 65.8 69.5 69.7 75.1 75.2 72.3 69.8 Ti02 0.61 0.53 0.56 0.49 0.38 0.45 0.51 A1203 17.5 14.2 15.5 12.8 11,1 12.3 13.8 Fe203 4.09 5.15 3.67 2.43 3.07 4.60 3.73 MnO 0.06 0.08 0.05 0.04 0.05 0.05 0.05 MgO 1.05 1.57 0.39 0.21 0.25 1.38 0.41 CaO 3.01 2.39 2.89 1.88 3.67 2.00 2.91 Na20 5.90 5.71 5.66 5.58 5.44 6.39 - 8.50 K20 1.67 0,61 1.41 1.15 0.64 0.30 0.14 P 20s 0.28 0.25 0.25 0.23 0.18 0.29 0.18 H20 1.63 1.68 1.38 1.48 0.89 1.17 0.63 C02 0.95 n.d. 0.68 0.38 1.03 n.d. 0.08 Ba (ppm) 615 308 551 695 255 246 126 Rb 18 7 15 14 10 5 < 4 Sr 210 306 337 260 273 203 436 Nb 3 3 4 4 2 3 4 Y 33 36 40 35 26 43 31 Zr 107 107 111 100 82 86 120 Cr 8 9 8 7 11 11 10 Ni 11 13 12 13 12 15 14 Cu 8 12 18 < 7 < 7 <7 11 Zn 85 116 98 68 35 63 34 V 13 4 8 7 21 69 62 La 20 21 18 20 16 19 10 Ce 45 46 33 22 38 52 40 Nd 25 30 16 16 20 28 18 Sm 7.9 8.4 6.6 5.5 3.7 5.0 5.8 Eu 2.1 2.4 2.0 1.6 1.2 1.2 1.6 Dy 4.6 5.9 6.6 6.8 5.1 7.3 5.0 Er 2,2 2.5 2.3 34 3.7 3.4 2.5 Yb 2.6 4.3 2.6 3.2 2,:8 4.0 4.7 1. Abbreviations are: LD = H-W Horizon, dacite flow unit, UD, 1 = Upper Dacite, lower member., UD, u = Upper Dacite, upper member, fp = feldspar porphyritic, dac = dacite, and rhy = rhyolite. 124 TABLE 4.6 Chemical analyses of WestG Seamount (WSMT) series (H-W Hanging Wall Andesite) volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C. Sample locations and descriptions are in Appendix A. Major and minor element analyses are recalculated to 100 percent on a volatile-free basis. Fe203 is expressed as total iron. Symbols are as defined in Fable 4.3r. Sample D126SA D124DB D35590 D41651 P124F P730 9L-WPR Unit1 E E E E L L ' L Rock Type1 b-ande b-ande andesite b-ande dacite dacite andesite Si02 (wt. %) 55.6 54.4 61.2 54.9 65.2 68.1 59.8 T102 0.77 .0.82 0.69 0.83 0.70 0.61 0.73 AI2O3 15.7 17.3 13.6 18.2 14.4 12.9 15.1 Fe203 11.4 11.8 9.46 11.2 6.84 4.90 6.11 MnO 0.15 0.18 0.18 0.20 0.09 0.08 0.10 MgO 5.05 6.27 3.78 4.98 2.11 1.46 2.11 CaO 7.66 5.79 8.87 5.32 5.02 7.27 9.65 N32O 2.89 3.12 1.96 3.71 5.09 4.07 " 6.13 K20 0.66 0.05 0.06 0.50 0.27 0.29 0.08 P2O5 0.17 0.27 0.17 0.20 0.23 0.24 0.27 H20 3.17 4.18 3.38 3.70 2.16 1.86 1.27 CO2 0.53 n.d. 0.38 0.42 0.36 0.15 2.18 Ba (ppm) 818 86 100 277 436 406 172 Rb 4 < 4 <4 6 4 4 < 4 Sr 473 299 640 416 315 544 302 Nb <2 <2 2 2 < 2 2 2 Y 23 29 23 26 26 25 26 Zr 62 78 69 71 69 68 71 Cr 25 19 18 34 15 15 16 Ni 23 16 17 22 13 13 14 Cu 66 28 51 53 23 24 50 Zn 94 173 86 117 86 85 80 V 256 16U 221 230 165 150 159 La 8 10 9 9 3 16 14 Ce 24 14 25 16 23 20 20 Nd 10 18 15 1 1 13 17 12 Sm 4.3 4.7 2.8 3.8 6.6 6.0 4.6 Eu 1.1 1.1 0.97 0.91 1.2 1.0 1.2 Dy 4.4 4.5 4.6 3.8 6.3 3.6 2.8 Er 2.4 3.0 2.0 2.9 2.3 2.6 1.6 Yb 1.7 2.9 2.4 28 3.5 3.0 2.4 1. Abbreviations are: E = early phase, L = late phase, and b-ande basaltic andesite. 125 TABLE 4.7 Chemical analyses of West G Seamount (WSMT) series (5E Andesite and Upper Dacite, upper member) volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C. Sample locations and descriptions are in Appendix A. Major and'minor element analyses are recalculated to 100 percent on a volatile-free basis. Fe203 is expressed as total iron. Symbols are as defined in Table 4.3. Sample Unit1 Rock Type SJ-5EA 5E andesite 10-1262-37* 5E basaltic andesite DL43 5E basalt DL423 5E andesite UD-ZrH UD.u basalt Si02 (wt. IS) 63.1 54.1 51.1 57.4 49.8 T102 0.90 0.92 0.93 0.83 1.12 AI2O3 14.7 16.6 16.8 17.0 20.8 Fe203 9.89 10.5 12.1 6.87 12.4 MnO 0.13 0.15 0.33 0.10 0.24 MgO 3.39 6.37 6:21 • 2.19 ~ 5.90 CaO 3.70 7.88 9.19 8.22 3.05 N320 2.37 3.00 3.03 6.72 -5.45 K20 1.54 0.15 0.15 0.09 0.98 P2O5 0.28 0.40 0.30 0.56 0.36 H20 3.37 4.15* 3.57 1.77 4.12 CO2 0.66 - 1.53 1.38 0.25 Ba (ppm) 434 134 113 182 522 Rb 28 < 4 <4 < 4 13 Sr 222 530 290 • 247 303 Nb 4 4 2 3 4 Y 31 34 23 40 40 Zr 91 88 51 67 123 Cr 18 30 75 18 16 Ni 17 8 50 22 16 Cu 78 63 ' 76 134 1 1 Zn 113 95 137 76 183 V 21 1 206 312 268 174 La 17 - 4 19 9 Ce 30 - 15 43 22 Nd 17 - 15 21 23 Sm 3.6 - 5.9 7.4 5.2 Eu 1.1 - 1.2 1.5 1.7 Dy 5.6 - 3.6 6.5 7.2 Er 2.3 - 1.4 3.7 4.8 Yb 1.1 1.8 3.4 3.1 1. Abbreviations are: 5E = 5E Andesite, and UD,u = Upper Dacite, upper member. 126 trends on AFM and FeO*/MgO diagrams (Appendix D). WSMT samples also plot in the calc-alkaline field on the MnO/TiC /^ P2O5 minor element diagram (Appendix D). Compared to N-type MORB (Fig. 4.4b), WSMT flows are strongly enriched in LIL elements except for Rb and K, which occur in MORB-like concentrations. They also show a distinct Nd and P enrichment, Nb and Ti depletion, slight to no depletion in the remainder of the HFS elements, and a strong Ni and Cr depletion. REE patterns (Fig. 4.4a) are flat to slightly HRE depleted with HRE 10 to 15 times chondrite levels. No Eu anomal ies are present. Oeochemical differences amongst lithologic units in the WSMT series are not major. Successively younger flow units in the Hanging Wall H-W Andesite contain more felsic members but retain similar chemical trends. A basaltic flow from the 5E Andesite unit has a much lower LIL element enrichment (except for Ba), more depleted HFS element content (except Nd and P), and higher Ni and Cr values (though still depleted relative to N-type MORB) than the basaltic andesite and andesite lavas. Mafic lavas of the Upper Dacite unit (upper member) display similar geochemical characteristics to the 5E Andesite lavas. WSMT series lavas have similar to slightly different chemical characteristics to EARC series flows. WSMT lavas generally have higher FeO*/MgO ratios and lower Rb, K, Ni andCr contents. The Arc Rifting (ARFT) series comprises clinopyroxene-phyric ultramafic lavas in the G-Flow unit and H-W Hori2on (as the mafic flow member), and feldspar + clinopyroxene porphyritic. mafic lavas in the Upper Mafic unit. Both lava types are basalts, based on their silica contents (Table 4.8). However, the clinopyroxene-phyric lavas, which have no plagioclase phenocrysts and anomalously high values of MgO (12 to 18.5 wt.SS), Cr (570 to 1550 ppm), and Ni (85 to 360 ppm), have ultramafic affinities. These rocks are best called komatiitic basalts (Arndt and Nisbet, 1982; Cameron and Nisbet, 1982), The komatiitic affinity is recognized on the basis of mineralogy (clinopyroxene phenocrysts and chromite microphenocrysts) and chemistry (anomalously high values of MgO for corresponding S1O2 contents, and similar trace element abundances - see Fig. 4.5b for comparison with an Archean komatiitic basalt from Munro Township, Ontario). The clinopyroxene-phyric ARFT lavas are not considered to be boninites because the ARFT rocks are too high in MgO and 127 too Rock / Chondrite a. ••- WSMT (HW Andesite, early) o- WSMT (HW Andesite, late) * - WSMT (5E Andesite) La Ce Nd Sm Eu Dy Er Yb 100 0 x Rock / MORB 10.0 1.0 •• 0.1 — N-type MORB • - WSMT (HW Andesi te, early) •o- WSMT (HW Andesi te , late) WSMT (5E Andesi te) •*- WSMT (5E Andesi te , basal t ) ' ' ' Qr~~^ *—1 Rb1 Ba K 5r La Ce Nb Nd P Zr Eu Ti Dy Y Yb Ni Cr Figure 4.4: Normalized trace element patterns for WSMT series units: a) chondrite normalized REE patterns, and b) N-type MORB normalized multi-element patterns. Each pattern represents the average (for n 12) for a respective unit. The range of values (for n >.2 only) in a particular sample suite is represented by the standard deviation (plotted as vertical bars). Analytical error in the REE plot is shown by an I-shaped bar. Arrows in the multi-element plot denote below detection limit-Data are from Tables 4.6 and 4.7, and the normalizing values used are in Appendix D. Abbreviations are: HW Andesite = Hanging Wall H-W Andesite, LIL = large ion lithophile elements, and HFS = high field strength elements. 128 TABLE 4.8 Chemical analyses of Arc Rifting (ARFT) series volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C. Sample locations and descriptions are in Appendix A. Major and minor element analyses are recalculated to 10O percent oh a volatile-free basis. Fe203 is expressed as total iron. Symbols are as defined in Table 4.3. Sample PR/124B* PR34* R-136 P46U-2 PR42* PR/32B* THL-EP Unit1 H-W GF GF GF UM UM UM Rock Type ' kom bas kom bas kom bas kom bas bas bas bas Si02 (wt. 85) 49.1 47.1 47.9 47.0 50.5 S1.9 52.6 Ti02 0.60 0.58 0.63 0.64 0.71 0.74 0.97 AI2O3 14.6 11.5 12.1 14.3 16.5 16.1 17.8 F82O3 10.9 11.4 11.0 11.4 11.8 10.9 9.04 MnO 0.22 0.29 0.22 0.21 0.25 0.29 0.17 MgO 12.7 18.4 15.0 16.5 7.32 8.52 5.42 CaO 8.50 9.01 11.45 7.76 7.86 8.49 . 8.16 Na20 2.97 1.48 1.44 2.02 4.62 2.69 ~ 5.26 K20 0.22 0.03 0.02 0.20 0.09 0.19 0.47 P2O5 0.21 0.18 0.19 0.18 0.27 0.24 0.18 H20 6.21* 4.99* 3.89 4.58 3.82* 3.61* 3.02 CO2 - 1.56 0.32 - - - 1.16 Ba (ppm) 515 78 32 273 151 161 334 Rb 5 <4 <4 <4 < 4 5 9 Sr 134 121 472 152 212 564 227 Nb 3 3 <2 2 - 3 4 3 Y 18 14 18 17 18 22 25 Zr 41 44 45 43 56 65 67 Cr 667 1550 1340 1310 48 67 368 Ni 85 360 344 318 14 21 79 Cu 85 79 117 91 10 42 46 Zn 327 71 86 82 87 92 91 V 252 216 271 277 242 216 297 La • — - 4 6 - - 3 Ce - - < 10 11 - - 15 Nd - - 18 17 - - 15 Sm - - 3.1 2.5 - - 6.2 Eu - - 0.93 0.55 - - 1,1 Dy - - 1.8 2.5 - - 4.0 Er - - 0.66 1.2 - - 2.0 Yb - - 0.50 1.0 - - 3.2 1. Abbreviations are: H-W •= H-W Horizon, mafic member, GF - G-Flow unit, UM •- Upper Mafic, unit, kom bas = komatiitic basalt, and bas = basalt. TiC^, a n d t o ° ' o w i n S'02>as w e ^ a s l a c k t n e essential minerals (clinoenstatite and orthopyroxene) of typical boninites (Cameron etal, 1979; Hickey andFrey, 1982; Walker and Cameron, 1983). ARFT komatiitic basalts and basalts, compared to N-type MORB values (Fig. 4.5b), are enriched in LIL elements, Nd and P. HFS elements are strongly depleted in the komatiitic basalts but only moderately so in the basalts. Also, ARFT komatiitic basalts show strong enrichment in Ni and Cr contents whereas ARFT basalts are depleted in these two elements. REE patterns for the komatiitic basalts (Fig. 4.5a) display LRE enrichment and slight to strong HRE depletion with HRE 3 to 10 times chondritic levels. ARFT basalt REE patterns (Fig. 4.5a) are more or less flat with a slight HRE depletion and HRE 10 to 20 times chondritic levels. Additional data reside in the chemistry of relict phases. Clinopyroxene phenocrysts from ARFT series flow units have compositions that cluster within the augite field in the pyroxene quadrilateral (Appendix D). Clinopyroxenes from the komatiitic basalts (Tables 4.9, D.3, 0.4 and D.5) are characterized by low Ti02 and moderately high Cr203 contents whereas from the basalts (Tables 4.9 and D.6), they contain distinctly higher Ti02 and lower Cr203 values. AI2O3 contents are low, display variable core to rim zoning, and correlate positively with increasing T1O2 concentrations. This zoning is best developed in clinopyroxenes from flows in the H-W Horizon mafic flow member (Table D.5) and the Upper Mafic unit (Table D.6). Some basalt clinopyroxenes also show a decrease in Mg/( Mg + Fe) ratios and CaSi03 component in zoning from core to rim. Compositions of chromite microphenocrysts (Tables 4.10 and D.9), found only in G-Flow komatiitic basaltic lavas, are plotted ona Mg/(Mg + Fe 2 +) versus Cr/(Cr+Al) diagram in Figure 4.6; fields from other mafic to ultramafic lava suites are shown for comparison. ARFT series chromites have high Cr/(Cr+Al) ratios ; relative to spinels from MORB's and komatiites, but are similar to those in boninites and ophiolites (those formed in island arc settings). Variation in some ARFT series chromites of Mg/( Mg + Fe2+) ratios might be the result of metamorphism-induced re-equilibration, according to similar observations by Crawford and Cameron (1985). 130 100 Rock / Chondri te ••- ARFT (komatiitic basalt) o- ARFT (basalt) a. La Ce Nd Sm Eu Dy Er - Yb N-type MORB ARFT ( komat i i t i c basal t ) ° - ARFT (basalt) *~ Munro Twp. Rock / MORB Rb Ba K 5r La Ce Nb Nd P Zr Eu Ti Dy Y Yb Ni Cr Figure 4.5: Normalized trace element patterns for ARFT series units: a) chondrite normalized REE patterns, and b) N-type MORB normalized multi-element patterns. The geochemical pattern for an Archean komatiitic basalt sample from Munro Township, Ontario (sample DC123: Canil, 1987) is plotted in (b) for comparison. Each ARFT pattern represents the average (for n i2) for a respective unit. The range of values (for n 12 only) in a particular sample suite is represented by the standard deviation (plotted as vertical bars). Analytical error in the REE plot is shown by an I-shaped bar-. Arrows in the multi-element plot denote below detection limit. ARFT data are from Table 4.8, and the normalizing values used are in Appendix D. Abbreviations are: LIL = large ion lithophile elements, and HFS = high field strength elements. TABLE 4.9 Representative electron miceprobe analyses of clinopyroxene phenocrysts in A rc Rifting (ARFT) series volcanic recks, Thelwood Formation mafic si l ls, and Flower Ridge Formation basalts. Sample locations and descriptions are in Appendix A . Analyses are from the data set in Appendix D. Symbol " - " denotes below detection limit. Sample PR/124B R136 -2 R136-1 PR42 P206 P243 Unit 1 H-W Mafic G-Flow Unit G-Flow Unit Upper Mafic Unit MM, Thelwood Fm basalt, FR Fm Analysis No. 2 F32-5C F32-1R C2-2C C2-4R D32-5C D32-4R D18-2C D18-1R B14-3C B14-1R D18-1C S i 0 2 (wt %) 52.81 50.74 52.69 53.50 51.48 53.21 50.57 51.40 52.01 51.24 51.88 T i 0 2 0.27 0.32 0.20 0.24 0.30 0.24 0.57 0.57 0.37 0.57 0.45 A l 2 0 3 2.55 4.17 2.04 2.33 3.08 2.14 4.63 3.16 3.63 2.75 2.39 C r 2 G 3 0.27 0.67 0.85 0.65 1.03 0.63 0.13 0.06 0.20 0.09 -FeO 6.30 5 7 4 4.17 4.13 4.23 4.34 6.63 7.75 5.84 9.10 7.85 MnO 0.18 0.13 0 . i 4 0.10 0.13 0.13 0.15 0.17 0.17 0.31 •0.19 MgO 15.72 14 81 16.37 16.43 15.83 16.56 14.04 14.44 15.41 14.83 15.22 CaO 22.24 22.23 22.70 23.00 23.34 22.83 22.82 21.93 21.87 19.95 •21.14 Na 20 0.10 0.18 0.14 0.12 0.14 0.10 0.17 0.20 0.18 0.29 0.19 Total 100.44 98 .99 99.30 100.45 99.56 100.18 99.71 9 9 6 8 99.68 99.13 99.34 Mg/(Mg+Fe) 3 0.816 0.821 0.875 0 8 7 3 0.870 0.872 0.791 0.769 0.825 0.744 0.776 100 x Wo 4 45.4 47.0 46.6 47.5 48.0 46.3 48.0 45.6 45.7 41.8 43.6 En 44.6 43.5 46.7 45.8 45.2 46.8 41.1 41.8 44.8 43.3 43.7 Fs 10.0 9.5 6.7 6.7 6.8 6.7 10.9 12.6 9.5 14.9 12.7 1. Abbreviations are: H-W Mafic = H-W Horizon, mafic flow member, MM = mafic si l l member, Fm = Formation, and FR = Flower Ridge. 2. Letter at end of analysis number denotes location of analysis in the c rys ta l : C = cere, R = r im. 3. Ratios are calculated using atomic fractions. Structural formulae are calculated based on 6 oxygens. 4. Pyroxene end member phases: Wo = CaSi0 3 , En = M g ^ i ^ , and Fs = F e ^ i ^ . Values are calculated using atomic fractions and normalizing to their sum. TABLE 4.10 Representative electron microprobe analyses of chromite microphenocrysts in G-Flow komatiitic basalts. Analyses are from data set in Appendix D. Sample locations and descriptions are in Appendix A.. Sample R136 -2 R136-1 Analysis No.1 A36-2C A36-1R A25-1C Si02 (wt. S) 0.19 0.12 0.11 Ti02 0.13 0.16 0.13 Al203 8.46 7.59 8.15 Cr203 . 59.39 59.06 59.33 FB203 2 2.67 3.62 3.64 FeO 19.88 20.15 17.47 MgO 8.78 8.39 10.16 MnO 0.36 0.39 0.34 Total 99.89 99.45 99.33 Cr/(Cr+Al) 3 0.825 0.839 0.830 Mg/(Mg+Fe2+) 0.440 0.426 0.509 Fe3+/(Fe3++Cr+Al) 0.034 0.047 0.046 1. Letter at end of analysis number denotes location of analysis in the crystal: C = core, R = rim. 2. Fe203 was calculated assuming stoichiometry. 3. Ratios are calculated using atomic fractions. 133 0.90-Q 0.80 < + H 0.70 H k. U „ 0.60-boninites + ophiolites komatiites 0.50-1 1 1 1 1 1 i 0.20 0.30 0.40 0.50 0 60 0.70 Mg/(Mg+Fe(+2)) Figure 4.6: Mg/(Mg+Fe2+) vs. Cr/(Cr+Al) diagram for ARFT komatiitic basalt chromite microphenocrysts. Outlined fields represent ranges in composition in chromites from other mafic to ultramafic volcanic suites (from Cameron and Nisbet, 1982). Data are from Table D.9 in Appendix D (cf. Table 4.10). Abbreviations are: c = core, r = rim. 134 4.3.3 THELWOOD AND FLOWER RIDGE FORMATIONS Three volcanic/Intrusive episodes are represented by units in the Thelwood and Flower Ridge Formations. The episodes comprise felsic volcanism (pyroclastic deposit units, Thelwood Formation), mafic magmatism (mafic sills, Thelwood Formation), and mafic volcanism (Flower Ridge Formation). The tectonic environment of these episodes is discussed in Chapter 5. Pyroclastic units in the Thelwood Formation range from dacite to rhyolite in composition, based on mineralogy and chemical composition (Table 4.11). Thelwood mafic sills and Flower Ridge extrusive rocks are basalts and basaltic andesites (Tables 4.11 and 4.12). There are also rare sills that are andesitic to dacitic in composition. No iron enrichment trend is shown on an AFM diagram, and only crudely so in the tholeiitic field on a SiC^ versus FeO*/MgO diagram (Appendix D). Thelwood and Flower Ridge samples lie in the arc tholelite field in a MnO/TiC^/^Os minor element diagram (Appendix D). The felsic pyroclastic rocks have higher concentrations of FeO*, Ti02, Zr and Y than the felsic volcanic rocks of the Myra Formation. REE patterns (Fig. 4.7a) are flat to slightly HRE depleted with HRE 20 to 30 times chondritic values; they also display negative Eu anomalies. Thelwood mafic sills and Flower Ridge basalts are characterized by high Ti02 concentrations and FeO*/MgO ratios. They are enriched in LIL elements, Nd and P, and show marked Ni and Cr depletion relative to N-type MORB (Fig. 4.7b). HFS element concentrations are similar to or enriched relative to N-type MORB. Analogous geochemical patterns are observed in samples from the Mariana back-arc basin (Fig. 4.1a) and the Geotimes unit (a marginal basin remnant) of the Oman ophiolite (Fig. 4.7b). REE patterns in the Thelwood and Flower Ridge mafic volcanic samples (Fig. 4.7a) are flat with HRE .15 to 30 times chondritic values. Relict clinopyroxene compositions (Tables 4.9 and D.7) are Ca-rich, plotting in the augite field within the pyroxene quadrilateral (Appendix D), and contain relatively low T1O2, and non-detectable to low Cr203 contents. The pyroxenes can be chemically zoned in FeO*, Na20, Ti02 and MnO. 135 TABLE 4.11 Chemical analyses of Thelwood Formation volcanic and magmatic rocks, Buttle Lake Camp, Vancouver Island, B.C. Sample locations and descriptions are in Appendix A. Major and minor element analyses are recalculated to 100 percent oh a volatile-free basis. Fe203 is expressed as total iron. Symbols are as defined in Table 4.3. Sample SBT-ZrC P3A P28D MM-ZrH D34293 D43106 • DW242 Unit1 PYR PYR PYR MM MM MM MM Rock Type 1 dacLT dacLT rhy T b-ande andesite andesite basalt S102 (wt. S) 69.0 68.3 73.4 55.7 59.1 57.3 51.8 Ti02 0.65 0.85 0.42 1.43 1.28 1.22 1.34 AI2O3 13.6 11.5 . 12.0 14.5 14.4 13.2 15.3 6.78 9.01 4.72 14.0 11.8 • 12.1 15.1 MnO 0.15 0.19 0.13 0.25 0.25 0.26 0.26 MgO 1.85 2.60 0.77 4.31 3.16 4.47 5.02 CaO 3.76 3.38 2.54 5.90 5.46 7.28 6.05 N320 3.31 1.28 1.52 3.39 3.91 3.72 - 4.13 K20 0.71 2.70 4.42 0.06 0.07 0.06 0.78 P2O5 0.19 0.19 0.08 0.46 0.57 0.39 0.22 H20 1.67 3.26 1.47 3.42 2.74 2.74 3.30 C02 0.20 0.48 n.d. 0.76 0.15 0.61 0.24 Ba (ppm) 240 1460 2020 68 35 77 349 Rb 13 31 51 <4 < 4 <4 5 Sr 389 191 132 210 196 172 227 Nb 6 4 6 4 4 <2 3 Y 46 44 52 39 47 32 28 Zr 174 156 223 109 130 81 79 Cr 14 33 14 23 13 24 6 Ni 12 20 14 21 10 18 15 Cu 16 15 15 14 < 7 <7 61 Zn 98 111 95 102 74 82 102 V 24 155 55 273 11 1 286 578 La 7 13 16 4 6 6 9 Ce 24 23 32 18 21 21 16 Nd 22 14 1 1 22 28 18 15 Sm 5.3 5.7 8.7 5.0 5.9 3.3 5.4 Eu 1.1 1.5 1.8 1.5 2.0 1.4 1.6 Dy 7.9 8.9 12 6.5 1 1 5.5 4.4 Er 4.6 5.0 6.8 3.9" 4.9 2.8 2.9 Yb 3.8 5.3 4.9 5.2 6.2 3.0 3.5 1. Abbreviations are: PYR = pyroclastic deposit unit, MM = mafic sills, dac LT = dacite lapilli-tuff, rhy T = rhyolite tuff, and b-ande = basaltic andesite. TABLE 4.12 Chemical analyses of Flower Ridge Formation volcanic rocks, Buttle Lake Camp, Vancouver Island, B.C. Sample locations and descriptions are in Appendix A. Major and minor element analyses are recalculated to 100 percent on a volatile-free basis. Fe203 is expressed as total iron. Symbols are as defined in Table 4.3. Sample Rock Type' P28F-1 basalt, Ls PR-85-20C* b-ande, Pbx PR-85-30A* basalt SiO? (wt. %) 45.3 54.2 49.8 Ti02 1.38 1.26 1.26 A1203 19.1 15.9 16.7 Fe203 13.8 12.8 14.4 MnO 0.33 0.21 0.26 MgO 5.18 4.90 6.44 CaO 9.44 6.05 8.12 Na20 4.75 4.44 2.60 K20 0.62 0.07 0.26 P2O5 0.22 0.21 0.22 H20 1.48 2.84* 4.99* C02 n.d. - -Ba(ppm) 425 97 171 Rb 4 4 6 Sr 271 221 202 Nb 2 5 3 Y 28 28 28 Zr 65 81 73 Cr 25 43 61 Ni 30 14 19 Cu 81 25 123 Zn 123 75 85 V 380 273 368 La 3 - -Ce 10 - -Nd 11 -Sm 3.9 - -Eu 1.2 - -Dy 7.1 - -Er 2.8 - -Yb 2.7 — — 1. Abbreviations are: Ls = lapilli-stone, Pbx = pyrxlastic breccia, and b-ande = basaltic andesite. 137 100 Rock / Chondrite Thelwood, pyroclastic units "°- Thelwood, mafic sills Flower Ridge Fm La Ce Nd Sm Eu Dy Er ~ Yb too.o 10.0 Rock / MORB 1.0 — N-type MORB Thelwood, ma f i c s i l l s o- F lower Ridge F m *~ Geot imes unit, Oman Ophtol i te HFS Rb Ba K 5r La Ce Nb Nd P Zr Eu Ti Dy Y Yb Ni Cr Figure 4.7: Normalized trace element patterns for Thelwood and Flower Ridge Formation units: a) chondrite normalized REE patterns, and b) N-type MORB normalized multi-element patterns. The geochemical pattern for a sample from the Geotimes unit (a marginal basin remnant) in the Oman Ophiolite (0M5666: Alabaster etal, 1982) is plotted in (b) for comparison. Each pattern (this study only) represents the average (for n 12) for a respective unit. The range of values (for n 12 only) in a particular sample suite is represented by the standard deviation (plotted as vertical bars). Analytical error in the REE plot is shown by an I-shaped bar. Arrows in the multi-element plot . denote below detection limit. Thelwood and Flower Ridge data are from Tables 4.11 and 4.12, and the normalizing values used are in Appendix D. Abbreviations are: LIL = large ion lithophile elements, and HFS = high field strength elements. 138 4.4 PETROGENESIS OF THE PRICE AND MYRA FORMATIONS Fieldwork has established five distinct volcanic assemblages in the Myra and Price Formations (Table 4.1). These separations can by corroborated and elucidated by chemistry. This section presents the analysis of the chemical data to show whether different parent magmas are involved, and whether different magma source regions are required. Also, the style of magmatic differentiation is investigated for each group. 4.4.1 DELINEATION OF MAGMATIC LINEAGES Two geochemical methods to test for comagmatic associations utilize Pearce element-ratio diagrams (Pearce, 1968; Nicholls, 1988; Russell and Nicholls, 1988), and trace element process identification diagrams (Allegre and Minster, 1978). Pearce element-ratio diagrams consist of ratios of elements (expressed in atomic percent) not involved in magmatic differentiation. These incompatible element ratios will cluster about a constant value characteristic of the magma. Consequently, plots of these elements in comagmatic lavas should overlap. Conversely, distinct clusters indicate different magmas. I f one or both of the numerator elements is not incompatible (i.e. these elements take part in fractionation), the resulting Pearce element-ratio plot will define unique trends with slopes governed by the stoichiometry of the elements in the fractionating phases. Comagmatic lavas, therefore, should fall on the same trend as long as the behavior of the chosen elements remains the same during fractionation. Trace element identification diagrams involve plotting the ratios of a highly incompatible element (e.g. Ce or Ba) and moderately incompatible element (e.g. Sm, Yb or Sr) against the highly incompatible element. Near-horizontai trends on such plots indicate that the samples are related by fractional crystallization processes. Steeply inclined trends denote partial melting processes. Both of these tests are utilized to examine possible comagmatic relationships among the five volcanic ser ies. A test of the comagmatic relationships between the two felsic volcanic series, VARC and PSMT, useda Ti/Zr versus Y/Zr Pearce element-ratio diagram in Figure 4.8. The diagram shows two 139 0.8 0.7 0.6 O.S H N 0.4-0.3 -0.2 0.1 H 0.0 II 25 — i — 50 o PSMT (H-W dacite) • PSMT (Upper Dacite) o VARC (H-W Horizon) • VARC (North Dacite) • EARC (Price Fm) 75 Ti/Zr 100 125 150 Figure 4.8: Ti/Zr vs. Y/Zr Pearce element-ratio diagram comparing PSMT and VARC series samples with each other, and with EARC series samples. The incompatible element ratios for the PSMT and VARC series samples form two distinct clusters, indicating two different magmas - one corresponds to PSMT series samples (I) and another to VARC series samples (II). EARC series samples form a trend which intersects the PSMT cluster, allowing for the hypothesis that PSMT series represents evolved EARC magma. Crosses represent analytical error. Values are from Tables 4.3, 4.4 and 4.5, and Appendix D (H-W Horizon samples only). 140 distinct clusters: one representing the H-W Horizon rhyolites and North Dacite flows (VARC series), and the other after H-W Horizon dacite and Upper Dacite (lower member) lavas (PSMT series). Thus a different magma clearly is indicated for each of the two series. Relationships among the felsic lavas and the EARC series are tested on Ti/Zr versus Y/Zr, and Yb/Zr versus Y/Zr plots in Figures 4.8 and 4.9, and a Cen versus (Ce/Sm)n diagram in Figure 4.10. In Figure 4.9, the two felsic volcanic series again define distinct areas. EARC series and PSMT series (H-W Horizon dacite) samples plot together, which is consistent with the hypothesis of the same magma for both series. Figure 4.8 contains a compatible element, Ti, with respect to more mafic volcanic units. Therefore EARC samples would lie on a trend governed by the variation in Ti. The resultant trend in Figure 4.8 intersects the PSMT series cluster. This and a similar relationship in Figure 4.10 are permissive of the supposition that the PSMT series represents evolved EARC magma, whereas VARC magmatism requires a separate source. Scatter shown by some PSMT series -(Upper Dacite) samples in the above diagrams may indicate affects by later processes (i.e. magmatic differentiation) as to not conserve any one or more of the elements used. WSMT and EARC data plot as separate but close clusters on a Yb/Zr versus Y/Zr Pearce element-ratio diagram in Figure 4.11. Due to the scatter in the plots the comagmatic hypothesis must be rejected. If there was a common parent magma, its chemistry has been affected by other processes that do not conserve Yb, Y and/or Zr(e.g. assimilation, magma mixing, magmatic differentiation: Nicholls, 1988; Russell and Nicholls, 1988). Field relationships also are not definitive. The EARC series represents a widespread effusive event and underlies the entire Buttle Lake Camp. The WSMT series is much more limited in its extent occurring in the lower to middle portions of the Mine Sequence, mainly at the northwest end of the Camp (Chapters 3 and 5). Therefore the WSMT series units can either represent resumption of mafic to intermediate EARC volcanism — but on a more restricted and intermittant basis - or have originated from a separate magmatic event. Relationships among chemistries of the two felsic volcanic series and WSMT series are shown on a Ti/Zr versus Y/Zr Pearce element-ratio diagram in Figure 4.12. The cluster defined by the VARC samples clearly rejects any comagmatic association. The PSMT cluster, however, does not H I 0,8-] 0.7-0.6-0.5 N 0.4 0.3 0.2 0.1 0.0 9 • • EARC (Price Fm) o PSMT (H-W dacite) • PSMT (Upper Dacite) 93 VARC (H-W Horizon) o VARC (North Dacite) 0.00 0.01 0.02 0.03 Yb/Zr 0.04 0.05 Figure 4.9: Yb/Zr vs. Y/Zr Pearce element-ratio diagram com par ing EARC series samp les lo PSMT and VARC series samples. Samples from the EARC and PSMT (H-W dacite) series lie together indicating a possible comagmatic relationship whereas VARC series samples form their own distinct cluster (therefore are from a different magma than both the EARC and PSMT series). PSMT (Upper Dacite) samples may imply modification due to magmatic differentiation since evolution from EARC magama. Crosses represent analytical error. Values are from Tables 4.2, 4.3, 4.4 and 4.5. E tn v . « u 3-2-1 0 a EARC (Price Fm) » PSMT (H-W dacite) • PSMT (Upper Dacite) B VARC (H-W Horizon) a VARC (North Dacite) + Q L* • a -> - 1 — 10 20 30 40 (Ce) n 50 60 70 Figure 4.10: Cen vs. (Ce/Sm)n trace element'process identification diagram for EARC--PSMT series' and VARC series units. Near-horizontal trends denote samples that are related by fractional crystal-lization processes. Samples from the EARC and PSMT ( HW dacite) series, and the VARC series form distinctive linear trends supporting origins from different magma sources. Origin of PSMT (Upper Dacite) series is unclear in this diagram (see Fig. 4.9). EARC—PSMT series cannot be distinguished from VARC series in this diagram. Solid arrow represents EARC-PSMT series; open arrow represents VARCseries. Crosses represent analytical error. Values are from Tables 4.2, 4.3, 4.4 and4.5. 142 0.8 0.7 H 0.6 0.5 CJ 0.4 -j 0.3 1 0.2 0.1 U N > 0.0 H 4 • EARC (Price Fm) * WSMT (HW Andesite. ear ly) ^ WSMT (HW Andesite, late) * WSMT (5E Andesite) —• 1 ' 1 1 1— 0.00 0.01 0.02 0.03 Yb/Zr 0.04 0.05 Figure 4.11: Yb/Zr vs. Y/Zr Pearce element-ratio digram comparing WSMT series sampler EARC series samples. Resulting clusters are closely spaced but separate, rejecting the comagmatic hypothesis. WSMT series units may have originated from a different magma source or represent a more restricted continuation of EARC volcanism (see text). Cross represents analytical error. Values are from Tables 4.2,4.6 and 4.7. 0.8 0.7 -0.6 -0.5 5 0.4 > 0.3 0.2 0.1 H 0.0 A A KWSMT (5E Andesite) * WSMT (HW Andesite, ear ly) a WSMT (HW Andesite, late) « PSMT (H-W dacite) B VARC (H-W Horizon) 50 100 150 T i / Z r 200 Figure 4.12: Ti/Zr vs. Y/Zr Pearce element-ratio diagrams comparing WSMT series samples to PSMT and VARC series samples. PSMT series samples lie on the same trend as WSMT (HW Andesite) samples, indicating a possible link through magmatic differentiation. However, field relationships rule against this possibility. VARC series samples clearly reject any comagmatic association with WSMT units. Cross represents analytical error. Values are from Tables 4.2,4.6 and 4.7. eliminate a possible link through magmatic differentiation because both PSMT and WSMT data lie on the same trend (would be caused by variation in Ti during differentiation). Field evidence (Chapters 3 and 5), though, makes it unlikely that the two volcanic series shared the same magma. ARFT volcanic series lavas represent a discrete magmatic series within the Myra and Price Formations. This is based on the ARFT series being composed of mostly ultramafic to mafic volcanic rocks, and field relationships among units within the Myra Formation. (ARFT lavas are from a distinctive eruptive source area, and become more common in higher stratigraphic levels of the Myra Formation relative to the less mafic volcanic units of the VARC, PSMT and WSMT series.) Summarizing, the five volcanic series in the Price and Myra Formations originated from at least three different magmas. The different magmas correspond to the EARC - PSMT series, the VARC series, and the ARFT series. Each is discussed separately below. The WSMT series may be related to the EARC series magmatic event or to a separate one - a distinction cannot be made. 4.4.2 EARLY ARC (EARC) - PRICE SEAMOUNT (PSMT) LINEAGE EARC basaltic andesite and andesite represent evolved partial melts from an upper mantle source region (cf. Gill, 1981). Diagnostic trace element compositions of the lavas, relative to N-type MORB (see above), reflect similar characteristics in the source region. The depletion in HFS elements may signify that the mantle source area underwent previous episodes of melt extraction (Saunders and Tarney, 1984), or contained incompatible element-rich minor phases such as rutile, sphene and zircon in themelt residue (Saunders etal., 1980). The first proposal is favoured because the same depletion pattern is seen in all mafic lavas in the Price and Myra Formations, regardless of likely differences in the degree of partial melting. If the latter proposal were true, varying degrees of partial melting, which govern the amounts of the minor phases remaining in the residue, should be reflected by variations in the contents of HFS elements. The LIL element enrichment is a diagnostic feature of mafic to intermediate volcanic rocks in modern oceanic island arc systems (Fig. 4.1) and is proposed to represent metasomatism of the mantle source region by a LIL element enriched fluid phase emanating from the subducted, dehydrating oceanic crust (e.g. Gill, 1981; Myson, 1982; Saunders 144 and Tarney, 1984). The origin of the apparent enrichment in Nd and P is not clear. It may be the result of original mantle heterogeneity present prior to subduction, of contamination by a subducted sediment component (Pearce, 1982; Andrew, 1987), or of the nature of the normalizing values used. Phases involved in fractional crystallization of EARC magma as it evolved to more felsic compositions (represented by the PSMT series) are inferred by observed phenocryst assemblages and modelled fractionation vectors in a Zr versus Ti covariation diagram (cf. Pearce and Norry, 1979) in Figure 4.13. The direction of the fractionation vector from andesite to dacite and rhyolite is largely due to magnetite fractionation (Pearce and Norry, 1979). This is also indicated in an experimental study by Spulber and Rutherford (1983) on the derivation of a I0W-K2O, high Si02 melt from fractionation of a primitive oceanic tholeiite under hydrous conditions. They found that at shallow depths (Pfluid < 2 kb) the crystallization of Fe-Ti oxides was the major factor contributing to the amount of SiC^ enrichment in the residual liquid, and that amphibole only becomes a factor at pressures 1 2 kb (a H2O 1 06)- Upper Dacite (lower member) samples indicate a possible reversal in the direction of the vector (to lower Zr and Ti values) implying the presence of a hydrous phase or zircon in the final stage of fractional crystallization of the EARC magma. No hydrous phenocryst phases were observed in these PSMT lavas; therefore, magnetite and zircon fractionation most likely accounts for the reversal. 4.4.3 YOLCANIC ARC (VARC) LINEAGE VARC lavas lack an observed, appropriate parental mafic magma (section 4.4.1). Detailed fieldwork argues that the complete absence of suitable parental material is real. A source for the VARC lavas should show geochemical characteristics similar to the VARC lavas themselves, namely: low concentrations of HFS elements, low total REE abundances, and a depletion trend in HRE. This is consistent with melts generated by partial melting of lower crust (Spulber and Rutherford, 1983) or fractional crystallization of a primitive mafic magma (Meijer, 1983; Spulber and Rutherford, . 1983). The partial melting hypothesis is favoured here. In this case, the source rock type would have been an island arc tholeiitic basalt or basaltic andesite. A similar partial melting proposal is 145 10' £ a a 10-10' Q EARC (Price Fm) o PSMT (H-W dacite) • PSMT (Upper Dacite, low) • PSMT (Upper Dacite, up) 10^  Zr (ppm) i o -Figure 4.13: Zr vs. Ti covariation diagram for EARC-PSMT series samples. Fractionation trend, according to modelled vectors by Pearce and Norry (1979), corresponds to: (1) plagioclase + clino-pyroxene + olivine fractionation within the andesites, (2) plagioclase + clinopyroxene + olivine + magnetite fractionation from andesite to dacite/rhyolite, and (3) plagioclase + a hydrous silicate phase (amphlbole and/or biotite) + magnetite fractionation within the felsic units. Trend (3) also can be the result of zircon fractionation instead of the hydrous phase( s). Abbreviations are: low = lower member, and up = upper member felsic flow blocks. Cross represents analytical error. Values are from Tables 4.2 and 4.5, and Appendix D (PSMT series samples only). suggested by Lapierre etal (1985) to explain the origin of the massive sulphide hosting Balaklala Rhyolite located in a similar volcano-tectonic setting within the Paleozoic West Shasta district, California. Fractionation within the VARC magma yielded two types of flow units: quartz + feldspar porphyritic (QFP), and feldspar porphyritic (FP) types. Based on field relationships in the most voluminous VARC series unit (H-W Horizon), the FP lavas preceded the QFP flows. Plotted on a Zr versus Ti diagram in Figure 4.14, samples from both flow types delineate a fractionation vector from high to low Ti and Zr abundances. A possible fractionating assemblage based on observed phenocryst assemblages, and modelled fractionation vectors (cf. Pearce and Norry, 1979) could consist of alkali feldspar, magnetite and zircon. Also, initially, the magma was saturated in silica (FP lava phase). During fractionation the magma became oversaturatod in silica and thus precipitated quartz (QFP flows). This precipitation may also have been brought about by a combination of lower temperatures and decreasing water content (Sakuyama, 1983). Potassium feldspar was not a fractionating phase in this magma; this is supported by petrographic studies of the QFP lavas in which no K-feldspar phenocrysts were observed. The presence of a hydrous silicate phase in VARC series lavas, although implied in Figure 4.14, is only observed in samples from the uppermost VARC series unit, the Upper Rhyolite, which contain pseudomorphs after amphibole phenocrysts (section 3.2.2.9). 4.4.4 ARC RIFTING (ARFT) LINEAGE ARFT magmas were derived from similar upper mantle sources as the EARC and WSMT magmas. This is inferred by the same LIL element, Nd and P enrichment, and HFS element depletion trends displayed by the ARFT series lavas. ARFT komatiitic basalts represent primary melts. This is supported by low amounts of phenocrysts, high MgO, Cr and Ni concentrations, and the presence of chromite microphenocrysts in the lavas. ARFT basalts might be related to the komatiitic basalts by simple magmatic differentiation. Information on the genesis of ARFT komatiitic basalts can be taken from experimental work on ultramafic lavas, and comparisons with studies on ultramafic volcanic rocks in island arc settings. A 147 10' g 1 0 3 4-10" 10' B V A R C (H-W Horizon, QFP) • V A R C (H-W Horizon, FP) 1 0 ^ Zr (ppm) i o -Figure 4.14: Zr vs. Ti covariation diagram for VARC series samples (H-W Horizon only). Fractionation trend, according to modelled vectors by Pearce and Norry (1979), corresponds to alkali feldspar + a hydrous silicate phase (amphibole and/or biotite) + magnetite fractional crystallization. Trend can also be the result of zircon fractionation (see text). Abbreviations are: QFP = quartz + feldspar porphyritic rhyolite, and FP = feldspar porphyritic rhyolite. Cross represents analytical error. Values are from Tables 4.3 and 4.4, and Appendix D. 148 recent, relevant experimental study is by Elthon and Scarfe (1984) on a high-MgO basalt from the Tortuga ophiolite in Chile. Studies on the latter (boninites and high-MgO andesites) include those by Tatsumi (1982), Cameron etal. (1983), and Kyser etal (1986). These works provide estimates of upper and lower limits on temperature and pressures of formation, water content, and extent of partial melting for ARFT komatiitic basalt genesis. These experiments suggest that the ARFT komatiitic basalts could have formed at 1300a C at pressures between 15 and 25 kb by moderate to high degree (215 percent) of partial melting of a hydrous (resultant liquids contained 1 to 2 wt.* H2O) depleted mantle peridotite. ARFT series komatiitic basaltic lavas underwent none to only minor fractional crystallization prior to eruption. Early fractionating phases were chromite (present as microphenocrysts) and probably olivine (implied by the presence of chlorite pseudomorphs - see Chapter 3). The observed augite phenocrysts may have formed because of rapid low pressure crystallization rather than high pressure fractional crystallization processes in the source, region. In the high pressure experiments by Elthon and Scarfe (1984), clinopyroxene compositions closest lo those in the ARFT lavas coexisted with liquids having 8.5 to 9.5 wt.* MgO. For liquids having ARFT komatiitic basaltic MgO concentrations (12 to 18 wt.*), coexisting clinopyroxenes were found to have lower CaO (15 wt.*) and higher A1203 ( 7 wt.*) than those in the ARFT lavas (23 wt.* CaO and 2 to 3 wt* A1203). Variation in A1203 abundance is a potential indicator of pressure because Al solubility in augite is found to increase with increasing pressure (Orove and Bryan, 1983). Therefore, a possible process to account for the ARFT komatiitic basalt clinopyroxenes, based largely on their compositions, was low pressure (i\kb) fractional crystallization. The absence of plagioclase phenocrysts might be explained by possible high temperature of extrusion or the low A1203 content of the ARFT komatiitic basalts, which would favour crystallization of clinopyroxene before and in greater abundance than plagioclase (Crawford and Cameron, 1985). ARFT series basalts were formed by possible fractional crystallization of magmas similar to those that produced the komatiitic basalts. Geochemical evidence supporting this is illustrated on a Zr versus Ti covariation diagram in Figure 4.15. The resulting fractionation trend follows a modelled a ARFT (komatiitic basalt) • ARFT (basalt) E a a 10-4-10' Zr (ppm) 10" Figure 4.15: Zr vs. Ti covariation diagram for ARFT series samples. The fractionation trend according to modelled vectors by Pearce and Norry (1979), corresponds to plagioclase + clinopyroxene + olivine fractional crystallization in the ARFT basalt lavas. Clustering of ARFT komatiitic basalt lavas indicate no fractionation of phases involving Ti or Zr. Cross represents analytical error. Values are from Table 4.8 and Appendix D. 150 vector representing plagioclase + clinopyroxene + olivine fractional crystallization (Pearceand Norry, 1979). Presence of plagioclase and Ca-rich clinopyroxene phenocrysts in ARFT series basalts indicate a low pressure environment (< 10 kb, probably *1 kb) during fractionation (cf. Elthonand Scarfe, 1984). 4.5 PETRQGENES1S OF THE THELWOOD AND FLOWER RIDGE FORMATIONS Magmas responsible for the felsic Thelwood Formation pyroclastic deposit units may represent fractional crystallization derivatives of a more mafic parental magma or partial melts of arc crustal material, both in a volcanic arc setting. Characteristics of a parental magma are not known except that it would have contained the high abundances of HFS elements reflected in the pyroclastic deposit samples. Ubiquitous negative Eu anomalies in these samples represent fractionation of plagioclase or low Eu + 3 /Eu + 2 values in the fractionating magma. Thelwood Formation mafic sills and Flower Ridge Formation basalts were not produced from as depleted a mantle source as volcanics in the Price and Myra Formations. A major geochemical difference is in the HFS element concentrations that show N-type MORB values rather than those typical of depleted island arc basalts (Fig. 4.1). These characteristics could imply that the source region for the mafic sill magmatism did not experience previous melting episodes related to subduction, which would have depleted the HFS elements (Saunders and Tarney, 1984). Alternatively, these HFS elements could have undergone some sort of replenishment, possibly by mantle counterflow in parts of the mantle wedge (Hawkins etal, 1984; NyeandReid, 1986) where non-depleted mantle material replaces that depleted by episodes of partial melting. Similarities between the two sets of formations consist of distinctly enriched Ba.Nd andP contents. The prevalence of this enrichment could indicate a similar mantle source region to that responsible for the volcanic units in the Myra and Price Formations. Differences would be due to modifications in the source region caused by subduction processes. The Thelwood mafic sills and Flower Ridge basalts display strong Ni and Cr depletions indicating early olivine + clinopyroxene ± spinel fractionation. Later, lower pressure fractional 151 crystallization involved plagioclase + Ca-rich clinopyroxene + magnetite based on observed phenocryst assemblages. The uppermost sills in the Thelwood Formation represent melts that evolved to andesitic and", less commonly, dacitic compositions. 4.6 CONCLUSIONS Volcanic stratigraphy in the Price and Myra Formations is the result of volcanic arc and intra-arc or back-arc volcanism. At least three distinct magmatic lineages are recognized: (1) Early Arc (EARC) - Price Seamount (PSMT) lineage, (2) Volcanic Arc (VARC) lineage, and (3)Arc Rifting (ARFT) lineage. Volcanic products from these magmatic sources commonly display overlapping field relationships indicating that they were partly contemporaneous. The WSMT volcanic series may be related to the EARC magmatic lineage or to a separate one - a distinction cannot be made. ARFT komatiitic basalts represent primary melts whereas the other mafic to intermediate volcanic rocks in the Price and Myra Formations are products of magmatic differentiation. Source region for the ultramafic to mafic magmas was an upper mantle peridotite depleted in HFS elements and variably enriched in LIL elements (both relative to N-type MORB) as a result of a subducted, dehydrating oceanic crust slab. LIL and HFS element patterns, relative to N-type MORB, for the ultramafic to intermediate volcanic rocks are similar to those from modern arc and back-arc or intra-arc settings (Fig. 4.1). The two felsic volcanic series in the Myra Formation, the PSMT and VARC series, were generated from two distinct sources. PSMT series units represent products from evolved EARC magma. VARC series units are products from magma formed by partial melting of lower crustal portions of a volcanic arc. Units in the Thelwood and F lower Ridge Formations represent volcanism associated with a more evolved phase of basin development, relative to that associated with the Myra Formation (Thelwood Formation mafic sills, and Flower Ridge Formation mafic flows and pyroclastic deposits), and a volcanic arc (Thelwood Formation pyroclastic deposit units). LIL and HFS element patterns, relative to N-type MORB, for the mafic units are similar to those observed in marginal basins and mature back-arc basins (Figs. 4. la and 4.7b). Magmas responsible for the Thelwood and Flower Ridge mafic volcanic units were derived from less depleted (relative to N-type MORB) mantle sources than those for the Pr-ice and Myra Formations. A similar mantle source region, though, is inferred because the Thelwood and Flower Ridge mafic volcanic units display the same, characteristic enriched geochemical signature for Ba, Nd and P as in the ultramafic to intermediate volcanic rocks of the Price and Myra Formations. 153 CHAPTER 5  DEPOSITION*!. HISTORY 5.1 INTRODUCTION Units of the Buttle Lake Sicker Group represent sedimentation and volcanism in an oceanic island arc system that evolved from early to mature arc, to an incipient rift tectonomagmatic setting. Proposed models governing evolution of such systems (e.g. Karig, 1971; UyedaandKanamari, 1979; Dewey, 1980; Hawkins et al., 1984; Tamaki, 1985) involve the break up of the island arc along its volcanic zone. The initial feature is a rift system which may or may not develop into a spreading center. The important aspects of this initial event are the morphology of the affected crust and the associated volcanic activity, because of the consequences regarding the distribution of volcanogenic and sedimentary products. An additional important aspect of island arc evolution is the occurrence of exhalative hydrothermal mineralization in zones of extension (cf. Carey and Sigurdsson, 1984). Although only Fe- and Mn-rich sediments have been documented in recent island arc systems (Cronan etal., 1984), ancient analogues commonly contain polymetallic volcanogenic massive sulphide deposits. The most studied example of this is the Tertiary Kuroko district of Japan. Recent studies on these deposits suggest that they formed in regions of extension in an island arc setting (e.g. Scheibner and Markham, 1976; Hutchinson, 1980; Uyeda and Nishiwaki, 1980; Cathles etal, 1983). This study shows that the Paleozoic Buttle Lake massive sulphide deposits are also an excellent example of exhalative hydrothermal mineralization in an extensional island arc environment. Volcanogenic sedimentation in extonsional or rift basins in oceanic island arcs has only recently begun to be investigated in detail. Models for such sedimentation have been put forth by Karig and Moore (1975), Klein (1975) and Carey and Sigurdsson (1984). The model by Carey and Sigurdsson (1984) is appropriate here because it concentrates on generation, transport and deposition of arc-derived volcaniclastic material into the developing basin. Paleozoic units in the Buttle Lake Camp afford a good opportunity to study volcaniclastic sedimentation and volcanism in an ancient island arc setting. The two lower formations, the Price and Myra, are an example of diverse and complex volcanism and sedimentation over a relatively small area (a rift basin formed by intra-arc rifting). The two upper formations, the Thelwood and Flower Ridge, represent a less complicated style of volcanogenic deposition over a much more extensive region (a more evolved basin). This chapter reconstructs the volcanic and depositional history of the Buttle Lake island arc system. The discussion below, treats the Price and Myra Formations, and the Thelwood and Flower Ridge Formations separately because of the differences of scale involved, and the probable unconformable relationship between the Myra and Thelwood Formations (Chapter 3). This synthesis is based largely on field relationships of the units, but is also supported by the detailed petrochemistry and inferred magmatic evolution described separately in Chapter 4. Deposition of the Buttle Lake massive sulphide deposits is discussed under depositional history of the Price and Myra Formations. 5.2 DEPOSITIONAL HISTORY OF THE PRICE AND MYRA FORMATIONS Units in the Price and Myra Formations represent volcanism and volcanogenic sedimentation in an intra-arc rift environment within an oceanic Island arc system. More specifically, most of the preserved Price and Myra stratigraphy in the mine property indicates that deposition occurred in a northwest-southeast trending rift basin (minimum dimensions being 2 to 3 km wide and 10 km long), named here as the Buttle Lake Camp basin (BBSN). The rifted nature is implied by the marked linear distribution of many of the lithologic units in the Myra Formation (Mine Sequence), including the ore deposits (Fig. 3.2). This rift basin received volcanogenic material from: (1) seamount centers located along the strike of the basin but beyond the mine-area boundaries to the northwest and southeast respectively, (2) volcanic arc volcanism to the northeast, and (3) rifting-related volcanic activity to the southwest. The volcanogenic material that filled the rift basin consisted of varying proportions of non-explosive (lava flows, hyaloclastites) and explosive (pyroclastic and hydroclastic) products. Factors 155 governing the eruptive style included water depth, magmatic volatile content, magma composition, and infiltration of external water (Kokelaar, 1986). That volcanism and volcanogenic sedimentation occurred in a subaqueous environment is indicated clearly by the presence of pillowed flows and hyaloclastite, and hydrothermal stratiform deposits throughout the section. Consequently, volcaniclastic deposits were emplaced by sediment gravity flow processes,.whether the unit originated directly from an eruption or was later remobilized due to sloughing from unstable volcanic slopes. A general summary of volcanogenic products and their expected emplacement processes is in Table 5.1. The variability and complexity of the volcanic and sedimentation events of the Price and Myra Formations makes a detailed synthesis difficult. To better facilitate reconstruction, the section is broken into four volcanic/volcanogenic sedimentation cycles (in order of decreasing relative age): the Price-H-W cycle, the Interzonecycle, the L-M-P (Lynx-Myra-Price) cycle, and the Upper cycle. These cycles coincide respectively with: a lower rifting and massive sulphide mineralization event, renewed arc volcanism and basin-filling sedimentation, an upper rifting and massive sulphide mineralization event, and major rift volcanism. Litho-stratigraphic units (Chapter 3) and associated magmatic events (Chapter 4) in each cycle are summarized in Table 5.2, and in two generalized geologic cross section reconstructions of the Price and West G sections in Figure 5.1. The Buttle Lake Camp massive sulphide deposits are shown in an idealized longitudinal section reconstruction of the mine-area rift basin in Figure 5.2. Evolution of the Buttle Lake Camp rift basin, in terms of the four cycles, is shown schematically in Figure 5.3. For orientation purposes, the scheme followed in Chapter 3 (Fig. 3.2) is also adopted here. 5.2.1 PRICE - H-W CYCLE The Price - H-W cycle marks the initial formation of the rift basin, and the deposition of the H-W massive sulphide orebody The lowermost unit in this cycle, the Price Formation, represents a major period of early arc volcanism (i.e. development of the volcanic arc). Volcanic activity consisted mainly of non-explosive, effusive events. Upon cessation of this volcanic event, rifting produced a rift zone - the mine-area rift basin or Buttle Lake Camp basin (BBSN). Initial i ABLt 5.1 Summary of volcanogenic products and emplacement processes in the Buttle Lake Camp basin. Source Prooucts Emplacement Process Volcanic arc and searn cunts Rift pyroclastic deposits flows, flow breccias flow breccias, hyaloclastites remobilized pyroclastics flows flow breccias, hyaloclastites hydroclastic deposits debris flows, turbidity currents, suspension fallout extrusion onto the basin floor from linear vents (fault-focussed?) or point sources (seamounts) debris flows debris flows ana turbidity currents due to. slope instability or seismic activity fissure-fed extrusions onto sea floor debris flows debris flows, minor turbidity currents Non-volcanic argillite chert,jasper massive sulphides - suspension fallout, turbidity currents - hydrothermal precipitation (exhalites) - hydrothermal precipitation (exhalites) TABLE 5.2 Litho-stratigraphic units and associated volcanic series present in each of the four volcanic/volcanogenic sedimentation cycles (Price - H-W, Interzone, L-M-P, and Upper cycles) i n the B uttle Lake Cam p basi n. Cycle Litho-Stratigraphic Units Volcanic Series1 PRICE — H-W Price Formation EARC H-W Horizon VARC, PSMT,ARFT INTERZONE Hanging Wall H-W Andesite WSMT Ore Clast Breccia unit VARC, ARFT, PSMT, WSMT Lower Mixed Volcaniclastics WSMT, PSMT Upper Dacite (lower member) PSMT North Dacite VARC 5E Andesite WSMT L-M-P Lynx-Myra-Price Horizon VARC, WSMT Upper Dacite (upper member) WSMT G-Flow unit ARFT UPPER Upper Mixed Volcaniclastics ARFT, VARC Upper Rhyolite unit VARC Upper Mafic unit ARFT 1. Series names are: EARC = Early Arc series, VARC = Volcanic Arc series, PSMT = Price Seamount series, WSMT =WestG Seamount series, and ARFT = Arc Rifting series. 158 Figure 5.1: Generalized geologic cross section reconstructions (to predeformation state) of the (a) Price section and (b) West G section, Buttle Lake Camp, Vancouver Island. The sections show the relative positions of the five volcanic series: EARC(DCp), VARC ( w ) , PSMT(*xX), WSMT (+++), and ARFT ( v v v ) , and the four volcanic/volcanogenic sedimentation cycles: Price - H-W (PH), Interzone (I), L-M-P (L), and Upper (U). The Lynx-Myra-Price (L-M-P) Horizon is shown by an open circle pattern ( o ° 0 ) . Blank areas within the Myra Formation denote volcaniclastic units of mixed or undefined provenance. Unit symbols are as in Figure 3.4 except 5E = 5E Andesite. 2 0 0 0 ft 5 0 0 m No vertical exaggeration b . SW N E D C t u u L 1 i i > i < i i i ' i i . n " ) l w r T i — — ^ ^ r r ~ r T » • + + + + + » + • + + » + 7->+ + tj-i m " * ' * f * ,, 1 II ' II " ' L e H y l ^ r * t H t r n + »>\",''^-y'Tv;iiiii/ii|WM»'i II i y .iVTiff t\fir£Z _—r-r(~i* t n t H 8 b * H t + • + + v + j j J T T t T - T " T T T T __ r t -rrTT+*t* + * * + + + + + * + + + * t + + , t t l t l I — - ' - ' <f** * — - r+ +++••++ + + <- + t t J - * ' , , —-1 -r -pr f + + * ti + + + + + + +,+ + + + + ++ + + + + + + + + + + • •* ferx + + + + + + + + + + + + + + + + + + + + + + + + + +2 + + + + + + + + + + + , , , V I I ii+ + + + + + + + + + + + •*• + + + + + » + + + + + + + + +• + , , — " ^ • . : : / V • • •• .'. . P H P H o NW H CO U l LYNX H-W -MYRA PRICE SE 1 1 ::::::::::io::::::::::::::::: DCt - " ; ; ! ; ; ; ; ! ! " ! ! ! " " : " " : " " " - i n u 1 u % + / > L J f t t t t t t + P t * t t + t t | t i t t + + t t + t t + t t + + t t + t + + t t t + t t + t + t J » # J | " f^c4L+ + + + + + + + + + + + + + + + + + + + + + t + + +• + + + + J- + 44 + + L 1 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + * ' + - t t g iJ-J-J-J-»4-4-4- + *« . 4-1 1 3Z-, I + + + -f+ + + + + 1- + + T - r i - ^ - - r i - - T T - r T ^ T - T T - T T > i T ^ ^ ' • i ' ' T T T T T T T T T T T I I T T T T T + + + T * ^ ' " ' I U ' ' i l l J- 4- 4- 4- + k + + 4- + 4.+ + 4. + + + + + + + + + + + + - + 4.4. + + + + + >, . . . . . . . . . . . . . . . . . • » . . . . . . . . . . . . . . . . . • " " PH PH 1 \ H-W ' DCp 4000 ft 1000 m Vertical exaggeration is 2x Figure 5 . 2 : Idealized longitudinal section reconstruction to predeformation state of the Myra Formation (Mine Sequence), Buttle Lake Camp, Vancouver Island, showing the Buttle Lake massive sulphide deposits. Rock unit patterns and symbols are as in Figure 5 . 2 . Ore zone symbols are: S = S-Zone, GH = G-Hanging Wall Zone, WG = West 6 , L = Lynx, M = Myra, P = Price, and H-W = H-W deposit. Solid pattern represents massive sulphide deposits; vertical lined pattern denotes chert deposits; wavy lined pattern represents hydrothermal ly altered and mineralized feeder zones. West G, Lynx, H-W-Myra, and Price refer to section lines defined in Figure 3 . 2 . o 161 Figure 5.3: Evolution of the Buttle Lake Camp rift basin (BBSN). Figure 5.3a, the Price-H-W Cycle, represents initial formation of the BBSN, characterized by massive sulphide mineralization (H-W deposit: solid pattern), felsic arc volcanism (VARC series flows (dashes) and volcaniclastics (dots)), and hemipelagic sedimentation (argillite member, H-W Horizon: vertical lined pattern). Figure 5.3b, the Interzone and L-M-P Cycles, represents basin widening by intra-arc rifting, accompanied by shedding of volcaniclastic debris (Ore Clast Breccia unit (OCB) and Lower Mixed Volcaniclastic (LMV)), and seamount volcanism at opposite ends of the BBSN (PSMT and WSMT series). Resumption of VARC volcanism coincided with another period of massive sulphide mineralization (Lynx-Myra-Price Horizon (L-M-P): solid pattern). Rift volcanism (G-Flow unit (Gf): ARFT series) marks the final event in this stage. Figure 5.3c, the Upper Cycle, represents continuation of basin widening with diminishing felsic arc volcanism (Upper Rhyolite (UR): VARC series) and increasing rift volcanic activity (Upper Mafic unit (UM): ARFT series). End of BBSN development probably coincided with failed or aborted rifting. F i g u r e 5.3a C* INTERZONE & L - M - P C Y C L E S NE SW F i g u r e 5 .3b V O L C A N I C A R C BBSN PSMT to SE WSMT to NW BARC R E M N A N T A R C Pelagic Sediments UPPER CYCLE V O L C A N I C A R C F i g u r e 5.3c 165 topography of the basin contained numerous irregular, fault-bound ridge and trough structures (Figs. 5.1 and 5.3; cf. Carey and Sigurdsson (1984), and Leitch (1984)). This interpretation was made by examining the distribution of H-W Horizon felsic flows and volcaniclastic units relative to the argillite member, using the assumption that argillite deposition was horizontal. Little if any volcaniclastic or epiclastic sedimentation occurred during the opening of the rift basin. This initial lack of sedimentation on basin or trough floors could indicate that a subaqueous environment existed for the entire island arc system, and that rifting took place in a marginal region of the volcanic arc (Hawkins etal, 1984) instead of in the topographically higher central area (Karig, 1971; Carey and Sigurdsson, 1984). Formation of the rift zone was accompanied by regional hydrothermal circulation in the sub-sea floor (section 3.4). Locally within the BBSN, more intense geothermal systems developed, focussed around rift-related faults (cf. Andrews and Fyfe, 1976). One such system created the H-W feeder zone and produced metal-rich fluids that, upon interaction with cold seawater, deposited sulphide mineralization near and on the sea floor in the discharge area. The accumulating sulphide pile most likely was located in a small trough structure resulting in the formation of the large H-W massive sulphide deposit (Fig. 5.3). Water depth at this stage cannot be determined directly but probably was in excess of 2000 m based on the formation of exhalative massive sulphide deposits rather than vein deposits (i.e. boiling in the geothermal system was restricted by a significant hydrostatic head: Cathles etal, 1983), on comparisons with fluid inclusion work in the Kuroko district (Pisutha-Arnond and Ohmoto, 1983), and on depths of modern basins or troughs in the Southwest Pacific region (e.g. Karig and Mammerickx, 1972). Waning stages of the H-W mineralization event coincided with deposition of rhyolitic tuff and lapilli-tuff beds adjacent to and overlying the massive sulphide bodies, and by sheet-like felsic flows in the VARC region of the mine property. These deposits marked the start of a major phase of rhyolitic volcanism in the volcanic arc area. Hydrothermal activity associated with sulphide mineralization apparently stopped soon after the start of this volcanic activity, as is implied by the lack of significant hydrothermal alteration in units overlying the massive sulphide bodies. Explosive activity in the 166 active arc area eventually dim inished allowing for a period of hemipelagic sedimentation (argillite member, H-W Horizon). The next major phase of volcanic activity in this cycle consisted of volcanic arc (VARC) volcanism, a short-lived rift-related (ARFT) phase, and the start of the PSMT event. Initially, the products consisted of trough-filling rhyolite flows and flow breccias, local accumulations of coarse, rhyolite component-rich volcaniclastic debris flow deposits (VARC series), and ultramafic volcanic flows, hyaloclastite and peperite deposits (ARFT series). This volcanic activity then temporarily ceased resulting in another, less extensive phase of argillite deposition. Resumption of occasional VARC volcanism yielded a series of widespread unwelded to welded, subaqueous pyroclastic flow deposits. Also, the PSMT series event began with the emplacement of the H-W Horizon dacite. Distribution of these lavas was controlled by the ridge and trough structures, and previously erupted rhyolite flows. Some regions in the mine-area experienced only limited volcanogenic or sediment deposition in the H-W Horizon part of this cycle. Areas of higher relief (ridge structures) within the central and the distal (towards the ARFT region) portions of the BBSN did not show a noticeable break in the argillite - pyroclastic sedimentation pattern, and thus only consisted of the argillite member. Some of the thinnest areas of the H-W Horizon are found in the antiformal hinge areas in the Lynx and West G sections (Figs. 3.6 and 5. lb). Here, instead of representing distal environments, these regions may have existed as topographical highs during and after development of the BBSN. 5.2.2 INTERZONE CYCLE The Interzone cycle represents a complex volcanogenic sedimentation phase due to the presence of different centers of volcanism active simultaneously around and within the BBSN. Start of this cycle is marked by eruption of andesitic lavas (Hanging Wall H-W Andesite) from a source northwest of the West G section (WSMT series: Fig. 5.2). Approximately at the same time, rift-related mafic volcanism resumed in the ARFT region of the Price area; this is reflected in the mafic volcanic dominant lower portions of the Ore Clast Breccia unit. The mafic lavas may have exploded upon coming in contact with water saturated sediments resulting in mixed mafic hyaloclastite and sediment deposits. These were then incorporated into the Ore Clast Breccia unit. Shedding of volcaniclastic debris into the BBSN began after emplacement of the Hanging Wall H-W Andesite. The resultant deposits are thickest in the H-W - Myra and Price sections (Fig. 5.2) with the coarsest components occurring in the Price area. The first unit to be deposited is the unique and characteristic Ore Clast Breccia unit. This unit represents a slump/slide deposit (olistostrome) which probably contains disrupted H-W Horizon deposits with attendant sulphide mineralization, albeit from different deposits than the H-W massive sulphide bodies, and mafic hyaloclastite. A break . in the deposition of the Ore Clast Breccia unit is indicated by the Interzone Rhyol ite member which marks resurgence of rhyolitic volcanism in the VARC area. Distal parts (towards the ARFT region) of this felsic unit contain thinly bedded tuffs and occasional radiolarian-bearing chert beds. Presence of this member implies a basin-wide hiatus in both mass flow processes, and mafic volcanic activity. Resumption of volcaniclastic sedimentation into the BBSN (Lower Mixed Volcaniclastics) consisted of mass flow processes from volcaniclastic accumulations in the Price area and from andesite-dominant volcaniclastic deposits in the West 0 section. The latter deposits, supplied by WSMT volcanic activity, are a combination of debris flows, and pyroclastic flow and fallout deposits. In the Price area, the volcaniclastic components reflect increasing contribution of new felsic volcanic material (PSMT series) and diminishing H-W Horizon input. Increased shedding of these volcanic components from sources outside both the Price and West 6 areas indicates the creation of topographical highs (e.g. growth of seamount volcanoes) in the respective source regions. The final depositional events in the Interzone cycle consist of material generated by the eruption of felsic (PSMT: Upper Dacite, lower member) and mafic to intermediate (WSMT: 5E Andesite) lavas and pyroclastic material from the Price and West 6 regions respectively. Possibly coincident with these two volcanic events, volcanic activity in the VARC area produced sheet-like felsic flows and flow breccias (North Dacite: Fig. 5. la). The end of the Interzone cycle is marked by the first appearance of Lynx-Myra-Price Horizon units (rhyolite tuffs and sulphide mineralization). 168 5.2.3 L-M-P CYCLE Prior to the deposition of the first L-M-P cycle units, a local rifted zone developed within the underlying andesitlc flows of the Interzone cycle (i.e. 5E Andesite). This zone became more restricted in lateral extent and size towards the Price section. Hydrothermal activity accompanied this event with selected sites developing more intense geothermal systems, as represented by the Lynx feeder zone. Discharge of the evolved fluids onto the sea floor resulted in sulphide mineralization and the formation of the 6-Zone massive sulphide deposits (section 3.2.2.6: West G, Lynx - South Wall Zone and G-Zone, Myra, and Price). Felsic arc volcanism resumed from the VARC region and possibly the WSMT source area early during the G-Zone mineralization episode. The volcanic activity was explosive in nature producing abundant rhyolitic.pyroclastic material emplaced by turbidity current and, less commonly, debris flow processes. These deposits were generally confined to trough structures. After the cessation of the rhyolitic volcanic activity, the geothermal system still was active and produced ore fluids which formed both proximal and distal massive sulphide lenses (section 3.2.2.6). The filling of trough structures by the felsic volcanic deposits prevented major sulphide accumulations in any one area, like the H-W deposit, and instead favoured the formation of numerous smaller, but more laterally extensive, bodies. Linear expressions of the rift basin still influenced their distribution and resulted in their characteristic linear northwestern trends. The massive sulphide deposits become less extensive and smaller towards the H-W - Myra and Price areas, mimicking the geometry of the rift zone. The G-Zone mineralization event ended because of renewed rift volcanism (ARFT series: G-Flow unit). The buried hydrothermal system did not die immediately, but produced strong hematite and carbonate alteration in parts of the overlying ultramafic flows. The rift volcanic event was followed by the resumption of volcanism in both the West G and Price regions. Volcanic activity in the West G section consisted of andesitic volcanism (continuation of the 5E Andesite), which produced pillowed flows, flow breccias, pyroclastic deposits, and volcaniclastic debris flow deposits. Volcanic activity in the Price area comprised continuation of volcaniclastic sedimentation and the eruption of mafic to intermediate flows (Upper Dacite, upper member). Flows in the Price area were emplaced through previously erupted felsic flow or dome debris, and incorporated this debris within the flow units. The source area for the felsic volcanic debris might have breached the sea surface prior to this andesitic flow event, because the incorporated felsic volcanic blocks are rounded and moderately to strongly altered indicating reworking in a high energy environment. Deposition of the unit, however, took place in a subaqueous environment. The volcanic events in both the West G and Price areas were relatively short-lived. A second, localized rifting phase occurred after.the volcanic events described above, and took place in the West G section and in areas further to the northwest of the mine property. This rifting event was associated with a period of volcanogenic sedimentation fed largely by rhyol itic eruptions from sources related to the VARC and WSMT series. The resulting felsic pyroclastic deposits covered a much wider area than those associated with the underlying G-Zone event; they occur mainly in the West G and Lynx areas and only sparodically in the H-W - Myra and Price sections because of a probable paleotopographical effects (Figs. 5.1 and 5.2). Hydrothermal activity related to this phase of rifting occurred in the West.6 region - and areas further northwest - and probably had similar characteristics to the G-Zone system. The resultant mineralized horizon, called the G-Hanging Wall Zone, contains hydrothermal massive sulphide deposits in the West G (S-Zone) and Lynx (G-Hanging Wall zone) area, and jasper and chert beds in the H-W - Myra and Price sections (Fig. 5.2). Water depths during the G-Hanging Wall Zone mineralization event (and the earlier G-Zone event) probably were i. 2000 m (see section 5.2.1). The end of the G-Hanging Wall Zone m ineral ization event is followed by another phase of rift volcanism (continuation of the G-Flow unit). Products from this phase are more extensive than those associated with the G-Zone event and occur mainly in the Lynx and West G areas, being thickest towards the ARFT region. Emplacement of these lavas did not immediately stop the hydrothermal activity. Thus various portions of the unit (in the Lynx and West G areas) suffered strong hematite and carbonate alteration. This volcanic event marked the end of the L-M-P cycle. 170 5.2.4 UPPER CYCLE The Upper cycle represents the final major volcaniclastic sedimentation event (Upper Mixed Volcaniclastics) in the Myra Formation (Mine Sequence), and the strengthening of intra-arc rifting volcanism and corresponding diminishing activity from the volcanic arc region. Volcanogenic sedimentation into the BBSN was controlled by rift volcanic activity and erosion of material from the two seamount source areas. This period of sedimentation eventually ceased, probably due to a lull in rift volcanism. This hiatus allowed for the deposition of siliceous argillite and chert (Upper Rhyolite unit) throughout the central regions of the BBSN. About the same time, rhyolite volcanism resumed in the volcanic arc area and deposited widespread pyroclastic-rich deposits that eventually overlapped the siliceous argillite and chert deposits. These explosive eruptions were accompanied by extrusion of rhyolite lavas in the source area, indicated by accessory clasts of rhyolite flow material that are an integral part of the pyroclastic deposits. The abundance of rhyolite clasts and the presence of coarsening-upward pyroclastic sequences in the VARC region imply that effusive activity became dominant towards the later stages of this volcanic event. Sulphide mineralization may also have occurred in the VARC area as some of the rhyolite pyroclastic beds contain variably sulphide bearing accidental lithic clasts. The end of the volcanic arc phase coincided with the resumption of rift volcanic activity (ARFT series: Upper Mafic unit). The resulting deposits comprise volcaniclastic material, solely derived from rift volcanism (Fig. 5.3), consisting of basaltic hydroclastic and pyroclastic breccias, and lesser hyaloclastite and flow breccia deposits. These deposits covered almost the entire BBSN (Fig. 5.3). Towards the VARC region, the deposits comprised greater amounts of reworked mafic volcanic breccia deposits and thinly bedded turbidity current deposits, reflecting an increasingly distal environment relative to the rift source area. It is not clear when the Upper cycle ended because of the probable unconformity at the Myra Formation - Thelwood Formation contact. Regardless, it seems that this volcanic event was responsible for the final unit deposited in the BBSN (and possibly this arc system) prior to cessation of volcanism on all fronts, either in preparation for another period of intra-arc rifting (in a different area of the volcanic arc) or on approaching the end of subduction. 171 5.2.5 GENESIS OF THE BUTTLE LAKE DEPOSITS Field anctchemical evidence documented in this study allows a genetic model to be constructed for the Buttle Lake massive sulphide deposits in terms of tectonic processes and associated volcanism. The area of deposition for the Price and Myra Formations was an evolving intra-arc rift environment which may not have developed into a back-arc rifting system - it most likely represents an aborted or failed rift (cf. Cathles et af, 1983). Deposition within the evolving rift basin (referred to as the Buttle Lake Camp basin) followed a.common sequence of events: (1) mafic to intermediate arc volcanism, (2) rifting, hydrothermal convection and sulphide mineralization, (3) felsic arc volcanism, (4) ultramafic to mafic rift volcanism, and (5) volcanogenic sedimentation; This sequence repeated itself twice during the course of island arc evolution in the Buttle Lake Camp. (Technically, the Lynx-Myra-Price Horizon contains two cycles in detail (sections 3.2.2.6 and 5.2.3) but is considered as part of one major cycle in this discussion.) Evolution of these events and their effects on associated sulphide mineralization is outlined below. The first series of events in the development of the Buttle Lake deposits involved periods of mafic to intermediate arc volcanism (e.g. Price Formation and 5E Andesite). Rifting, marked by high-angle normal faults, created complex patterns of ridge and trough structures along the rift basin floor (based on topography necessitated by drawing of reconstructed cross sections, e.g. Fig. 5.1). These structures are mainly bound in accumulations of flows (rather than dominantly volcaniclastic sequences). As a consequence of numerous faults (documented normal fault spacing in modern rift basins can average 50 m: Arcyana, 1975) and a relatively high thermal regime, submarine hydrothermal metamorphism occurred. The driving mechanism for hydrothermal fluids could be from shallowly emplaced magma chambers or cupolas (Cathles, 1983; Alabaster and Pearce, 1985). Locally, more intense geothermal systems developed around high angle faults and represent feeder zones to exhalative mineralization on the sea floor. They are characterized by development of crosscutting, conically to cylindrically shaped, moderately to strongly altered zones (e.g. H-W feeder zone: Fig. 3.5; G-Zone feeder zone: Fig. 3.6). Discharge areas were within trough structures. The evolved hydrothermal fluids in these systems became metal-rich and, upon interaction with cold 172 seawater in the discharge areas, precipitated sulphides and sulphates near or at the seafloor. Precipitation of hydrothermal silica (chert and jasper) deposits from these systems could occur in distal parts of the horizon relative to the discharge area (e.g. G-Hanging Wall Zone, Price section). Explosive and effusive felsic arc volcanic activity accompanied the mineralization events, resulting in formation of massive sulphide hosting, rhyolite-rich units (e.g. H-W Horizon, Lynx-Myra-Price Horizon). The final events of a general sequence consisted of ultramafic to mafic rift volcanism (e.g. G-Flow unit), and volcanogenic sedimentation. The rift-related lavas, if voluminous enough, influenced the life of contemporaneous sulphide-generating geothermal systems. Sudden covering by the flows prevented further sulphide mineralization by choking hydrothermal activity (e.g. G-Zone and G-Hanging Wall Zone, Lynx area) - rather than allowing hydrothermal activity to develop to maturity and seal itself (e.g. H-W deposit). Premature cessation of sulphide mineralization is indicated by the presence of widespread hematite and carbonate hydrothermal alteration in overlying flow units. Volume of the ultramafic to mafic lavas, which increased in successively younger cycles, was governed by the growth of the intra-arc rift zone (Fig. 5.3). Volcanogenic sedimentation commonly coincided with another phase of mafic to felsic arc or mafic rift volcanism. Resulting mixtures of volcaniclastic debris and flows buried previously deposited massive sulphide deposits and generally preserved them. Multiple ore horizons in the BBSN demonstrate the effects of rift basin floor morphology and timing of concomitant felsic volcanism on distribution of the sulphide mineralization . If no competing felsic volcanic activity interrupted the hydrothermal discharge, the sulphides formed linear mounds in hosting trough structures (H-W deposit, Figs. 3.5 and 5.2). However, where deposition of pyroclastic or flow units occurred during the geothermal event, potential sites for massive sulphide mineralization became filled and sealed to varying degrees. This smoothed irregularities along the bottoms of trough structures, decreased their relief but preserved and accentuated their linear character. Where systems were not sealed, continued venting of hydrothermal fluids caused precipitation of sulphides on top of the felsic volcanic deposits; the resultant sulphide deposits were narrower, thinner and more linear (G-Zone and G-Hanging Wall Zone type: Fig. 5.2) relative to the 173 mound types. Furthermore, migration of the discharge areas during this felsic volcanic activity formed a series of stacked bodies that conformed to the ever increasing basin floor elevation (South Wall Zone, Lynx area: Fig. 3.6). Some epigenetic deposits also occurred around the vent region due to permeation of fluids upwards through the pyroclastic cover (South Wall Zone, Lynx area; Myra ore zone). 5.3 DEPOSITIONAL HISTORY OF THE THELWOOD AND FLOWER RIDGE FORMATIONS The Thelwood and Flower Ridge Formations represent sedimentation and volcanism that covered larger areas than the extensional, intra-arc rift basin regime of the Price and Myra Formations. Deposition was in a more evolved basin, probably back-arc, setting in an island arc system shown schematically in Figure 5.4. The following synthesis describes separately the Thelwood and Flower Ridge Formations. 5.3.1 THELWOOD FORMATION The Thelwood Formation represents a sediment-sill complex (Fig.5.4). It is composed of siliceous tuffaceous sediment and subaqueous pyroclastic deposits, and penecontempora-neous mafic sills. The source for most of the volcanogenic material is intermediate to felsic explosive (phreatomagmatic, based on common blocky and non- to weakly vesiculated shards) volcanism in a volcanic arc area. Absence of coarse clastic deposits and presence of numerous thinly bedded, siliceous tuffaceous sediment sequences implies a distal environment relative to active parts of the volcanic arc. The amount of material from the volcanic arc decreases up section as is reflected by fewer subaqueous pyroclastic flow and resedimented deposits. The uppermost parts of this complex contain argillite and chert layers reflecting more pelagic conditions. However, even in these sections rhyolite pyroclastic deposits are present, and represent Plinian eruptions in the arc area. (The Plinian nature is implied by the sudden appearance of pyroclastic beds in the tuffaceous sediment sections, overall fineness of the constituents, and rhyolitic composition.) Sill magmatisrn originated from possible rifts developed 174 T H E L W O O D F O R M A T I O N F L O W E R RIDGE F O R M A T I O N ^ y y y . y . y y y y y y v v y_ v y y y y y v y ^ v y v ^ y v ^ v v- v ^ v ^ v ^ ^ ^ Figure 5.4: Schematic representations of the depostional setting for the Thelwood and Flower Ridge Formations. Thelwood Formation is a sediment-sill complex formed near a possible back-arc spreading center, distal from a volcanic arc. Flower Ridge Formation represents basaltic explosive and effusive activity from a possible back-arc spreading center. 175 beneath the cover of the siliceous tuffaceous sediment and subaqueous pyroclastic deposits (Fig. 5.4). Mafic sills occur throughout the formation but are more common in the lower portions. The thickest sills are located along the Myra Formation - Thelwood Formation contact. This may reflect proximity to the rifting center and/or an initial major pulse of rift magmatism that also selected the contact area as the zone of least resistance. The sediment-sill complex defines the depositional setting of the basin, based on recent work on a similar sediment-sill complex documented in the Guaymas Basin in the Gulf of California (Einsele, 1985). In order to facilitate sill formation over lava flows, sedimentation rate in the basin must have been high, in the order of 1 to3m/ 10OO yr (Einsele, 1985), and water depth plus unconsolidated sediment thickness combined was in excess of 2000 m (Francis, 1982; Einsele, 1985). The hosting sediments (commonly the tuffaceous sediment units) provided little physical opposition to the intruding magmas. As a result of sill intrusion though, the surrounding sediments become indurated. Thus subsequent intrusions generally occurred above the previous phase (Kastner andSiever, 1983; Einsele, 1985). This resulted in numerous sills interbedded with sedimentary rocks. The end of sill emplacement coincided with mafic volcanism of the Flower Ridge Formation, which represents the extrusive phase of the magmatic event responsible for the sill emplacement. 5.3.2 FLOWER RIDGE FORMATION The Flower Ridge Formation represents volcanogenic sedimentation proximal to a probable back-arc spreading center where environment of deposition changed from deep subaqueous to a more shallow marine environment (Fig. 5.4). Initial volcanic activity was sporadic enabling partial continuation of tuffaceous sediment deposition in the lower portions. Volcanism eventually became more regular, supplying the basin with basaltic volcaniclastic material emplaced by sediment gravity flow processes (mainly as debris flows). The reworked volcaniclastic component gradually decreased in abundance up section, being replaced by coarser, relatively unreworked pyroclastic deposits, basaltic flows and flow breccias. Some of the pyroclastic sequences contain agglutinate deposits which indicate shallow marine to possible subaerial conditions in parts of the basin and source area. The strongly amygdaloidal nature of the constituents probably also reflects a shallower marine environment for the source region, although vesicularity should be used with caution when trying to determine water depth (Dudas, 1983; Kokelaar, 1986). The transition to coarser volcaniclastic deposits and flows is indicative of a prograding, shallow marine volcaniclastic apron from a vent area. Eruption of the basaltic products was mainly explosive in nature, thus representing either Strombolian (due to magmatic explosivity) or Surtseyan (involving magma-water interactions) style volcanism (Kokelaar, 1986). The uppermost section marks the cessation of basaltic volcanism, accompanied by variable erosion of the unit. Quiescent conditions with minor subsidence then prevailed, during which extensive shelf carbonate deposits, the Buttle Lake Formation, formed. 5.4 CONCLUSIONS The Price and Myra Formations represent deposition within an intra-arc rift setting which followed a general sequence of events: (1) mafic to intermediate arc.volcanism, (2) rifting, hydrothermal convection and sulphide mineralization, (3) felsic arc volcanism, (4) ultramafic to mafic rift volcanism, and (5) volcanogenic sedimentation. This sequence was repeated twice and formed two massive sulphide mineralized horizons (H-W and Lynx-Myra-Price). The overall composition of the volcanic units became more mafic up section. However the rift system did not develop into amarginal (back-arc?) basin with an active spreading center. Instead the Buttle Lake Camp basin (BBSN) represents a failed or aborted rift (though this is not exactly known due to the unconformable relationship between the Myra and Thelwood Formations). Massive sulphide mineralization was governed by configuration of the hosting extensional depressions (trough structures). Where the trough was barren of sediment, large mound-like sulphide deposits of the H-W deposit formed. Variable filling of troughs by felsic pyroclastic material yielded narrower, thinner, but more linear massive sulphide bodies such as the G-Zone and G-HangingWall Zone deposits. Life of the sulphide-producing geothermal system commonly was ended abruptly by the sudden eruption of ultramafic rift volcanic units. Thelwood and Flower Ridge Formations indicate a major change in depositional style and environment from the underlying Myra Formation. The Thelwood Formation is a sediment-sill complex consisting of siliceous tuffaceous sediments, subaqueous pyroclastic deposits and penecontemporaneous mafic sills. The Flower Ridge Formation, the final main Sicker Group volcanic phase in the Buttle Lake Camp, represents basaltic explosive to effusive activity from a back-arc (?) spreading center system. The Thelwood sills are probable early, intrusive equivalents to the Flower Ridge units. The end of the Flower Ridge volcanic episode (documented outside the mine-area) was followed by a minor period of erosion before extensive deposition of the shelf carbonates of the Buttle Lake Formation. 1 7 8 - CHAPTER 6  SUMMARY AND CONCLUSIONS 1. The Buttle Lake Camp ts a Paleozoic volcanogenic polymetallic massive sulphide district in central Vancouver Island, B.C. The ore deposits consist of many individual massive sulphide lenses grouped into several major zones within two main felsic volcanic stratigraphic intervals in the Paleozic Sicker Group within the Buttle Lake uplift. They are currently being mined by Westmin Resources Ltd. through the operation of two underground mines, the H-W and Lynx. Total size and grade of the orebodies(current reserves plus past production) are 20,812,OOO tonnes-at 2.30 g Au/t, 58.3 gAg/t, 2.12wt.Jf Cu, 0.67wt.S?Pb, and 6.46wt.£Zn. This is a minimum estimate because the large H-W orebody is still open in two directions. 2. A revised stratigraphy is proposed for the Paleozoic Sicker Group rock units in the Buttle Lake uplift. The revised units, in order of decreasing age, are: Price Formation, Myra Formation, Thelwood Formation, Flower Ridge Formation, Buttle Lake Formation, and Henshaw Formation. Only the first four formations are present in the Buttle Lake Camp. Age relationships are not well known with definite ages only determined for the Myra and Buttle Lake Formations. U-Pb dating established a Late Devonian (370 Ma) 8ge for the Myra Formation. Whole rock Rb-Sr isotopic analysis of the lower Myra Formation units yielded a comparable Late Devonian age of 365 Ma. 3. The lowermost unit exposed in the Buttle Lake Camp, the Price Formation (also referred to as the Footwall H-W Andesite), is a thick sequence (> 300 m) of massive to pillowed, pyroxene + feldspar porphyritic basaltic andesite flows and flow breccias, and minor associated fine to coarse pyroclastic rocks. This unit has been intersected in drillcore throughout the property but is exposed at surface only in a small region southwest of the mouth of Thelwood Creek. The base of this formation is not known. 4. The sulphide deposit-bearing Myra Formation (also referred to as the Mine Sequence) consists of a 310 to 440 m thick sequence of complex volcanic-dominant stratigraphy. Myra Formation lithologic units exhibit remarkable linear continuity (>7 km) along the northwestern trend of the ore zones, but abrupt lateral northeast to southwest facies changes. The Myra Formation is divided into ten general litho-stratigraphic units (in decreasing relative age): H-W Horizon, Hanging Wall H-W Andesite, Ore Clast Breccia unit, Lower Mixed Volcaniclastics, Upper Dacite/ 5E Andesite / North Dacite, Lynx-Myra-Price Horizon, G-Flow unit, Upper Mixed Volcaniclastics, Upper Rhyolite unit, and Upper Mafic unit. The lowermost Myra Formation unit is the predominantly rhyolitic H-W Horizon. This horizon varies in thickness from approximately 15 m to 200 m and occurs throughout the mine-area. It consists of dacitic to rhyolitic flows and domes, pyroclastic deposits, argillite, and sulphide mineralization. H-W Horizon units vary laterally from bedded argillite and felsic tuffs towards the back-arc rifting (ARFT) region to complex felsic domal and flow assemblages towards the volcanic arc (VARC)area. It can be divided into five parts: (1) an argillite member, (2) a felsic flow member (consists of three flow types: a quartz + feldspar porphyritic rhyolite, an aphyric to feldspar porphyritic rhyolite, and a feldspar porphyritic dacite), (3) a pyroclastic and volcaniclastic member, (4) a mafic flow member, and (5) a massive sulphide member. It is this unit that hosts the large H-W massive sulphide deposit. The Hanging Wall H-W Andesite is an up to 100 m thick unit mainly consisting of feldspar porphyritic basaltic andesite to andesite flows and related breccias. The proportion of flow and flow breccia units to pyroclastic deposits is 80:20 in the central regions of all sections, but approximately 40:60 in the VARC region of the Price section. The Ore Clast Breccia unit represents a series of volcaniclastic submarine debris flow deposits and lesser pyroclastic deposits. The unique feature of this unit is the presence of massive sulphide clasts and lenses or 'rafts' (olistoliths) of pyrite mineralized rhyolite coarse tuff to lapilli-tuff. The horizon is up to 90 m thick and is found thoughout the mine-area, being best developed in the central region in the Price end. The Ore Clast Breccia unit can be divided into three mappable members: ( D a rhyolite-rich volcaniclastic breccia having from 10 to 50 percent non-andesite or mafic volcanic constituents (average is 25 percent); (2) a rhyolite-poor volcaniclastic breccia with less than 10 percent non-andesite or mafic volcanic constituents; and (3) the Interzone Rhyolite, a 160 rhyolite pyroclastic horizon. Generally, the rhyolite-rich member occurs in the lower to middle parts of the unit whereas the rhyolite-poor member is found in the middle to upper portions. The Interzone Rhyolite generally is found in the middle to upper portions of the Ore Clast Breccia unit but it can occur at any level within the Ore Clast Breccia unit because it marks a paleosurface present at the time of its emplacement. The Lower Mixed Volcaniclastics represent andesite dominant volcaniclastic deposits. The unit is up to 90 m thick and occurs throughout the property. It contains deposits of volcaniclastic breccias, tuff-breccias, bedded lapilli-tuff and coarse to fine tuff, and minor subaqueous pyroclastic flow deposits. The coarse clastic deposits occur mainly in the central region in the Price end and the West G end of the mine-area, whereas the Lynx and H-W-Myra sections contain relatively greater sequences of finer grained, bedded deposits. Generally the Lower Mixed Volcaniclastics thicken from the Price area to the H-W-Myra section, before gradually thinning towards the Lynx and West G sections. Towards the ARFT region this horizon 'merges' with the Hanging Wall H-W Andesite and Ore Clast Breccia units resulting in an andesite-rich volcaniclastic unit. The Lower Mixed Volcaniclastics in the VARC area directly overlies the Hanging Wall H-W Andesite. The Upper Dacite / 5E Andesite / North Dacite units represent three approximately contemporaneous yet different eruptive events which occurred in non-overlapping relationships throughout the mine property. The Upper Dacite unit is present in the Price section and comprises two general parts: the Upper Dacite lower member and the Upper Dacite upper member. The lower member consists of dacite to rhyolite hyaloclastite, flow breccia and subaqueous pyroclastic deposits. The upper member is made up of feldspar porphyritic intermediate flows containing variably rounded felsic flow blocks, and subaqueous pyroclastic deposits. The 5E Andesite is best developed at the West G end and consists of up to a 250 m thick sequence of massive to pillowed, feldspar porphyritic basaltic andesite to andesite flows and lesser flow breccia deposits. Both the Upper Dacite and the 5E Andesite units are thickest in their respective central regions; they thin markedly towards the middle sections (Lynx and H-W- Myra) of the mine-area. The North Dacite, a feldspar porphyritic felsic 181 flow unit, "is only present in the VARC area'where it occupies the same general stratigraphic position as the other two litho-stratigraphic units. The Lynx-Myra-Price Horizon represents the upper massive sulphide mineralized felsic volcanic units in the mine-area (i.e. the West G, Lynx, Myra and Price ore zones). This unit consists of mainly quartz + feldspar crystal vitric rhyolite tuffs and lapilli-tuffs, and can be divided into two spatially distinct units: (1) the G-Zone member, and (2) the G-Hanging Wall Zone member. The latter contains an additional lithologic unit comprising pale chert, jasper and black argillaceous chert. The two members are separated by units from upper parts of the 5E Andesite in the West G and Lynx sections, and by the Upper Dacite upper member in the Price section and possibly the H-W-Myra section. In the West G and Lynx areas the separation is 30 to 150 m whereas in the Price end, it is 10 to 60 m. Both zones vary in thickness from 1 to 45 m, but generally the G-Zone member is thicker -than the G-Hanging Wall Zone member (though the latter is more laterally extensive). The G-Flow unit represents a number of thin (2 to 15 m thick) but widespread, massive to pillowed, pyroxene-phyric ultramafic flows and related breccias, and hyaloclastite deposits overlying the two members of the Lynx-Myra-Price Horizon. In the H-W-Myra, Lynx and West G sections, the G-Flow unit also contains distinctly purple zones. These zones mainly consist of hyaloclastite and flow breccia, and are moderately to intensely altered to carbonate and hematite. The unit, thickest in the West G and Lynx areas, becomes steadily thinner towards the Price section. Laterally, it disappears towards the VARC region but thickens towards the ARFT area. The Upper Mixed Volcaniclastics represents a mafic to intermediate volcanic dominant . volcaniclastic unit consisting of bedded fine to coarse tuff and lapilli-tuff sequences, and massive coarse lapilli-tuff to tuff-breccia deposits. Purplish hematite alteration is present irregularly in both types. The unit is up to 50 m thick and occurs throughout the mine property, being best developed in the central regions of all four sections. The Upper Rhyolite unit is the stratigraphically highest rhyolite horizon in the Mine Sequence. Distribution of rock types in the Upper Rhyolite unit consists of two general parts: (1) a pyroclastic deposit-rich member; and (2) a siliceous argillite-chert dominant member. In 182 most areas the siliceous argillite - chert member underlies the pyroclastic member. The pyroclastic deposit member is up to 50 m thick and made up of bedded, rhyolite coarse tuff to lapilli-tuff, and lesser fine tuff and tuff-breccia deposits. This member displays a distinct lateral facies variation from the VARC region to the ARFT area: it is thickest and coarsest towards the VARC region. The pyroclastic deposits in the central region are variably but distinctly purple due to pervasive hematite alteration. The siliceous argillite - chert member consists of thin to medium laminated beds of grey to black siliceous argillite, pale chert, rhyolite fine tuff, and minor jasper. This member ranges from 1 to 15 m in thickness and is largely confined to the central regions of all sections. The Upper Mafic unit is the uppermost litho-stratigraphic unit in the Myra Formation. It is present throughout the property being thickest (> 200 m ) in the ARFT region and thinning to approximately 5 to 20 m towards the VARC area. As the Myra Formation - Thelwood Formation contact possibly represents an unconformity, this unit is missing in areas and notably thin in others. The main rock types present are basaltic in composition and occur mainly as hydroclastic and pyroclastic deposits largely composed of pyroxene + feldspar porphyritic mafic flow clasts. Less common deposits include flow and flow breccia units, and mixed sedimentary and pyroclastic units. 5. The Thelwood Formation (also referred to as the Sharp Banded Tuff) is a 270 to 500 m thick bedded sequence of siliceous tuffaceous sediments, subaqueous pyroclastic flow deposits and penecontemporaneous mafic sills. This unit is present throughout the mine property but the best exposures occur on the west side of the mouth of Thelwood Creek and around Myra Falls. The rock units can be grouped into three general, repetitive units: (1) tuffaceous sediment units, (2) pyroclastic deposit units, and (3) mafic sills. Components of all three occur within each generalized unit. Tuffaceous sediment units range from 5 to 30 m in thickness and consist of massive to bedded tuffaceous mudstone and siltstone, mudstone, and vitric ± crystal fine tuff. Minor chert layers are also present. Also present are up to 20 percent coarse grained subaqueous pyroclastic deposits. Pyroclastic deposit units range from 4 to 25 m in thickness and consist of vitric-lithici fine lapilli-tuff to coarse tuff beds intercalated with up to 50 percent tuffaceous sediment deposits. Mafic sills consists of 1 to 90 m thick, massive basaltic to basaltic andesite sills. They are found throughout the Thelwood Formation but are generally more common in the lower portions. They also seem to be associated with the tuffaceous sediment units. Some of thickest sills are found at the Myra Formation - Thelwood Formation contact. Contacts of sills can be finer grained than the interiors and reflect chilled margins. Locally, flame-like protrusions of tuffaceous sediment into sills, and hyaloclastitic margins are observed, and are interpreted to be the result of intrusion into wet, unlithified sediment. 6. The Flower Ridge Formation is the uppermost Paleozoic unit exposed in the Buttle Lake Camp. The unit is basaltic in composition and consists mainly of moderately to strongly amygdaloidal feldspar ± pyroxene porphyritic basaltic lapilli-tuff, tuff-breccia and pyroclastic breccia. Some of these units represent agglutinate deposits. Other rock types of this formation are fine to coarse mafic tuffs, basalt flows and flow breccias, and bedded tuffaceous mudstone and argillaceous sediments. The top of the Flower Ridge Formation is not on the mine property - only the lower 650 m can be observed. Traverses on the west side of Flower Ridge south of the south end of Buttle Lake, however, show that this formation extends to the contact with the overlying Buttle Lake Formation. The contact with the underlying Thelwood Formation is conformable and characterized by the first appearance of abundant scoriaceous volcanic clasts in either pyroclastic or sedimentary beds. 7. Subsequent intrusive phases on the mine property, from oldest to youngest, are: (1) Paleozoic or Triassic diabase dikes, (2) Triassic basaltic sills and dikes related to the Karmutsen Formation, (3) Jurassic feldspar porphyry and quartz diorite dikes related to the Island Intrusions, and (4) Jurassic or younger quartz + feldspar porphyritic rhyolite and hornblende gabbro dikes. The Jurassic feldspar porphyry and quartz diorite dikes are the most abundant intrusive phase. 8. Various lithologic and structural observations suggest that the Myra Formation -Thelwood Formation contact is a possible unconformity (either a period of erosion or non-deposition) in the Late Devonian to Early Mississippian. After deposition of the Thelwood Formation, the contact may have become a site for low angle faults in Late Paleozoic time, or a decollement during Mesozoic deformation due to different deformational behavior above and below the contact. 9. Price and Myra Formations are composed of a range of mafic to felsic volcanic rocks. Intermediate phases are the dominant rock type. Fieldwork has defined four volcanic source regions 184 for Myra Formation lithologies. Along with' the Price Formation, volcanic products from these areas can be grouped into five volcanic series: the early arc series (EARC: Price Formation), the volcanic arc series (VARC: H-W Horizon, felsic flow member; Ore Clast Breccia unit, Interzone Rhyolite; North Dacite; Lynx-Myra-Price Horizon; and Upper Rhyolite unit), the Price seamount series (PSMT: H-W Horizon, dacite flow unit; and Upper Dacite, lower member), the West 0 seamount series (WSMT: Hanging Wall H-W Andesite; 5E Andesite; and Upper Dacite, upper member), and the arc rifting series (ARFT: H-W Horizon, mafic flow member; G-Flow unit; and Upper Mafic unit). 10. The volcanic series are the result of at least three distinct and partly contemporaneous magmatic lineages: Early Arc Crust-Price Seamount lineage, Volcanic Arc lineage, and Arc Rifting lineage. Source region for the ultramafic to intermediate magmas was an upper mantle peridotitie depleted in high field strength elements and variably enriched in LIL elements (both relative to N-type MORB) as a result of a subducted, dehydrating oceanic crust slab. The felsic volcanic series, the PSMT and VARC series, originated from two distinct sources. The PSMT series represent products from evolved EARC magma whereas the VARC series represent products from magma formed by partial melting of lower crustal portions of a volcanic arc. 11. Clinopyroxene-phyric lavas in the ARFT series, called komatiitic basalts on chemical and mineralogical grounds, represent primary melts. These liquids probably formed at 1300° C at pressures between 15 and 25 kb by moderate to high degree (115 percent) of partial melting of a hydrous upper mantle peridotite. 12. Mafic units in the Thelwood and Flower Ridge Formations are from magmas derived from less depleted (relative to N-type MORB) and LIL element poorer mantle sources than those for the Price and Myra Formations. Magma generation may have occurred in a region further removed from a subduction zone. 13. The Price and Myra Formations represent deposition within an intra-arc setting which followed a general sequence of repeated events comprising: mafic to intermediate arc volcanism; rifting, hydrothermal convection and sulphide mineralization; felsic arc volcanism; ultramafic to mafic rift volcanism; and volcanogenic sedimentation. This sequence was repeated twice and formed two massive sulphide mineralized horizons (H-W and Lynx-Myra-Price). Deposition of the volcanics and volcanogenic sediments probably occurred in an evolving rift basin and was strongly controlled by basin floor morphology. 14. Massive sulphide mineralization was governed by configuration of the hosting extensional depressions (trough structures). Where the trough was barren of sediment, large mound-like sulphide deposits of the H-W deposit formed. Variable filling of troughs by felsic pyroclastic material yielded narrower, thinner, but more linear massive sulphide bodies such as the 3-Zone and G-Hanging Wall Zone deposits. Life of the sulphide-producing geothermal system commonly was ended abruptly by the sudden eruption of ultramafic rift volcanic units. 15. Thelwood Formation indicates a major change in depositional style and environment from the underlying Myra Formation. It represents a sediment-sill complex consisting of siliceous tuffaceous sediments, subaqueous pyroclastic deposits and penecontemporaneous mafic sills. The complex probably formed in part because of high sedimentation rate relative to mafic sill magmatism. The sills represent an early phase of the magmatic event responsible for the overlying volcanic units of the Flower Ridge Formation. 16. Flower Ridge Formation is the final main Sicker Group volcanic phase in the Buttle Lake Camp and represents basaltic explosive to effusive activity from a possible back-arc spreading center. Deposition was in a much more shallow marine setting than during the underlying Thelwood event. End of this volcanic episode (documented outside the mine-area) was followed by a minor period of erosion before extensive deposition of the shelf carbonates of the Buttle Lake Formation. 186 . REFERENCES Abbey, S., 1980, Studies in "standard samples" for use in the general analysis of silicate rocks and minerals, Part 6. 1979 edition of "usable" values: Geol. Surv. Can., Pap. 80-14, 30 pp. Abbey, S., 1981, The search for "best values" - a study of three Canadian rocks. Geostand. Newsl., v. 5, p. 13-27. Abbey, S., 1983, Studies in "standard samp les" of silicate rocks and minerals 1969-1982. Geol. Surv. Can., Pap. 83-15, 114 pp. Alabaster, T., Pearce, J. A., and Mai pas, J., 1982, The volcanic stratigraphy and petrogenesis of the Oman ophiolite complex: Contrib. Mineral. Petrol., v. 81, p. 168-183. Alabaster, T., and Pearce, J. A., 1985, The interrelationship between magmatism and ore-forming hydrothermal processes in the Oman Ophiolite: Econ. Geol., v. 80, p. 1-16. Allegre, C. J., and Minster, J. E., 1978, Quantitative models of trace element behavior in magmatic processes: Earth Planet. Sci. Lett., v. 38, p. 1-25. Andrew, A., 1987, Lead and strontium isotope study of five volcanic and intrusive rock suites and related mineral deposits, Vancouver Island, British Columbia: unpubl. Ph.D. thesis, The University of British Columbia, 254 p. Andrews, A. J., and Fyfe, W. S., 1976, Metamorphism and massive sulphide generation in oceanic crust: Geoscience Canada, v. 3, p. 84-94. Arculus, R. J., and Johnson, R. W., 1978, Criticism of generalized models for the magmatic evolution of arc-trench systems: Earth Planet. Sci. Lett, v. 39, p. 118-126. Arcyana, 1975, Transform fault and rift valley from bathyscaph and diving saucer: Science, v. 190, p, 108-116. Arndt.N.T., and Nisbet, E.G., 1982, What isakomatiite?, in Arndt, N. T., and Nisbet, E. G., eds., Komatiites: George Al len & Unwin Ltd., London, p. 19-27. Bargar, K. E„ and Beeson, M. H., 1981, Hydrothermal alteration in research drill hole Y-2, Lower Geyser basin, Yellowstone National Park, Wyoming: Am. Mineral., v. 66, p. 473-490. Basaltic Volcanism Study Project, 1981, Basaltic volcanism on the terrestrial planets: Pergamon Press, Inc., New York, p. 193-213. Bence, A. E., andAlbee, A. L., 1968, Empirical correction factors for theelectron microanalysis of silicates and oxides: J. Geol., v. 76, p. 382-403. Berman.R. G., 1979, The Coquihalla volcanic complex, southwestern British Columbia: unpubl. M.Sc. thesis, The University of British Columbia, 170 p. Bird, D. K., Schiffman, P., Elders, W. A., Williams, A. E., and McDowell, S. D., 1984, Calc-silicate mineralization in active geothermal systems: Econ. Geol., v. 79, p. 671-695. 187 Bischoff, & L , and Dickson, F. W., 1975, -Seawater-basalt interaction at 200° C and 500 bars: Implications for the origin of sea-floor heavy-metal deposits and regulations of sea-water chemistry: Earth Planet. Sci. Lett, v. 25, p. 576-614. Boldy, J., 1977, (Uncertain exploration facts from figures: Can. Inst. Min. Met, Bull., v. 70, no. 781, p. 86-95. Boynton, M. V., 1984, Cosmxhemistry of the rare earth elements: meteorite studies, in Henderson, P., ed., Developments in geochemistry 2: Rare earth element geochemistry: Elsevier, New York, p. 63-114. Brandon, M. T., Orchard, M. J., Parrish, R. R., Sutherland Brown, A., and Yorath, C. J., 1986, Fossil ages and isotopic dates from the Paleozoic Sicker Group and associated intrusive rocks, Vancouver Island, British Columbia: Geol. Surv. Can., Pap. 86^  IA, p. 683-696. Burke, W. H., Denison, E. A., Hetherington, E. A., Koepnick, R. B., Nelson, H. F., and Otto, J. B., 1982, Variation of seawater 8 7 S r / 8 6 S r throughout Phanerozpic time: Geology, v. 10, p. 516-519. Cameron, W. E., McCulloch, M. T., and Walker, D. A., 1983, Boninite pedogenesis: chemical and Nd-Sr isotopic constraints: Earth Planet. Sci. Lett., v. 65, p. 75-89. Cameron, W. E., and Nisbet, E. G., 1982, Phanerozoic analogues of komatiitic basalts, in Arndt.N. I , and Nisbet, E. G., eds., Komatiites: George Allen & Unwin Ltd., London, p. 29-50. Cameron, W. E., Nisbet, E. G., and Dietrich, V. J., 1979, Boninites, komatiites and ophiolitic basalts: Nature, v. 280, p. 550-553. Carey, S., and Sigurdsson, H. A., 1984, A model of volcanogenic sedimentation in marginal basins, in Kokelaar, B. P., and Howells, M. F., eds., Marginal basin geology: Geol. Soc. Lond, Spec. Publ., no. 16, p. 37-58. Carvalho, I. G., 1979, Geology of the Western Mines district, Vancouver Island, British Columbia: unpubl. Ph.D. thesis, The University of Western Ontario, 294 p. Canil, D., 1987, The geochemistry of komatiites and basalts from the Deadman Hill area, Munro Township, Ontario, Canada: Can. J. Earth Sci., v. 24, p. 998- 1008. Cathles, L. M., 1983, An analysis of the hydrothermal system responsible for massive sulfide deposition in the Hokuroku basin of Japan: Econ. Geol. Mon. 5, p. 439-487. Cathles, L. M.,Guber,A. L., Lenagh. T. C.andDudas, F. 0., 1983, Kuroko-type massive sulfide deposits of Japan: Products of an aborted island-arc rift: Econ. Geol. Mon. 5, p. 96-114. Clapp, CM., 1912, Southern Vancouver Island: Geol. Surv. Can., Memoir 13, 208 p. Clapp, C. H., and Cooke, H. C, 1917, Sooke and Duncan map-areas, Vancouver Island: Geol. Surv. Can., Memoir 96,445 p. Coleman, R. G., 1977, Ophiolites: Ancient oceanic lithosphere?. New York, Springer-Verlag, 229 p. Crawford, A. J., and Cameron, W. E., 1985, Petrology and geochemistry of Cambrian boninites and low-Ti andesites from Heathcote, Victoria: Contrib. Mineral. Petrol., v. 91, p. 93- 104. 188 Cronan, D S^., Moorby, S. A., Glasby, G. P. kKnepler, K., Thomson, J., and Hodkinson, R., 1984, Hydrothermal and volcaniclastic sedimentation on the Tonga-Kermadec Ridge and in its adjacent marginal basins, in Kokelaar, B. P., and Howells, M. F., eds,, Marginal basin geology; Geol. Soc. Lond., Spec. Publ., no. 16, p. 137-149. Dewey, J. F., 1980, Episodicity, sequence, and style at convergent plate boundaries: Geol. Assoc. Canada Spec. Paper 20, p. 553-573. Dostal, J . , and Strong, D. F., 1983, Trace-element mobility during low-grade metamorphism and silicification of basaltic rocks from Saint John, New Brunswick: Can. J. Earth Sci., v. 20,' p. 431-435. Dudas.F. 0., 1983, Theeffectof volatile content on the vesiculation of submarine basalts: Econ. Geol. Mon. 5,p. 134-141. Dudas, F. 0., Campbell, I. H., and Gorton, M. P., 1983, Geochemistry of Igneous rocks in the Hokuroku district, Northern Japan: Econ. Geol. Mon. 5, p. 115-133. Edge, R. A., and Ahrens.L. H., 1962, The determination of Sc,Y,Nd,Ce and La in silicate rocks by a combined cation exchange-spectrochemical method. Anal. Chim. Acta., v. 26, p. 355-362. Einsele.G., 1985, Basaltic complexes in young spreading centres: genesis and significance: Geology, v. 13, p. 249-252. Elthon, D., and Scarfe, C. M., 1984, High-pressure phase equilibria of a high-m8gnesia basalt and the genesis of primary oceanic basalts: Am. Mineral., v. 69, p. 1-15. Evarts, R. C, and Schiffman, P., 1983, Submarine hydrothermal metamorphism of the Del Puerto Ophiolite, California: Am. J. Sci., v. 283, p. 289-340. Ewart.A., 1979, A review of the mineralogy and chemistry of Tertiary-Recent dacitic, latitic, rhyolitic, andsalic volcanic rocks, in Barker, F., ed., Trondhjemites, dacites, and related rocks: Elsevier, New York, p. 13-121. Fisher, R. V., 1961, Proposed classification of volcaniclastic sediments and rocks: Geol. Soc. Am., Bull., v. 72, p. 1409-1414. Fisher, R. V., 1966, Rocks composed of volcanic fragments: Earth-Sci. Rev., v. 1,p. 287-298. Fisher, R. V., 1984, Submarine volcaniclastic rocks in Kokelaar, B. P., and Howells, M. F., eds., Marginal basin geology: Geol. Soc. Lond., Spec. Publ., no. 16, p. 5-28. Fiske, R. S., and Matsuda, T., 1964, Submarine equivalents of ash flows in the Tokiwa Formation, Japan: Amer. J. Sci., v. 262, p. 76-106. Fisher, R. V., andSchmincke, H.-U., 1984, Pyroclastic rocks: Springer-Verlag, Heidelberg, 472 p. Floyd, P. A., and Winchester, J. A., 1978, Identification and discrimination of altered and metamorphosed volcanic rocks using immobile elements: Chem. Geol., v. 21, p. 291-306. Francis, E, H., 1982, Magma and sediment - I Emplacement mechanism of late Carboniferous tholeiite sills in northern Britain: J. Geol. Soc. London, v. 139, p. 1-20. 189 Fryer, B. J., 1977, Rare earth evidence in iron formations for changing Precambrian oxidation states: Geochim. Cosmochim. Acta, v. 41, p. 361-367. Fyles, J. T., 1955, Geology of the Cowichan Lake area, Vancouver Island, B. C: B. C. Depy. Mines Pet. Resources, Bull. 37, 69 p. Gass, I. G.,andSmewing, J. D., 1973, Intrusion, extrusion and metamorphism at constructive margins: Evidence from the Troodos Massif, Cyprus: Nature, v. 242, p. 26-29. Gelinas, L., Mellinger, M.,andTrudel, P., 1982, Archean mafic metavolcanicsfrom theRouyn-Noranda district, Abitibi Greensone Belt, Quebec. 1. Mobility of the major elements: Can. J. Earth Sci., v. 19, p. 2258-2275. Gibson, H. L., Watkinson, D. H., andComba, C. D. A., 1983, Silicification: Hydrothermal alteration in an Archean geothermal system within the Amulet Rhyolite Formation, Noranda, Quebec: Econ. Geol., v. 78, p. 954-971. Gill, J. B., 1981, Orogenic andesites and plate tectonics: Springer, New York, 390 p. _ Gill.J. B., Stork, A. L., and Whelan, P. M., 1984, Volcanism accompanying back-arc basin development in the southwest Pacific: Tectonophysics, v. 102, p. 207-224. Gladney, E. S., Burns, C. E., and Roelandts, I., 1983, Compilation of elemental concentration in eleven United States Geological Survey rock standards: Geostand. Newsl., v. 7, p. 41-44. Gossan, G. J., 1986, Miocene and Pliocene silicic tuffs in marine sediments of the East Coast Basin, New Zealand: unpubl. Ph.D. thesis, Victoria University of Wellington, New Zealand, p. 56-64. Govindaraju, K., 1984, 1984 compilation of working values and sample descriptions for 170 international reference samples of mainly silicate rocks and minerals: Geostand. Newsl., v. 8, p. 3-15. Grove, T. L., and Bryan, W. B., 1983, Fractionation of pyroxene-phyric MORB at low pressure: An experimental study: Contrib. Mineral. Petrol., v. 84, p. 293-309. Gunning, H. G., 1931, Buttle Lake map area, Vancouver Island, B. C: Geol. Surv. Can., Summary Rep., 1930, part A, p. 56A-78A. Hawkins, J. W., Bloomer, S. H., Evans, C. A.,andMelchior, J. T., 1984, Evolution of intra-oceanic arc-trench systems: Tectonophysics, v. 102, p. 175-205. Henley, R.W, and Ellis, A.J., 1983, Geothermal systems ancient and modern: A geochemical review: Earth-Science Reviews, v. 19, p. 1-50. Hickey, R. L., and Frey, F. A., 1982, Geochemical characteristics of boninite series volcanics: implications for their source: Geochim. Cosmochim. Acta, v. 46, p. 2099-2115. Hickson, C. J., 1986, Quaternary volcanics of the Wells Gray-Clearwater area, east central British Columbia: unpubl. Ph.D. thesis, The University of British Columbia, 357 p. Hickson, C. J., and Juras, S. J., 1986, Sample contamination by grinding: Can. Mineral., v. 24, p. 585-589. 190 Hobbs.B.I., Means, W. D., and Williams, P. F., 1976, An outline of structural geology: John Wiley and Sons, New York, 571 p. Horsky, S. J., 1980, Determination of praseodymium by graphite furnace atomic absorption spectrometry: At. Spectrosc., v. 1., p. 129-130. Horsky,S.J. and Fletcher, W. K., 1981, Evaluation of a combined ion exchange-graphite furnace atomic absorption procedure for determination of rare-earth elements in geological samples-. Chem. 6eol.,v. 32, p. 335-340. Hughes, C. J., 1982, Igneous petrology: Elsevier, Amsterdam, 551 p. Humphris, S. E., and Thompson, 0., 1978, Hydrothermal alteration of oceanic basalts: Geochim. Cosmochim. Acta, v. 42, p. 107-125. Hutchinson.C.S., 1974, Laboratory handbook of petrographic techniques: John Wiley and Sons, New York, 527 p. Hutchinson, R. W., 1980, Massive base metal sulfide deposits as guides to tectonic evolution: Geol. Assoc. Canada Spec. Paper 20, p. 659-684. Irvine, J. N., and Baragar, W. R. A., 1971, A guide to the classification of the common volcanic rocks: Can. J. Earth Sci., v. 8, p. 523-549. Isachsen.C, Armstrong, R. L., and Parrish, R. R., 1985, U-Pb, Rb-Sr, and K-Ar geochemistry of Vancouver Island igneous rocks: Abstract in LITHOPROBE project publication No. 10, p. 21. Jeffery, W. G., 1965, Lynx, Paramount, Price (Western Mines Ltd.): B.C. Dept. Mines Pet. Resources, Annual Report 1964, p. 157-166. Jeffery, W. G., 1970, Buttle Lake: Miscellaneous Open File Report, B. C. Ministry of Energy, Mines and Petroleum Resources. Jones, D. L., Silberling, N. J., and Hillhouse, J., 1977, Wrangellia - a displaced terrane in northwestern North America: Can. J. Earth Sci., v. 14, p. 2565-2577. Juras, S. J., 1986, A Paleozoic welded, subaqueous pyroclastic flow, Vancouver Island, British Columbia: International Volcanological Congress - New Zealand, 1 -9 February 1986, Abstracts, p. 52. Juras, S. J., Hickson, C. J., Horsky, S. J., Godwin, C. I., and Mathews, W. H., (in press), A practical method for the analysis of rare earth elements in geological samples by graphite furnace atomic absorption and x-ray fluorescence: Chem. Geol. Karig, D. E., 1971, Origin and development of marginal basins in the western Pacific: J. Geophys. Res.,v. 76, p. 2542-2561. Karig, D. E., and Mammerickx, J., 1972, Tectonic framework of the New Hebrides island arc: Mar. Geol.,v. 12, p. 187-205. Karig, D. E., and Moore, G. F., 1975, Tectonically controlled sedimentation in marginal basins: Earth Planet. Sci. Lett., v. 26, p. 233-238. 191 Kastner, M., and Siever, R., 1983, Siliceous sediments of the Guaymas Basin: The effect of high thermal gradients on diagenesis: J. Geol., v. 91, p. 629-641. Klein, G., 1975, Sedimentary tectonics in Southwest Pacific marginal basins based on leg 30 Deep Sea Drilling Project cores from the South Fiji, Hebrides, and Coral Sea Basin: Geol. Soc. Am., Bull., v. 86, p. 1012-1018. Kokelaar.B. P., 1982, Fluidization of wet sediment during the emplacement and cooling of various igneous bodies: J. Geol. Soc. London, v. 139, p. 21 - 33. Kokelaar, B. P., 1986, Magma-water interactions in subaqueous and emergent basaltic volcanism: Bull. Volcano1.,v. 48, p. 275-289. Krogh.T. E., 1973, A low contamination method for hydrothermal decomposition of zircon and extraction of U and Pb for isotopic age determinations: Geochim. Cosmochim. Acta, v. 37, p. 485-494. Kullerud, G., and Yoder, H. S., 1959, Pyrite stability relations in the Fe-S system: Econ. Geol., v. 54, p. 533-572. Kyser, T. K., Cameron, W. E., and Nisbet, E. G., 1986, Boninite petrogenesis and alteration history: constraints from stable isotope compositions of boninites from Cape Vogel, New Caledonia and Cyprus: Contrib. Mineral. Petrol., v. 93, p. 222-226. Lapierre, H., Cabanis, B., Coulon, C, Brouxel, M., andAlbarede, F., 1985, Geodynamic setting of Early Devonian Kuroko-type sulfide deposits in the Eastern Klamath Mountains (Northern California) inferred by the petrological and geochemical characteristics of the associated island-arc volcanic rocks: Econ. Geol., v. 80, p. 2100-2113.. Large,R. R., Herrmann, W., and Corbett, K. D., 1987, Base metal exploration of the Mount Read volcanics, Western Tasmania: Pt. I. Geology and exploration, Elliott Bay: Econ. Geol., v. 82, p. 267-290. Le Bas, M, J., Le Maitre, R. W., Streckeisen, A., andZanettin, B., 1986, Chemical classification of volcanic rocks based on the Total Alkali-Silica diagram: J. Petrology, v. 27, p. 745-750. Leake, B. E., Hendry, G. L , Kemp, A., Plant, A. G., Harrey, P. K., Wilson, J. R., Coats, J. S.,Aucott, J. W., Lunel, T. and Howarth, R. J., 1969, The chemical analysis of rock powders by automatic X-ray fluorescence: Chem. Geol., v. 5, p. 7-86. Leitch, E. C., 1984, Marginal basins of the SW Pacific and the presevation and recognition fo their ancient analogues: a review: in Kokelaar, B. P., and Howells, M. F., eds., Marginal basin-geology: Geol. Soc. Lond., Spec. Publ., no. 16, p. 97-108. Liou, J. G., Maruyama, S., andCho, M., 1985, Phase equilibria and mineral parageneses of metabasites in low-grade metamorphism: Mineral. Mag., v. 49, p. 321-333. Ludden, J., Gelinas, L., and Trudel, P., 1982, Archean mafic metavolcanicsfrom the Rouyn-Noranda district, Abitibi Greensone Belt, Quebec. 2. Mobility of trace elements and petrogenetic • constraints: Can. J. Earth Sci., v. 19, p. 2276-2287. Ludwig, K. R., 1980, Calculation of uncertainties of U/Pb isotopic data: Earth Planet. Sci. Lett, v. 46, p. 212-220. 192 Macdonald^ G. A., 1972, Volcanoes: Prentice-Hall, Inc., EnglewoodCliffs, New Jersey, 510 p. Maris, C. fc P., and Bender, M. L , 1982, Upwellingof hydrothermal solutions through ridge flank sediments shown by pore water profiles: Science, v. 216, p.623. Massey, N. W. D., and Friday, S. J., 1987, Geology of the Cowichan Lake area, Vancouver Island (92C/16): B. C. Ministry of Energy, Mines and Petroleum Resources, Geological Fieldwork, 1986, Paper 1987-1, p. 223-229. Meijer, A., 1983, The origin of low-K rhyolites from the Mariana frontal arc: Contrib. Mineral. Petrol., v. 83, p. 45-51. Miyashiro, A., 1972, Metamorphism and related magmatism in plate tectonics: Am. J. Sci., v. 272, p. 629-656. Miyashiro, A., 1974, Volcanic rock series in island arcs and active continental margins: Am. J. Sci., v. 274, p. 321-355. Moody, J., 1979, Serpentinites, spilites, and ophiolite metamorphism: Can. Mineral., v. 17, p. 871-889. Mottl.M. J., 1983, Metabasalts, axial hot springs, and the structure of hydrothermal systems at mid-ocean ridges: Geol. Soc. Am., Bull., v. 94, p. 161 -180. Mottl, M. J., and Holland, H. D., 1978, Chemical exchange during hydrothermal alteration of basalt by seawater. I. Experimental results for major and minor components of seawater: Geochim. Cosmochim. Acta, v. 42, p. 110.3-1116. Mullen, E. D., 1983, MnO/T^/^Os: a minor element discriminant for basaltic rocks of oceanic environments and its implications for pedogenesis: Earth Planet. Sci. Lett., v. 62, p. 53-62. Muller, J. E., 1977a, Evolution of the Pacific margin, Vancouver Island and adjacent regions: Can. J. Earth Sci., v. 14, p. 2062-2085. Muller, J. E., 1977b, Geology of Vancouver Island: GAC-MAC-CGU Annual Mtg, April 1977,Field Trip Guidebook, Trip 7,54 p. Muller, J. E., 1980, The Paleozoic Sicker Group of Vancouver Island, British Columbia: Geol. Surv. Can.; Pap. 79-30, 23 p. Muller, J.E., and Carson, D.J. T., 1969, Geology and mineral deposits of Alberni map-area, B. C. (92F): Geol. Surv. Can., Paper 68-50, 52 p. Muller, J. E., Northcote, K. E., and Carlisle, D., 1974, Geology and mineral deposits of Alert-Cape Scott map-area, Vancouver Island, British Columbia: Geol. Surv. Can., Paper 74-8, 77 p. Murphy, B. J., and Hynes, A. J., 1986, Contrasting secondary mobility of Ti, P, Zr, Nb, and Y in two metabasaltic suites in the Appalachians: Can. J. Earth Sci., v. 23, p. 1138-1144. Mysen.B.O., 1982, The role of mantle anatexis, in Thorpe, R. S., ed., Orogenic andesites: J.Wiley and Sons, p. 489-522. 193 Nicholls, J. , The statistics of Pearce element diagrams and the Chaves closure problem: submitted to Contrib. Mineral. Petrol. Nye, C. J., and Reid, M. R., 1986, Geochemistry of primary and least fractionated lavas from Okmok Volcano, Central Aleutians: Implications for arc magmagenesis: J. Geophys. Res., v. 91, no. BIO,p. 10271-10287. Palmer, A. R., 1983, The Decade of North America Geology 1983 geologic time scale: Geology, v. 11, p. 503-504. Parrish, R., and Roddick, J. C., 1985, Geochronology and isotope geology for the geologist and explorationist: Geol. Assoc. Can., Cordilleran Section, Short Course no. 4, 71 p. Pearce, J. A., 1978, Petrogenetic studies of metabasalts using immobile trace element ratios: J. Geol. Soc.,Lond.,v. 135, p. 192-215. Pearce, J. A., 1982, Trace element characteristics of lavas from destructive plate boundaries, in Thorpe, R. S., ed., Orogenic andesites: J. Wiley and Sons, p. 525-548. Pearce, J. A., and Cann, J. A., 1973, Tectonic setting of basic volcanic rocks determined using trace element analyses: Earth Planet. Sci. Lett, v. 19, p. 290-300. Pearce, J. A., and Norry, M. J., 1979, Petrogenic implications of Ti, Zr, Y, and Nb variations in volcanic rocks: Contrib. Mineral. Petrol., v. 69, p. 33-47. Pearce, T. H., 1968, A contribution to the theory of variation diagrams: Contrib. Mineral. Petrol., v. 11, p. 15-32. Plsutha-Arnond, V., andOhmoto, H., 1983, Thermal history, and chemical and isotopic compositions of the ore-forming fluids responsible for the Kuroko massive sulfide deposits in the Hokuroku district of Japan: Econ. Geol. Mon. 5, p. 523-558. Reed, M. H., 1983, Seawater-basalt reaction and the origin of greenstones and related ore deposits: Econ. Geol., v. 78, p. 466-485. Reed, M. H., 1984, Geology, wall rock alteration, and massive sulfide mineralization in a portion of the West Shasta district, California: Econ. Geol., v. 79, p. 1299-1318. Robinson, P.-, Higgins, N. C. and Jenner, G. A., 1986, Determination of rare-earth elements, yttrium and scandium in rocks by an ion exchange—X-ray fluorescence technique: Chem. Geol., v. 55, p. 121-137. Russell, J. K., and Nicholls, J., Analysis of petrologic hypotheses with Pearce element ratios: submitted to Contrib. Mineral. Petrol. Sakuyama,M., 1983, Petrology of arc volcanic rocks and their origin by mantle diapirs: J. Volcanol. Geotherm. Res., v. 18, p. 297-320. Sangster.D. F., 1977, Some grade and tonnage relationships among Canadian volcanogenic massive sulphide deposits: Geol. Surv., Can., Paper 77-1 A, p. 5-12. Saunders, A. D., and Tarney, J., 1984, Geochemical characteristics of basaltic volcanism within back-arc basins, in Kokelaar, B. P., and Howells, M. F., eds., Marginal basin geology: Geol. Soc. Lond.,Spec. Publ., no. 16, p. 59-76. 194 Saunders, A. D., Tarney, J., and Weaver, S. D., 1980, Transverse geochemical variations across the Antarctic peninsula: implications for the pedogenesis of calc-alkaline magmas: Earth Planet. Sci. Lett, v. 46, p. 344-360. Scheibner, E., and Markham, N., 1976, Tectonic setting of some strata-bound massive sulfide deposits in New South Wales, Australia, in Wolf, K. H., ed., Handbook of strata-bound and stratiform ore deposits: New York, Elsevier, v. 6, p. 56-77. Schmid, R., 1981, Descriptive nomenclature and classification of pyroclastic deposits and fragments: Recommendations of the IUGS Sub-commission on the Systematica of Igneous Rocks: Geology, v. 9, p. 41-43. Sen Gupta, J. G., 1976, Determination of lanthanides and yttrium in rocks and minerals by atomic-absorption and flame-emission spectrometry: Talanta, v. 23, p. 343-348. Sen Gupta, J. G., 1981, Determination of yttrium and rare-earth elements in rocks by graphite-furnace atomic absorption spectrometry: Talanta, v. 28, p. 31-36. Sen Gupta, J. G., 1984, Determination of scandium, yttrium and lanthanides in silicate rocks and four new Canadian iron-formation reference materials by flame atomic-absorption spectrometry with microsample injection: Talanta, v. 31, p. 1045-1051. Sen Gupta, J. G., 1985, Determination of the rare earths, yttrium and scandium in silicate rocks and four new geological reference materials by electrothermal atomization from graphite and tantalum surfaces: Talanta, v. 32, p. 1 -6. Seraphim. R. H., 1980, Western Mines-Myra, Lynx and Price deposits: Can. Inst. Min. Met, Bull., v. 73, no. 823, p. 71-86. Seyfried, W. E., Jr., and Bischoff, J. L., 1981, Experimental seawater-basalt interaction at 300° C and 500 bars: Chemical exchange, secondary mineral formation and implications for the transport of heavy metals: Geochim. Cosmochim. Acta, v. 45, p. 1937-1947. Snyder, G. L., and Fraser, G. D., 1963, Pillowed lavas, I: Intrusive layered lava pods and pillowed lavas Unalaska Island, Alaska: U. S. Geol. Surv., Prof. Paper 454-B, 23 p. Spooner, E. T. C, andFyfe, W. S., 1973, Sub-sea-floor metamorphism, heat and mass transfer: Contrib. Mineral. Petrol., v. 42, p. 287-304. Spulber, S. D., and Rutherford, M. J., 1983 The origin of rhyolite and plagiogranite in oceanic crust: An experimental study: J. Petrol., v. 24, p. 1 -25. Stacey, J. S., and Kramer, J. D., 1975, Approximation of terrestrial lead isotope evolution by a two-stage model: Earth Planet. Sci. Lett., v. 26, p. 207-221. Steele, T. W., Wilson, A., Goudvis, R., Ellis, P. J., and Radford, A. J., 1978, Trace element data (1966-1977) for the six "NIMROC" reference standards: Geostand. Newst.v. 2, p. 71-106. Stern, C, and Elton, D., 1979, Vertical variations in the effects of hydrothermal metamorphism in Chilean ophiolites: Their implications for ocean floor metamorphism: Tectonophysics, v. 55, p. 179-213. 195 Strelow, Fr-W. E., Victor, A. H., and Weinert, C. H. S. W., 1978, Ion exchange chromatography applied to the separation and accurate determination of some trace elements in rocks: Geostand. Newsl., v. 2, p. 49-55. Sutherland Brown, A., and Yorath.C. J., 1985, Lithoprobe profile across Southern Vancouver Island: Geol. Soc. Am., Cord. Section Mtg., May 1985, Vancouver, B. C., Field Trip Guidebook, p. 8-1-8-23. Sutherland Brown, A., Yorath, C. J., Anderson, R. G., and Dom, K., 1986, Geological maps of southern Vancouver Island, LITHOPROBE 1: Geol. Surv. Can., Open File 1272, 10 sheets. Tamaki.K., 1985, Two modes of back-arc spreading: Geology, v. 13, p. 475-478. Tatsumi, Y., 1982, Origin of high-magnesian andesites in the Setouchi volcanic belt, southwest Japan, II. Melting phase relations at high pressures: Earth Planet. Sci. Lett., v. 60, p. 305-317. Thompson, M., and Howarth, R. J., 1973, The rapid estimation and control of precision by duplicate determinations: The Analyst, v. 98, p. 56-60. Thompson, M., and Howarth, R. J., 1978, A new approach to the estimation of analytical precision: . J. Geochem. Exploration, v. 9, p. 23-30. Uyeda, S., and Kanamori, H., 1979, Back-arc opening and the mode of subduction: J. Geophys. Res., v. 84, no. B3, p. 1049-1061. Uyeda, S., and Nishiwaki, C, 1980, Stress field, metallogenesis and mode of subduction: Geol. Assoc. Canada Spec. Paper 20, p. 323-339. Wakita, H., Rey, P., and Schmitt, R. A., 1971, Abundances of the 14 rare-earth elements and 12 other trace-elements in Apollo 12 samples: five igneous and one breccia rocks and four soils: Proc. 2nd Lunar Sci. Conf., p. 1319-1329. Walker, D. A., and Cameron, W. E., 1983, Boninite primary magmas: Evidence from the Cape Vogel Peninsula, PNG: Contrib. Mineral. Petrol., v. 83, p. 150-158. Walker, R. R., 1980, Western Mines - Myra, Lynx and Price deposits: A discussion: Can. Inst. Min. Met., Bull., v. 73, no. 823, p. 86-88. Walker, R. R., 1983, Westmin Resources' massive sulfide deposits, in Mineral deposits of Vancouver Island: GAC-MAC-CGU Annual Mtg, May 1983, Field Trip Guidebook, Trip 9, p. 5-19. Walker, R. R., 1985, Westmin Resources' massive sulfide deposits, Vancouver Island: Geol. Soc. Am., Cord. Section Mtg., May 1985, Vancouver .B.C., Field Trip Guidebook, p. 1-1-1-13. Williams, H., and McBirney, A., 1979, Volcanology: Freeman, Cooper and Co., San Francisco, 391 p. Wood, D. A., Marsh, N. G., Tarney, J., Joron, J . -L , Fryer, ,P. and Treuil, M., 1981, Geochemistry of igneous rocks recovered from a transect across the Mariana Trough, Arc, Fore-arc, and ' Trench, Sites 453 through 461, Deep Sea Drilling Project Leg 60, in Hussong, D. M., Uyeda, S. etal, eds, Init. Rep. Deep Sea drill. Proj.,U. S. Government Printing Office, Washington, D. C.,v. 60, p. 611-645. 196 Wood, D. A„ Mattey, D. P., Joron, J.-L., Marsh, N. 6., Tarney, J., andTreuil, M., 1980, A geochemical study of 17 selected samples from basement cores recovered at Sites 447, 448, 449,450 and 451, Deep Sea Drilling Project Leg 59, in Kroenke, b,, Scott, R. etdl, eds, Init. Rep. Deep Sea drill. Proj., U. S. Government Printing Office, Washington, D. C, v. 59, p. 743-752. Wright, J. V., Smith, A. L., and Self, S., 1980, A working terminolgy of pyroclastic deposits: J. Volcano!. Geotherm. Res., v. 8, p. 315-336. Wright, J. V., and Cas, R. A. F., 1986, Critical assessment of the concept of subaqueous pyroclastic flows and ignimbrites: International Volcanological Congress - New Zealand, 1-9 February 1986, Abstracts, p. 89. Yamada.E., 1984, Subaqueous pyroclastic flows: their development and their deposits, in Kokelaar, B. P., and Howells, M. F., eds., Marginal basin geology: Geol. Soc. Lond., Spec. Publ., no. 16, p. 29-35. Yole, R. W., 1963, An Early Permian fauna from Vancouver Island: Bull. Canadian Petroleum Geology, v. 11, p. 138-149. Yole, R. W., 1965, A faunal and stratigraphic study af Upper Paleozoic rocks of Vancouver Island, British Columbia: unpubl. Ph.D. thesis, The University of British Columbia, 254 p. Yole, R. W., 1969, Upper Paleozoic stratigraphy of Vancouver Island, British Columbia: Geol. Assoc. Can., Proc., v. 20, p. 30-40. Yorath.C. J., Clowes, R. M., Green, A. G., Sutherland Brown, A., Brandon, M. T., Massey, N. W. D., Spencer, C., Kanasewich, E. R., and Hyndman, R. D., 1985, Lithoprobe - Phase I: Southern Vancouver Island: preliminary analyses of reflection seismic profiles and surface geological studies: Geol. Surv. Can., Paper 85- IA, p. 543-554. York.D., 1967, The best isochron: Earth Planet. Sci. Lett., v. 2, p. 479-482. York.D., 1969, Least squares fitting of a straight line with correlated errors: Earth Planet. Sci. Lett.v. 5, p. 320-324. 197 APPENDIX A SAMPLE LOCATIONS AND DESCRIPTIONS A.1 GUIDE TO SAMPLE LOCATION AND DESCRIPTION TABLES Four sample location and description tables are given. Table A. 1 contains all outcrop samples taken from the Price Hillside (see Fig. A. 1); Table A.2 contains drillcore samples from surface and underground diamond drillholes in the Price area (sections 183+00 E and 172+00 E); TableA.3 contains drillcore samples from surface and underground diamond drillholes in the West G, Lynx, and H-W-Myra sections. Sample locations in the latter two tables are given in terms of mine coordinates (northing) and elevation relative to sea level, both in feet. Table A. 4 contains longitude and latitude locations for the isotopically analyzed samples described in Tables A. 1 to A.3. Unit abbreviations refer to the legend in the Price Hillside geology map (Fig. 3.1), and in the Price and H-W-Myra geologic cross sections (Figs. 3.4 and 3.5). Abbreviations in the rock type/description column for all three tables are: Constituents are listed in order of increasing abundance. Those in round brackets () are present only in minor (< 5 %) amounts; double round brackets (()) denote trace amounts. Square brackets [] contain clarification of a lithic constituent. Samples from epiclastic deposits are indicated by quotation marks around the pyroclastic size term (e.g. "FLT"). Alteration is represented by the main mineral phase(s) present: actinolite, carbonate, chlorite, epidote, sericite and silica. Purple denotes hematite alteration. amph = amphibole FT = fine tuff CT = coarse tuff LT = lapilli-tuff FLT = fine lapilli-tuff CLT = coarse lapilli-tuff cc = calcite chl = chlorite ep = epidote f = feldspar q = quartz px = pyroxene py = pyrite TABLE A.1 Sample location and description table for Price Hillside samples. Sample names are prefixed by "PR- " . Analyt ical names are given in brackets beside the sampie name. "T.S." indicates that a thin section was made. Symbol " * " in the T.S. column represents electron microprobe analysis. XRF and AA stand for x- ray fluorescence and atomic absorption analysis respectively. Sample Unit T.S; XRF AA Isotope Rock Type/Description t Price Hillside. Figure A . l 83 -9A DCml r -/ vitr ic - q+f crystal - lithic Rhyolite CT 83-15A DCt bedded tuffaceous mudstone and siltstone 83-16B DCm6 4 q crystal Rhyolite FT, serici te, pyrite mineralized 83-16C (P16C) DCm6 4 4 4 KAr felsic FLT, si l ica + serici te, pyrite mineralized 83-22G DCm4 4 lithic Andesite FLT, epidote 8 3 - 2 2 J DCm4 4 vitr ic Andesite LT, epidote > chlorite 83-22K DCm 10 4 contorted, schistose mafic LT 83-27C.0 DCm8 / lithic - f+(px) crystal mafic CT 83 -31A DCm6H bedded, q+f crystal - vi tr ic Rhyolite FT-CT. purple 83-32C (P32C) DCt / 4 4 laminated tuffaceous mudstone 83-33A.B.C DCt 4 feisic cognate lithic - lithic [andesite flow clasts] - f c rys ta l - v i t r ic CT, FLT 83-34B DCm 10 4 f+px+(q) crystal - mafic cognate lithic mafic CT, chlorite 83-34C DCm9 4 q+f crystal - felsic cognate lithic - iithic [q+f porphyrit ic rhyol i te] Rhyolite CT 83-34E DCm9 4 black and gray, laminated, tuffaceous argil l i te 83-41D DCm5U 4 f c rys ta l , f porphyritic mafic and felsic "FLT", (purple) 83-43F DCt/DCm 4 contorted, schistose mafic? LT 83-44B (P44BA) DCm5U 4 4 4 RbSr f+(px) porphyritic felsic flow clast, purple 84-46B DCm6Hc red and pale'green, laminated chert 8 4 - 4 6 J (P46J-1.2) DCm7 4 4- 4 px porphyritic uitramafic f low, actinolite groundmass, chl-(ep) amygdules 84-46K DCm9 4 q+f crystal - lithic [q+f porphyritic rhyolite] - felsic. cognate lithic Rhyolite CT--FLT 84 -49A (P49A-4) DCt 4 4 4 massive to laminated tuffaceous mudstone 84-49C DCt.bs 4 mafic s i l l , intersertal 84 -50A DCt 4 bedded, f crystal - v i t r ic FT and tuffaceous siltstone 84-51C DCt 4 lithic [andesite flow clasts] - f crysta l - felsic cognate lithic - v i t r ic FLT 84-52B DCt 4 lithic [andesite flow clasts] - f crysta l * felsic cognate lithic - v i t r ic CT, FT 84-55A,B DCm9 q+f crystal - lithic [q+f porphyrit ic rhyoiite] Rhyolite CT, CLT 84 -630 DCm8 4 (f porphyritic felsic), f c rys ta l , f porphyrit ic andesite, f+(px) porphyrit ic mafic "FLT" 84 -71A (P71A) DCm3 4 4 4 q+f porphyritic rhyolite, f porphyrit ic andesite "FLT", epidote matrix 84-72C DCm3 4 (q+f porphyritic rhyolite), f porphyrit ic andesite, andesite cognate lithic "FLT", ep matrix 84 -73A DCm3 4 f porphyritic Andesite flow clast, epidote TABLE A . l (continued) Sample Unit T S . XRF AA Isotope. Rock Type/Description * 84-73F DCm3 / > (rhyolite FT, massive sulphide - pyrite), f+(px) porphyrit ic andesite "LT", epidote matrix 84 -736 (P73G) DCm3 -/ 4 r V f+(px) porphyritic Andesite flew clast, si l ica + epidote, q amygdules 84-86C (P86C) DCm9 -/ r V 4 black chert, massive 84 -87A DCmSL f crystal - felsic cognate lithic FLT [hyaloclastite], purple 84-95D DCm4 V (felsic), mafic, f porphyritic andesite "FLT" 64-99D.E DCm3Z 4 f porphyritic andesite cognate lithic - f+q crysta l - felsic cognate lithic Rhyolite FLT, CT 64-101C (P101C) DCm Id -/ 4 4 f porphyritic felsic flow 84-102A.B DCp -/ f porphyritic Andesite flow, chlorite > epidote 64 -103A (P1C3A) DCm In 4 f V 4 f c rys ta l , lithic [f porphyrit ic andesite], felsic cognate lithic "FLT" 84-104B.D DCm5U B = f porphyritic mafic f low; D = f porphyrit ic felsic flow clast, si l ica + albite > epidote 84-107C DCm5L 4 lithic [f porphyritic pseudo pillow breccia] - felsic cognate lithic FLT [hyaloclastite], purple 84 -108A DCm5L -/ f porphyritic felsic flow clast [pseudo piliow breccia?], purple 84 -109A DCm5L 4 lithic [f porphyritic andesite, f porphyrit ic fels ic] FLT, (purple) 84-112E (P112E) DCm8 4 4 4 flow banded, (f porphyritic) felsic flow clast, s i l ica 84-113B DCm6H 4 lithic [q+f porphyritic rhyolite] - f+q crysta l - felsic cognate lithic [vitrophyric rhyolite] FLT 84-115B DCm2 f crysta l Andesite FT, maroon FT clasts, epidote 84 -118A DCm3R/DCm1 A px porphyritic uitramafic hyaloclastite, epidote matrix 84-118G CP 1186) DCm3R 4 4 4 q+f porphyritic Rhyolite flow breccia [from a rhyolite "raff], si l ica > carbonate 84-121 (P121) DCm6H 4 4 4 f+q crystal - vi tr ic Rhyolite FLT-CT, serici te 84-122D (P122D) DCp 4 4 4 f+px porphyritic Andesite f low, epidote, (ep-chl amygdules) 84-124B (PR/124B) DCm 1 m 4* 4 px porphyritic uitramafic f low, actinolite, (chl amygdules) 84-124C DCm i A 4 lithic [q+f crystal rhyolite FT] - f+q porphyrit ic felsic cognate lithic Rhyolite FLT 84-124D (P124D) DCm2 4 4 4 f porphyritic Andesite flow, chlorite + epidote, (chl-ep amygdules) 84-124F (P124F) DCm2 4 4 4 f+((px)) porphyritic Andesite flew breccia, epidote, (chl-ep-q amygdules) 85 -4A DCm4 f porphyritic felsic, f porphyrit ic andesite "FLT" 85-8C DCm3R (py mineralized rhyolite FT), f porphyrit ic andesite, px porphyrit ic mafic "LT", ep matrix 85-8D DCm 1A bedded, f+q crystal - vi tr ic Rhyolite FT 85-9B DCm3Z 4 f+q crystal - f porphyritic andesite cognate lithic - felsic cognate lithic FLT-CT 85-1OA DCm4 4 f crystal - lithic [andesite flow clasts] FLT, chlorite i epidote 85-12C DCm3Z 4 white spotted, radiolaria-bearing black chert, massive 85-12F DCm2 4 f+((px)) porphyritic Andesite f low, epidote > chlorite, (chl-ep amygdules) 85-13D DCm9 bedded, f+q crystal - lithic [q+f pprphyrit ic rhyoli te] Rhyolite CT, maroon FT, purple TABLE A.1 (continued) Sample Unit T S . XRF AA isotope Rock Type/Description 85-16C 85-18F 85-186 85-18L 85-18N 85-19A.B 85-20B.C 65-22A 85-24A.B LD-Zr (LD-ZrH,C) Mrl-Zr (MM-ZrH.C) SBT-1 (P206) SBT-Zr (SBT-ZrH,C) SJ-R136 (R-136) UD-Zr (UD-ZrH) UR-Zr (UR-ZrH,C) TRb DCm8 DCm8 DCm9 DCm9 DCm 10 DCfr Jqd DCm3Z DCt DCm7 4 4 4 4 DCm Id 4 DCt.bs -/ DCt.bs 4* 4 4* DCm5U 4 DCm9 4 4 4 4 r v 4 4 4 4 4 4 4 f v UPb RbSr UPb UPb coarse-grained, plagioclase - pyroxene - magnetite gaboro f porphyritic andesite [epidote + si l ica], f+((px)) porphyrit ic mafic "FLT", epidote matrix aphyric felsic, epidote sediment, f porphyrit ic mafic "FLT" (px porphyritic mafic) - q+f crysta l - lithic [f+q+ampn porphyrit ic rhyol i te] Rhyolite LT (argillite, msssive sulphide-pyrite), f+q c rys ta l , q+f porphyritic rhyolite "FLT" lithic [f+px porphyritic mafic flow c lssts , epidote sediment clasts] CLT f crystal - v i tr ic - mafic cognate lithic - f porphyrit ic mafic essentia! clast ic FLT coarse-grained, plagioclase - amphibole - quartz quartz diorite q+f crystal - felsic cognate lithic [aphyric and f+q porphyrit ic types] FLT f+((px)) porphyritic felsic flov/, (epidote) ((px porphyritic)) mafic s i l l , intersertal , chlorite mesostasis f+px porphyritic mafic s i l l , mtergranular, (chl-ep amygdules) f crystal - lithic [andesite flow clasts] - felsic cognate lithic FLT. welded px porphyritic ultramafic flow, actinolite groundmass, chl-ep-(cc) amygdules f porphyritic andesite flow, chlorite > epidote, ((chl-ep amygdules)) f+q+(amph) crystal - felsic cognate lithic - lithic [q+f porphyrit ic rhyoli te] Rhyolite CT Price Hillside, outside area shown in Figure A . l ; locations are given in terms of mine coordinates (see Fig. 3.2 for orientation) 83-3A (P3A) DCt / 4 4 lithic [andesite flow c last l - f crysta l - felsic cognate I'thic FLT [154+80 N. 174+00 E) 83-280 (P28D) DCt 4 4 4 q+f crystal Rhyolite FT [161+50 N, 167+30 E) 83-28F (P28F-1) DCfr 4 4 4 f crystal - mafic cognate lithic - f porphyrit ic mafic essential clastic FLT (163+80 N, 167+50 E) 85-2 IF (P243) DCfr 4* f+(px) crystal - vi tr ic - f+px porphyrit ic mafic essential clastic FLT [66+00 N, 153+00 E) 85-30A DCfr 4 4 f crystal - v i t r ic - mafic cognate lithic - f+(px) porphyrit ic mafic essential clastic FLT [160+00 N, 165+00 E) 85-32B (PR/32B) DCm 10 4 4 f+px porphyritic mafic flow breccia, epidote, (chl-ep amygdules) (62+00 N, 210+00 E) THL-EP. CHL . DCm 10 4 4 4 f+px porphyritic mafic flow clasts, epidote [EP], chlorite [CHL] [50+00 N, 215+00E} TABLE A.2 Sample location and description table for Price section dril lcore samples. Analytical names are given in brackets beside the sampie name. Ai l samples listed were analyzed by x-ray flourescence and atomic absorption exept those with "xrf" beside their sample name (denotes XRF analysis only). Symbol " * " indicates electron microprobe analysis. Northing and elevation coordinates are in feet. Sample Northing' Elevation Unit Isotope Rock Type/Description Section 183+00 E (coordinates refer to Fioures 5.3 and 5.4) PR50-685 (PR50A) 146+70 400 DCm5NI RbSr f porphyritic felsic f low, sericite > carbonate PR32-2108 (D2108) 143+70 -1255 DCp f porphyritic Andesite f low, epidote > chlorite, (q amygdules) PR32-2114 (D2114) 143+70 -1260 DCp f porphyritic Andesite f low, epidote > chlorite, (q amygdules) PR32-2214 (D2214) * 143+70 -1480 DCp px+f porphyritic Andesite f low, epidote > chlori te, (q-ep-chl amygdules) PR35-267 (D35267) 109+70 1700 DCm5L f+((px)) porphyritic felsic flow ciast, purple PR35-590 (D35590) 110+20 1360 DCm2 f porphyritic Andesite f low, epidote, (chl-q-ep amygdules) PR55-745 (D55745) 110+70 1240 DCm2 f porphyritic Andesite f low, chlorite + ser ic i te, (q-chl-cc amygdules) PR39-903 (D59905) 106+80 1220 DCml r q+f porphyritic Rhyolite flow clast, s i l ica PR41-646 (D41646) 109+00 1300 DCm2 f+((px)) porphyrit ic Andesite f low, epidote, (chl-ep amygdules) PR41-651 (D41651) 109+00 1300 DCm2 f+((px)) porphyritic Andesite f low, epidote, (chl-ep amygdules) PR45-106 (D45106) 99+20 1980 DCt.bs mafic s i l l , intersertal PR45-606 (P43606) 99+40 1570 DCmlO (px? porphyrit ic), ultramafic hyaloclastite, carbonate > ser ic i te, purple PR43-1121 (DPI 121) 99+70 1050 DCmSL flow layered, f+((px)) porphyrit ic felsic flow clast, purple, ((q amygdules)) PR73-620 xrf 133+30 210 DCmlq q+f porphyritic Rhyolite flow breccia, serici te PR75-545 xrf 130+80 100 DCmlq flow banded, (f+q porphyrit ic) Rhyolite flow P15 -20 -632 (P13-20) 124+00 860 DCm Id f porphyritic felsic flow P I 3 - 2 6 - 1 2 2 ( P I 3 - 2 6 ) 117+10 1360 DCp f porphyritic Andesite f low, chlorite, (chl-ep-q amygdules) 9L-V/PR * 108+70 1360 DCm5R f+(px) porphyritic Andesite flow clast, epidote, (chl-q-ep amygdules) Section 172+00 E (coordinates represent projected locations in Fiaures 3.3 and 3.4) PR34-293 (D34294) 103+50 2180 DCt.bs mafic s i l l , intersertal PR34-1259 (PR34) xrf 103+00 1400 DCm7 px porphyritic ultramafic f low, actinolite groundmass, chl-ep amygdules PR42-1051 (PR42) xrf, * 99+50 1590 DCm 10 f+px porphyritic mafic f low, epidote > chlorite, (chl-ep amygdules) P I3^74 -70 (P13-74) 127+00 1000 DCmld f porphyritic felsic flow TABLE A.3 Sample location and description table for West 6, Lynx, and H-W-Myra sections dri l lcore samples. Analyt ical names are given in brackets beside the sample name. Ail samples iisted were analyzed by x-ray flourescence and atomic absorption exept those with "xrf" beside their sample name (denotes XRF analysis only). Symbol " * " indicates electron microprobe analysis. Northing and elevation coordinates are in feet. ' » Sample Northing Elevation Unit Isotope Rock Type/Description ' Section 5+00 E (West 6: coordinates refer to Fia. 3.7) 10--1257-56? (DL1257) 124+60 1540 DCm6H f+q crystal - v i t r ic Rhyolite CT, s e n a t e , pyrite mineralized 10--1259-423 (DL423) 123+40 1520 DCm5E f porphyritic Andesite f low, albite + epidote > carbonate 10--1259-498 (DL498A) 124+20 1570 DCmSE RbSr f porphyritic Andesite f low, si l ica + albite 10--1262-37 xrf 120+20 1300 DCm5E f porphyritic Andesite f low, chlorite > epidote, (chl-q-ep amygdules) 10--1265-1095 (D1265A) 133+50 200 DCm2 RbSr f+(px) porphyritic Andesite f low, epidote, (ep-chl-q amygdules) 10--1266-43 (DL43) 132+70 1230 DCm5E f+px porphyritic mafic f low, epidote + chlorite, (chl-cc-ep amygdules) S J - -5EA 123+70 1270 DCmSE RbSr f porphyritic Andesite f low, epidote + s i l ica, q-chl amygdules Section 60+00 E (Lynx: W169-284 (DW284) V/169-295 (DW295) coordinates refer to Fig. 3.6) 113+70 1010 DCm7 113+70 1000 DCm6H ultramafic flow breccia [hyaloclastite], carbonate > ser ic i te, purple q+f crystal - lithic Rhyolite FT-CT, ser ic i te, pyri te mineralized Section 124+00 E (H-W-Myra: coordinates refer to Fig. 3.5) P I 3 - 3 0 2 - 1 0 9 4 (D1094) P I 3 - 3 0 6 - 1 1 4 2 (D1142) P13 -306 -1362 (D1362) P13 -306 -1412 (D1412A) W140-1387 (DW140A) H-W Feeder Zone 3 118+80 -450 DCm Id RbSr ' 127+40 -220 DCmlq 127+80 -280 DCmlq 128+10 -470 DCmlq RbSr 129+20 2 0 2 DCmlq RbSr, KAr 120+00 -700 DCp KAr f porphyritic felsic f low, carbonate q+f porphyritic Rhyolite flow breccia, serici te q+f porphyritic Rhyolite flow q+f porphyritic Rhyolite flow q+f porphyritic Rhyolite vi trophyre, serici te f porphyritic Andesite f low, si l ica + ser ic i te, pyri te mineralized H-W-Mvra section, north W141-242 (DW242) 140+00 W143-1631 (SJ-R90) 155+00 W143-2357 (SJ-R78) 155+00 650 DCt.bs -600 DCrr,5N RbSr -1300 DCm If RbSr mafic s i l l , intergranular, (q-chl amygdules) f porphyritic felsic now, (q amygdules) f porphyritic Rhyolite flow, s i l ica, purple 1. RbSr analytical name for this sample was D1110A. 2. Coordinates represent projected locations. 3. H-W Feeder Zone sample was only analyzed for K-Ar isotopic analysis. Location for this sample is approximate only. TABLE A.4 Longitude and latitude locations (in decimal degrees) for isotopically analyzed samples described in Tables A.l to A.3. Names in brackets denote analytical names. Sample Table Isotope Longitude Latitude 83-16C (PI60 A.l KAr 125.57 49.56 83-44B (P44BA) A.1 RbSr 125.57 49.56 SBT-Zr (SBT-ZrH,C) A.1 UPb 125.57 49.56 SJ-R136 (R-136) A.1 RbSr 125.57 49.56 UD-Zr (UD-ZrH) A.l UPb 125.57 49.56 UR-Zr (UR-ZrH,C) A.1 UPb 125.57 49.56 PR30-685 (PR30A) A.2 RbSr 125.57 49.56 10-1259-498 (DL498A) A.3 RbSr 125.62 49.59 10-1265-1095 (D1265A) A.3 RbSr 125.62 49.59 SJ-5EA A.3 RbSr 125.62 49.59 P13-306-1094 (Dl110A) A.3 RbSr 125.58 49.57 P13-306-1412 (D1412A) A.3 RbSr 125.58 49.57 W140-1387 (DW140A) A.3 RbSr, KAr 125.58 49.57 H-W Feeder Zone A.3 KAr 125.58 49.57 W143-1631 (SJ-R90) A.3 RbSr 125.58 49.57 W143-2357 (SJ-R78) A.3 RbSr 125.58 49.57 204 A.2 DETAILED DESCRIPTIONS OF VOLCANICLASTIC CLAST TYPFS AND PYROCLASTIC DEPOSITS. • MYRA FORMATION A.2.1 H--W HORIZON, PYROCLASTIC AND VOLCANICLASTIC MEMBER The bedded crystal-lithic-vitric lapilli-tuff, and coarse to fine tuff sequences are composed of 10 percent broken plagioclase crystals; I to 10 percent, subangular to angular, occasionally embayed, quartz crystal fragments; trace apatite grains; and a variety of lithic clasts. Main clast types are: 15 percent, variably compacted, feathery to subrounded, occasionally quartz or feldspar porphyritic, perlitic-textured, felsic cognate lithic clasts; 1 to 10 percent, subrounded, feldspar + quartz porphyritic rhyolite accessory lithic clasts; and 15 percent, subangular to subrounded, variably feldspar porphyritic, hyalopilitic andesite( ?) accidental lithic clasts. Minor but ubiquitous types include trace to 3 percent, subrounded, fine tuff or argillite accidental lithic clasts, and 1 percent massive sulphide - pyrite + sphalerite (+ pyrrhotite in welded units) - accidental lithic clasts. The matrix component is very fine-grained and consists of an altered mesostasis of quartz + feldspar ± epidote ± chlorite. A.2.2 ORE CLAST BRECCIA UNIT, VOLCANICLASTIC BRECCIA MEMBERS Clast types in the rhyolite-rich and rhyolite-poor volcaniclastic breccia members largely consist of green, angular to subrounded, plagioclase ± pyroxene porphyritic andesite flow clasts; medium to dark green, subangular to angular, calcite and chlorite amygdaloidal, aphyric to pyroxene-phyric mafic volcanic flow and/or cognate lithic clasts; and medium to dark green, angular (feathery) to subrounded, feldspar porphyritic, hyalopilitic andesite accessory to cognate lithic clasts. Less abundant clast types consist of accidental lithics and comprise: cream -white to light green, subrounded to blocky, plagioclase porphyritic dacite flow clasts; bedded rhyolite fine tuff ± chert rip-up clasts; gray to light green, blocky to subrounded, quartz -* feldspar porphyritic rhyolite; irregularly-shpaed, blocky to rounded, massive sulphide (pyrite » reddish sphalerite + 205 galena > chalcopyrite + pyrite) clasts; and rounded, dark gray to black argillite clasts. Hand samples of typical Ore Clast Breccia, volcaniclastic breccia member deposits are in Figs. A.2, A.3 and A.4. A.2.3 LOWER MIXED VOLCANICLASTICS, SUBAQUEOUS PYROCLASTIC FLOW DEPOSITS The subaqueous pyroclastic flow deposits comprise approximately 10 percent, broken to euhedrai, plagioclase crystals; 20 to 40 percent, variably stretched, feathery-terminated relict pumice clasts; and 15 percent, subrounded, occasionally perlitic-textured, cognate lithic clasts. The matrix is relict glass shard-rich with both cuspate and platy types. Alteration of the shards has produced, in many cases, a fine-grained mesostasis, now epidote ± chlorite. In welded examples the deposits display good eutaxitic and compaction textures (see Appendix B). A.2.4 UPPER RHYOLITE UNIT, PYROCLASTIC DEPOSIT MEMBER The most common rock type in the pyroclastic member are coarse tuff to lapilli-tuff deposits. These deposits contain a 15 to 30 percent (up to 60 percent locally) crystal component comprising 15 percent, i 2.5 mm long, euhedrai to broken plagioclase; 1 to 10 percent, up to 4 mm in diameter, broken and embayed quartz; trace chlorite pseudomorphs after euhedrai amphibole; and accessory phases of zircon and apatite. Many quartz and feldspar crystals have rel ict silica liquid inclusions (now fine-grained chlorite ± sericite). The clast component is varied but generally consists of 10 to 40 percent, equant and subrounded, quartz + feldspar porphyritic rhyol ite accessory clasts; 10 to 40 percent, subrounded to rounded, perlitic-textured, weakly feldspar-phyric to aphyric, mica-poor felsic cognate lithic clasts; trace to 3 percent, brownish-red, blocky to lensoidal, chlorite ± epidote amygdaloidal essential (scoria?) fragments; trace to I percent (up to 7 percent in some areas towards the VARC region) oblate to lensoidal, variably quartz + feldspar porphyritic, very fine-grained sericite-rich cognate lithic clasts; and trace to 5 percent, subangular to subrounded, chloritic, aphyric to weakly feldspar-phyric, hyalopilitic mafic(?) volcanic accidental lithic clasts. The quartz + feldspar porphyritic accessory clasts are the most common clast type in these deposits. F'gure A.2: Feldspar ± pyroxene porphyritic andesite flow clast dominant sample, rhyolite-poor volcanoclastic breccia member, Ore Clast Breccia unit, Price Hillside. Non-andesite clast types present are: rhyolite fine tuff clasts (R), and variably oxidized massive sulphide (pyrite) fragments (S). Matrix is very fine grained and made up of mainly epidote and quartz. Scale divisions are in mm and cm. Figure A.3: Feldspar porphyritic andesite cognate lithic clast dominant sample, rhyolite-poor . volcaniclastic breccia member, Ore Clast Breccia unit, Price Hillside. The cognate lithic clasts are dark green and angular to feathery in shape. Other clast types present are: quartz + feldspar porphyritic rhyolite (R), feldspar porphyritic andesite flow clasts (A), oxidized massive sulphide clasts (S), and feldspar porphyritic dacite (D). Scale divisions are in mm and cm. 207 Figure A. 4: Mafic volcanic clast dominant sample, rhyolite-rich volcaniclastic breccia member, Ore Clast Breccia unit, Price Hillside. Mafic volcanic clasts (M) are medium to dark, green, subangular to angular (wispy in places), and variably pyroxene-phyric. Other clast types present are: pyrite mineralized rhyolite fine tuff (rT), quartz-feldspar porphyritic rhyolite (R); feldspar porphyritic andesite flow clasts (A) and cognate lithic clasts (Av), and pyrite mineralized Price Formation(?) andesite (P). The very fine grained matrix is composed of mainly epidote and quartz. Scale divisions are in mm and cm. 208 They contain 5 percent, up to 7 mm long, plagioclase phenocrysts; 2 percent, <; 3 mm in diameter, weakly to strongly embayed quartz phenocrysts; and trace, i 2 mm long, chlorite pseudomorphs after euhedral amphibole phenocrysts. The matrix component makes up 25 percent of a pyroclastic deposit and consists of a very fine-grained aggregate of quartz + chlorite + sericite + feldspar ± epidote. This assemblage may reflect devitrification of relict vitric debris. A.2.5 UPPER MAFIC UNIT, HYDR0CLAST1C AND PYROCLASTIC DEPOSITS The main clast type in the hydroclastic and pyroclastic deposits of the Upper Mafic unit is basaltic flow clasts. These clasts are angular to subrounded, and weakly amygdaloidal with i l mm in diameter, chlorite and epidote amygdules. The clasts contain 20 percent euhedral, < 2 mm long, plagioclase phenocrysts; 1 to 5 percent, euhedral, < 3 mm long (up to 7 mm in places), clinopyroxene phenocrysts; and trace opaque oxide (magnetite?) microphenocrysts. The fine-grained groundmass is composed of feldspar microlites (hyalopilitic to hyalophitic texture) in an epidote + albite ± chlorite altered mesostasis. The phenocrysts have undergone moderate to strong alteration. Plagioclase phenocrysts are moderately to strongly altered to epidote + chlorite, pyroxene crystals are moderately to completely altered to chlorite ± actinolite, and opaque oxide m icrophenocrysts are completely altered to leucoxene. 209 • APPENPIX B  SUBAQUEOUS PYROCLASTIC DEPOSITS B.l INTRODUCTION Subaqueous volcaniclastic deposits are an important lithology in Sicker Group lithologic units in the Buttle Lake Camp, Vancouver Island. They are generated by subaqueous and/or subaeriai eruptions which produce lava flows and related breccias, pyroclastic flows and fallout ash, or are from subaqueously remobilized pyroclastic, hydroclastic or epiclastic materials. Fisher (1984) reviewed these types of deposits with emphasis on those emplaced by subaqueous sediment gravity flow processes. Of particular interest is the recognition of subaqueous pyroclastic deposits, especially ones emplaced as pyroclastic flows. This deposit type is only recently beginning to be studied in detail and consequently remains controversial. This appendix establishes a nomenclature for these deposits and provides evidence for the presence of subaqueous pyroclastic deposits in the Buttle Lake Camp. Special emphasis is given to subaqueous pyroclastic deposits emplaced in a hot state. For more complete reviews of these deposit types the reader is referred to Fisher (1984), Fisher and Schmincke( 1984), and Yamada (1984), and references therein. Subaqueous pyroclastic deposits occur throughout the Sicker Group units in the Buttle Lake Camp. Subaqueous pyroclastic deposits in the Myra Formation are associated with argillite beds, massive sulphide mineralization, mafic hyaloclastite and peperite, and intermediate to felsic volcanic flow and flow breccia deposits containing variable amounts of pillowed flows or flow clasts. Subaqueous pyroclastic deposits in the Thelwood Formation are intercalated with fine-grained, siliceous tuffaceous sediment sequences. Similar deposits h8ve not been recognized in the Price Formation whereas pyroclastic deposits in the Flower Ridge Formation (related to emergent basaltic volcanism) may have been deposited in both subaqueous and subaeriai envrionments (see Chapter 3) and are not discussed here. 210 B.2 NOMENCLATURE AND TERMINOLOGY Subaqueous pyroclastic deposits are defined here as deposits containing greater than 75 percent pyroclastic^ material (defined by Fisher and Schmincke (1984) as products produced directly from volcanic processes, irrespective of later processes that may recycle such material) deposited in a subaqueous environment. If the deposit can be proven to have been emplaced as a pyroclastic flow, it is called a subaqueous pyroclastic flow deposit. This is regardless of whether a primary flow was hot or cold during emplacement. However, distinguishing between cold subaqueous pyroclastic flow deposits and subaqueous pyroclastic deposits formed from remobilized pyroclastic debris originally deposited on a submerged volcanic slope is difficult at best, and can only be done through association and relationships with surrounding stratigraphy. Pyroclastic deposits in general are classified according to their components and grain size. .;. Four kinds of components are found in a pyroclastic deposit (after Wright etal, 1980; Fisher and Schmincke, 1984): juvenile vesiculated fragments, glass shards, crystals, and lithic clasts. Juvenile vesiculated fragments (also called essential fragments) consist of all densities of vesiculated clasts, from highly vesiculated pumice and scoria, to denser, less well vesiculated juvenile magmatic fragments. Non-vesiculated juvenile clasts are classified as cognate lithics (see below). Glass shards fall into two categories: those representing walls of small broken bubbles or the junctions of gas bubbles developed by the vesiculation of magma (usually felsic in composition), and those formed from non-vesiculation processes, in particular thermal shock or spalling from rapid quenchingduring hydroclastic (phreatomagmatic or phreatic) eruptions. The vesiculated type consists of three end member shapes: cuspate or lunate shaped fragments that are commonly Y-shaped in cross-section, flat plates from glass walls separating large flattened vesicles, and pumice fragments. Shards formed from hydroclastic processes commonly have blocky shapes and few vesicles. The latter shard type comprises the predominant type recognized at Buttle Lake. Crystals are considered as a discrete juvenile component and consist of euhedral, whole or broken crystals, separated from or enclosed by quenched magma (i.e. glass). Shattered crystals are common in subaqueous pyroclastic deposits (Fisher, 1984). 211 li't/iicclasts is a term used to describe the dense components in a pyroclastic deposit. .They may be subdivided into non-veslculated juvenile vitric clasts (cognate lithics) and country rock which has been explosively ejected during eruption. If the latter comprises fragmental co-magmatic volcanic rocks from previous eruptions, they are termed accessory lithics. Fragments derived from the subvolcanlc basement, non-volcanic deposits around the vent area, or picked up locally during transport (e.g. mudstone rip-ups, massive sulphide clasts) are called accidental 1 ithics. Grain size classification of pyroclastic deposits (Table B. 1) consists of three main types: ash (< 2 mm), lapilli (2-64 mm), and bombs or blocks (> 64 mm) (Fisher, 1961; Schmid, 1981). Tuff is the consolidated equivalent of ash and is subdivided into fine and coarse grained varieties (Table B. 1). Also, for the purposes of this study only, lapilli is subdivided into fine and coarse lapilli (see Table B. 1). Mixture terms and end-member rock terms used for pyroclastic fragments are after Fisher (1966) and shown in Figure B. 1. Rock names for mixtures of pyroclastic and epiclastic fragments are after Schmid (1981) and are in Table B.2. B.3 'HOT''SUBAQUEOUS PYROCLASTIC FLOW DEPOSITS. BUTTLE LAKE CAMP - FACT OR FICTION Subaqueous pyroclastic flow deposits are the result of hot pyroclastic flows from land into water, or a consequence of a column collapse or voluminous 'boiling-over' type of eruption, both from underwater vents. Whether such flows remain hot during and after emplacement in a subaqueous environment is still quite controversial. Documented cases are few (cf. Fisher, 1984; Fisher and Schmincke, 1984) and even those are subject to dispute (Wright and Cas, 1986). Two critical aspects are necessary to substantiate such deposits, according to Wright and Cas (1986): 1) documentation of the depositional environment, and 2) evidence of hot emplacement. The first point is usually made on stratigraphic grounds whereas the latter is indicated by welding textures of shards and pumice, gas segregation pipes, or well-developed columnar jointing. Emplacement processes for hot pyroclastic flows in a subaqueous environment such that the flow remains hot are not well understood. Emplacement and subsequent welding probably involves the inhibition of volatile 212 TABLE B. 1 Granulomere classification of pyroclastic deposits (modified after Schmid, 1981). Clast size Pyroclast Pyroclastic deposit, consolidated block, bomb pyroclastic breccia, agglomerate 64 mm coarse lapillus coarse lapillistone 32 mm -fine lapillus fine lapillistone 2 mm coarse ash grain coarse tuff 0.1 mm fine ash grain fine tuff 213 Blocks and bombs > 64 mm Figure B.I: Mixture terms and end-member rock terms for pyroclastic fragments (after Fisher, 1966). TABLE B.2 Terms for mixed pyroclastic— epiclastic rocks (after Schmid, 1981). Average Pyroclastic Tuffites Epiclastic clast size (mixed pyroclastic — epiclastic) (volcanic and/or nonvolcanic) > 64 mm i 64 mm, > 2 mm i 2 mm, > 0.1 mm i 0.1 mm (i 1/256 mm) pyroclastic breccia, agglomerate lapillistone coarse tuff fine tuff tuffaceous breccia, tuffaceous conglomerate tuffaceous breccia, tuffaceous conglomerate tuffaceous sandstone tuffaceous siltstone tuffaceous mudstone breccia, conglomerate breccia, conglomerate sandstone siltstone mudstone Volume percent 100 to 75 % pyroclasts <• 75 to 25 % < 25 % 215 escape from the flow. Water surrounding a hot pyroclastic flow deposit could create a thin steam carapace around the flow during cooling(cf. Fisher, 1984). The presence of welded subaqueous pyroclastic flow deposits has been documented in Sicker Group lithologies within the Buttle Lake Camp. They mainly occur in the H-W Horizon and Ore Clast Breccia unit of the Myra Formation (Mine Sequence), and in the pyroclastic deposit units of the Thelwood Formation. These deposits were initially recognized in hand sample or drillcore by a marked primary planar orientation (eutaxitic texture) of relict pumice and cognate lithic clasts relative to overlying or underlying unwelded pyroclastic deposits. However, this texture alone apparently is not conclusive in defining a subaqueous welded deposit (Wright and Cas, 1986) as supposedly similar textures can be formed diagenetically. This would not explain the observation of why one pyroclastic flow deposit had suffered 'diagenetic flattening' and immediately surrounding deposits did not. Other diagnostic textures observed in the Buttle Lake Camp area (see section B.4) are compaction textures of crystals into relict vitric clasts and of relict shards against crystals and accessory lithic clasts, and fine feathery terminations of flattened pumice or cognate lithic clasts (a texture unlikely to have been produced by diagenetic flattening). The best evidence for a hot state during emplacement of these deposits is the presence of baked accidental lithic clasts in both the Myra and Thelwood Formation units. This is discussed separately below (also see section B.4). Subaqueous pyroclastic flow deposits in the H-W Horizon and Ore Clast Breccia unit of the Myra Formation contain up to 2 percent, massive sulphide clasts as part of their accessory lithic clast component. In unwelded deposits, these clasts comprise pyrite and sphalerite, and minor zoisite/clinozoisite and quartz. In welded pyroclastic flow deposits (or ones that display a marked flattened texture) the massive sulphide clasts contain pyrrhotite in equal or greater abundance than pyrite. The presence of pyrrhotite is the key because no massive sulphide deposit or feeder zone sulphide mineralization within the Buttle Lake Camp contains pyrrhotite. The only other documented occurrence of pyrrhotite in the Myra Formation is in some argillite beds where it is found as thin, discontinuous laminae alone or with pyrite. A probable explanation for the presence of pyrrhotite in massive sulphide clasts within the welded pyroclastic flow deposits is that it represents a conversion of pyrite to pyrrhotite due to high temperature (1 743° C at 10 bars: Kullerud and Yoder, 1959). Temperatures equal to or greater than 740*° C have been documented in subaeriai pyroclastic flow deposits (cf. Fisher and Schmincke, 1984). Thus the presence of pyrrhotite in the massive sulphide clasts corroborates the hypothesis of a hot state for the hosting subaqueous pyroclastic flow deposit. Subaqueous pyroclastic flow deposits in the Thelwood Formation also contain welded units though not they are not common. A key component of these deposits is tuffaceous mudstone rip-up clasts (up to 40 cm by 10 cm) which are commonly present in the basal portion of a flow unit. The rip-up clasts in unwelded subaqueous pyroclastic flow deposits generally are pale green-gray and composed of very fine grained quartz and feldspar, and minor epidote and/or chlorite. The same type of clast in welded pyroclastic deposits have undergone a moderate to strong pervasive epidote alteration resulting in a yellowish green colour that is most intense along the clast margins. This is attributed to hydrothermal alteration of a water saturated, partially lithified mudstone clast by a hot gaseous host, namely welding of a subaqueous pyroclastic flow deposit. 21 B.4 EXAMPLES OF TEXTURAL EVIDENCE FOR WELDED SUBAQUEOUS PYROCLASTIC  FLOW DEPOSITS. BUTTLE LAKE CAMP. VANCOUVER ISLAND Figure B.2: Welded, quartz+feldspar crystal rhyolite subaqeous pyroclastic flow deposit, H-W Horizon, Myra Formation, Price section. Sample displays a good eutaxitic texture. Brownish red clasts (s) are massive sulphide fragments (pyrrhotite+sphalerite). Scale divisions are in mm and cm. Figure B.3: Photomicrograph of welded sample in Figure B.2. Lensoidal clasts (fiamme) are flattened pumice or cognate lithic fragments. Note compaction texture of feldspar (f) and quartz' (q) crystals into the fiamme. Field of view is 3 mm x 4 mm. 218 Figure B.4; Photomicrograph of a welded, feldspar crystal subaqeous pyroclastic flow deposit, Lower Mixed Volcaniclastics, Myra Formation, Price section. Brown strands are strongly flattened pumice (fiamme). Note good compaction textures of feldspar crystals (c) into the fiamme. F ield of view is 3 mm x 4 mm. 219 Figure B.5: Tuffaceous mudstone rip-up clasts in (a) an unwelded subaqueous pyroclastic flow Jeposit, and (b) a welded subaqueous pyroclastic flow deposit, pyroclastic deposit unit, Thelwood Formation, Price Hillside. Note the difference in epidote content between the two. In the welded sample the mudstone clast suffered a pervasive epidote alteration, especially intense along the margin. This was not the case in the unwelded sample. The clast in the welded unit was only partly lithified prior to incorporation into the flow (as is shown by deformation of the sediment laminae, and by penetration of pyroclastic components into the clast margin). Scale divisions are in mm and cm. Figure B.6: Welded, subaqueous pyroclastic flow deposit, pyroclastic deposit unit, Thelwood Formation, Price Hillside. Sample displays a good eutaxitic texture caused by flattened pumice (fiamme: f) and felsic cognate lithic clasts (L). Scale divisions ore in mm and cm. figure B.7: Photomicrographs of welded sample in Figure B.6. Top photomicrograph shows feldspar crystal compacted into a deformed and flattened pumice clast. Bottom photomicrograph is of shattered feldspar crystals (c). Field of view in both photomicrographs is 3 mm x 4 mm. 222 APPENDIX C  ANALYTICAL PROCEDURES C.l SAMPLE SELECTION AND PREPARATION Chemical analysis of metavolcanic rock units in the Buttle Lake Camp helped to characterize similar rock types that occur at different stratigraphic intervals and to enabled the determination of the petrogenesis of the volcanic units. Samples were selected for whole rock X-ray fluorescence and atomic absorption analysis by concentrating on flow phases, either from massive flows, flow breccias, or coarse lapilli to pyroclastic breccia size clasts in volcaniclastic units. In some instances, pyroclastic flow deposits were also sampled. For- major lithologies, at least four samples of the same unit were taken: three from different localities in the mine area with a duplicate sample taken at one of the three sites. It was felt that this sampling pattern would give a more realistic idea of the chemical homogeneity or heterogeneity of a particular unit. Least altered samples were selected whenever possible but since the study is dealing with metavolcanic rocks, one has to be aware of possible element mobility suffered by the rock units and therefore limitations of the results of the analyses. This is discussed in Chapter 4. Once the samples were chosen they were reduced to a powder form (less than 200 mesh) for the appropriate analytical technique. Prior to crushing the samples, a study of sample contamination by grinding was undertaken (Hickson and Juras, 1986). In examining five types of sample-preparation apparatus commonly used in geological laboratories (tungsten carbide and chrome steel shatterboxes, an agate mortar, a corundum-ceramic handmill, and hardened steel-disk grinding plates) it was found that for this study the apparatus best suited for low contamination, relatively quick grinding time and ability to handle reasonable sample sizes was the tungsten carbide shatterbox. This method contributed Co,W and variable but minor Nb contamination. To prevent against cross contamination, the shatterbox was cleaned by grinding S1O2 sand for approximately one half the sample grinding time followed by cleaning with compressed air and nylon brushes. 223 C.2 X-RAY FLUORESCENCE The method chosen for whole rock major, minor and trace element analyses was pressed powder X-ray fluorescence (XRF). This technique was favoured over the fused disk method (for major element analyses only) because of a much simpler sample preparation, procedure. However in using pressed powder method, potential problems caused by the sample matrix may be encountered. Ensuring an even and fine (less than 200 mesh) grain size and multiplying the number of counts by the mass absorption coefficient correction can minimize this problem. Another potential problem for this method concerns moderately to strongly chloritic samples. It was found that in such samples the counts for theMg peak were at times anomalously high (N. Mortimer, oral communication 1986). Though the cause was not established, it probably reflected sensitivity to the grinding and pellet formation techniques (i.e. destruction of the chlorite structure during grinding, concentration of chlorite grains near or at the surface of the pellet). No other element was similarly affected. Samples that displayed such Mg anomalies were corrected by calibration with results from atomic absorption analysis (by N. Mortimer). The correction was applied to all mafic and intermediate volcanic rock samples. It was not applied to felsic volcanic (sericite and quartz dominant) and ultramafic volcanic (actinolite and pyroxene dominant) rock samples as, for these samples, atomic absorption check analyses corroborated the XRF values. Though these potential problems outlined above may favour arguments for having used the fused disk XRF method for the major elements, the results proved to be more than adequate for their intended use; to generally characterize the principal volcanic suites present in the Buttle Lake Camp. Petrogenetic interpretations solely relied on trace and minor element abundances (for which the pressed powder XRF method is commonly utilized) and observed phenocryst assemblages. Two separate XRF machines were used for the analyses. Most of the work was conducted on the fully automated Philips PW 1400 XRF unit in the Department of Oceanography at UBC. This' machine uses a rhodium tube and was operated by B.L. Cousens. The elements analyzed and operating conditions are given in Table C. 1. Three elements were analyzed using the Philips 1410 XRF unit in ABLE C. 1 X-ray fluorescence spectrometry machine parameters for major and trace element analyses. PEAK 26 BACKGROUND COUNT TIMES ELEMENT LINE FILT COLL DET XTL UPL LWL Kv Ma II ANGLE' ' +OFF -OFF PEAK / BACKt Rh Tube PW 1400 S i Ka No C ' F • T / RAP 80 20 60 40 7 126A 32 230 2 30 0 00 40 20 T i Ka No C F L i F 200 75 25 60 40 2 750A 86 2 70 0 OO 1 o o 40 20 A l Ka No C F TIRAP 80 20 60 40 8 339A 37 875 1 0 0 0 00 40 20 Fe Ka No C F L i F 200 85 15 60 40 1 937A 57 670 0 00 1 60 40 20 Mn Ka No C F L i F 200 75 15 60 40 2 103A 63 210 1 50 0 00 40 20 MQ Ka No C F TIRAP 80 20 30 60 9 889A 45 210 0 0 0 1 20 80 40 Ca Ka No f • F L i F 200 80 20 60 20 3 360A 1 13 160 1 40 0 00 40 20 Na K a No C F TIRAP 80 20 30 60 1 1 909A 55 250 0 0 0 1 70 80 40 K Ka No f L i F 200 80 20 60 40 3 744A 136 775 2 0 0 0 00 40 20 P Ka No C F Ge 80 20 30 60 6 15SA 14 1 120 0 00 1 50 10O 40 Ba La No f F L i F 200 80 20 60 40 2 776A 87 220 1 20 0 00 100 50 Co Ka NO f F L i F 220 80 20 60 40 1 791A 77 955 0 54 0 54 100 50 C r Ka No C F L i F 200 80 20 60 40 2 291A 69 520 1 0 0 0 00 40 20 Cu Ka Yes C F S ' L i F 200 80 20 60 40 . 1 542 A 45 0 6 0 0 00 0 62 40 20 Nb K a NO f S L i F 200 62 20 60 40 0 748A 21 430 0 40 0 40 100 40 N i Ka No f F S L i F 200 80 20 60 40 1 659A 48 670 1 20 0 60 40 20 RD K a No f S L i F 200 80 20 60 40 0 927A 26 660 0 40 0 90 100 50 S r Ka No f s L i F 200 75 25 60 40 0 877A 25 175 0 60 0 60 40 20 V Ka No c F L i F 200 80 20 60 40 2 505A 77 135 4 0 0 2 60 40 20 Y Ka No f 5 L i F 200 80 20 60 40 0 831A 23 BOO 0 60 0 60 50 20 Zn Ka No f F S L i F 200 80 20 60 40 1 437A 4 1 810 0 72 0 OO 40 20 Z r Ka No f S L i F 200 80 20 60 40 0 78BA 22 580 0 74 0 74 50 20 Mo Tube PW 1440 La L a . NO f F L i F 200 81 30 60 50 2 665A 82 970 1 23 0 40 100 10O Ce No f F L i F 200 81 30 60 50 2 56 1A 7 1 680 0 58 0 0 0 100 100 Nd L a , No f F L i F 200 8 1 30 60 50 2 370A 72 120 0 00 0 68 100 t o o t B a c k g r o u n d coun t t i m e s a r e the same f o r b o t h p o s i t i v e and n e g a t i v e o f f s e t s . 1 ( C o u r s e c o l l i m a t o r ' ) F i n e c o l l i m a t o r 1 ) F low c o u n t e r *) S c i n t i l a t i o n c o u n t e r the Department of Geological Sciences at UBC. These elements, Ce, La and Nd, were analyzed using a molybdenum tube. Machine conditions are given in Table C.I. For both XRF units, tracings of the peaks to be analyzed were taken and the peak and background counting positions optimized to achieve the best peak to background (signal to noise) ratio. C.2.1 PELLET FORMATION Three grams of powder were weighed out on a Mettler Balance to an accuracy of ± 0.1 gm. The powder was placed in a paper cup and three drops of polyvinylalcohol (PVA) binder was added and mixed thoroughly using a spatula. The sample was then placed in a piston apparatus and hand pressed into the desired shape with a follower placed in the piston chamber. The follower was removed and the chamber filled with « 5 cm 3 (1 tsp) of boric acid which acts as a casing along the sides and back of the pellet giving it extra strength. A piston was then placed in the chamber and the apparatus was put into a hydraulic press. The sample powder was subjected to a pressure of approximately 300 MPa for approximately 2 minutes. The pellets were stored in single layers in box tops, rock powder side up and covered with tissue paper. C.2.2 ACCURACY, PRECISION AND DETECTION LIMIT The actual numerical value for the concentration of an element in a sample is determined by comparison to a set of standards of known composition. The standards were chosen so that they bracketed the entire range of compositions expected in the unknowns. The data was reduced using a calculated regression line from the net counts obtained (after corrections) versus the known composition. The composition of the unknown samples was then calculated from the regression estimate. The procedure for the trace and major elements vary slightly from each other. Both determinations use a correction based upon the mass absorption coefficient (MAC). The MAC for the trace elements is calculated from the previously determined major elements. Since this is not the case for the major elements themselves the uncorrected counts for all major elements being analyzed are TABLE C.2 Major element calibration, n r s t line of each element is the regression estimate of tne composition for each standard. Tne second line gives tne reference values for the concentration of the element in the standard. The third sine is the difference between the reference concentration ana the calculated concentration for each standard. O x i d e AGV-1 W-1 GA GH SY -2 BHVO-1 GSP-1 J G - 1 NIM-N J B - 1 BCR-1 G-2 NIM-G MRG- 1 N I M - i OLQ-1 S i O , 60 . 87 52 . 17 69 . 84 74 .92 60 .91 47 . 32 68 .20 69 .70 51 .50 52 . 72 54 .74 71 .87 75 .32 38 .54 65 .57 66 .58 59 .61 52 . 72 69 . 95 75 .85 60 . 10 49 .90 67 .32 72 .35 52 .64 52 .60 54 .53 69 .22 75 . 70 39 . 32 63 . 63 65 .93 1 . 26 -0 . 55 -0 . 1 1 -0 .93 0 .81 -2 . 58 0 .88 -2 .65 - 1 . 14 0 . 12 0 .21 2 .65 -0 . 38 - 0 . 78 1 .94 0 .65 Al , 0 , 18 .08 15 . 10 14 . 12 12 .91 12 .30 15 . 32 14 .53 14 . 86 16 .60 14 .69 13 .75 13 .52 12 .46 10 .02 15 .31 15 .43 17 . 19 15 .02 14 .51 12 .51 12 . 12 13 .85 15 .28 14 .20 16 .50 14 .62 13 . 72 15 .40 12 .08 8 .50 17 . 34 16 . 37 0 .89 0 .08 -0 .39 0 .40 0 . 18 1 .47 -0 .75 0 .66 0 . 10 0 .07 0 .03 - 1 .88 0 . 38 1 .52 -2 .03 - 0 . 94 F e , 0 , 6 88 10 69 2 .71 1 . 58 6 .02 12 . 3 1 3 .81 2 .40 9 .02 9 .42 13 . 17 2 . 50 2 O O 17 . 27 1 .51 4 . 53 6 .81 1 1 .09 2 .83 1 .34 6 . 28 12 . 23 4 .28 2 . 17 8 .90 9 .04 13 .42 , 2 .67 2 .04 17 .82 1 .40 4 .29 0 .07 -0 .04 -0 . 12 0 .24 -0 .26 0 .08 -0 .47 0 .23 0 . 12 0 .38 00 . 25 - 0 . 17 -0 .04 -0 .55 0 . 1 1 0 . 24 MgO 0 . 0 6 .20 1 57 0 .08 2 83 6 .98 1 .29 1 .64 7 .25 7 . 18 3 .01 1 . 1 1 0 . 13 13 . 49 0 .58 0 .88 1 . 52 6 63 0 .95 0 .03 2 .70 7 .31 0 .97 0 .76 7 . 50 7 .76 3 .48 0 .75 0 .06 13 .49 0 46 1 .04 • - 1 . 52 -0 43 0 62 0 .05 0 13 -0 33 0.032 0 .88 -0 . 25 -0 . 58 -0 . 47 0 .36 0 .07 0 .00 0 12 - 0 16 CaO 4 . 38 10 82 2 . 75 0 .93 7 67 1 1 .50 2 24 2 .63 1 1 . 87 8 98 6 .89 2 .00 0 . 96 14 15 0 79 3 43 4 95 10. 98 2 . 45 0 69 7 98 1 1 . 33 2 .03 2 . 17 1 1 .50 9 35 6 97 1 .96 0 78 14 77 0 68 3 24 -0 .57 -0 16 0 30 0 24 -0 . 31 0 . 17 0 .21 0 .46 0 .037 - 0 37 -0 .08 0 .04 0 . 18 -0 62 0 1 1 0 19 Na ,0 4 . 4 4 2 43 3 . 21 3 . 79 4 . 37 2 73 2 69 3 . 10 2 .69 2 68 3 39 3 64 3 45 0 67 0. 39 4 . 36 4 . 32 2 . 15 3 . 55 3 . 85 4 34 2 29 2 81 3 39 2 .46 2. 79 3. 30 4 . 06 3 36 0 7 1 0. 43 4 . 23 o 12 0. 28 -0 . 34 -0 .06 0. 03 0 .44 -0 . 12 3 . 39 2 .46 2 . 79 3 . 30 4 . 06 3 36 0. 7 1 -o . 04 0. 13 K , 0 2 88 0. 65 4 16 5 .02 4 . 15 0 48 5 55 4 46 0 . 25 1 38 1 . 63 4 . 17 4 . 97 0. 17 15 41 3 . 49 2 . 92 0. 64 4 03 4 76 4 . 48 0 54 5 51 3 96 0 .25 1 . 42 1 . 70 4 . 46 4 .99 0. 18 15. 35 3 . 49 -0 04 O. 01 0. 13 0 26 - 0 . 33 -0 06 0 04 0. 05 -0 OO - 0 . 04 - 0 . 07 - 0 . 29 ' -0 02 -o 01 0 . 06 -0 13 T i O , 1 .06 1 . 02 0. 40 0 09 0. 1 1 2 . 75 ' 0. 67 0. 37 0 . 18 1 . 33 2 . 19 0 . 44 0 . 10 3 55 0 . 0 0 . 64 1 06 1 . 07 0. 38 O 08 0 14 2 69 0. 66 0. 27 0 . 20 1 . 34 2 . 26 0 . 48 0 09 3 . 69 0 . 04 0 . 64 -0 00 -0 05 0. 02 0. 01 - 0 . 03 0. 06 0. 01 0. 10 -0 02 - 0 . 01 - 0 . 07 - 0 . 04 0. 01 - 0 . 14 - 0 . 04 0 . 02 MnO 0. 10 0. 16 0. 09 0. 06 0 32 0 17 0. 04 0. 08 0 19 0. 15 0. 18 0 . 03 0 02 0 . 15 0 01 0 . 10 0. 10 0. 17 0. 09 0 05 0. 32 0 17 0. 04 0. 06 0 . 18 0. 15 0. 18 0. 03 0 02 0. 17 0 . 01 0 . 09 -o . OO -o . 01 - 0 . 00 0. 01 0. 00 - 0 . 00 - 0 . 00 0 02 0 .01 - 0 . 00 - 0 . OO - 0 . 00 0. 00 - 0 . 02 0. 00 0 . 01 0. 52 0. 17 0. 16 0. 01 0. 42 0 . 20 0. 29 0. 14 0 02 0. 27 0. 36 0. 14 0. 01 0 . 06 0. 12 0. 22 0. 51 0. 14 0. 12 0 01 0. 43 0 28 0. 28 • 0 . 09 0. 03 0 . 26 0 . 36 0 . 13 0 01 o. 06 .0. 12 0 26 0. 01 0. 03 0. 04 o. 00 -0 . 01 - 0 . 08 0. 01 0. 05 - 0 . 01 0. 01 l - 0 . OO O. 01 0. OO 0. OO 0. 00 - 0 . 04 ro ro first compared to the calibration curve then a MAC is calculated for each element. This is repeated in an iterative process until the results converge. Results for the standards used in the major element calibration are"Tound in Table C.2. The difference between the recommended value and the calculated value (Table C.2) is a measure of the error in the determination. Results for the standards used in the trace elements calibrations as well as the correlation coefficient and standard deviation are found in Table C.3. Plots of calibration lines for trace elements analyzed are found in Hickson (Appendix B: 1986). Precision is strongly influenced by the counting error. This error depends only on the total accumulated counts and represents the maximum possible precision that can be obtained. Other potential errors affecting precision include device errors from short and long term fluctuations and drift in the actual instrumental conditions, operational errors from the non-reproducibilily of instrumental conditions, and specimen errors from surface abnormalities, grain size heterogeneities, and packing problems to name a few. In an effort to assess these combined errors sixteen pressed powder pellets of a homogenized rock powder were.prepared. These pellets were distributed throughout the unknown samples in the XRF run and treated as unkowns. The accumulated statistics are shown in Table C.4. In terms of ppm or wt.* the replicate analyses for Ce, Nd, and P2O5 have relative errors greater than 10 percent, AI2O3, Co, Cu, Rb, Y, and Zn have relative errors between 5 and 10 percent, and the rest of the elements analyzed have relative errors of less than 5 percent. The discrepancies between the errors calculated for concentrations and in terms of counts is thought to be due to a combination of roundoff errors and peculiarities in the calibration lines and corrections. Another method to estimate the precision is by using duplicate samples (Thompson and Howarth, 1973, 1978). Using a method derived for less than 50 samples (Thompson and Howarth, 1978) indicates that the measured level of precision is a reasonable approximation for most elements over the concentration range measured. The measured level of precision appears too low for K2O, MgO and Rb, and Cr at low concentrations (< 5 0 ppm). The results of this statistical analysis are found in Hickson (Appendix B: 1986). 228 TABLE C.3 Trace element regression analyses. Heading abbreviations are: REPORTED ppm = ppm values as reported by Steel etal. (1978), Gladney etat(\<&Z\ Abbey (1983) and Govindaraju (1984); CALCULATED ppm = calculated ppm value after corrections, ± value represents the counting error (in percent). Detection limits are in ppm. Values were calculated using the computer program TRACERED (Hickson, 1986). Ba: slope = 6.0264 intercept = -21.2878 r = 0.99811 la = 37.048 STANDARD REPORTED ppm CALCULATED ppm DETECTION LIMIT AGV-1 1221 1232 ± 0.8 % 11.4 W-1 162 167 ± 2.9 % 9.4 GA 850 813 ± 1.0 % 11.9 SY-2 460 454 ± 1.6 % 12.9 BHVO-1 135 113 ± 2.9 % 7.8 GSP-1 1270 1307 ± 0.8 % 12.0 NIM-N 102 95 ± 5.0 % 10.7 JB-1 490 561 ± 1.3 % 10.3 G-2 1880 1818 ± 0.6 % 12.7 NIM-G 120 111 ± 4.1% 10.0 MRG-1 50 24 ± 3.4 % 3.5 DR-N 390 392 ± 1.6 % 11,1 BE-N 1061 1103 ± 0.9 % 12.5 Ce: slope = 0.2405 intercept = 5.6936 r - 0.93820 . 1<T. = 26.331 STANDARD REPORTED ppm CALCULATED ppm DETECTION LIMIT AGV-1 71 73 ± 8.7 % 11.9 W-1 25 63 ± 10.8 % 5.2 SY-2 210 155 ± 4.3 % 16.5 BHVO-1 39 30 ± 26.1 % 20.3 JB-1 87 59 ± 11 A % 14.9 G-2 160 183 ± 3.3 % 9.4 NIM-G 200 213 ± 0.0 % 12.7 MRG-1 25 32 ± 25.9 % 12.9 GH 50 51 ± 10.9 % 10.6 BCR-1 53 41 ± 17.1 % 17.8 Standards NlM-N and NIM-S were analyzed also but gave negative net peaks. 229 TABLE C.3 (continued) Cr: . slope = 0.1889 intercept = -12.1854 r - 0.99766 1* = 12.584 STANDARD - REPORTEDppm CALCULATED ppm DETECTION LIMIT A6V-1 12 11 ± 3.7 % 1.0 W-1 120 130 ± 1.1 % 2.7 6A 12 15 ± 4.4 % 1.2 SY-2 12 11 ± 5.5 % 1.5 BHVO-1 300 277 ± 0.7 % 3.7 6SP-1 13 12 ± 5.0 % 1.5 JB-1 400 400 ± 0.5 % 3.4 6-2 9 9 ± 5.3 % 1.1 NIM-G 12 15 ± 5.0 % 1.3 MRG-1 450 476 ± 0.5 % 3.7 NIM-S 12 18 4.8 % 1.3 DR-N 42 40 ± 2.3 % 2.0 BE-N 381 361 ± 0.6 % 3.4 Cu: slope = 1.1954 intercept = -6.2152 r = 0.97953 1<T =9.833 STANDARD REPORTED ppm CALCULATED ppm DETECTION LIMIT AGV-1 60 61 ± 3.0 % 3.4 W-1 114 123 ± 2.4 % 5.3 GA 18 19 ± 7.7% 2.7 BHVO-1 140 127 + 2.5 % 6.6 GSP-1 34 33 ± 5.3 % 3.8 NIM-N 14 9 ± 15.8 % 5.0 JB-1 56 60 ± 4.0 % 4.6 G-2 11 7 ± 13.9% 3.4 MRG-1 135 124 ± 2.9 % 7.8 NIM-S 19 17 ± 8.9 % 3.8 DR-N 50 47 ± 4.9 % 5.1 BE-N 61 84 ± 3.1 % 3.7 Standard SY-2 was analyzed also but calculated value was equal to or less than the detection limit. La: slope = 0.1956 intercept = -10.7174 r = 0.99164 1* =5.063 STANDARD REPORTEDppm CAtCULATED ppm DETECTION LIMIT AGV-1 38 39 ± 5.9 % 3.4 W-1 10 6 ± 16.9 % 2.6 BHVO-1 17 17 ± 10.8 % 2.9 JB-1 36 45 ± 5.2 % 2.7 G-2 92 92 ± 2.9 % 3.4 NIM-G 105 100 ± 2.6 % 3.5 MRG-1 10 13 ± 14.2 % 2.3 BCR-1 27 29 ± 7.4% 3.1 Standard NIM-N was analyzed also but calculated value was equal to or less than the detection limit. 230 TABLE C.3 (continued) Nb: slope = 2.3676 intercept = -0.8524 r = 0.93390 Iff = 2.642 STANDARD , _ ; REPORTED ppm CALCULATED ppm DETECTION LIMIT AGV-1 15 16 ± 4.0 % 1.2 W-1 8 1 ± 10.1 % "1.7 GA 10 14 ± 4.2 % 0.9 SY-2 23 18 ± 4.2 % 2.0 BHVO-1 19 20 ± 3.8 % 1.5 GSP-1 25 26 ± 2.6 % 1.3 G-2 13 12 ± 4.7 % 1.3 MRG-1 20 21 ± 4.1 % 1.6 DR-N 6 7 i 9.5 % 1.2 Standards NIM-N and .NIM-S were analyzed also but gave negative net peaks. Nd: slope = 0.2267 intercept = -5.8817 r = 0.93413 la = 7.883 STANDARD REPORTED ppm CALCULATED ppm DETECTION LIMIT AGV-1 37 30 ± 7.6% 5.4 W-1 15 15 ± 15.0 % 4.4 GA 25 23 ± 9.3 % 4.5 SY-2 71 66 ± 4.1 % 5.3 BHVO-1 42 19 ± 12.5 % 5.9 NIM-N 2 8 ± 23.4% 0.7 JB-1 21 26 ± 8.9 % 3.6 G-2 58 43 ± 5.2 % 5.6 NIM-G 68 86 ± 3.5 % 4.3 MRG-1 19 25 ± 11.6 % 4.3 GH 25 23 ± 8.7 % 4.2 BCR-1 26 28 ± 9.0 % 4.5 NIM-L 45 61 ± 3.8 % 3.1 Standard NIM--S was analyzed also but gave a negative net peak. Ni: slope = 0.2852 intercept- 1.7714 r = 0.99739 Iff = 6.888 STANDARD REPORTED ppm CALCULATED ppm DETECTION LIMIT AGV-1 17 21 ± 5.6 % 1.8 W-1 75 88 ± 2.1 % 2.5 GA 7 . 6 ± 9.4% 1.3 SY-2 10 16 ± 5.6 % 1.1 BHVO-1 120 121 ± 1.7 % 3.1 GSP-1 10 7 ± 7.0 % 1.3 NIM-N 120 110 ± 1.6 % 3.1 JB-1 135 127 ± 1.4 % 3.0 G-2 5 4 ± 11.2 % 1.1 NIM-G 8 7 ± 5.5 % 0.8 MRG-1 195 187 ± 1.4 % 3.9 DR-N 16 17 ± 8.0 % 2.4 BE-N 296 304 ± 0.9 % 3.0 Standard NIM-S was analyzed also but gave a negative net peak TABLE C.3 (continued) Rb: slope = 4.3236" intercept = 4.3318 r = 0.99954 la =3.402 STANDARD REPORTED ppm CALCULATED ppm DETECTION LIMIT A6V-1 67 65 ± 1.4 % 1.7 W-1 21 21 ± 5.3 % 2.1 6A 175 174 ± 0.6 % 1.5 SY-2 220 227 ± 0.5 % 1.6 BHVO-1 10 8 ± 20.4 % 4.1 6SP-1 255 252 ± 0.4 % 1.5 JB-1 41 40 2.5 % 1.9 6-2 170 166 ± 0.6 % 1.5 NIM-G 320 319 ± 0.3 % 1.4 DR-N 70 70 ± 1.4 % 1.8 BE-N 43 48 ± 2.5 % 2.0 Standards NIM-N and MRG-1 were analyzed also but NIM-N gave a negative net peak whereas the value for MRG-1 was equal to or less than the detection limit. Sr: slope = 59.5417 intercept = 3.6448 r = 0.99835 1» = 10.497 STANDARD REPORTED ppm CALCULATED ppm DETECTION LIMIT AGV-1 662 668 ± 0.3 % 2.1 W-1 187 181 ± -1.0 % 2.6 GA 310 312 ± 0.5 % 1.9 SY-2 275 271 ± 0.6 % 2.3 BHVO-1 418 391 ± 0.6 % 2.7 GSP-1 240 239 ± 0.6 % 2.0 NIM-N 260 263 ± 0.7 % 2.2 JB-1 440 455 ± 0.5 % 2.2 G-2 478 474 ± 0.4 % 1.9 NIM-G 10 13 ± 10.2 % 2.0 MRG-1 260 271 ± 0.8 % 2.7 NIM-S 62 66 ± 1.9 % 2.0 DR-N 400 398 ± 0.5 % 2.3 V: slope = 0.9759 intercept = -35.2562 r = 0.99655 la = 9.382 STANDARD REPORTEDppm CALCULATED ppm DETECTION LIMIT AGV-1 123 123 ± 0.5 % 0.6 W-1 260 265 ± 0.5 % 1.3 GA 38 32 ± 1.0 % 0.6 SY-2 52 50 ± 1.5 % 1.3 BHVO-1 320 325 0.3 % 0.9 GSP-1 53 48 ± 0.8 7, 0.6 NIM-N 220 208 + 0.8 % 2.3 JB-1 210 196 ± 0.5 % 1.0 G-2 36 44 0.9 % 0.5 NIM-S 17 31 ± 2.3 % 0.7 DR-N 230 225 ± 0.5 % 1.2 BE-N 244 256 ± 0.3 % 0.7 232 TABLE C.3 (continued) Y: slope = 1.5253 intercept = 7.4486 r = 0.89513 la = 2.846 STANDARD' REPORTED ppm CALCULATED ppm ' DETECTION LIMIT A6V-1 21 23 ± 3.3 % 1.6 W-1 25 23 ± 5.8 % 3.0 6A 21 26 ± 2.0 % 0.8 BHVO-1 27 26 ± 5.8 % 3,2 6SP-1 29 30 ± 1.6 % 0.9 JB-1 26 25 ± 4.3 % 2.3 6-2 11 15 ± 2.7 % 0.6 MR6-1 16 15 ± 15.1 % 5,0 NIM-S 20 17 ± 1.1 % 0.4 DR-N 30 27 ± 3.5 % 2.1 BE-N 30 31 ± 4.1 % 2.5 Standard NIM-N was analyzed also but calculated value was equal to or less than the detection limit. Zn: slope = 1.7488 intercept = -1.2199 r - 0.99030 1<r - 6.337 STANDARD REPORTED ppm CALCULATED ppm DETECTION LIMIT A6V-1 88 84 ± 1.8 % 3.1 W-1 84 90 ± 2.1 % 3.5 6A 80 73 ± 1.9 % 3.0 BHVO-1 105 101 ± 2.0 % 4.2 GSP-1 103 106 ± 1.4 % 2.8 NIM-N 68 60 ± 2.8 % 4.0 JB-1 84 87 ± 2.0 % 3.4 G-2 85 82 ± 1.7 % 2.9 NIM-G 50 48 ± 2.6 % 2.7 MRG-1 190 184 + 1.4 % 5.0 NIM-S 10 18 ± 6.9 % 1.5 DR-N 145 148 ± 1.3 % . 3.5 BE-N 120 131 ± 1.6 % 3.6 Zr: slope = 27.1220 intercept = 7.1767 r = 0.99329 Iff = 16.000 STANDARD REPORTED ppm CALCULATED ppm DETECTION LIMIT AGV-1 225 242 ± 0.5 % 1.5 W-1 100 99 ± 1.1 % 2.0 GA 150 153 ± 0.6 % 1.6 SY-2 280 . 273 ± 0.5 % 2.2 BHVO-1 180 176 ± 0.7 ?. 2.0 GSP-1 530 510 0.3 % 2.0 NIM-N 23 17 ± 3.0 % 1.4 JB-1 155 146 ± 0.7 % 1.8 G-2 300 314 t 0.4 % 1.6 NIM-G 300 276 t 0.4 % 2.0 MRG-1 105 11 1 ± 1.2 % 2.1 NIM-S 33 22 4.6 % 3.1 DR-N. 125 132 ± 0.8 % 1.7 BE-N 270 305 + 0.4 % 1.6 TABLE C.4 Results of sixteen replicate sample analyses. PPM B a Co C r Cu Mn Nb NI Rb S r V Y Z n Z r C a N d 277 58 365 25 1245 19 120 11 430 154 18 IOO 120 65 28 28 j 19 283 47 367 25 1247 20 125 11 447 145 20 97 126 54 59 25 63 272 58 370 25 1259 20 143 11 462 158 19 1 17 124 59 54 28 18 267 53 376 28 1258 19 130 13 448 159 18 101 1 19 52 56 3 1 23 278 60 371 25 1250 18 135 11 452 146 19 104 126 55 41 26 27 288 55 370 26 1248 20 124 11 436 145 17 98 120 60 65 26 30 278 53 370 28 1252 20 127 12 442 149 18 103 120 57 60 29 29 277 47 365 24 1247 19 126 12 437 161 17 99 122 48 38 25 30 284 50 376 23 1266 19 124 13 435 159 17 96 1 17 51 46 28 26 278 5 1 376 30 1249 19 137 13 454 152 19 108 125 65 55 23 23 284 5 t 382 27 1255 20 123 11 431 147 18 99 1 19 62 43 24 24 274 52 373 26 1256 20 126 12 446 153 20 103 126 28 55 36 26 ?? 54 370 28 1248 20 124 1 1 434 150 17 97 122 57 58 32 30 287 52 37 1 28 1236 19 124 11 439 173 18 IOO 12 1 49 63 26 19 285 56 376 26 1264 19 129 12 446 151 24 lO I 12 1 56 31 20 282 59 372 20 1245 19 126 1 1 426 152 18 98 120 44 48 X 279 . 6 53 5 37 1 . 9 25 9 125 1 . 6 19.4 127.7 116 441 .6 153.4 18.6 lO I . 3 121 .7 52.4 26 19 SD 5 8 4 . 0 4 5 2 . 4 7 . 7 0 6 6 . 0 0.8 9 8 7 3 1 .7 5.2 2.8 9.83 10 .65 tX 2 1 7 5 1 2 9 . 3 0 6 3 . 1 4 . 7 6 9 2.2 4.85 9 4 5. 1 2.3 18. 76 40 66 C T S Ba Co C r Cu Mn Nb N i Rb S r V V Zn Z r C e N d 66 48 1709 3 1 6646 86 248 20 1499 1885 56 270 740 14 10 12 25 67 39 1708 29 6623 87 245 19 1482 1852 63 251 736 12 6 32 19 65 47 1720 30 6663 91 283 18 1576 1893 59 310 754 13 13 12 18 64 43 1745 33 6630 87 262 26 1524 1893 56 226 724 11 12 14 16 66 49 172 1 30 6628 82 272 19 1540 1856 58 276 758 12 12 16 18 68 45 1720 31 6635 90 250 19 1486 1850 53 260 725 12 9 15 16 66 43 17 16 33 6636 92 256 21 1508 1860 67 272 729 10 15 17 16 66 39 1708 28 6651 84 250 20 1459 1901 53 256 718 13 9 17 18 67 4 t 1737 28 666 1 84 249 24 1475 1894 S3 254 708 13 14 17 15 66 4 t 1743 34 6607 82 269 23 1504 1870 58 278 737 10 8 16 16 67 42 1761 32 6628 90 249 20 1468 1852 55 263 720 11 to 18 17 65 42 1720 31 6608 92 253 21 1508 1869 62 271 751 14 13 15 15 777 44 1724 33 6648 91 250 18 1480 1877 52 258 733 14 13 15 16 68 43 1747 33 6622 86 251 19 1508 1946 68 , 266 738 6 14 18 16 67 45 1729 31 6638 85 257 21 1504 1855 777 265 726 13 12 67 48 1738 25 6650 88 257 20 1463 1876 57 263 725 11 13 X 66 44 1728 31 6636 87 256 20 1499 1877 58 265 733 1 1 .56 16 67 SD 1 3 16 2 17 3 10 2 30 25 6 17 14 2.31 3 . 82 *% 1 . 7 7 1 1 O 7 7 3 3 9 4.1 10. 7 2.0 1.3 10.3 6.5 1 9 20.0 2 1 .0 r , TABLE C.4 (continued) wt. •/. Fe >0> MnO TIO. CaO K .0 SIO. A l . 0. MgO NarO P . O . 12 .81 0 . 16 1 .58 8 .89 0 79 46. 82 16. 29 B 14 4.21 0. 34 11 .96 0 16 1 .59 8 .96 0. 79 47. 86 16. 23 8 .04 4 06 0.34 1 1 .91 0 . 16 1 . 58 8 91 0. 79 47. 93 16. 11 8 . 16 4 .13 O 31 1 92 0 15 1 .53 8.78 0. 76 49. 14 15. 51 7 86 4 .02 0 33 1 1 . 76 O . 16 1 58 8.90  79 48 41 15 99 7 .94 4.14 0 34 12 .65 0 . 15 1 52 8.70 0 76 48. 56 15. 41 7 .86 4 .07 0. 33 1 1 88 0 . 17 1 .68 9 . 26 O. 8 1 45 . 82 17 . 27 8 .52 4 26 O 35 12 . 76 O . 16 1 .60 9.02 0. 79 46 . 54 16 39 8 .21 4 . 22 0 33 1 1 . 75 O . 16 1 6 1 9 08 0. 79 47 . 21 16 52 B 28 4 . 27 O 34 1 1 .96 0 . 17 1 67 9.26 0. 81 45 16 17 . 49 8 74 4 39 0 36 1 1 9 1 O . 15 1 54 8 73 0. 76 49. 01 15 52 7 99 4 06 0. 34 1 1 .82 0 .14 1 . 45 8 46 0. 74 5 1 . 4 1 14 37 7 48 3 8 1 O. 32 1 1 . 97 0 17 1 69 9 . 32 0. 82 44 . 89 17 . 68 8 64 4 49 O 35 1 1 . 70 0 . 15 1 .49 8 6 1 0. 76 50 29 14 . 96 7 83 3 89 0 33 1 1 . 85 0 . 16 1 60 8 97 0. 79 47 . 47 16. 36 8 . 27 4 20 0 34 1 1 . 26 0 . 15 1 .47 8 59 0. 75 51 . 27 14 . 75 7 . 57 3 87 0.33 X 11. 992 0. 157 1 574 8 902 0. 78 1 47.987 16 053 8.< 096 4 . 130 0.31937 so 0. 409 0.0086 0.07 1 0.251 0.0233 1 .955 O 946 0 35 0 1837 0.0724 *•/. 3 4 5 . 4 4 5 2 8 3 1.0 4 I . 1 S >.9 4 .3 4 .5 22 7 n e t / c t s Fe • Q i MnO T IO I CaO K .0 SIO, A l . O i MgO Na.O P . O . 66809 6560 17867 I 1226 2286 19268 14951 3937 968 1 121 70105 6543 17916 1 IOO 3 2 173 16741 14861 3874 964 1 107 64970 6603 1804 1 1 1033 2158 1694 1 14873 3928 968 1 1 10 65328 6529 17919 10986 2167 17069 14610 3822 937 1 105 65735 6552 17949 1 1019 2 170 17 190 14728 3931 960 1108 67662 6575 17895 1 11 19 2157 17965 14788 3895 96 1 1 103 65250 6566 17993 1 104 1 2174 17427 14732 3832 966 1093 72220 6543 17962 1 1 157 2 172 17848 14892 3913 973 1 105 61985 6560 17986 10917 2134 15851 14550 3868 939 1075 68744 6524 17924 1 1022 2169 16494 15567 3846 955 1047 63447 6539 17848 1 1019 2138 16691 14589 3894 969 1072 62403 6576 17945 10942 2154 15614 14862 3978 963 11 16 68050 6596 18094 1 1 122 2168 17972 14984 3996 973 1 131 6 1497 6572 178 16 10858 2 155 15370 14575 3851 966 1077 7 1 135 6566 17954 11249 2181 19529 14819 3943 966 1112 68616 6584 17929 1 1 182 2184 18751 ' 14918 4027 962 1 130 X 66497 6562 17940 1 1056 2171 17295 14762 3908 962 1 101 SD 3245 23 69 1 1 1 34 1221 160 60 10 23 t% 4 9 .4 .4 1 OO 1 .6 7 . 1 ,1 . 1 1 5 1.1 2.1 A third method to assess the precision of the results is to mix two compositionally different samples in exactly 1:1 proportions and homogenize the powder well. The resulting mixture should analytically represent the mean of the two separate samples. In this study this was done by mixing powders from both a basalt sample and rhyolite sample. The results are shown in Table C.5. Most elements show consistent results with differences of less than 5%. As with the Thompson-Howarth test, MgO is inconsistent but K2O and Rb show agreement whereas the result for Cu is poor. The detection limit is directly dependent in the counting error and is defined as the ratio of signal to noise that is twice the standard deviation (Thompson and Howarth, 1973). Equations used and their derivations are in Hickson (Appendix B: 1986). The lower limit of useful determinations (confidence limit) is about three times the detection limit or six standard deviations of tne background count-rate. As the detection limit is approached the counting error becomes large becoming the chief source of error in the analysis. For this reason and also because of variable matrix make-up from sample to sample, the detection limit should ideally be calculated for each sample. However when deal ing with a similar set of rocks a representative sample may suffice. The standards used in this study represent such a suite and detection limits calculated for them (Table C.3) are taken as representative for the analysis. C.3 ATOMIC ABSORPTION PROCEDURE FOR THE DETERMINATION OF RARE EARTH ELEMENTS C.3.1 INTRODUCTION Rare earth elements (REE) are a group of fifteen elements with similar chemical properties. Consequently the association of distinctive REE abundance patterns with specific minerals and geochemical processes enable them to be used as tracers in various geologic studies. The use of REE in the geological samples however has been limited by the necessity of using either neutron activation or mass spectroscopy for their determination. Facilities for such analyses are not common and commercial analyses are expensive. Routine analysis of rock samples by atomic absorption (AA) and 236 TABLE C.5 Results of mixed sample analysis. Sample Dl 412A is a quartz + feldspar porphyritic meta-rhyolite and sample 5104 is an alkali olivine basalt. Sample D1412A 5104 Mix Calculated Mean Difference % S1O2 (wt.S) 69.93 44.85 58.00 57.24 -0.76 0.13 Ti02 0.24 2.64 1.32 1.44 0.12 8.33 AI2O3 14.07 14.81 14.66 14.44 -0.22 1.52 Fe203 4.17 13.55 8.42 8.87 0.45 5:07 MnO 0.05 0.18 0.12 0.12 0.00 0.00 MgO 1.25 8.10 4.10 4.68 -0.58 12.39 CaO 1.53 9.78 5.26 5.66 0.40 8.55 Nt^ O 4.13 4.96 4.48 4.55 0.07 1.54 K 20 4.23 1.64 3.05 2.94 -0.11 3.74 P2O5 0.06 0.63 0.36 0.35 -0.01 2.86 Ba (ppm) 1350 1400 1394 1375 -19 1.38 Cr 33 215 118 124 -6 4.84 Cu 23 74 43 48.5 5.5 11.34 Nb 3 103 54 53 1 1.89 Ni 17 151 76 84 8 9.52 Rb 41 33 36 37 -1 2.70 Sr 225 1005 608 615 7 1.14 V 33 . 201 117 117 0 0.00 Y 16 25 19 20.5 -0.5 2.44 Zn 56 120 86 88 -2 2.27 Zr 145 250 189 197.5 -8.5 4.30 X-ray fluorescence (XRF) methods are common and the equipment is often readily available. Thus, because an'in house' analysis has the advantage of greater analytical control and lower costs, various workers have~attempted to develop methods of REE analysis utilizing AA and XRF (Fryer, 1977; Sen Gupta, 1976, 1981; Horsky and Fletcher, 1981; Robinson etal, 1986). Sen Gupta (1976) was the first to investigate flame atomic absorption spectrometry analyses for REE in rocks and minerals. The REE were separated by means of a double calcium oxalate and single hydrous ferric oxide co-precipitation procedure. However only samples with relatively high REE contents were analyzed successfully. Sensitivity for this method was later enhanced by the use of a flame microsample injection technique combined with small samples in small solution volumes (Sen Gupta, 1984). The first study to suggest using graphite furnace atom ic absorption spectrometry for REE analyses in geologic materials was by Horsky (1980) in a preliminary investigation on the determination of praseodymium. This lead to the developement of a technique to determine REE (La, Sm, Eu, Yb and Lu) in geologic samples using graphite furnace atomic absorption after separation of the REE by an ion exchange procedure (Horsky and Fletcher, 1981). This exchange scheme used a 26 X 1.2 cm column of Bio Rad® AG50VV-X8 (200-400 mesh) cation resin to seporate the REE from most other constituents. Adequate sensitivity was only obtained for Sm, Eu and Yb. Sen Gupta (1981, 1985) also investigated the graphite furnace atomic absorption method for REE analyses in geologic materials. He used a separation scheme similar to his earlier work (Sen Gupta, 1976) and achieved moderate to good sensitivities for middle to heavy REE. Analysis of light REE by AA is not generally feasible because of the need for very high atomization temperatures (> 3000° C). Existing pressed powder XRF techniques can yield acceptable results for the light REE in most types of geologic samples. Analysis of the remainder of the REE by XRF methods is hampered by poor sensitivities. This necessitates making spiked standards (Leake et al, 1969) or using preconcentration techniques such as an ion exchange-thin film technique (Fryer, 1977; Robinson et al, 1986) in order to achieve reasonable results. The purpose of this study was to obtain an adequate light to heavy REE range on a large number of geologic samples rapidly and relatively inexpensively. The graphite furnace technique of Horsky and Fletcher (1981) was chosen for the middle to heavy REE as it uses a simpler decomposition and analytical method than that employed by Sen Gupta (1985) and Robinson etal{\ 986). Pressed powder XRF.technique was used for the determination of the light REE (see section C.2). C.3.2 METHODS Samples were digested using hydrofluoric and perchloric acid following the procedure outlined in Horsky and Fletcher (1981). To facilitate multiple digestions three banks of 10-place beaker holders with 30 ml Teflon® beakers were used on a hot plate. This enabled handling and aggitation of either the bank of beakers or individual beakers during the drying process. Teflon® stir sticks were used to break up the crust that formed on the sample surface during the final stages of evaporation of the perchloric and hydrofluoric acids. Total time for complete digestion of a batch of 30 samples averaged 2 days but ranged from 1 to 3 days. The column chemistry procedure of Horsky and Fletcher (1981) was modified by the use of 30, 15 X 1 cm BioRad® Econo-columns'" packed with Bio Rad® AG50W-X8 (200-400 mesh) cation resin. The general sequence of elution of the REE from the resin column with 3 M hydrochloric acid is known to be from Y through to La-Y is accompanied by Sr and La by Ba (Edge and Ahrens, 1962; Strelow etal, 1978). The columns were calibrated by passing through them a weakly acidic solution spiked with Ba and " S r . The columns were then eluted with 200 ml of 3 M HCl. Theeluantwas collected in 2 ml portions. Presence of " S r was checked with a Gieger counter; Ba was analyzed for by nitrous oxide flame atomic absorption. The calibration of the smaller columns used here indicated that Sr was eluted sooner than in the larger columns used by Horsky and Fletcher. Consequently, these columns were first eluted with only 30 ml of 3 M HCl, rather than the previously recommended 50 ml, to remove the major elements. The REE, along with Sr and Ba, were collected by elution with a further 150 ml of 3 M HCl; this solution was evaporated to dryness. The residue was dissolved in 1 ml concentrated HCl and made up to 5 ml with distilled H20 The columns were cleaned in preparation for subsequent batches by passing 60 ml of 6 M HCl through the columns followed by three, 10 ml washings with distilled H20. Final solutions were analyzed by graphite furnace atomic absorption. Single element calibration standards were prepared following Horsky and Fletcher (1981). A Perkin Elmer® As-1 Autosampler was used to inject, in triplicate, 20-ul aliquots of standard and unknown solutions into the Perkin Elmer® 603 atomic absorption spectrophotometer with the HGA®-2200 graphite furnace. The pyrolytically-coated graphite tubes were replaced when loss of sensitivity on a known standard exceeded 15 percent of the value expected from anew tube (ranging from 40 to 100 triplicate analyses per tube). Factors governing this were the atomization temperature and whether or not the gas flow was interrupted during atomization. The graphite cones were thoroughly cleaned when the tubes were changed, thus prolonging their 1 ife to over 6000 analyses. Single element and rock standards were run at the beginning and end of each run. Dupl icate unkowns and standard samples were also run with each batch. Operating conditions and sensitivities are summarized in Table C.6. The outlined procedure enables the determination of Sm,Eu,Dy,Er and Yb in batches of up to 30 rock samples. The process, from whole rock powder to analysis by graphite furnace atomic absorption, can be completed in five to six days. C.3.3 RESULTS AND DISCUSSION Over 150 volcanic rock samples were analyzed representing a composition range from ultramafic rxks to rhyolite. Results show that adequate sensitivity and accuracy were achieved for the five REE analyzed. Concentrations for standard rock samples compare favourably to recommended values (Table C.7) whereas selected unknown samples compare well with results from neutron activation analyses (Fig. C. 1). The atomic absorption technique was also investigated for the analysis of gadolinium. However inadequate sensitivity was achieved using the method outlined above for most rock types. High silica rocks required up to three digestions whereas glassy basalts usually dissolved in one digestion. In some samples, the residues (checked by SEM-EDS scans) consisted of small amounts of sulphides (pyrite) or oxides (spinels)! These were dissolved by the addition of 1 ml of nitric acid in the final decomposition. Precipitation of minor amounts of Al-chloride compounds sometimes 240 TABLE C.6 Operating conditions for the determination by graphite furnace atomic absorption of Sm, Eu, Dy, Erand Yb using the Perkin Elmer® 603 with an HGA®-2200 graphite furnace. Parameter*1 Sm Eu Dy Er Yb Wavelength (nm) 430.3 460.3 421.2 400.8 246.4 Slit(nm) 0.14 0.2 0.2 0.2 0.2 Lamp current (mA) 45 35 35 35 35 Dry: time (s) 20 20 20 20 20 ramp (s) 25 25 25 25 25 temp.. C O 110 110 110 110 - 110 Char: tlme(s) 20 20 20 20 20 ramp(s) 15 15 15 15 15 temp. CC) 1,700 1,500 1,500 1,800 1,500 Atomize: time (s) 12 10 13 8 10 temp. C C ) * 2 2,800 2,800 2,880 • 2,900 2,800 Argon gas flow * 3 (cc/min) 80 60 80 80 60 Sensitivity (ug/ml)* 4 0.04 0.003 0.008 0.006 0.006 * ' Varian® single-element hollow-cathode atomic absorption lamps and Perkin Elmer® pyrolytically-coated graphite tubes were used in all determinations. Results were recorded in peak height mode with 4 s integration. * 2 Atomization temperature was calibrated with a Silicon® photodiode temperature sensor. * 3 Gas flow was set at 7 s normal during atomization for Sm, Eu and Yb; gas was interrupted during first 3 s of atomization for Dy and Er. * A Sensitivity is in ug/ml for absorbance of 0.0044 with 20-ul injection. 241 TABLE C.7 Determination of Sm, Eu, Dy, Er and Yb in international standard rocks (all values in ppm). Element MRG-1 NIM-G NIM-N SY-2 SY-3 (gabbro) (granite) (norite) (syenite) (syenite) Sm A* 1 5 16 1 15 100 HF*2 4.1 21 <1 16 97 SG* 3 — 16 — 18 110 UBC* 4 4.5 15 1.5 14 95 Eu A 1.4 0.4 0.6 2.4 14 HF 1.5 0.4 0.8 2.8 19 SG — 0.5 — 2.3 14 UBC 1.4 0.5 0.4 2.4 - 1 4 DY A 3 16 — 20 80 SG — 17 — 20 119 UBC 3 16 1.4 18 >30 Er A 1.2 10 — 12 50 SG — 12 — 14 52 UBC 1.5 10 0.9 13 >35 Yb A 1 14 0.6 17 - 65 . HF 1.6 20 1 17 75 SG — 15 — 15 53 UBC 1.2 13 0.7 19 >50 * ' Usable values from Abbey (1980, 1981, 1983). * 2 Horsky and Fletcher (1981). * 3 Sen Gupta (SY-2, 1981; SY-3, 1984 ; NIM-G, 1985). * 4 This study. Figure C.l; Chondrite normalized REE patterns for a Quaternary-aged alkali olivine basalt from Well's Gray Park, B.C. (solid squares), and a Devonian-aged meta-andesite from central Vancouver Island, B.C. (solid circles). Sm, Eu, Dy, Er and Yb were analyzed by graphite furnace atomic absorption. La, Ce and Nd were determined by pressed powder X-ray fluorescence. Open symbols represent neutron activation analyses of the same samples. occurred in the solutions prior to passage through the columns. These were eliminated by warming the solutions sjiightly. No sample solution was passed through the columns until all particulate matter was dissolved. Blanks and samples of >99.9% pure silica sand were processed through the analytical procedure to test for contamination resulting from the acids or sample preparation (Hickson and Juras, 1986). None were detected. Possible interference effects from non-REE were considered. In the analytical scheme described here only Fe, Ba and Sr were present in some sample solutions above few ug/ml levels. Fe does not interfere (Sen Gupta, 1981). Possible interference effects from Ba and Sr were checked using 10OO ppm spiked solutions; none were found. Operating parameters in Table C.6 represent optimal instrumental conditions for REE concentrations in common geological samples. However when dealing with a sample set which spans a wide composition range, these parameters may be either too sensitive or not sensitive enough. Sensitivities for low concentrations may be improved by restricting the gas flow rate during atomization. For relatively high concentrations the sample may be diluted by altering the gas flow rate during atomization or choosing an alternative spectral line of lesser intensity (cf. Horsky and Fletcher, 1981). C.3.4 CONCLUSIONS The modified graphite furnace atomic absorption technique of Horsky and Fletcher (1981) provides a simple and rapid method of obtaining accurate middle to heavy REE (Sm, Eu, Dy, Er and Yb) values for most geologic samples. Combined with X-ray fluorescence analysis for the light REE (La, Ce and Nd), a sufficient light to heavy REE range can be obtained enabling petrogenetic and provenance studies on the rock suites analyzed. Procedures outlined can be used to process in five to six days batches of up to 30 rock samples from whole rock powder to analysis by both graphite furnace atomic absorption and X-ray fluorescence. 244 C.4 DETERMINATION OF WATER AND CARBON DIOXIDE The procedure used in this study for the determination of water and carbon dioxide is a modification from that of Hutchinson (1974) and described in detail in Berman (1979). Generally the apparatus consists of an open-bore furnace with a silica tube running through it and in which samples are placed. The tube is attached at both ends to drying tubes (a set of two each) by means of tygon tubing and rubber stoppers wrapped in teflon tape. Nitrogen-, cleaned by passing through the first set of drying tubes, passes through the silca tube and then through the final set of drying tubes that collect any water and carbon dioxide given off by the sample. Water is absorbed in the first tube by magnesium perchlorate and carbon dioxide is absorbed in the second tube by ascarite. The one way flow of nitrogen ends in a beaker containing mineral oil, in which the flow rate can be visually estimated. The analytical procedure involved placing an accurately weighed sample of approximately one gram into the furnace (1050-1100 degrees Celsius) for about one hour. The drying tubes were weighed before and after each run and the respective differences, divided by the intial weight of the sample, yielded the weight percent water and carbon dioxide in the sample. The sum of water and carbon dioxide values was checked against the difference in weight of the sample before and after the run (i.e. loss on ignition). If the values were not with in \0% a duplicate run was made. C.5 ELECTRON MICROPROBE ANALYSIS Relict clinopyroxene phenocrysts and chromite microphenocrysts were analyzed by electron microprobe. The analyses were done using an automated three channel ARL-SEMQ microprobe in the Department of Geological Sciences at the University of British Columbia. The accelaration voltage was set at 15 kv and the beam current was 40 mA. The beam diameter used was approximately 1 urn. Calibrations were made using both natural and synthetic mineral standards and the raw data was reduced using the method of Bence and Albee (1968). 245 APPENDIX D  ANALYTICAL DATA This appendix contains analytical data used and referred to from some sections in Chapter 4 to supplement the tabulated values in that chapter. Duplicate and miscellaneous XRF whole rock chemical analyses are in Table D. 1. Analyses taken from an XRF whole rock data file of Westmin Resources Ltd. are in Table D.2. AFM diagrams, Si02 vs. FeO*/MgO diagrams and MnO/TIO^/^Os minor element discriminant diagrams for determination of magmatic series (calc-alkaline or tholeiitic) of the volcanic units in the Buttle Lake Camp are in Figures D. 1, D.2 and D.3, respectively. Normalization values used for the multi-element diagrams and rare-earth element diagrams in Chapter 4 are in Table D. 11. Electron microprobe analyses of clinopyroxene phenocrysts from various mafic and ultramafic volcanic rocks in units of the Myra Formation, Thelwood Formation and Flower Ridge Formation are in the following tables: Table D.3 (6-Flow unit), Table D.4 (G-Flow unit), Table D.S (H-W Horizon mafic flow member), Table D.6 (Upper Mafic unit), Table D.7 (Ihelwood Formation mafic sills), and Table D.8 (Flower Ridge Formation), Values from these tables are plotted on six pyroxene quadrilateral diagrams in Figure D.4. Electron microprobe analyses of chromite microphenocrysts from komatiitic basalt samples (G-Flow unit) are in Table D.9. Electron microprobe analyses of amphibole alteration of pyroxene phenocrysts and groundmass phases are in Table D. 10. 2 TABLE D. 1- Duplicate and miscellaneous XRF whole rock chemical analyses, Buttle Lake Camp, Vancouver Island, B.C. Sample locations and descriptions are in Appendix A. Major and minor element analyses are recalculated to 10O percent on a volatile-free basis. Fe203 is expressed as total iron. Sample name symbols" * " and" \ " indicate analysis by Midland Earth Science Associates and duplicate sample, respectively. Symbols " <", " n.d.", " - ", and " * " denote below detection limit, not detected, not analyzed for, and loss on ignition only, respectively. Sample D2114*' LD-ZrH' LD-ZrC* f D1094 D1362*' PR73-620* Dl 142 Unit1 Price Fm LD LD LD H-W H-W H-W Rock Type1 fp b-ande fp rhy fpdac fp rhy,ab gfp rhy qfp rhy qfp rhy Si0 2 (wt. %) 54.1 73.3 69.5 71.6 68.0 70.3 64.0 T1O2 0.80 0.50 0.52 0.52 0.25 0.22 0.30 A1203 16.7 13.5 15.7 14.0 16.6 16.7 19.0 Fe203 9.45 3.09 4.08 2.45 3.05 3.18 4.13 MnO 0.19 0.05 0.06 0.03 0.05 0.05 0.07 MgO 6.38 0.33 0.48 0.47 0.94 1.84 2.09 CaO 6.83 2.52 2.78 1.11 2.93 1.94 2.98 N&20 5.09 5.35 5.22 9.44 5.99 3.56 1.82 K 20 0.16 1.12 1.41 0.14 2.10 2.13 5.51 P 2 O 5 0.30 0.24 0.25 0.24 0.09 0.05 0.10 H20 4.30* 0.93 1.93* 0.97 2.79* 2.70* 2.82 C02 - n.d. - 0.27 - - 0.82 Ba (ppm) 158 483 601 144 582 1910 2460 Rb 2 14 15 < 4 41 38 131 Sr 446 311 313 139 342 213 358 Nb 3 3 5 4 5 5 3 Y 25 35 . 42 35 22 16 20 Zr 63 106 102 103 135 125 167 Cr - 9 _ 9 . 6 7 4 Ni 12 13 - 1 1 3 3 9 Cu 54 14 18 15 15 13 11 Zn 79 91 82 64 28 38 62 V 191 4 25 1 28 26 69 La _ 16 - 19 - - 16 Ce - 39 - 26 - - 17 Nd - 19 - 15 - - 10 Sm - 6.5 - 5.2 - - 2.3 Eu - 2.1 - 1.2 - - 0.65 Dy - 6.5 - 5.4 - - 3.0 Er - 3.0 - 2.7 - - 3.3 Yb - 2.7 - 3.6 - - 2.2 1. Abbreviations are: LD = H-W Horizon, dacite, H-W = H-W Horizon, fp = feldspar porphyritic, qfp = quartz+feldspar porphyritic, b-ande = basaltic andesite, dac = dacite, rhy = rhyolite, and alb = albitized. 247 TABLE D-.T (continued) Sample D41646' D35743 P46J-1 1 DW284 P43606 THL-CHL DW 140/ Unit1 HWAnde HW Ande 6-Flow 6-Flow G-Flow UM H-W Rock Type1 fp ande fp ande,ser k-bas k-bas, alt k-bas.alt bas, chl qfp rhy,' S1O2 (wt. * ) 60.1 59.3 49.5 39.6 43.5 44.2 66.1 Ti0 2 0.76 0.73 0.59 0.68 0.67 1.24 0.24 AI2O3 14.6 17.6 13.0 18.8 16.4 21.4 18.9 10.2 10.8 10.2 15.4 9.65 14.3 3.97 MnO 0.18 0.16 0.20 0.21 0.17 0.24 0.04 MgO 3.9.8 3.59 15.6 8.97 5.99 7.98 3.33 CaO 7.46 3.52 8.46 11.9 20.6 5.21 0.92 Ne^ O 2.40 0.94 2.07 1.12 0.45 3.83 0.44 K 20 0.14 3.17 0.21 3.10 2.38 1.32 6.02 P2O5 0.18 0.19 0.17 0.22 0.19 0.28 0.04 H20 3.03 3.99 4.61 4.65 3.32 4.55 3.26 CO2 0.38 1.38 0.94 5.44 11.77 n.d. n.d.. Ba (ppm) 82 834 342 1170 391 892 4520 Rb <4 41 <4 58 55 28 110 Sr 790 68 128 160 143 185 131 Nb <2 2 3 <2 2 <2 10 Y 23 23 16 24 20 29 31 Zr 66 82 40 42 43 78 243 Cr 23 ' 14 1 190 571 923 43 9 Ni 17 13 313. 136 221 39 12 Cu 48 15 82 38 < 7 93 8 Zn 86 140 73 '138 94 150 76 V 229 236 262 425 280 415 48 La 11 11 2 20 17 13 9 Ce 31 16 <10 12 27 19 25 Nd 15 9 12 14 1 1 16 19 Sm - 5.3 3.2 2.9 2.5 3!4 7.8 6.1 Eu 1.5 0.27 0.52 0.59 0.73 2.8 1.0 -Dy 5.1 4.2 4.0 2.7 2.9 5.0 9.2 Er 2.2 1.8 1.9 1.9 1.2 3.1 2.4 Yb 2.3 1.6 1.8 2.1 1.2 4.5 13 1. Abbreviations are; HWAnde = Hanginging Wall H-W Andesite, UM •= Upper Mafic, H-W = H-W Horizon, fp - feldspar porphyritic, qfp ^ quartz+feldspar porphyritic, ande - andesite, k-bas = komatiitic basalt, bas-basalt, rhy = rhyolite, v = vitrophyre, ser = sericitized, alt = carbonate + hematite + sericite alteration, and chl ---chloritized. 248 TABLE D.l-(continued) Sample Unit1 Rock Type1 UR-ZrC* - - U R qfx.l RT, chl UR-ZrH* 1 UR qfx.l RT, chl PI 12E ND or UR fp rhy P32C hmpl.THEL tf mudstone P49A-4~ hmpl.THEL tf mudstone SBT-ZrH' pyr,THEL dacite LT MM-ZrC mm, THE basalt Si02 (wt. %) 59.6 59.6 80.2 81.4 89.3 68.6 50.5 Ti02 0.45 0.44 0.21 0.21 0.17 0.63 1.52 AI2O3 20.2 20.2 10.1 9.22 4.51 13.5 16.2 Fe203 7.03 7.08 1.37 2.78 1.81 6.64 15.0 MnO 0.15 0.14 0.03 0.03 0.04 0.16 0.30 MgO 3.63 3.55 0.18 0.86 0.55 2.01 4.88 CaO 2.35 2.66 1.34 0.99 2.01 4.35 7.13 Ns^ O 2.61 2.67 6.45 4.39 1.34 3.46 3.96 K 20 3.77 3.48 0.07 0.09 0.24 0.45 0.07 P2O5 0.21 0.18 0.05 0.03 0.03 0.20 0.44 H20 3.23* 3.09* 0.45 0.94 1.04 1.47 4.12 C02 - - n.d. n.d. n.d. 0.53 1.12 Ba (ppm) 1200 1210 52 37 135 159 61 Rb 76 66 < 4 <4 < 4 7 <4 Sr 308 381 144 101 125 433 183 Nb 4 4 5 2 4 3 2 Y 22 24 35 28 17 43 38 Zr 92 89 147 76 71 170 103 Cr 10 6 8 12 15 15 22 Ni 4 3 14 16 20 12 18 Cu 10 <7 <7 <7 < 7 <7 16 Zn 87 76 27 20 28 92 104 V 108 99 <2 5 39 21 274 La _ _ 26 5 5 9 16 Ce - 42 15 18 38 12 Nd - - 20 9 10 29 15 Sm - - 2.9 3.0 3.4 5.6 6.8 Eu - - 0.94 0.67 0.40 1.4 1.8 Dy - - 6.3 4.0 1.9 7.1 7.4 Er - - 3.2 1.9 1.0 4.0 3.6 Yb - - 2.9 2.4 1.2 4,0 5.2 1. Abbreviations are: UR = Upper Rhyolite, ND ^ North Dacite, THEL = Thelwood Formation, hmpl = siliceous tuffaceous sediment unit, pyr = pyroclastic deposit unit, mm = mafic si l l , qfx.l RT = quartz+ feldspar crystal, lithic rhyolite tuff, fp = feldspar porphyritic, rhy = rhyolite, tf ^ tuffaceous, LT = lapilli-tuff, and chl = chloritized. TABLE D.I (continued) Sample P103A P71A DL498A P86C Unit1 ~~ H-W OCB 5E UR Rock Type1 ande rhy LT ande rhy LT ande, sil+ab chert Si02 (wt. SS) 62.8 59.8 76.9 93.7 Ti0 2 0.69 0.70 0.39 0.09 A I 2 O 3 17.8 17.8 12.6 2.47 Fe203 6.42 8.73 0.91 2.23 MnO 0.11 0.16 0.03 0.11 MgO 3.23 4.91 0.29 0.74 CaO 3.63 2.23 2.01 0.33 Nc^O 3.48 4.52 5.78 0.04 K 20 1.56 0.97 0.95 0.25 P 2 O 5 0.28 0.18 0.14 0.04 H20 2.85 3.65 0.98 0.83 C O 2 nd. 0.40 0.14 0.15 Ba (ppm) 893 770 315 124 Rb 24 15 15 6 Sr 235 289 165 10 Nb 7 2 8 3 . Y 35 26 30 13 Zr 149 78 158 37 Cr 11 18 5 13 Ni 13 16 17 39 Cu 25 68 <7 23 Zn 121 294 38 51 V 109 174 36 22 La 24 9 32 8 Ce 30 18 55 9 Nd 11 11 18 10 Sm 4.6 2.6 4.8 3,0 Eu 1.2 0.88 1.2 0.30 Dy 8.1 3.9 3.6 1.5 Er 3.0 2.2 1.9 0.6 Yb 2.4 1.8 2.5 1.0 1. Abbreviations are: H-W = H-W Horizon, HW Ande = Hanginging Wall H-W Andesite, 5E = 5E Andesite, OCB = Ore Clast Breccia unit, UR = Upper Rhyolite, ande = andesite, rhy = rhyolite, LT-lapilli-tuff, and sil+ab = silicified + albitized. TABLE D.2 XRF fused disk whole rock chemical analyses on mine property samples from XRF data file of Westmin Resources Ltd., Buttle Lake Camp, Vancouver Island, B.C. Analyses were done by X-ray Assay Laboratories Ltd. Major and minor element analyses are recalculated to 100 percent on a volatile-free basis. Fe203 is expressed as total iron. LOI represents loss on ignition. Symbols" <' ' and " - " denote'below detection limit and not analyzed for, respectively. Sampie R19 R20 R102 R107 R84 R87 R88 R109 R92 ' R l 10 Unit 1 Price Fm Price Fm Price Fm Price Fm Price Fm Price Fm Price Fm Price Fm H-W, dac H-W, dac Section1 Price Price Price Price HW-Myra HW-Myra HW-Myra Price Price Price Rock Type1 fp ande fo ande fp b-ande fp b-ande fp ande fp b-ande fp b-ande fp ande fp dacite fp dacite S i0 2 (wt. %) 58.7 57.7 54,5 54.3 59.5 54.8 54.3 58.3 67.1 67.0 T1O2 0.76 0.73 0.92 0.9C 0.71 0.83 0.77 0.76 0.61 0.70 A1 2 0 3 16.4 16.9 19.3 18.5 18.1 ' 19.0 19.1 17.2 15.5 15.6 Fe 20 3 8.29 8.99 8.61 9.56 5.83 9.25 8.28 8.12 4.60 4:80 MnO 0.14 0.13 0.13 0.20 0.06 0.18 0.14 0.12 0.07 0.07 MgO 4.93 4.38 3.96 4.38 4.25 3.75 5.61 4.84 1.48 1.27 CaO 7.13 8.64 9.16 8.70 5.72 8.04 8.38 7.40 4.09 3.49 Na20 3,23 1.93 2.14 2.68 5.49 2.81 2.46 2.57 4.90 5.74 K 20 0.28 0.40 1.02 0.51 0.10 1.14 0.73 0.50 1.39 0.88 P 2 0 5 0.19 0.20 0.24 0.27 0.24 0.20 0.23 0.19 0.25 0.25 LOI 4.84 3.08 3.62 3.39 2.70 5.70 3.85 3.77 3.85 2.54 Ba (ppm) 350 350 420 160 90 350 310 370 520 360 Rb - - 10 <10 <10 30 20 10 10 '20 Sr 300 400 580 660 360 380 380 630 260 630 Zr 90 100 110 120 120 90 80 130 110 100 Ni 22 17 18 19 15 17 ' 17 17 6 2 Cu 69 69 65 67 44 44 58 62 9 24 Zn 77 78 70 72 51 59 51 66 69 88 1. Abbreviations are: H-W, dac = H-W Horizon, dacite flow, fp = feldspar porphyritic, ande = andesite, and b-ande = basaltic andesite. c n o TABLE D.2 (continued) Sample R 128 R56 R57 R43 R105 R16 R27 R94 R36 R91 Unit1 H-W H-W H-W H-W H-W H-W H-W OCB UR ND Section1 HW-Myra Price HW-Myra Lynx Lynx Price Price Price HW-Myra, HW-Myra Rock Type ! qfp rhy qfp rhy qfp rhy fp rhy fp rhy qfx.v RT qfx RT qfxRT qfx Ri fp dacite Si0 2 (wt. * ) 70.5 73.0 72.1 73.9 71.9 74.4 70.5 74.1 79.2 68.2 Ti0 2 0.28 0.30 0.30 0.41 0.56 0.25 0.36 0.23 0.25 0.59 A1 2 0 3 15.6 13.9 16.0 14.2 15.7 13.3 15.3 13.2 10.0 15.2 Fe 2 0 3 2.98 2.85 1.63 1.11 0.99 2.69 3.94 2.07 1.78 4.66 MnO 0.04 0.06 0.03 0.02 0.03 0.04 0.04 0.05 0.04 0.08 MgO 1.19 1.06 2.22 0.19 0.34 1.63 2.61 0.59 0.42 0.69 CaO 1.52 2.21 1.95 1.85 3.08 4.08 3.1 1 3.60 3.73 1.92 Na20 6.12 5.48 1.49 7.48 5.27 1.28 1.25 3.68 3.65 5.61 K 2 0 1.69 1.06 4.22 0.77 2.00 2.29 2.76 2.44 0.87 2.93 P 2 0 5 0.08 0.08 0.06 0.07 0.16 0.04 0.13 0.04 0.06 0.12 LOI 1.62 2.00 3.70 1.54 2.77 3.81 3.36 4.00 3.08 2.08 Ba (ppm) 710 570 2200 180 1810 1800 4600 660 310 710 Rb 40 20 60 <10 20 - - <10 10 50 Sr 310 230 60 210 240 180 180 210 100 210 Zr 130 120 1 10 150 160 120 110 80 130 190 Ni — 2 3 2 1 1 4 13 3 4 5 Cu 8 9 7 8 8 15 140 16 9 29 Zn 49 35 62 19 17 39 750 31 22 58 1. Abbreviations are: H-W = H-W Horizon, OCB = Ore Clast Breccia unit, Interzone Rhyolite, UR = Upper Rhyolite, ND = North Dacite, qfp = quartz+feldspar porphyritic, fp = feldspar porphyritic, rhy = rhyolite, qfx RT = quartz+ feldspar crystal rhyolite tuff, and v = vitric. TABLE D.2 (continued) Sample R45 R85 R86 Rl 1 R8 R21 R22 R66 R35 Unit 1 HW Ande HW Ande HW Ande UD, 1 UD, u UD, u UD, j UM UM Section1 HW-Myra HW-Myra HW-Myra Price Price Price Price WestG HW-Myra Rock Type 1 fp ande fp b-ande fp b-ande fp dacite fp rhy fp rhy fp rhy basalt b-ande S i0 2 (wt. %) 56.3 54.8 54.2 69.8 70.4 72.2 70.8 49.6 54.8 Ti0 2 0.83 0.80 0.86 0.59 0.59 0.57 0.66 0.87 0.84 A1 2 0 3 18.4 17.2 17.8 149 14.7 13.4 14.1 i 7.9 18.9 Fe 2 0 3 9.18 10.1 10.6 4.00 3.43 3.82 4.61 1 1.0 7.82 MnO 0.09 0.16 0.14 0.10 007 0.05 0.04 0.21 0.17 MgO 5.33 4.30 5.24 0.57 0.58 0.54 0.64 8.40 3.76 CaO 4.42 9.61 7.65 3.01 4.71 2.98 2.52 9.48 7.87 Na20 4.99 .2.61 3.20 6.55 4.70 5.64 5.93 2.32 4.59 K 2 0 0.25 0.30 0.06 0.33 0.65 0.59 0.55 0.06 0.87 P 2 O 5 0.21 0.22 0.25 0.14 0.17 0.21 0.15 0.16 0.38 LOI 3.47 2.70 3.47 1.27 1.61 2.88 1.90 5.93 4.31 Ba (ppm) 76 280 1 10 250 400 300 250 70 600 Rb 10 <10 10 - <10 <10 <10 10 20 Sr 360 510 350 330 360 160 270 290 420 Zr 80 80 70 130 120 80 110 50 60 Ni < 3 < 3 3 10 1 1 3 5 15 20 Cu 51 54 41 21 55 1 1 50 64 75 Zn • 76 47 60 61 20 39 61 56 67 1. Abbreviations are: HWAnde = Hanging Wall H-W Andesite, UD, 1 = Upper Dacite, lower member, UD, u = felsic flow blocks within the Upper Dacite, upper member, UM = Upper Mafic, ande = andesite, b-ande = basaltic andesite, rhy = rhyolite, and fp = feldspar porphyritic. TABLE D.2 (continued) Sample R72 R99 R32 R64 R76 R97 R73 R23 R31 Unit1 THEL, mm THEL, mm THEL, mm THEL, mm THEL, mm THEL, mm THEL, mm is intr Is Intr Section1 Price HW-Myra HW-Myra West 6 West 6 HW-Myra West G Price Price / Rock Type1 basalt b-ande b-ande b-ande andesite andesite dacite FP FP Si0 2 (wt. %) 51.2 54.3 54.5 52.5 56.8 63.0 64.6 65.0 61.3 Ti0 2 1.48 1.44 1.46 1.69 1.72 0.86 0.95 0.54 0.58 A1 2 0 3 16.5 16.2 16.4 16.1 15.0 14.9 15.2 16.1 17.0 Fe 2 0 3 13.9 1 1.9 12.4 14.7 1 1.8 6.85 7.21 5.52 7.04 MnO 0.25 0.25 0.24 0.29 0.24 0.20 0.13 0.13 0.37 MgO 4.73 5.36 5.50 3.72 2.99 2.21 1.77 2.39 3.21 CaO 7.20 4.74 5.31 6.63 6.46 7.03 3.37 5.72 5.66 Na20 4.02 5.26 3.69 3.73 4.06 3.67 4.88 3.54 3.68 K 2 0 0.50 0.25 0.20 0.27 0.39 1.00 1.56 0.93 1.04 P 2 O 5 0.22 0.30 0.30 0.37 0.54 0.28 0.33 0.13 0.12 LOI 7.00 3.85 3.85 5.16 5.77 4.23 3.54 3.79 3.93 Ba (ppm) 240 240 210 170 190 230 490 550 600 Rb 10 10 10 10 20 30 30 - 20 Sr 160 150 160 1 10 150 210 140 340 410 Zr 50 80 90 70 90 110. 120 100 100 Ni < 3 < 3 3 8 7 6 5 6 3 Cu 63 12 17 31 1 1 < 7 9 31 37 Zn 85 40 91 110 90 65 74 67 120 1. Abbreviations are: THEL, mm = Thelwood Formation, mafic si l ls, Is Intr = Island Intrusions, b-ande = basaltic andesite, ande = andesite, and FP = feldspar porphyry dike. Figure D.I: AFM diagrams for: a) EARC-PSMT volcanic series, b) WSMT volcanic series, c) ARFT volcanic series, and d) mafic volcanic-units in the Thelwood and Flower Ridge Formations, Buttle Lake Camp, Vancouver Island, B.C. No distinct Fe enrichment trends (i.e. tholeiitic) are present. Probable calc-alkaline trends are shown in (a) and (b). Unit abbreviations are: HWAnde = w Hanging Wall H-W Andesite, e = early phase, 1 = late phase, 5E = 5E Andesite, and kom = komatiitic. Values are from S Tables 4.2, 4.5, 4.6, 4.7, 4.8, 4.1 1, 4.12, D. 1 and D.2. 255 S i 0 2 (wt.X) Figure D.2: Tholeiitic versus calc-alkaline determination based on the Si0 2 vs. FeO*/MgO diagram after Miyashiro (1974) for all mafic and intermediate volcanic units in the Buttle Lake Camp; a) Price and Myra Formations, b) Thelwood and Flower Ridge Formations. Most samples from the Price and Myra Formations plot in the calc-alkaline field or around the dividing line. WSMT (5-F.) series samples plot in both fields. All samples from the Thelwood and Flower Ridge Formations plot in the tholeiitic field. Values are from Tables 4.2,4.6, 4.7, 4.8, 4.11 -, 4.12, D. 1 and D.2. a. T102 / \ EARC / \ / \ \ / M O R B \ 50/ \ \ \50 / \ \ 0. \ L C A B MnO* 10 50 A P 2 0 5 * 1 0 T i 0 2 WSMT MnO* 10 P 2 0 5 * I 0 ARFT MnO* 10 TJ02 Thelwood & \ Flower Ridge P 2 0 5 * I 0 M n 0 » l 0 P 2 0 5 * 10 Figure D.3: M n O / T ^ ^ O s minor element discriminant diagrams (after Mullen, 'l 983) for mafic (oasaltic and basaltic andesite compositions) volcanic units in the Buttle Lake Camp: a) EARC series, b) WSMT series, c) ARFT series, and d) Thelwood and Flower Ridge Formations. Field abbreviations are: CAB = calc-alkaline basalts, IAT = island arc tholeiites, MORB = mid-ocean ridge basalts, and 01 = ocean island basalts. EARC, WSMT and ARFT series samples plot in the CAB field and around the IAT-CAB boundary. Thelwood and Flower Ridge samples plot in the IAT field and around the CAB-I AT boundary. Values are from Tables 4.2, 4 .6 ,4 .7 ,4 .8 ,4 .11,4 .12,D. l andD.2. TABLE D.3 Electron microprobe analyses of c;inopyroxene pnenocrysts from a komatiitic basalt sample, G-Flow unit, Myra Formation. Sample name is R136- 1 and was collected from tne Price Hillside (see Appendix A). Analyses on the same grain are indicated by similar first parts of an analytical name. Letter at the end of the analytical name refers to beam position on grain: C = core, M = margin, and R = rim. Structural formulae are calculated based on 6 oxygens. Ratios are calculated using atomic fractions. Pyroxene end member phases (Wo = CaSi0 3, Fs = F e 2 S i 2 0 6 , En = Mg 2 Si 2 0 6 ) are calculated using atomic fractions and normalizing to their sum. B27-1M B27-2C B27-3R B28-1R B28-2C B28-4M B29-5C B29-1M C30-1C S i0 2 53.35 53.21 53.87 52.02 52.45 51.66 53.31 53.39 52.77 Ti0 2 0.23 0.30 0.24 0.41 0.48 0.28 0.26 0.29 0.26 • A1 2 0 3 2.39 2.16 2.05 2.99 2.53 236 2.33 2.29 2.50 C r 2 0 3 0.70 0 46 0 64 0.82 0.34 0 5 5 0.50 0.46 0.65 FeO 4.40 4.87 4.33 5.31 5.03 4.55 4.64 4.76 4.48 MnO C.l 3 0.13 0.09 0.1 1 0. ;4 0.12 0.14 0.12 OJ 1 MgO 16.02 15 86 16.44 14.71 16.04 16.23 16 34 16.32 16.04 CaO 22.35 . 22.82 22.79 22.93 22.63 23.07 22.89 22.81 22.88 Na20 0.14 0.11 0.10 0.15 O.i 2 0.13 0.12 0.13 0.13 Total 100.71 99.92 100.55 100.45 99.56 98.95 100.55 100.57 99.82 Si 1.9536 1.9513 1.0565 1.9049 1.9331 1.9192 1.9415 1.9440 1.9364 Ti 0.0063 0.0083 0.0066 0.01 13 C.0078 0.0078 0.0077 0.0079 0.0072 Al 0.1022 0.0934 0.0878 0.1722 0.1099 0.1033 0.1000 0.0983 0.1081 Cr 0.0201 0.0133 0.0184 0.0237 0.0099 0.0162 0.0144 0.0132 0.0189 Fe 0.1335 0.1494 0.1315 0.1626 0.1550 0.1414 0.1413 0.1449 0.1375 Mn 0.0040 0.0040 0.0028 0.0034 0.0044 0 0038 0.0043 0.0037 0.0034 Mg 0.8663 0.8669 0.8900 0.8029 0.8812 0.8987 0.8870 0.8857 0.8773 Ca 0.8882 0.8966 0.8868 0.8996 0.8936 0.9183 0.8932 0.8899 0.8996 Na 0.0098 0.0078 0.0070 0.0106 0.0086 0.0094 0.0085 0.0092 0.0092 Mg/(Mg+Fe) 0.866 0.853 0.871 0.832 0.850 0'.864 0.863 0.859 0.865 Wo 47.0 46.9 46.5 48.2 46.3 46.9 46.5 46.3 47.0 En 45.9 45.3 46.6 43.0 45.7 45.9 4 6 2 46.1 45.8 Fs 7.1 7.8 6.9 8.7 8.0 7.2 7.4 7.5 7.2 TABLE D.3 (continued) D32-1R D32-2M D32-3M D35-5C D32-4R D32-6R D32-7C E33-5C E33-2M Si0 2 . 52.30 51.48 52.1 : 51.48 53.21 52.43 50.97 52.15 • 52.36 Ti0 2 0.21 0.30 0.27 0.30 0.24 0.20 0.31 0.22 0.24 AI2O3 1.91 3.10 2.67 3.08 2.14 2.07 3.12 2.16 2.27 C r 2 0 3 0.58 0.95 1.04 1.03 0.63 0.67 1.02 0.69 0.81 FeO 4.41 4.35 3.98 4.23 4.34 4.00 4.31 4.15 4.00 MnO 0.1 1 0.09 0.10 0.13 0.13 0.10 0.1 1 0.1 1 0.1 1 MgO 17.1 1 15.90 16.05 15.83 16.56 16.69 15.77 16.83 16.38 CaO 22.03 23.15 23.06 23.34 22.83 22.86 23.05 22.46 23.C1 Na20 0.12. 0.15 0.15 0.14 0.10 0.12 0.13 0.14 0.12 Total 99.28 99.47 99.43 99.56 100.18 99.14 98.79 98.91 99.30 Si 1.9438 1.9022 1.9209 1.9012 1.9433 1.9355 1.8977 1.9301 1.9312 Ti 0.0058 0.0083 0.0075 0.0083 0.0066 0.0056 0.0087 0.0061 0.0067 Al 0.0829 0.1350 0.1 160 0.1351 0.0921 0.0901 0.1369 0.0942 0.0987 Cr 0.0169 0.0278 0.0303 0.0301 0.0182 0.0196 0.0300 0.0202 0.0236 Fe 0.1358 0.1344 0.1227 0.1306 0.1326 0.1235 0.1342 0.1284 0.1234 . Mn 0.0034 0.0028 0.0031 0.0041 0.0040 0.0031 0.0035 0.0034 0.0034 Mg 0.9388 0.8757 0.8818 0.8714 0.9014 0.9184 0.8751 0.9284 0.9005 Ca 0.8689 0.9165 0.9108 0.9235 0.8933 0.9042 0.9195 0.8906 0.9093 Na 0.0086 0.0107 0.0.107 0.0100 0.0071 0.0086 0.0094 0.0100 0.0086 Mg/(Mg+Fe) 0.874 0.867 0.878 0.870 0.872 0.881 0.867 0.879 0.879 Wo 44.7 47.6 47.6 48.0 46.3 46.5 47.7 45.7 47.0 En 48.3 45.5 46.0 45.3 46.8 47.2 45.4 47.7 46.6 Fs 7.0 7.0 6.4 6.8 6.9 6.3 7.0 6.6 6.4 01 TABLE D.3 (continued) E33-1R E34-4M E34-2M E34-1R E34-6M E34-7R E34-8M E34-9R S i0 2 51.45 52.71 51.54 51.07 51.94 52.00 51.76 52.97 / Ti0 2 0.23 0 24 0.35 0.32 0.34 0.28 0.22 0.25 AI2O3 2.00 1.94 3.81 3.43 3.44 3 0 9 2.40 1.91 C r 2 0 3 0.73 0'62 1.13 1.00 1.00 0 94 . 0.73 0.74 FeO 4.39 4.18 4.7 1 • 4.65 4.59 4.40 4.13 4.27 MnO C.09 0.1 1 0.14 0.12 0.15 0.13 0.10 0.1 1 MgO 16.99 19 89 15.54 15.94 15.17 16 03 16.47 16.55 CaO 22.52 22.70 22.60 22.44 22.78 22.77 22.62 22.83 Na 20 0.12 0.13 0.17 0.15 0.18 0.17 0.13 0.1 1 Total 98.52 99.52 99.99 99.12 99.59 99.81 98.56 99.74 Si 1.9178 1.9384 1.8939 1.8937 1.9141 1.91 13 1.9241 1.9442 Ti 0.0064 0.0066 0.0097 0.0089 0.0094 0.0077 0.0061 0.0069 Al 0.0879 0.0841 0.1650 0.1499 0.1494 0.1339 0.1051 0.0826 Cr 0.0215 0.0180 0.0328 0.0293 0.0291 0.0273 0.0215 0.0215 Fe 0.1369 0.1286 0.1447 0.1442 0.1415 0.1352 0.1284 0.131 1 Mn 0.0028 0.0034 0.0044 0.0038 0.0047 0.0040 0.0031 0.0034 Mg 0.9440 0.9258 0.851 1 0.8810 0.8332 0.8782 0.9125 0.9054 Ca 0.8994 0.8944 0.8898 0.8915 0.8994 08967 0.9009 0.8978 Na 0.0087 0.0093 0.0121 0.0108 0.0129 0.0121 0.0094 0.0078 Mg/(Mg+Fe) 0.873 0.878 0.855 0.859 0.855 0.867 0.877 0.874 Wo 45.4 45.9 47.2 46.5 48.0 46.9 46.4 46.4 En 47.7 47.5 45.1 46.0 44.5 46.0 47.0 46.8 Fs 6.9 6.6 7.7 7.5 7.6 7.4. 6.6 6.8 TABLE D.4 Electron microprobe analyses of clinopyroxene phenocrysts from a komatiitic basalt sample, G-Flow unit, Myra Formation. Sample name is R136-2 and was collected from the Price Hillside (see Appendix A). Analyses on the same grain are indicated by similar first parts of an analytical name. Letter at the end of the analytical name refers to beam position on grain: C = cere, M = margin, and R = rim. Structural formulae are calculated based on 6 oxygens Ratios are calculated using atomic fractions. Pyroxene end member phases (Wo = Ca5i03, Fs = Fe 2 Si 2 06, En = Mg2Si 20 6) are calculated using atomic fractions and normalizing to their sum. C2-1R C2-2C C2-4R D3-1R D3-4C D3-2M E4-2C E4-1R E5-2M S102 52.83 52.69 53.50 52.19 54.18 53.74 53.1 1 52.70 52.96 Ti0 2 0.19 0 20 0.24 0.33 0.20 0.25 0.25 0.19 0.23 A 1 2 0 3 1.96 2 04 2.23 3.40 2.06 2.36 2.15 2.03 2.03 C r 2 0 3 0.60 0.85 0.65 1.03 0.66 0.77 0.44 0.66 0.63 FeO " 4.25 4.17 4.13 4.56 4.42 4.25 4.56 4.05 4.42 MnO 0.12 0.14 0.10 0.13 C.I 2 0.10 0.12 0.1 1 0,12 MgO 16.91 16.37 16.48 15.88 16.44 16 21 16.33 16.67 16.66 CaO 22.67 22.70 23.00 ' 22.58 22.65 22.72 22.52 22.79 23.14 Na20 0.12 0.14 0.12 0.19 0.13 0.13 0.15 0.12 0.12 Total 99.65 99.30 100.45 100.29 100.86 100.53 99.63 99.32 100.31 Si 1.9400 1.9424 1.9462 1.9085 1.9609 1.9517 1.9496 1.9409 1.9359 Ti 0.0052 0.0055 0.0066 0.0091 0.0054 0.0068 0.0069 . 0.0053 0.0063 Al 0.0848 0.0886 0.0956 0.1465 0.0879 0.1010 0.0930 0.0881 0.0875 Cr 0.0174 0.0248 0.0187 0.0298 0.0189 0.0221 0.0128 0.0192 0.0182 Fe 0.1 305 0.1286 0.1256 0.1395 0.1338 0.1291 0.1400 0.1247 0.1351 Mn 0.0037 0.0044 0.0031 0.0040 0.0037 0.0031 0.0037 0.0034 0.0037 Mg 0.9256 0.8995 0.8936 0.8655 0.8869 0.8775 0.8935 0.9151 ' 0.9077 Ca . 0.8920 0.8966 0.8965 0.8847 0.8783 0.8841 0.8857 0.8993 0.9063 Na 0.0085 0.0100 0.0085 0.0135 0.0091 0.0092 0.0107 0.0086 0.0085 Mg/(Mg+Fe) 0.876 0.875 0.877 0.861 0.869 0.872 0.865 0.880 0.870 Wo 45.8 46.6 46.8 46.8 46.3 46.8 46.1 46.4 46.5 En 47.5 46.7 46.6 45.8 46.7 46.4 46.6 47.2 46.6 Fs 6.7 6.7 6.6 7.4 7.0 6.8 7.3 6.4 6.9 u s i — o TABLE D.4 (continued) E5-3C F6-1C F8-1C F8-2C F8-3R * F9-2M G10-1M G1C-2M 01.O-3M Si0 2 53.02 52.06 52.46 52.49 51.87 51.90 52.47 52.72 ' 51.61 Ti0 2 0.21 0.23 0.24 0.2.1 0.24 0.22 0.26 0.25 0.31 A1 2 0 3 2.16 2.12 1.99 2.00 2.67 2 42 1.92 1.98 2.95 C r 2 0 3 0.61 0.77 0.58 0.61 0.83 0 92 0.48 0.50 1.06 FeO 4.10 4.05 4.30 4.39 4.15 4.24 4.55 4.51 5.06 MnO • 0.12 0.1 1 0.14 0.12 0.09 0 1 1 0.14 0.13 0.12 MgO 16.96 16 49 16.52 15.50 16.04 16.24 1613 16.42 15.57 CaO 22.83 23.04 22.76 22.91 23.30 22.95 23.09 22.98 23.15 Na 20 0.12 0.12 0.13 0.1 1 0.15 0.15 0.13 0.07 0,16 Total 100.13 98.99 99.12 99.34 99.34 99.15 99.17 99.56 99.99 Si 1.9364 1.9283 1.9389 1.9372 1.9167 1.9213 1.9418 1.9412 1.9038 Ti 0.0058 0.0064 0.0067 0.0058 0.0067 0.0061 0.0072 0.0069 0.0086 Al 0.0930 0.0925 0.0867 0.0870 0.1 163 0.1056 0.0837 0.0859 0.1283 Cr 0.0 1 76 0.0225 0.0169 0.0178 0.0242 0.0269 0.0140 0.0146 0.0309 Fe 0.1252 0.1255 0.1329 0.1355 O.i 282 0.1313 0.1408 0.1389 0.1561 Mn 0.0037 0.0035 0.0044 0.0038 0.0028 0.0034 0.0044 0.0041 0.0037 Mg 0.9232 0.9104 0.9101 0.9077 0.8835 0.8961 0.8898 0.901 1 0.8561 Ca 0.8934 0.9144 0.9013 0.9059 0.9225 0.9103 0.9156 0.9066 0.9149 Na 0.0085 0.0086 0.0093 0.0079 0.0107 0.0108 .0.0093 0.0050 0.01 14 Mg/(Mg+Fe) 0.381 0.879 0.873 0.870 0.873 0.872 0.863 0.866 0.846 Wo 46.0 46.9 46.4 46.5 47.7 47.0 47.0 46.6 47.5 En 47.5 46.7 46.8 46.6 45.7 46.2 45.7 46.3 44.4 Fs 6:4 6.4 6.8 7.0 6.6 &.8 7.2 7.1 8.1 ro TABLE D.4 (continued) GI0-4M G10-5M G10-6M G10-7M G10-9R Si0 2 51.02 50.68 53.31 51.23 51.73 Ti02 0.28 0.39 0.28 0.44 0.22 A1 20 3 3.23 3.53 2.03 3.84 1.96 Cr 2 0 3 1.13 0.93 0.50 0.69 0.59 FeO 4.33 4.72 4.51 5.31 4.63 MnO 0.09 0.11 0.13 0.14 0.09 MgO 15.67 15.34 16.21 15.32 16.46 CaO 23.12 23.14 22.97 22.80 22.85 N^O 0.16 0.16 0.12 0.18 0.12 Total 99.03 Si 1.8956 Ti 0.0078 Al 0.1414 Cr 0.0332 Fe 0.1345 Mn 0.0028 Mg 0.8678 Ca 0.9203 Na 0.0115 Mg/(Mg+Fe) 0.866 Wo 47.9 En 45.1 Fs 7.0 99.00 100.06 1.8870 1.9505 0.0109 0.0077 0.1549 0.0875 0.0274 0.0145 0.1470 0.1380 0.0035 0.0040 0.8513 0.8840 0.9231 0.9004 0.0116 0.0085 0.853 0.865 48.0 46.8 44.3 46.0 7.7 7.2 99.95 98.65 -1.8889 1.9274 0.0122 0.0062 0.1669 0.0861 0.0201 0.0174 0.1637 0.1443 0.0044 0.0028 0.8420 0.9141 0.9007 0.9122 0.0129 0.0087 0.837 0.864 47.2 46.3 44.2 46.4 8.6 7.3 [ABLE D.5 Electron microprobe analyses of clinopyroxene phenocrysts from'a komatiitic basalt sample, mafic flow member, H-W Horizon, Myra Formation. Sample name is PR/124B and was collected from the Price Hillside (see Appendix A). Analyses on the seme grain are indicated by similar first parts of an analytical name. Letter at the end of the analytical name refers to beam position cn grain: C = core, M = margin, and R =. rim. Structural formulae are calculated based on 6 oxygens. Ratios are calculated using atomic fractions. Pyroxene end member phases (Wo = CaSiC^, Fs = Fe 2Sl205, En = Mg2Si205) are calculated using atomic fractions and normalizing to their sum. B28-3R B28-1M B28-6C B28-7M C29-1C C29-2M C29-3bR C29-3R C29-6M 5i0 2 50.17 52.76 . 51.27 52.50 51.78 50.38 50.16 48.92 49.88 n o 2 0.45 0.26 0.42 0.30 0.24 0.45 0.39 0.59 0.47 A1 20 3 4.75 3.72 4.30 2.46 2.49 4.64 4.21 5.62 ,5.13 Cr 203 0.39 0.78 0.32 0.16 0.23 0.54 0.98 0.37 0.43 FeO 7.04 5.54 6.47 6.55 6.68 6.39 5.85 7.54 7.01 MnO 0.17 0.15 0.13 0.19 0.15 0.1 1 0.14 0.21 • 0.13 MgO 14.51 14.97 14.32 15.28 16.1 1 14.57 14.67 14.10 13.98 CaO 21.86 22.76 22.62 22.16 21.12 22.58 22.37 21.62 22.46 Na20 0.19 0.15 0.20 0.15 0.14 0.14 0.12 0.17 0.15 Total 99.53 101.1 ! 100.05 99.75 98.94 99.80 98.90 99.05 99.64 Si 1.8681 1.9180 1.8937 1.9409 1.9287 1.8687 1.8754 1.6368 1.8581 Ti 0.0126 0.0077 0.0117 0.0083 0.0067 0.0126 0.0110 0.0167 0.0132 Al 0.2084 0.1594 0.1872 0.1072 0.1093 0.2028 0.1855 0.2487 0.2252 Cr 0.01 15 0.0224 0.0093 0.0047 0.0068 0.0158 0.0290 0.01 10 0.0127 Fe 0.2192 0.1684 0.1998 0.2025 0.2081 0.1982 0.1832 0.2368 0.2184 Mn 0.0054 0.0046 0.0041 0.0059 0.0047 0.0035 0.0044 0.0067 0.0041 Mg 0.8053 0.81 12 0.7883 0.8420 0.8944 0.8055 0.8175 0.7841 0.7762 Ca 0.8721 0.8865 0.8951 0.8778 0.8428 0.8973 0.8961 0.8698 0.8964 Na 0.0137 0.0106 0.0143 0.0108 0.0101 0.0101 0.0087 0.0124 0.0108 Mg/(Mg+Fe) 0.786 0.828 0.798 0.806 0.811 0.803 0.817 0.768 0.780 Wo 46.0 47.5 47.5 45.7 43.3 47.2 47.2 46.0 47.4 En 42.5 43.5 41.9 43.8 46.0 42.4 43.1 41.5 41.0 Fs • 1 1.6 9.0 10.6 10.5 10.7 10.4 9.7 12.5 1 1.5 - ro TABLE D.5 (continued) D30-1R D30-2C D3C-3R E31-1R E31-2aM E31-3C F32-1R F32-2M F32-5C Si02 53.53 52.00 53.56 52.85 53.46 50 79 50.74 50.67 ' 52.81 Ti0 2 0.26 0.38 0 25 0.26 0.27 0 5 4 0.32 0.42 0.27 A1 2 0 3 2.10 3.79 2.05 2.48 2.36 5.12 4.17 4.35 2.55 C r 2 0 3 0.36 0.57 0.39 0.42 C.43 0.27 0.67 0.39 0.27 FeO 5.57 6.00 5.81 5.85 5.98 6.81 5.74 6.76 6.30 MnO 0.13 0.1 1 0.12 0.14 0.17 0.12 0.13 0.16 0.18 MgO 16.08 15.12 16.05 15.72 15.66 14.00 14.81 14.33 15.72 CaO 22.23 22.1 1 21.71 22.22 22.10 22.21 22.23 22.56 22.24 Na20 0.1 1 0.15 0.10 0.17 0.13 0.17 0.18 0.16 0.10 Total 100.37 100.23 100.04 100.1 1 100.47 100.03 98.99 99.80 100.44 Si 1.9554 1.9091 1.9616 1.9408 1.9534 1.8766 1.8897 1.8813 1.9364 Ti " 0.0071 0.0105 0.0069 0.0072 0.0074 0.0150 0.0090 0.01 17 0.0074 Al 0.0904 0.1640 0.0885 0.1073 0.1016 0.2230 0.1830 0.1904 0.1 102 Cr 0.0104 0.0165 0.01 13 0.0122 0.0124 00079 0.0197 0.01 14 0.0078 Fe 0.1702 0.1842 0.1780 0.1797 0.1827 0.2104 0.1788 0.2099 0.1932 . Mn 0.0040 0.0034 ' 0.0037 0.0044 0.0053 0.0038 0.0041 0.0050 0.0056 Mg 0.8755 0.8274 0.8762 0.8604 0.8529 0.7710 0.8221 0.7930 0.8592 Ca 0.8701 0.8697 0.8519 0.8743 0.8617 0.8792 0.8870 0.8975 0.8737 Na 0.0078 0.0107 0.0071 0.0121 0.0092 0.0122 0.0130 0.01 15 0.0071 Mg/(Mg+Fe) 0.837 0818 0.831 0.827 0.824 0.786 0.821 0.791 0.816 Wo 45.4 46.2 44.7 45.7 45.4 47.3 47.0 47.2 45.4 En 45.7 44.0 46.0 44.9 45.0 41.4 43.5 41.7 44.6 Fs 8.9 9.8 9.3 9.4 9.6 11.3 9.5 1 1.0 10.0 ro o -fc. TABLE 0.5 (continued) 343- IC 034-2C G36-1M G36-2C G36-3C G36-4R G37-1C G37-3R G37-4M Si0 2 52.59 50.57 51.93 53.45 52.74 49.16 52.06 50.53 • 51.77 Ti0 2 0.25 0.43 0.31 0.29 0.21 0.48 0.26 0.41 0.40 A1 2 0 3 2.58 4.42 3.8 1 2.83 2.25 4 77 2.39 4.13 4.54 Cr 203 0 .45 0.57 0.58 0.16 C.34 0.60 0.35 0.77 0.49 FeO 5.59 6.28 5.62 6.74 5.77 6.62 6.05 5.90 6.28 MnO 0.18 0.14 0.12 0.15 0.1 3 0.16 0.18 0.13 0.13 MgO 15.98 14.63 15.01 15.39 16.07 14.56 16.04 15.19 14.59 CaO 22.16 22.31 22.44 21.97 22.35 22.18 22.09 22.71 22.34 Na 2 0 0.1 1 0.15 0.15 0.12 0.10 0.14 0.15 0.12 0.15 Total 99.89 99.50 99.97 1.01.10 99.96 98,67 99.57 99.39 100.69 Si 1.9341 1.8787 1.9102 1.9450 1.9401 1.8497 1.9271 1.8712 1.8947 Ti 0 .0069 0.0120 0.0086 0.0079 0.0058 0.0136 0.0072 0.01 14 0.01 10 Al 0.1 1 18 0.1935 0.1652 0.1214 C.0975 0.21 15 0.1043 0.1803 0.1958 Cr 0.0131 0.0167 0.0169 0.0046 0.0099 0.0178 0.0102 0.0225 0.0142 Fe 0 .1719 0.1951 0.1729 0.2051 0.1775 0.2183 0.1873 0.1827 0.1922 Mn 0 .0056 0.0044 0.0037 0.0046 0.0041 0.0051 0.0056 0.0041 0.0040 Mg 0 .8760 0.8101 0.8230 0.8347 0.881 1 0.8166 0.8850 0.8384 0.7959 Ca 0 .3732 0.8880 0.8844 0.8566 0.8809 0.8942 0.8761 0.9010 0.8760 Na 0.0078 0.0108 0.0:07 0.0085 0.0071 0.0102 0.0108 0.0086 0.0106 Mg/(Mg+Fe) 0:'336 0.806 0.826 0.803 0.832 0.789 0.825 0.821 0.805 Wo 45.5 46.9 47.0 45.2 45.4 46.4 45.0 46.9 47.0 En 45.6 42.8 43.8 44.0 45.4 42.3 45.4 43.6 42.7 Fs 8.9 10.3 9.2 10.8 9.2 1 1.3 9.6 9.5 10.3 cn TABLE D.6 Electron microprobe analyses of clinopyroxene phenocrysts from a basaltic flow clast sample, Upper Mafic unit, Myra Formation. Sample name is PR42 and was collected from DDH PR42, collarred on the Price Hillside (see Appendix A). Analyses on the same grain.are indicated by similar first.parts of an analytical name. Letter at the end of the analytical name refers to beam position on grain: C = core, M = margin, end R .= rim. Structural formulae are calculated based on 6 oxygens. Ratios are calculated using atomic fractions. Pyroxene end member phases (Wo = CaSiC>3, Fs = Fe2Si20g, En = Mg 2Si 206) are calculated using atomic fractions and normalizing tc their sum. Symbol" - " denotes below detection limit. / B15-1M B15-2R B16-1R B16-3C D18-1R D18-2C D18-3M D18-5M D18-6R Si0 2 50.41 Ti0 2 0.46 A1 2 0 3 4.15 C r 2 0 3 0.13 FeO 5.15 MnO 0.10 MgO 14.91 CaO 23.58 Na20 0.12 50 78 51.31 0.42 0.48 3 74 3.81 0.12 0.34 5.00 5.03 0.08 0.12 15.09 15.09 23.59 23.36 0.18 0.17 51.18 51.40 0.41 0.57 3.76 3.16 0.13 0.06 4.99 7.75 0.12 0.17 14.98 14.44 23.68 21.93 0.17 0.20 50.57 49.47 0.57 0.54 4.63 4.48 0.13 -6.63 7.42 0.15 0.18 14.04 13.71 22.82 22.67 0.17 0.20 5 i .32 47.79 0.34 1.24 3.40 7.35 0.33 0.15 5.47 7.81 0.16 0.l'8 15.22 12.38 23.03 22.56 0.14 0.25 Total 99.01 99.00 99.71 99.42 99.68 99.71 98.68 99.41 99.71 Si 1.8787 1.8908 1.8948 1.8965 1.9137 1.8782 1.8673 1.9036 1.7903 Ti 0.0129 0.01 18 0.0133 0.01 14 0.0160 0.0159 0.0153 0.0095 0.0349 Al 0.1823 0.1641 0.1658 0.1642 0.1387 0.2027 0.1993 0.1486 0.3245 Cr 0.0038 0.0035 0.0099 0.0038 0.0018 0.0038 - 0.0097 0.0044 Fe 0.1605 0.1557 0.1553 0.1546 0.2413 0,2059 0.2342 0.1697 0.2447 Mn 0.0032 0.0025 0.0038 0.0038 0.0054 0,0047 0.0058 0.0050 0.0057 Mg 0.8282 0.8375 0.8306 0.8274 0:8013 0.7772 0.7713 0.8415 0.6913 Ca 0.9415 0.941 1 0.9243 0.9402 0.8748 0.9081 0.9168 0.9152 0.9055 Na 0.0087 0.0130 0.0122 0.0122 0.0144 0.0122 0.0146 0.0101 0.0182 Mg/(Mg+Fe) 0.838 0.843 0.842 0.843 0.769 0.791 0.767 0.832 0.739 Wo 48.8 48.7 48.4 48.9 45.6 48.0 47.7 47.5 49.2 En 42.9 43.3 4 3 5 43.0 41.8 41.1 40.1 43.7 37.5 Fs 8.3 8.0 8.1 8.0 12.6 109 12.2 8.8 13.3 TABLE D.6 (continued) D18-8M D18-9M Dl8-1 OR E19-1R E19-2M E19-3C E19-4R E19-5R F20-1C S i0 2 50.76 50.90' 48.95 51.97 51.22 5119 50.68 50.30 52.93 Ti0 2 0.48 0.53 0.88 0.58 0.59 0 65 0.9C 0.36 •' 0.29 A1 2 0 3 3.83 4.63 4.50 2.64 2.55 3 26 4.64 4.98 3.17 C r 2 0 3 - 0.37 - 0.05 0.05 0.05 0.18 0.06 0.38 FeO 6.90 6.31 8.79 9.32 9.51 9.02 8.75 8.30 4.42 MnO 0.18 0.10 0.17 0.23 0.24 0 22 0.22 0.19 0.09 MgO 14.34 14.34 13 57 14.76 15.06 14.45 13.72 13.70 15.93 CaO 22.64 22.67 21.84 20.60 20.08 20.74 21.59 21.32 23.42 Na20 0.16 0.17 0.23 0.27 0.26 0.23 0.30 0.29 0.16 Total 99.29 100.02 98.93 100.42 99.56 99 86 100.98 100.00 100.79 Si 1.8944 1.8804 1.8525 1.9265 1.9176 1.9084 1.8712 1.8697 1.9234 Ti 0.0135 0.0147 0.0250 0.0162 0.0166 0.0182 0.250 0.0240 0.0079 Al 0.1685 0.2016 0.2007 0.1 153 0.1 125 0.1432 0.2019 0.2182 0.1358 Cr - 0.0108 - 0.0015 0.0015 0.0015 0.0053 0.0018 0.0109 Fe 0.2154 0.1950 0.2782 0.2889 0.2978 0.2812 0.2702 0.2580 0.1343 Mn 0.0057 0.0031 0.0054 0.0072 0.0076 00069 0.0069 0.0060 0.0028 Mg 0.7977 0 7896 0.7654 0.8155 0.8404 0.8030 0.7550 0.7590 0.8628 Ca 0.9053 0.8973 0.8855 0.8182 0.8055 0.8284 0.8541 0.8491 0.91 18 Na 0.01 16 0.0122 0.0169 0.0194 0.0189 00202 0.0215 0.0209 0.C1 13 Mg/(Mg+Fe) 0.787 0.802 0.733 0.738 0.738 0.741 0.736 0.746 • 0.865 Wo 47.2 47.7 45.9 42.6 41.4 43.3 45.4 45.5 47.8 En 41.6 42.0 39.7 42.4 43.2 42.0 40.2 40.7 45.2 Fs 1 1.2 10.4 14.4 15.0 15.3 14.7 1 14.4 13.8 7.0 ro TABLE D.6 (continued) F20-4C F20-3M 022-2M H24-3C H24-4C H24-5R H24-7R H24-6M H26-1C S i0 2 50.47 51.06 1 53.36 49.84 50.62 51.99 51.60 50.07 , 51.21 Ti0 2 0.49 0.53 0.30 0.50 0.54 0 46 0.48 0.51 '• 0.38 A1 2 0 3 3.96 3.62 0.63 4.96 4.81 4.16 4.49 4.74 3.35 C r 2 0 3 0.43 0.30 0.28 0.22 0.22 0 29 0.27 0.23 0.21 FeO 5.5.6 6.64 2.93 5.61 5.81 5.27 5.39 5.42 5.22 MnO 0.1 1 0.18 0.06 0.09 0.1 1 0.09 0.08 0.15 0.09 MgO 14.92 15.48 16.46 14.48 14.53 14.89 14.90 17.70 15.35 CaO 23.20 21.06 24.99 23.23 23.13 23.55 23.37 23.48 23.31 Na 20 0.19 0.28 0.23 0.17 0.17 0 19 0.17 0.14 0.16 Total 99.33 99.15 99.24 99.10 99.94 100.89 100.75 99.44 99.28 Si 1.3784 1.8995 1.9684 1.8589 1.8705 1.8967 1.8859 1.861 1 1.9012 Ti 0.0137 0.0148 0.0083 0.0140 0.0150 0.0126 0.0132 0.0143 0.0106 AT 0.1737 0.1587 0.0274 0.2180 0.2095 0 1789 0.1934 0.2076 0.1466 Cr 0.0127 0.0088 0.0082 0.0065 0.0064 0.0084 0.0078 0.0068 0.0062 Fe 0.1 731 0 2066 0.0904 0.1750 0.1795 0.1608 0.1647 0.1685 0.1621 Mn 0.0035 0.0057 0.0019 0.0028 0.0034 0.0028 0.0025 0.0047 0.0028 Mg 0.8277 0.8583 0.9050 0.8050 0.8003 0.8097 0.81 17 0.8144 0.8494 Ca 0.9251 0.8394 0.9877 0.9283 0.9157 0.9205 0.9151 0.9351 0.9272 Na 0.0137 0.0202 0.0165 0.0123 0.0122 0.0134 0.0120 0.0101 0.0115 Mg/(Mg+Fe) 0.827 0.806 0.909 0.821 0.817 0.834 0.831 0.829 .0.840 Wo 48.0 44.1 49.8 48.6 48.3 48.7 48.4 48.8 47.8 En 43.0 45.1 45.6 42.2 42.2 42.8 42.9 42.5 43.8 Fs 9.0 10.8 4.6 9.2 9.5 8.5 8.7 8.8 . 8.4 O CO TABLE D.6 (continued) H26-2M H26-3R Si02 50.80 50.63 T1O2 0.41 0.41 A1203 4.03 4.06 Cr 2 0 3 0.24 0.16 FeO 6.07 6.24 MnO 0.18 0.15 MgO 14.75 14.74 CaO 22.96 22.92 Na^ O 0.19 0.19 Total 99.63 99.50 Si 1.8859 1.8833 Ti 0.0114 0.0115 Al 0.1763 0.1780 Cr 0.0070 0.0047 Fe 0.1884 0.1941 Mn 0.0057 0.0047 Mg 0.8162 0.8172 Ca 0.9137 0.9135 Na 0.0137 0.0137 Mg/(Mg+Fe) 0.812 0.808 Wo 47.6 47.5 En 42.5 42.5 Fs 9.8 10.1 270 TABLE D.7 Electron microprobe analyses_of clinopyroxene phenocrysts from a mafic sill sample, Thelwood Formation. Sample name is P206 and was collected from the Price Hillside (see Appendix A). Analyses on the same grain are indicated by similar first parts of an analytical name. Letter at the end of the analytical name refers to beam position on grain: C = core, M = margin, and R = rim. Structural formulae are calculated based on 6 oxygens. Ratios are calculated using atom ic fractions. Pyroxene end member phases (Wo = CaSi03, Fs = Fe 2 Si 2 0 6 , En = Mg2Si206) are calculated using atomic fractions and normalizing to their sum. Symbol" - " denotes below detection limit. A13-1C B14- IM B14-2M B14-3C C15-1R C15-2M Si02 51.03 51.24 51.94 52.01 52.22 51.82 Ti02 0.57 0.57 0.60 0.37 0.30 0.21 A1 20 3 2.91 2.75 2.93 3.63 3.58 3.73 Cr 2 0 3 0.06 0.09 0.16 0.20 0.15 0.18 FeO 9.15 9.10 8.73 5.84 4.68 4.41 MnO 0.24 0.31 0.28 0.17 0.11 0.10 MgO 14.62 14.83 14.64 15.41 15.76 - 15.70 CaO 20.48 19.95 20.28 21.87 22.98 23.13 Na20 0.25 0.29 0.32 0.18 0.11 0.13 Total 99.31 99.13 99.88 99.68 99.89 99.41 Si 1.9140 1.9222 1.9291 1.9164 1.9149 1.9093 Ti 0.0161 0.0161 0.0168 0.0103 0.0083 0.0058 Al 0.1286 0.1216 0.1283 0.1576 0.1547 0.1620 Cr 0.0018 0.0027 0.0047 0.0058 0.0043 0.0052 Fe 0.2870 0.2855 0.2712 0.1800 0.1435 0.1359 Mn 0.0076 0.0099 0.0088 0.0053 0.0034 0.0031 Mg 0.8174 0.8292 0.8104 0.8463 0.8614 0.8622 Ca 0.8230 0.8019 0.8070 0.8634 0.9029 0.9131 Na 0.0182 0.0211 0.0230 0.0129 0.0078 0.0093 Mg/(Mg+Fe) 0.740 0.744 0.749 0.825 0.857 0.864 Wo 42.7 41.8 42.7 45.7 47.3 47.8 En 42.4 43.3 42.9 44.8 45.2 45.1 Fs 14.9 14.9 14.4 9.5 7.5 7.1 271 TABLE D.7 (continued) C15-3C E17-1R E17-2M EI7-3C E17-4C E17-5M Si02 52.54 51.09 50.58 51.01 51.36 52.07 T102 0.3.1 0.49 0.55 0.53 0.48 0.43 A1 20 3 3.43 2.48 3.23 2.54 2.73 2.02 Cr 2 0 3 - 0.08 0.07 0.05 - -FeO 5.76 8.76 8.62 9.59 8.26 9.22 MnO 0.17 0.23 0.22 0.28 0.22 0.24 MgO 15.31 15.21 14.98 15.01 15.01 . 15.61 CaO 22.43 19.97 20.14 19.55 20.42 19.33 N320 0.15 0.26 0.28 0.24 0.23 0.25 Total 100.10 98.57 98.67 98.80 98.71 . 99.17 Si 1.9269 1.9251 1.9044 1.9228 1.9274 1.9462 Ti 0.0085 0.0139 0.0156 0.0150 0.0135 0.0121 Al 0.1483 0.1101 0.1433 0.1128 0.1207 0.0890 Cr - 0.0024 0.0021 0.0015 - -Fe 0.1767 0.2760 0.2714 0.3023 0.2592 0.2882 Mn 0.0053 0.0073 0.0070 0.0089 0.0070 0.0076 Mg 0.8369 0.8542 0.8407 0.8433 0.8396 0.8696 Ca 0.8813 0.8062 0.8125 0.7896 0.8210 0.7741 Na 0.0107 0.0190 0.0214 0.0175 0.0167 0.0181 Mg/(Mg+Fe) 0.826 0.756 0.756 0.736 0.764 0.751 Wo 46.5 41.6 42.2 40.8 42.8 40.1 En 44.2 44.1 43.7 43.6 43.7 45.0 Fs 9.3 14.3 14.1 15.6 13.5 14.9 272 TABLE D.8- Electron microprobe analyses of clinopyroxene phenocrysts from-a basaltic flow clast sample, Flower Ridge Formation. Sample name is P243 and was collected from the Price Hillside. Analyses on the same grain are indicated by similar first parts of an analytical name. Letter at the end of the analytical name refers to beam position on grain: C = core, M = margin, and R = rim. Structural formulae are calculated based on 6 oxygens. Ratios are calculated using atomic fractions. Pyroxene end member phases (Wo = CaSiCj-, Fs = Fe 2 Si 2 0 6 , En = Mg 2Si 20 6) are calculated using atomic fractions and normalizing to their sum. Symbol" - " denotes below detection limit. A7-2C B6-4C D18-1C E19-3R F1-2M F l - IR Si02 52.11 51.28 51.88 50.61 • 50.98 52.96 T1&2 0.37 0.39 0.45 0.62 0.47 0.40 A1 20 3 2.38 2.73 2.39 3.54 3.99 3.29 Cr 2 0 3 0.05 0.06 - - 0.27 0.21 FeO 6.89 7.20 7.85 8.19 6.56 - 6.53 MnO 0.16 0.15 0.19 0.15 0.16 0.15 MgO 15.46 - 15.02 15.22 14.57 15.14 15.22 CaO 21.50 21.80 21.14 21.44 21.83 21.59 Na20 0.20 0.19 0.19 0.19 0.19 0.21 Total 99.12 98.82 99.31 99.31 99.59 100.56 Si 1.9394 1.9215 1.9341 1.8942 1.8905 1.9352 Ti 0.0104 0.0110 0.0126 0.0175 0.0131 0.0110 Al 0.1044 . 0.1206 0.1050 0.1562 0.1744 0.1417 Cr 0.0015 0.0018 - - 0.0079 0.0061 Fe 0.2145 0.2256 0.2447 0.2564 0.2034 0.1996 Mn 0.0050 0.0048 0.0060 0.0048 0.0050 0.0046 Mg 0.8576 0.8389 0.8457 0.8128 0.8368 0.8290 Ca 0.8573 0.8752 0.8444 0.8598 0.8673 0.8453 Na 0.0144 0.0138 0.0137 0.0138 0.0137 0.0149 Mg/(Mg+Fe) 0.800 0.788 0.776 0.760 0.804 0.806 Wo 44.4 45.1 43.6 44.6 45.5 45.1 En 44.4 43.2 43.7 42.1 43.9 44.2 Fs 11.1 11.6 12.6 13.3 10.7 10.7 273 Figure D.4: Pyroxene quadrilateral diagrams for compositions of clinopyroxene phenocrysts from G-Flow komatiitic basalts - (b) and(d), H-W Horizon ultramafic flow unit (c), Upper Mafic basalt (a), Thelwood Formation mafic sill (e), and Flower Ridge Formation basalt (f), Buttle Lake Camp, Vancouver Island, B.C. All clinopyroxene compositions plot towards the Mg end of the augite field. Values are from Tables D.3 to D.8. CaMgSi206 CaFeSi206 a. PR42 n = 29 (Fe*Mn)2Si206 CaFcSi206 Mg2Si206 CaMgSi206 b. R136-1 n - 26 (Fe+Mn)2Si206 CaFeSi206 P R / 1 2 4 B n = 28 Mg25i206 CaMgSi206 c. Mg2Si206 (Fe+Mn)2Si206 R136-2 n = 25 Mg2Si206 CaMgS1206 "9 Mg2Si206 CaMgS1206 f . (Fe+Mn)2Si206 CaFeSi206 (Fe+Mn)2Si206 CaFeSi206 P243 n - 6 Mg2Si206 (Fe+Mn)2Si206 276 TABLE D.9 Electron microprobe analyses'of chromite microphenocrysts from komatiitic basalt samples, G-Flow unit, Myra Formation. Sample names are R136-1 and R136-2 and were collected from the Price Hillside (see Appendix A). Analyses on the same grain are indicated by similar first two parts of an analytical name. Letter at the end of the analytical name refers to beam position on grain: C = core, M = margin, and R = rim. Fe203 was calculated assuming stochiometry. Structural formulae are calculated based on 4 oxygens. Ratios are calculated using atomic fractions. Sample R136-2 R136-2 R136-2 R136-2 R136-2 R136-2 Analytical No. A--36-IR A-36-2C A-36-3C A-36-4C H-11 - IC H-l1-2R Si02 0.12 0.19 0.11 0.10 0.09 0.10 Ti02 0.16 0.13 0.16 0.34 0.24 0.22 AI2O3 7.59 8.46 7.23 14.18 8.23 6.77 Cr203 59.06 59.39 60.00 51.30 56.22 57.30 Fe203 3.62 2.67 2.76 4.64 3.60 3.38 FeO 20.15 19.88 20.46 19.60 24.40 - 25.04 MgO 8.39 8.78 8.08 9.64 4.98 4.09 MnO 0.36 0.39 0.38 0.39 1.35 1.66 Total 99.45 99.89 99.18 100.19 99.11 98.56 Si 0.0041 0.0064 0.0038 0.0032 0.0032 0.0035 Ti 0.0041 0.0033 0.0041 0.0083 0.0063 0.0059 Al 0.3041 0.3352 0.2914 0.5439 0.3381 0.2832 Cr 1.5869 1.5780 1.6217 1.3194 1.5486 1.6076 Fe 3* 0.0926 0.0675 0.0711 0.1.136 0.0945 0.0902 Fe2+ 0.5728 0.5588 0.5852 0.5334 0.7110 0.7432 Mg 0.4250 0.4398 0.4117 0.4674 0.2586 0.2163 Mn 0.0104 0.0111 0.0110 0.0107 0.0398 0.0499 Cr/(Cr+Al) 0.839 0.825 0.848 0.708 0.821 0.850 Mg/(Mg+Fe2+) 0.426 0.440 0.413 0.467 0.267 0.225 F e 3 + / (Fe3++Cr+Al) 0.047 0.034 0.036 0.057 0.048 0.046 277 TABLE D.9 (continued) Sample _ R136-2 R136-2 R136-1 R136-1 .R136-1 Analytical No. I-12-1C I-12-2C A-25-1C A-26-1C A-26-3R SIQ2 0.19 0.18 0.11 0.09 0.16 Ti02 0.17 0.15 0.13 0.16 0.34 A1203 7.87 . 7.94 8.15 7.77 13.46 C r 2 0 3 58.74 59.10 59.33 59.58 50.74 3.20 3.42 3.64 3.92 5.02 FeO 19.09 19.78 17.47 17.01 . 19.72 MgO 8.96 8.74 10.16 10.39 9.15 MnO 0.44 0.41 0.34 0.37 0.69 Total 98.66 99.72 99.33 99.29 99.28 Si 0.0065 0.0061 0.0037 0.0030 0.0053~ Ti 0.0044 0.0038 0.0033 0.0040 0.0084 Al 0.3158 0.3160 0.3221 0.3072 0.5238 Cr 1.5807 1.5772 1.5723 1.5797 1.3240 Fe3+ 0.0818 0.0870 0.0920 0.0989 0.1248 Fe2+ 0.5436 0.5584 0.4897 0.4772 0.5443 Mg 0.4545 0.4397 0.5076 0.5193 0.4501 Mn 0.0127 0.0117 0.0096 0.0105 0.0193 Cr/(Cr+Al) 0.833 0.833 0.830 0.837 0.716 Mg/(Mg+Fe2+) 0.455 0.440 0.509 0.521 0.452 F e 3 * / (Fe^+Cr+Al) 0.041 0.043 0,046 0.050 0.063 TABLE D. TO Electron microprobe analyses of amphibole alteration of pyroxene phenocrysts and groundmass phases in volcanic flow units from the Price Formation, Myra Formation, and Flower Ridge Formation, Buttle Lake Camp, Vancouver Island, B.C. All amphiboles analyzed are in the tremolite—actifTolite series. Symbol" - " denotes below detection limit. Sample PR32-2214 PR32-2214 P243 P243 Analytical No. B3-3 D11-1 D18-3 F20-1 Unit Price Fm Price Fm Flower Ridge Flower Ridge Alteration phenocryst phenocryst phenocryst phenocryst SIO2 53.19 53.84 52.77 53.52 T1O2 - 0.05 -AI2O3 3.16 2.09 2.24 2.59 Cr 2 0 3 0.06 0.21 - 0.06 FeO 11.37 10.84 15.42 15.36 MnO 0.36 0.34 0.34 0.37 MgO 15.33 15.88 12.93 12.67 CaO 12.89 13.09 12.67 12.72 Na20 0.18 0.09 0.18 0.27 Total 96.54 96.37 96.60 97.56 Sample R136-1 R136-2 R136-2 9L-WPR Analytical No. F35-4 C2-3 B1-3 A8-2 Unit G-Flow G-Flow G-Flow Ore Clast Breccia Alteration groundmass phenocryst groundmass phenocryst Si02 57.67 56.70 56.00 54.81 Ti02 - - - -A1203 0.83 0.93 1.33 1.63 Cr 2 0 3 - - 0.05 FeO 8.14 7.81 8.43 13.05 MnO 0.26 0.26 0.23 0.39 MgO 17.39 18.19 17.78 14.56 CaO 13.16 13.13 13.32 12.87 N320 0.09 0.11 0.1 1 0.12 Total 97.54 97.13 97.25 97.44 TABLE D. U N-type MORB multi-element and chondrite rare earth element normalization values used in various figures in Chapter 4. The MORB values are from Saunders and Tarney (1984) and the~chondrite values are from Wakita etal (1971) - discussed In Boynton (1984). All values are in parts per million. N-type MORB Chondrite Rb 1 La 0.34 Ba 12 Ce 0.91 K 830 Nd 0.64 La 3 Sm 0.195 Ce 10 Eu 0.073 Sr 136 . Dy 0.30 Nb 2.5 Er 0.20 Nd 8 Yb 0.22 P 570 Zr 88 Eu 1.2 Ti 8400 Dy* 4.8 Y 35 Yb 3.5 Ni 138 Cr 290 * Value for Dy is calculated to correspond to a N-type MORB value for Tb (not analyzed in this study) of 0.71 ppm. 

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