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Geology and lithogeochemistry at the Hidden Creek massive sulphide deposit, Anyox, west-central British… MacDonald, Robert W.J. 1999

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GEOLOGY AND LITHOGEOCHEMISTRY AT THE HIDDEN CREEK MASSIVE SULPHIDE DEPOSIT, ANYOX, WEST-CENTRAL BRITISH COLUMBIA by ROBERT W.J. MACDONALD B.Sc. (Hons), Memorial University of Newfoundland A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Earth and Ocean Sciences) We accept this thesis as conforming to .the required standard: The University of British Columbia May, 1999 © Robert W.J. Macdonald, 1969 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 of fcar-fk cv^tL Occc*.-^ Sci a* The University of British Columbia Vancouver, Canada Date 2.L. . 1 ^ DE-6 (2/88) 11 ABSTRACT The Hidden Creek deposit constitutes the largest accumulation of massive sulphides in the Anyox Pendant, a volcanic-sedimentary succession preserved as a roof pendant along the eastern margin of the Coast Plutonic Complex, about 160 kilometres north of Prince Rupert, B.C. The deposit produced 21 Mt of ore grading 1.57% Cu, 9.26 g/t Ag and 0.17 g/t Au. It consists of 8 ore zones that occur near the volcanic-sedimentary contact. Each ore zone includes a number of lenticular to sheet-like, massive sulphide bodies consisting of pyrite, pyrrhotite and lesser chalcopyrite, with minor sphalerite and magnetite. Stockwork veins in the upper volcanic and lower sedimentary sequence are interpreted as footwall feeders to the massive lenses. The Anyox volcanic rocks are tholeiitic basalts and basaltic andesites with Zr/Y(avg)-2.4 and Zr/Ti*1000(avg):=:9.9. Although they are mainly normal mid-ocean ridge basalts (N-MORB), it is possible to distinguish enriched (E-MORB) and transitional (T-MORB) groups. N-MORBs have P/Ti ratios <0.075 and are depleted in the LREEs, whereas E-MORBs have P/Ti ratios >0.15 and are enriched in the LREE. T-MORBs are transitional between these two end-members. Hydrothermal alteration increases in proximity to mineralized zones. Chlorite-epidote-quartz alteration is prevalent in the footwall volcanic rocks. Alteration in the sedimentary sequence is zoned outward from a quartz-chlorite core to a quartz-sericite-pyrite margin. In the sediment-hosted ores, quartz and calcite are the common gangue minerals, whereas in volcanic-hosted ores, Mg-Ca-Al silicates are common. There is a strong association Ill between chalcopyrite and pyrrhotite in the sulphide lenses and in the underlying vein networks. Mass change calculations for the volcanic rocks indicates a progressive loss of CaO + Na20 and gain in MgO + FeO corresponding to breakdown of plagioclase and formation of chlorite during hydrothermal alteration. K has been added (now biotite) to upper volcanic rocks. Ti02/Zr ratios indicate that the detrital component in the sediments cannot be related to the volcanic rocks and must have been derived from a more evolved source. Chemical changes in the altered sediments are similar to those in the volcanic rocks, although they probably had higher initial K values. In the eastern Pacific Ocean, N-MORB is common but E-MORB and T-MORB are reported from Middle Valley on the Juan de Fuca Ridge, and along the East Pacific Rise from 11°-13°N. Alteration and mineralization in the sedimentary sequence at Hidden Creek are similar to sediment-hosted alteration and mineralization adjacent to sulfide deposits at Middle Valley and at Windy Craggy deposit (Triassic) in northern BC. Fluid inclusion data from the Hidden Creek deposit are similar to sediment-covered hydrothermal systems at Windy Craggy, and in the Guaymas Basin in the Gulf of California. The modern examples provide partial analogs for the seafloor setting and styles of mineralization at Anyox. iv TABLE OF CONTENTS ABSTRACT ii TABLE OF CONTENTS iv LIST OF TABLES viii LIST OF FIGURES ix LIST OF PLATES xi ACKNOWLEDGMENTS xii CHAPTER 1: INTRODUCTION 1 1.1 PURPOSE AND SCOPE OF STUDY 1 1.2 LOCATION AND ACCESS 4 1.3 DEPOSIT BACKGROUND 4 1.4 EXPLORATION HISTORY 8 1.5 PREVIOUS RESEARCH 10 CHAPTER 2: REGIONAL GEOLOGY 13 2.1 GEOLOGY OF THE ANYOX PENDANT 13 2.2 EASTERN ANYOX PENDANT 13 2.3 WESTERN ANYOX PENDANT 18 2.3.1 Cataclastic to Mylonitic Granitoid 18 2.3.2 Metasedimentary and Metavolcanic Rocks 18 2.3.3 Mafic Intrusive Complex 19 2.3.4 Ultramafic Rocks 22 2.4 TERTIARY INTRUSIVE ROCKS 24 2.5 STRUCTURE 26 2.6 METAMORPHISM 29 2.7 METALLOGENY 30 2.8 REGIONAL CORRELATIONS 33 2.9 SUMMARY 35 V C H A P T E R 3: L I T H O S T R A T I G R A P H Y O F T H E HIDDEN C R E E K MINE 37 3.1 INTRODUCTION 37 3.2 MAFIC VOLCANIC ROCKS 39 3.2.1 Massive Volcanic Rocks 39 3.2.3 Pillowed Flows 40 3.2.4 Volcanic Breccias and Fragmental Rocks 40 3.2.5 Gabbroic Rocks 44 3.3 VOLCANIC PETROGRAPHY 44 3.4 SEDIMENTARY ROCKS 50 3.4.1 Clastic Turbidites and Pelagic Mudstone 50 3.4.2 Limestones 53 3.5 SEDIMENTARY PETROGRAPHY 54 3.5.1 Porphyroclastic Sedimentary Rocks 59 3.6 TERTIARY INTRUSIVE ROCKS 62 3.7 STRUCTURE 64 3.7.1 Deformation of the Lithological Units 64 3.7.2 Fold Analyses 69 3.7.3 Discussion 75 3.8 HIDDEN CREEK MINE GEOLOGY: SUMMARY 77 C H A P T E R 4: L I T H O G E O C H E M I S T R Y 80 4.1 INTRODUCTION 80 4.1.1 Trace Element Systematics 80 4.1.2 Least Altered Rocks 82 4.2 VOLCANIC ROCKS 84 4.2.1 Major and Trace Element Compositions 84 4.2.2 Rare-Earth Elements 88 4.2.3 Ti02vsP205 91 4.2.4 AI2O3VSP2O5 94 4.2.5 Mass Changes During Alteration 96 4.2.6 Mineralogy 98 4.3 SEDIMENTARY ROCKS 100 4.3.1 Ti02vsZr 102 4.3.2 Rare-Earth Elements 102 4.3.3 Alteration 4.3.4 Mineralogy 4.4 TERTIARY MAFIC DYKES 4.4.1 Trace element chemistry 4.4.2 REE Elements 4.5 SUMMARY C H A P T E R 5: M I N E R A L I Z A T I O N AND O R E Z O N E S T R A T I G R A P H Y 5.1 THE HIDDEN CREEK ORE BODIES 5.1. 1 Nos. 1 and 5 Ore bodies 5.1.2 No. 4 Ore body 5.1.3 Nos. 2 and 3 Ore bodies 5.2 SEDIMENT HOSTED MINERALIZATION 5.2.1 Massive sulphide lenses 5.2.2 Marginal mineralization: Siliceous sulphides 5.2.3 Vein Stockworks 5.3 VOLCANIC HOSTED MINERALIZATION 5.3.1 Massive Sulphide Lenses 5.3.2 Vein stockworks 5.4 ORE ZONE STRATIGRAPHY 5.4.1 Nos. 2 and 3 ore zones 5.4.1.1 Stratigraphy - Alteration 5.4.1.2 Mineralization 5.4.2 Nos. 1 and 5 ore zones 5.4.2.1 Stratigraphy - Alteration 5.4.2.2 Mineralization 5.4.3 No. 4 ore zone 5.4.3.1 Stratigraphy - Alteration 5.4.3i2 Mineralization 5.5 SUMMARY AND DISSCUSSION C H A P T E R 6: S U M M A R Y A N D DISCUSSION 6.1 STRATIGRAPHY AND ORE ZONE GEOMETRY 6.2 SEAFLOOR SETTING 6.3 COMPARISON WITH OTHER SEAFLOOR DEPOSITS 6.4 PRIMARY LITHOGEOCHEMISTRY 159 6.5 GEOLOGICAL HISTORY 163 6.6 FUTURE EXPLORATION 164 6.6.1 Features of the Hidden Creek Mine 164 6.6.2 Mineral Potential of the East Anyox Pendent: 166 6.6.3 Future Exploration in the Hidden Creek Area 167 R E F E R E N C E S 169 APPENDED A - L I T H O C H E M I C A L D A T A A - l APPENDED B - M A S S C H A N G E C A L C U L A T I O N B- l APPENDIX C - Q U A L I T Y C O N T R O L C - l M A P I : H T D D E N C R E E K L I T H O L O G Y DISTRIBUTION B A C K P O C K E T M A P 2: H IDDEN C R E E K S T R U C T U R A L M A P B A C K P O C K E T viii LIST OF TABLES Table 1.1 Tonnage and grade of Hidden Creek production. 5 Table 2.1 Grade and tonnage of massive sulphide deposits in the Anyox Pendant. 31 Table 2.2 Copper-gold quartz veins of the Anyox Pendant. 32 Table 4.1 Chemical composition of representative least altered volcanic rocks. 83 Table 4.2 Chemical composition of representative altered volcanic rocks. 83 Table 4.3a REE compositions for volcanic rocks at Hidden Creek. 89 Table 4.3b REE compositions for sedimentary rocks at Hidden Creek. $9 Table 4.4 Representative mass changes for volcanic rocks at Hidden Creek. 97 Table 4.5 Chemical composition of representative altered and unaltered sediments. 101 Table 4.6 Chemical composition of mafic dykes at Hidden Creek. 107 Table 5.1 Mineable reserves at Hidden Creek for September, 1918. 114 Table 5.2 Significant drill intersections from 1993. 129 Table 6.1 Production and reserves of deposits of the east Anyox Pendant. 167 Table A.l Chemical composition of igneous and sedimentary rocks at Anyox. A-2 Table B.l Results of mass change calculations for Anyox volcanic rocks. B-6 Tabled Analysis of in house standards. C-3 ix LIST OF FIGURES Figure 1.1 Location of the Hidden Creek Mine, Anyox. 3 Figure Lib General geology of the east Anyox Pendant. 3 Figure 1.2 Generalized geology of the Hidden Creek mine area. 6 Figure 1.3 A composite stratigraphic section of the Hidden Creek mine. 6 Figure 2.1 Geology of the east and west Anyox Pendant. 14 Figure 2.2 Geological map of the area to the west of Mt. Clashmore. 20 Figure 3.1 Lithological distribution in the Hidden Creek area. 38 Figure 3.2 Major structural elements in the Hidden Creek area. 65 Figure 3.3 Structural domains used in fold analysis. 70 Figure 3.4 Orientation of structural elements from the North and Southeast domains. 72 Figure 3.5 Orientation of structural elements from the South and Gama domains. 74 Figure 3.6 Orientations of foliations in the central and west volcanics. 76 Figure 4.1a Yvs Zr immobile element plot. 81 Figure 4.1b Schematic explanation of alteration trends in mafic volcanic rocks. 81 Figure 4.2 Immobile element plots for the mafic volcanic rocks. 85 Figure 4.3 Ti02 vs Zr immobile element plots for the mafic volcanic rocks. 86 Figure 4.4 Variation diagrams for least altered mafic volcanic rocks. 87 Figure 4.5 REE profiles for representative mafic volcanic rocks. 90 Figure 4.6 Ti02 as P205 relations for the mafic volcanic rocks. 92 Figure 4.7 A1203 vs P205 relations for the mafic volcanic rocks. 95 Figure 4.8 Calculated mass changes for the mafic volcanic rocks. 99 Figure 4.9 Zr vs Ti/100 vs Y*3 ternary plot distinguishes volcanics and sediments. 101 Figure 4.10 Ti02 vs Zr for the sedimentary rocks. 103 Figure 4.11 REE profiles of the sedimentary rocks. 103 Figure 4.12 Whole rock variations in the sedimentary rocks. 105 Figure 4.13 AFM plot of volcanic rocks and Tertiary intrusives. 108 Figure 4.14 Zr vsTi/100 vs Y*3 plot for Tertiary mafic intrusives. 108 Figure 4.15 Zr vs Y plot for Tertiary intrusives. 110 Figure 4.16 REE profiles for Tertiary intrusives. 110 Figure 5.1 Generalized geology of the Hidden Creek Mine area. 113 Figure 5.2 Chemical composition of processed ore from the orebodies. 113 Figure 5.3 Drillhole and sample locations around the ore zones. 128 X Figure 5.4 Footwall and flanking stratigraphy of the Nos. 2 and 3 ore zones. 131 Figure 5.5 Stratigraphy flanking the No. 1 ore zone. 82-4 and 93 D6. 133 Figure 5.6 Molar proportion plots for rocks around the Nos. 2and 3 ore zones. 135 Figure 5.7 Stratigraphy flanking the No. 1 ore zone. 93D1, D2, D3, D4. 136 Figure 5.8 Molar proportion plots for rocks around the No. 1 ore zone. 138 Figure 5.9 Stratigraphy of the No.4 ore zone. 141 Figure 6.1 Generalized geology of the Hidden Creek mine area. 147 Figure 6.2 Schematic cross sections through the main ore zones at Hidden Creek. 148 Figure 6.3 Schematic stratigraphic setting of mineralization and alteration. 150 Figure 6.4 The location of Middle Valley along the Juan de Fuca Ridge. 153 Figure 6.5 Schematic block diagram of the Middle Valley system. 154 Figure 6.6. Location of the Windy Craggy massive sulphide deposit. 157 Figure 6.7 Interpreted geology of the Windy Craggy deposit (Peter ,1992). 158 Figure 6.8 Comparitve REE profiles from modem and ancient environments. 162 Figured Measured vs accepted values for MDRU standard ALB-1. C-5 Figure C.2 Measured vs accepted values for MDRU standard P-l. C-6 Figure C.3 Measured vs accepted values for MDRU standard QGRM-100. C-7 xi LIST OF PLATES Plate 2.1 Thick units of coarse-grained sandstone on the Granby Peninsula. 17 Plate 2.2 Mafic volcanic breccia along the western slope of Mt.Clashmore. 17 Plate 2.3 Screen of rust coloured siliceous siltstone in mafic intrusive. 21 Plate 2.4 Coarse isotropic pyroxene in undeformed dyke. 21 Plate 2.5 Rhythmic layering of mafic and anorthosite-rich phases in intrusive. 23 Plate 2.6 Multi-intrusive features in the mafic igneous suite. 23 Plate 2.7 Banded serpentinized peridotite. 25 Plate 2.8 Tectonic breccia in serpentinized peridotite. 25 Plate 2.9 Fold hinge in strained mafic intrusive. 28 Plate 2.10 Deformed plagioclase-rich sediment or volcanic rock. 28 Plate 3.1 Mafic pillow volcanics in the footwall of the No.2 ore zone. 41 Plate 3.2 Surface exposure of pillow breccia. 41 Plate 3.3 Quartz-cemented volcanic breccia in the footwall of the No. 6 ore zone 43 Plate 3.4 Banded quartz-chlorite-actinolite schist in drillcore. 43 Plate 3.5 Photomicrograph of mildly altered volcanic rock. 46 Plate 3.6 Photomicrograph of hydrothermally altered volcanic rock 46 Plate 3.7 Photomicrograph of altered volcanic rock. 49 Plate 3.8 Photomicrograph of biotite-actinolite metamorphic phases. 49 Plate 3.9 Interbedded turbidite-mudstone sequence. 52 Plate 3.10 Thinly bedded sandstone-siltstone turbidites. 52 Plate 3.11 Photomicrograph of sandy layer in the siltstone-sandstone turbidites. 55 Plate 3.12 Photomicrograph of a mudstone-siltstone boundary. 55 Plate 3.13 Cherty and sulphidized bedded clastic sediment. 56 Plate 3.14 Cherty clastic sediment from drill core. 56 Plate 3.15 Biotite and quartz-feldspar layers in altered sedimentary rock. 58 Plate 3.16 Relict bedding in quartz-chlorite-biotite-altered sediment. 58 Plate 3.17 Coarse porphyroclasts in altered sedimentary rock. 61 Plate 3.18 Photomicrograph of rotated porphyroclast in altered sediment 61 Plate 3.19 Fine to medium grained plagioclase-hornblende intrusive. 63 Plate 3.20 Coarse intergrown plagioclase and hornblende. 63 Plate 3.21 Flattened pillow volcanics. 67 Plate 3.22 Syncline in mudstone turbidites in the southern structural domain. 67 xii Plate 5.1a Sediment hosted pyritic lens in the No.l pit. 118 Plate 5.1b Massive sulphides on the east wall of the Nos 2/3 pit. 118 Plate 5.2a Massive sulphide intersection in hole 93 D9. 119 Plate 5.2b Photomicrograph of semi-massive sulphide layer. 119 Plate 5.3a Siliceous sulphides from the hangingwall of the No.l ore zone. 121 Plate 5.3b Examples of sulphide replacement of sandy layers in sediments. 121 Plate 5.4a Vein textures in sedimentary rocks. 123 Plate 5.4b Photomicrograph of Cpy-Sph-po in coarse carbonate gangue. 123 Plate 5.5a Sulphide veins in footwall mafic volcanics. 126 Plate 5.5b Photomicrograph of an altered sulphide vein margin. 126 ACKNOWLEDGEMENTS Xlll I wish to thank the many people who have made the completion of this work possible. Dr. John Thompsom and Dr. Richard Chase, whose guidance, assistance and enthusiasm, helped keep the project focussed. I extend a very special thanks to Dr. Tim Barrett for his tremendous efforts in coordinating many aspects of this project as well as for his expert insights into the geology and presentation of this work. Thanks to Ross Sherlock, Fiona Childe and Peter Lewis whose data, observations and discussions vastly improved the final product. Justin Vandenbrink and Bob Beck provided cheerful and capable field assistance, and Teddy, Jesse and Fudd made the slag pile feel like home. I would also like to thank other people at MDRU, fellow "drones" Sean McKinley and Chris Sebert; Arne Toma and Sonya Tietjen. Cliff James and TVI Pacific Inc. gave permission to work on the Anyox property, and made available historical geological material for the study. The Mineral Deposit research Unit (MDRU) funded this study as part of the Volcanogenic Massive Sulphide Deposits of the Canadian Cordillera project. Financial support for the project was provided by eleven member companies, the Science Council and British Columbia and the National Science and Engineering Research Council (NSERC). I would like to thank my family, especially my grandmother Margaret, for their constant encouragement during the course of this study, and finally to Nancy for her patience and support, especially over the final few months. 1 CHAPTER 1: INTRODUCTION 1.1 PURPOSE AND SCOPE OF STUDY The aim of this thesis is document the geological setting of the Cu-rich massive sulphide mineralization at the Hidden Creek Mine and to interpret its formation by comparison with massive-sulphide deposits and volcanism in modern seafloor environments. Several geological features, which were key to understanding the mineralizing system, are documented in detail in the following chapters and include: • The stratigraphy of the volcanic and sedimentary rocks and their primary and metamorphic petrology. • The metallogeny and morphology of the massive sulphide lenses and associated quartz-stockwork zones. • The origin of bedded siliceous rocks, which are spatially associated with the deposits. • The primary lithogeochemistry of the host rocks and paleotectonic setting of the deposit. • The lithochemistry, petrography and paragenesis of hydrothermal alteration assemblages associated with sulphide mineralization. These studies have produced clearer picture of the ore forming processes at the Hidden Creek Mine the results are presented as a geological model which can contribute to an 2 overall strategy for future mineral exploration at the mine, and for deposits in similar settings elsewhere. In the summers of 1993 and 1994, the author conducted detailed mapping and sampling around the Hidden Creek Mine, especially in the vicinity of the ore zones and a critical stratigraphic contact between the host volcanic and sedimentary rocks (Maps 1 and 2 -back pocket). Twenty-four drillholes totaling over 5300 metres were logged and sampled for lithogeochemical and petrographic studies. Several smaller mineralized zones, which occur along the same volcanic-sedimentary contact, were visited for comparative purposes; these include the Bonanza Mine, and the Eden and Redwing deposits (Figure 1.1). Reconnaissance mapping of sedimentary rocks on the Granby Peninsula, to the south of the minesite, and at Mt. Clashmore, to the northwest, was carried out to help evaluate the regional geology of the area. This thesis was funded entirely through the Mineral Deposit Research Unit (MDRU) at the University of British Columbia as part of a four year MDRU project on Volcanogenic Massive Sulphide Deposits of the North American Cordillera (VMS project). The Hidden Creek Mine was one of eight major deposits and several prominent occurrences studied by the VMS project, which was supported by eleven mineral exploration companies, the Science Council of British Columbia and National Science and Engineering Research Council, and managed by Dr. John Thompson and Dr. Tim Barrett. Dr. Richard Chase of the Department of Earth and Ocean Sciences, UBC, acted as co-supervisor of the thesis. Work at the Hidden Creek Mine in association with the VMS project included this thesis, a fluid inclusion study of the massive sulphide and stockwork zones by Ross Sherlock 4 (Macdonald, 1996, Macdonald et al., 1997), and U/Pb age dating of critical and sedimentary units in the stratigraphy by Fiona Childe (Childe, 1997). 1.2 LOCATION AND ACCESS The Hidden Creek Mine is located at 55° 26' north latitude and 129° 50' west longitude at an elevation of 125 to 175 metres above tidewater. The minesite is connected by gravel road to the now abandoned town of Anyox, 2.5 kilometres to the south. The town of Anyox served as the base of operations for the Hidden Creek Mine between 1914 and 1935, and provided a deep water harbour for the shipment of materials to and from the minesite (Figure 1.1). The old townsite and smelter operations are located at tidewater in the mouth of Granby Bay, along the western shore of Hastings Arm in Observatory Inlet. The area can be accessed by boat, helicopter or floatplane from the towns of Prince Rupert (160 kilometres to the south), Stewart (70 kilometres to the north) or Kitsault (25 kilometres to the east). 1.3 DEPOSIT BACKGROUND The Hidden Creek Mine is the largest of five known Cu-rich massive sulphide deposits in the Anyox pendant, a succession of Mesozoic and older volcanic, plutonic and sedimentary rocks preserved as a roof pendant along the eastern margin of the Coast Plutonic Complex. The deposit was discovered in 1901 and was owned between 1914 and 1935 by the Granby Consolidated Mining and Smelting Company. During this period, over 21 million tonnes of ore grading 1.57 % Cu, 9.25 g/t Ag and 0.17 g/t Au were mined. An additional 647 904 tonnes averaging 2.51 % Cu were mined from the 5 Bonanza deposit over this same period. The mine was closed on August 1, 1935 after an explosion caused collapse of the mine workings. It was purchased by The Consolidated Mining and Smelting Company of Canada, Limited, now Cominco Ltd., on October 25, 1935 (Davis et al., 1992). in outcrop and drill core are believed to be representative of the mined material. T A B L E 1.1 Grade and tonnage of Hidden Creek Production Orebody Tonnes Shipped % Copper 1 8,879,803 1.55 2 6,279,157 1.48 3 2,896,192 1.14 4 420,600 1.12 5 2,651,610 2.27 6 485,738 2.19 8 9,022 0.69 slide 59,678 1.13 TOTAL 21,681,800 1.57 The Hidden Creek orebodies formed eight mineralized zones that sat within the hinge zone or overturned east limb of the Hidden Creek Anticline, a broad, north plunging and east verging fold that dominates the structural style of the area (Figure 1.2). The known mineralized zones comprised discontinuous tabular to sheet-like, massive sulphide bodies consisting of pyrite, pyrrhotite and lesser chalcopyrite, with minor sphalerite and magnetite and associated quartz-sulphide-rich stockworks. Seven of the eight known ore Hidden Creek Deposits 56*26 • Massive and Pillowed Volcanic Rocks Sedimentary Rocks Alteration: ch*rt, chlorlta-•ericitt-bloite schitt Ore Zone £p Collapsed workings / " Surface trace w * volc-sed contact Figure 11 Generalized geology of the Hidden Creek mine area showing the distribution of ore S a ^ n S S The Nos. 7 and 8 ore zones are small subsurface depostts mdtcated by drilling (after Davis etal., 1993). V V V V V V V v v v V V V V V V V V V V ^ \j V V V V V V V V V V V V Y Turbidites: siltstone -mudstone, lesser sandstone, Altered turbidite: variably silicified, massive to laminated siltstone - argillite, locally Altered sediment: white to grey chert alternating with serlclte and biotite altered elastics across graded contacts; Altered sediment: Chlorite and actinolite- altered, variably siliceous clastic material, Intense chlorite - biotite alteration: pink to light grey. Mafic volcanic: intensely chlorite-biotite-talc? altered, Mafic volcanic-.light grey to green, mottled appearance, weak biotite-chlorite Po - Py - Cp: as fine to coarse disseminations, stringer veins and in bedding-parallel Po-Py ± Co, Sp, Gn: semimassive to massive in a Po-Py-Cp: disseminations, ' veins with biotite and chlorite-altered selvages and pyrite-rich, semimassive veins with Po-Py-Cp up to 15% as vein r - networks in metre-scale stockwork-like zones; LEGEND Po: Pyrrhotiu Py: Pyritt Cp: Chalcopyrite Sp: S p h a l e r i t e O n : G a l e n a FiP„re 1 3- A composite stratigraphic section of the Hidden Creek mine The section is Semaic and represents the grSss spatial distribution of the dominant hthological units and atSn asseXges?from the basal volcanic sequence through the contact zone and into the unaltered sedimentary sequence that overlies the ore zones. 7 zones were exploited during the life of the mine, with 95% of the production coming from the Nos. 1, 2, 3, 4 and 5 ore zones (Table 1.1). Currently, there is no safe access to the underground workings although the massive sulphide lenses and stockworks observed The ore bodies are located within tens of metres of the folded stratigraphic contact between a footwall of massive to pillowed flows and fragmental mafic volcanic rocks, and an overlying sedimentary unit comprised of mudstone and siltstone-sandstone turbidites (Figure 1.3). The Nos. 1, 4 and 5 ore zones were hosted in sedimentary rocks, whereas the Nos. 2 and 3 orebodies were hosted near the top of the footwall volcanic rocks. The No. 6 ore zone is reported to have straddled the contact, extending from the volcanic footwall into the sedimentary hangingwall (Nelson, 1935). The Nos. 7 and 8 zones represent minor sulphide lenses peripheral to the main ore lenses. These orebodies were outlined by drilling and are described as contact-type lenses (Nelson, 1935). Average production figures for the mine give recovered grades of 1.57% copper, 0.17 gram per tonne gold and 9.25 grams per tonne silver. However, the grades of significant portions of the No. 1 and 5 ore bodies exceeded 3% copper with higher than average gold and silver values. The best copper mineralization was concentrated in fold closures and the highest precious metal grades were associated with massive sulphide bodies in proximity to sediments (Rhodes and Jackisch, 1988). A broad zone of hydrothermal alteration associated with sulphide mineralization forms a halo around the volcanic-sediment contact, and is most intense and thickest in the vicinity of the Nos. 1 and 5 ore zones. Hydrothermally altered rocks related to sulphide mineralization contain variable amounts of chlorite, epidote, sericite and quartz, and are strongly foliated. This mineralogy is distinguished petrographically from a non-foliated 8 mineral assemblage of actinolite, red to green pleochroic amphibole, epidote and biotite which reflects an upper-greenschist facies, regional metamorphic overprint of the rocks. Sulphide-bearing, bedded siliceous rocks occur as discontinuous lenses in close spatial association to the main ore zones near the base of the sedimentary sequence. These zones have been previously interpreted as exhalative chert horizons reflecting a seafloor syn-geneic mineralizing event (Sharp 1980). 1.4 EXPLORATION HISTORY The Consolidated Mining and Smelting Company of Canada, Limited, now Cominco Ltd. purchased the Hidden Creek Mine and surrounding properties in October 1935. From 1936 to 1989, a number of exploration programs were carried out by Cominco and various joint venture partners. Most of this work was completed on the Hidden Creek, Double Ed and Eden properties (see Figure 1.1). During the course of these programs, 96 holes were drilled for an approximate total of 17,000 metres (Fox, 1989). Detailed geological studies and drilling from 1950 to 1954 resulted in the discovery of the Double Ed and Eden deposits. This work delineated a drill-indicated resource of 1,224,700 tonnes and a drill-inferred resource of 748,427 tonnes grading 1.3 % copper and 0.6 % zinc at Double Ed, and a drill-indicated resource of 158,757 tonnes of 1.3 % copper and 1.9 % zinc at Eden (summarized in Davis et al., 1992). In a 1982 joint venture with Mitsui, Cominco drilled 16 holes in the Hidden Creek area. Several new mineralized zones were identified under the No. 1 orebody, although copper values were erratic or low-grade. One intersection, obtained from a hole north of the old 9 mine workings and within the sedimentary sequence, graded 2.5 % copper, 0.5% zinc, 100.4 grams per tonne silver and 1.8 grams per tonne gold over 6.1 metres. From 1987 to 1988, a total of 13 drill holes were completed by Cominco Ltd. and Prospector Airways Ltd. in the Hidden Creek and Bonanza Creek areas and along the western shore of Granby Bay, but no significant mineralization was found. A major structural analysis of the Hidden Creek area was carried out in the fall of 1988 by the Mineral Exploration Research Institute (MERI) at McGill University. The study included structural and lithological mapping, and utilized core from the 1982, 1987 and 1988 drill programs. The study resulted in a more complex structural model for the area than that used by previous exploration programs, and also outlined a series of targets based on the revised geological interpretation. In 1990, Moss Management Ltd. and Boston Financial Corporation acquired the property and retained Glanville Management Ltd. to update the economic assessment of the property. This study indicated a open pit geological reserve of 10.8 to 13.6 million tonnes at a stripping ratio of 2:1 and grading 0.7 % to 0.75 % copper (Davis et al. 1993). In the fall and winter of 1992-93, TVI Copper (now TVT Pacific Inc.) undertook a comprehensive exploration program through Taiga Consultants Ltd. that included geological mapping, prospecting, geochemical and geophysical surveys, and 4256 metres of diamond drilling in the Hidden Creek area and on other nearby copper occurrences. The program included eleven definition holes designed to confirm reserves around the originally mined ore bodies, and ten exploratory holes to test several targets (Davis et al., 10 1993). Based on this program, Tyler (1993) concluded that the open pit potential in the vicinity of the old mine workings is uneconomic at current copper prices, but suggested considerable potential for mineralization at deeper levels in the mine as well as elsewhere in the volcanic-sedimentary sequence. Much of the geochemical and petrographic data in this study were obtained from material recovered by the 1992-1993 drilling program, and to a lesser extent from the 1988 and 1982 drill programs. 1.5 PREVIOUS RESEARCH The geology of the Hidden Creek area is extensively documented in numerous government and company reports published from the time of its discovery in 1901 to the present. Reports by McConnell (1912), Bancroft (1918), and Dolmage (1922) present detailed overviews of the geology at the Hidden Creek and Bonanza minesites, as well as the first regional stratigraphic correlations between the rocks of the Anyox Pendant and Hazelton group rocks to the east of the Coast Plutonic Complex. Nelson (1935) provides one of the more comprehensive pictures of the Hidden Creek Mine, with plan and cross-section maps of the orebodies, descriptions of the metallogeny and morphology of the different ore zones, and the tonnages and grades of the ore recovered from each zone. In keeping with the ideas of the day, Nelson (1935) interpreted the orebodies as epigenetic replacements formed as a result of the intrusion of amphibolitic greenstone (mafic volcanic) into argillites (turbidite-mudstone sequence). He described both volcanic- and sediment-hosted ore bodies, as well as heavy-sulphide, siliceous and stockwork ores. The results of a comprehensive study of the Unik River-Salmon River and Anyox areas 11 by the British Columbia Ministry of Energy Mines and Petroleum Resources (BCMEMPR) were presented in Grove (1965, 1986) and Carter and Grove (1972). Maclntyre (1986) includes rocks from Anyox in a comparative study of basalts hosting massive sulphides in the Alexander Terrane. Alldrick (1986) examined the stratigraphy and structure of rocks in the Anyox area. Brief summaries of the mineral deposits in the Anyox pendant can be found in the Annual Reports of the BCMEMPR from 1908 to the present, in Minfde reports for the Nass River map sheet 103O and 103P, and in Maclntyre and Ash (1994). Sharp (1980) studied the geology, geochemistry and sulphur isotopes of massive sulphide deposits (Master's thesis at the University of Alberta). He focused on the Hidden Creek, Bonanza and Double Ed deposits, and included a major review of the regional geology. Sharp identified both stratabound (volcanic-hosted) and strataform (sediment-hosted) ore zones and was the first to suggest a syngenetic origin for the orebodies. He postulated that the orebodies originally accumulated by precipitation from metalliferous brines in depressions on the seafloor, and interpreted the bedded siliceous rocks at Hidden Creek, which are closely associated with mineralization, as exhalative chert. Smith (1993) presented an interpretation of the paleotectonic setting of rocks in the eastern part of the pendant based primarily on geochemistry and Pb-Nd isotopic systematics of a suite of least altered volcanic rocks. Alldrick et al. (1996) described several Cu-Ag-Au quartz vein systems and compiled data on the Maple Bay area of the Western Anyox Pendant as part of a series of mineral deposit studies in the Stewart district. 12 Evenchick and Holm (1997) conducted regional mapping and rock sampling in portions of the Anyox Pendant as part of a larger study of the Nass River area (Evenchick et al, 1997). The work produced a more complex geological picture of the Anyox Pendant than had previously been reported, especially in the central and western portions. A critical fossil locality was resampled, and several samples were collected for 4 0Ar- 3 9Ar and U-Pb dating. 13 CHAPTER 2: REGIONAL GEOLOGY 2.1 GEOLOGY OF THE ANYOX PENDANT The Anyox Pendant is a Paleozoic to Mesozoic tectono-stratigraphic assemblage of volcanic, sedimentary and intrusive rocks occurring entirely within Early Tertiary granitoids of the Coast Plutonic Complex (Figure 2.1). Tectonostratigraphic units throughout the pendant are folded around northwest to northeast trending axes which are offset along prominent north-south trending faults. The eastern two-thirds of the pendant consists primarily of mildly to moderately metamorphosed Jurassic sedimentary rocks and Jurassic or Triassic mafic volcanic and sub-volcanic rocks. Horizontal shortening in the eastern block has resulted in at least two phases of folding and imbrication of the volcanic-sedimentary succession. The western third of the pendant comprises variably deformed and metamorphosed pre-Tertiary volcanic, sedimentary and intrusive rocks of uncertain age. Structural relationships in the western block are not well understood as stratigraphic units are poorly defined and the rocks are more highly strained, and contain broad cataclastic and mylonitic zones. 2.2 EASTERN ANYOX PENDANT The volcanic section of the Eastern Anyox Pendant has a maximum thickness of 3000 metres (Grove, 1986). Non-mineralized volcanic rocks which weather a pale green colour and vary from dark green to grey on fresh surfaces, are typically rich in actinolite and in places biotite and epidote. The lower volcanic sequence consists predominantly of fine-14 Tertiary granite, quartz monzonite, quartz monzodiorite volcanic and sedimentary Jurassic Bowser Lake Group: sandstone - siltstone turbidites Jurassic or Triassic pillowed volcanics, massive flows, minor tuff, intruded by gabbro pre-Tertiary rocks of uncertain age catadastic and mylonitic granitoid / volcanic and sedimentary rocks intruded by gabbro to quartz diorite; cut by shear zones mafic intrusive complex and ultramafic, cut by shear zones fault Symbols @ M a s s i v e S u l p h i d e Depos i t s 1. Hidden Creek 2. Bonanza 3. Redwing 4. Double Ed 5. Eden ® Tertiary depos i t s (•) detrital z i rcon (3) hard rock z i rcon PI foss i l locality Figure 2.1 Generalized geology of the Anyox Pendant (after Evenchick and Holm, 1997). Massive sulphide deposits are spatially associated with the volcanic-sedimentary contact. 15 grained to plagioclase phyric, massive to pillowed flows, and dykes or sills of basalt to basaltic andesite composition. The proportion of pillowed, volcaniclastic and fragmental units increases in the upper 600 metres of the volcanic sequence toward the contact with the overlying sedimentary rocks. Medium to coarse grained, equigranular gabbro occur within the volcanic sequence several kilometres north of the Hidden Creek Mine, but not in the overlying sedimentary sequence. These intrusions may represent either an older basement to the volcanic sequence or synvolcanic intrusions related to construction of the seafloor. During the course of this study, attempts were made to obtain isotopic ages from the mafic volcanic package, but they were unsuccessful owing to the lack of zircon-bearing rocks within the volcanic pile. Smith (1993) defined an isochron of 168 ± 37 Ma using 207Pb/204Pb vs 206Pb/204Pb isotopes from four samples in the mafic volcanic stratigraphy and showed "a positive correlation of 147Nd/144Nd and 143Nd/144Nd that corresponds to an age of approximately 194 Ma". These are the only age constraints available for the volcanic rocks at this time. Folded and hornfelsed sedimentary rocks overlie the mafic volcanic sequence along the entire length of the Eastern Anyox Pendant and extend eastward from the volcanic contact across Observatory Inlet to Alice Arm. The sedimentary sequence mainly comprises interbedded pelagic mudstone and massive to laminated siltstone and sandstone turbidites. Grading, cross-bedding, ripples and rip-up clasts are observed within the coarser units. Medium to coarse grained quartzo-feldspathic sandstones and amalgamated sandstone beds (2 to 15 metres thick) occur in the upper sedimentary 16 sequences on the Granby Peninsula (Plate 2.1), east of Carney Lake (Bancroft 1918), south of Tauw Creek and on Larcom Island (Evenchick and Holm, 1997). Small, discontinuous limestone lenses are common near the base of the sedimentary strata in the Hidden Creek area but represent only a minor constituent of the sedimentary sequence elsewhere in the Pendant (Grove, 1986; Sharp, 1980; Evenchick and Holm, 1997). Rusty weathering, bedded siliceous rocks crop out discontinuously in several places in the lower sedimentary sequence near the main contact with the underlying volcanic rocks. They comprise alternating layers of sericite or biotite and bone-white to grey, reddish or pale green saccaroidal quartz. These siliceous rocks are most conspicuous in the area of the Hidden Creek ore bodies where they form massive units up to 30 metres thick within a broad zone of intense hydrothermal alteration. Bedded siliceous rocks are also found in the sedimentary sequences overlying the volcanic host rocks of the Bonanza and Redwing deposits and are associated with several minor zones of mineralization along the contact. Although Sharp (1980) interpreted these rocks as metamorphosed exhalative cherts, the preservation of primary sedimentary structures and detrital quartz in some outcrops and core samples, together with lithogeochemical results presented in this thesis, indicate that at least part of this unit has a clastic sedimentary origin. The age of the sedimentary package is constrained only by fossils from two localities in the upper part of the sedimentary stratigraphy and a single sample of detrital zircons (Figure 2.1). Gauthier (1991) reported a tentative Bajocian age for a poorly preserved ammonite from the sedimentary package. Subsequently, well-preserved ammonites found near the original fossil locality are late Middle Jurassic, Bathonian to Callovian (Tipper, Plate 2.1: Thick units of coarse-grained sandstones with thinner silty interbeds located on the Granby Peninsula. These rocks represent some of the coarser units in the Anyox sedimentary sequence and are interpreted as occurring 100's of metres above the volcanic-sedimentary contact. Plate 2.2: Mafic volcanic breccia along the western slope of Mt. Clashmore. This unit overlies and is in stratigraphic (?) contact with intensely deformed mafic intrusive rocks and appears to occur at an erosional surface in the stratigraphy. 18 in Evenchick and Holm, 1997). Zircons from coarse sandstone beds on Granby Peninsula produced concordant to near concordant Early Jurassic U-Pb ages from 201 to 206 Ma (Childe, 1994), which provide a maximum possible depositional age for this part of the sequence. 2.3 WESTERN ANYOX PENDANT Recent mapping and sampling by Evenchick and Holm (1997) has identified four separate tectono-stratigraphic subdivisions in the Western Anyox Pendant each of which is more highly strained than rocks in the Eastern Anyox Pendant (Figure 2.1). 2.3.1 Cataclastic to Mylonitic Granitoid Cataclastic to mylonitic granitoids form a 500 metre to 2 kilometre wide, north-trending belt that forms the most easterly unit in the Western Anyox Pendant and is juxtaposed against the mafic volcanic rocks of the Eastern Anyox Pendant along steeply dipping north-trending faults. The rocks are cream to white weathering with textural varieties that range from cataclastites with angular random to oriented fragments, to strongly foliated and lineated mylonite with quartz ribbons (Evenchick and Holm, 1997). Carter and Grove (1972) and Grove (1986) previously mapped these rocks as Tertiary granite and Jurassic metamorphic rock. 2.3.2 Metasedimentary and Metavolcanic Rocks Metasedimentary and metavolcanic rocks occupy a fault panel, up to 2 kilometres wide, which is adjacent to the cataclastic and mylonitic zone described above. They also occur 19 in a second zone, over 4 kilometres wide, that extends eastward from the shores of the Portland Canal to the western slopes of Mt. Clashmore. Lithologies include black phyllite, green chlorite phyllite, siltstone, metasandstone, minor conglomerate, volcanic breccia with chlorite phyllite matrix (Plate 2.2), pillowed volcanics and minor marble and calc-silicate rocks (Evenchick and Holm, 1997). These rocks are intensely deformed and primary contacts between the units are rare. Detrital zircons, from a medium to coarse sandstone bed and a coarse conglomeratic bed, unit gave ages about 185 Ma (CA. Evenchick and V.J. McNicoll, pers. comm., 1999). Results of mapping by the author in an area about 2 kilometres west of Mt. Clashmore are shown in Figure 2.2. In this area, screens of laminated siliceous siltstone (Plate 2.3), up to 200 metres long and 40 metres thick, occur within relatively undeformed, two pyroxene gabbro or diorite (Plate 2.4). This mafic intrusion also contains one or more xenoliths of more highly strained gabbro, the latter a feature of the adjacent poly deformed gabbro intrusive complex (described below). Similar, weakly deformed mafic intrusives have been found elsewhere in the metavolcanic and metasedimentary package by Evenchick and Holm (1997). 2.3.3 Mafic Intrusive Complex The central part of the Western Anyox Pendant comprise variably deformed gabbroic intrusive rocks that outcrop in a belt about 300 to 800 metres wide on the western slopes of Mt. Clashmore. These rocks, mapped by the author over a two day period in the summer of 1994, are bounded to the west by ultramafic rocks, and to the east by the 20 <nj]TrT> pond 2 - Polydeformed Gabbro (minor Chlorlite Schist) 1 - Serpentinized Ultramafic 0 1 Kilometres Figure 2.2: Geological map of the area to the west of Mt. Clashmore. Zircons from AX-GC-12 yielded a 363 +51-1 Ma age. Plate 2.4: Coarse isotropic pyroxeneon a weather surface of undeformed diorite. Note the deformed gabbro xenolith in the upper left hand margin of the photo. 22 metasedimentary and metavolcanic rocks described above. These rocks are mostly fine to medium grained pyroxene-plagioclase gabbros with lesser gabbro pegmatites and anorthosites. Primary pyroxene crystals are replaced by psuedomorphs of hornblende, which in turn are altered to finer-grained assemblages of actinolite, chlorite and epidote. Primary plagioclase crystals are replaced by fine-grained aggregates of chlorite, epidote and sericite, giving these grains a cloudy appearance in thin section. Several different igneous phases form the gabbro suite. Early intrusives, characterized by rhythmic layers (1 to 20 centimetres thick) of mafic-rich and plagioclase-rich phases are intruded by and occur as inclusions (xenoliths) in medium grained, feldspar-rich to anorthositic intrusives (Plates 2.5 and 2.6). Fine grained green mafic dykes and thin aplitic dykes cut the two earlier phases. All three phases of the intrusive suite are penetratively foliated. Childe (1997) reported a U-Pb zircon age of 363 ± 3 Ma (Devono-Mississippian) for an anorthosite-rich phase of the intrusive complex. Rocks of the intrusive complex are therefore the oldest rocks currently recognized in the Anyox Pendant. 2.3.4 Ultramafic Rocks Serpentinized peridotites occur in a north-trending 50 metre wide belt within a linear depression that separates the mafic igneous complex to the east, from essentially undeformed gabbro intrusives with screens of siliceous siltstone to the west. The ultramafics, glassy green on fresh surfaces, weather brown to orange. The primary silicates have been entirely replaced by non-foliated, variably talc-altered serpentine, with Plate 2.5: Rhythmic layering of mafic and anorthosite-rich phases in deformed mafic intrusive rocks. Plate 2.6: Multi-intrusive features of the mafic igneous suite. Here an anorthosite-rich intrusive contains mafic xenoliths similar in appearance to the mafic banded layers seen in the photo above. The anorthoisite is in turn cut by the a later fine-grained green mafic phase. A l l the igneous phases are foliated. 24 minor epidote, carbonate and magnetite. Banding, commonly observed in outcrop, may reflect either compositional layering or a tectonic fabric in the protolith (Plate 2.7). Pseudomorphs of primary silicate minerals (pyroxene?) observed in hand specimen could not be identified in thin section due to serpentinization of the protolith. Banding in the ultramafic rocks predates serpentinization and is folded around moderate to steeply west-dipping axes. Discrete, high-angle, semi-ductile shears attenuate and rotate banded blocks of serpentinite, imparting a scaly appearance to some outcrops and forming broad zones of tectonic breccia in others (Plate 2.8). Thin seams of Fe-carbonate (ankerite) follow these later shears and dip steeply to both the west and east. 2.4 TERTDVRY iNTRUsrvE ROCKS Paleozoic and Mesozoic rocks of the Anyox Pendant are bounded to the north, east and south sides by the Coast Plutonic Complex, are intruded by numerous related satellite dykes, stocks and plugs. The intrusives dominantly granites, with lesser quartz monzonite and quartz monzodiorite (Evenchick and Holm, 1997). Typically these rocks are medium grained, light pink to light grey, and consist of mostly plagioclase and potassium feldspar, quartz and amphibole ± biotite. The intrusives are unmetamorphosed and unaltered and clearly post-date volcanogenic massive sulphide mineralization in the Pendant. Childe (1997) reported an Early Tertiary U-Pb age of 53 +51-1 for zircons from a nonfoliated diorite dyke in the Hidden Creek area. This age is in agreement with Early Tertiary ages previously reported from the eastern margin of the Coast Plutonic Complex, which completely surrounds the Anyox pendant (Grove, 1986). 25 Plate 2.8: Tectonic breccia in a serpentinized peridotite. 26 2.5 STRUCTURE Interpretation of the main structural elements in the Anyox Pendant is hindered by a lack of clear regional-scale marker horizons within the volcanic, intrusive and sedimentary units that make up the tectono-stratigraphic sequences. Previous work by Nelson (1935), Grove and Carter (1972), Sharp (1980), Grove (1986) Fox (1989) and Evenchick and Holm (1997) recognized an overall north-south structural grain for the major tectonic elements within the Anyox Pendant as well as less regionally extensive cross-structures. The contact between the volcanic and sedimentary rocks is the main marker horizon in the Eastern Anyox Pendant. The contact is folded around gently north-plunging megascopic folds, which are upright to overturned and east-verging, and include the Hidden Creek Anticline (see Figure 3.2). The surface trace of the contact has a north-south trend. Volcanic rocks are exposed in the cores of anticlines at both the Hidden Creek and Bonanza mines. Grove (1986) and Fox (1989) identified several less significant northeast-trending fold sets, and also imbrication of the volcanic and sedimentary units that modified the contact. Prominent northeast-trending structures occur in the area of the Hidden Creek massive sulphide deposits and may in fact predate the north-trending structures (section 3.7). Evenchick and Holm (1997) divided the Anyox Pendant into domains of broadly similar fold orientations based on structural analyses of the sedimentary and volcanic rocks. Their work shows that bedding, cleavage and fold axis orientations rotate from predominantly northeast-trends in the southern parts of the Eastern Anyox Pendant, to northwest-trends in the north. Fold interference in both areas is reflected by diffuse trends of poles to bedding in stereonet plots. Structural 27 measurements taken in the present study from both the Bonanza Mine area and on the Granby Peninsula are consistent with measurements from Evenchick and Holm (1997). Furthermore, detailed structural analysis of the Hidden Creek Mine contained in this study (Chapter 3) and Fox (1989) show similar rotations in structural elements from south to north across the mine stratigraphy. Tectono-stratigraphic assemblages in the Western Anyox Pendant are offset along high angle, north-trending faults, and internally are inhomogeneously deformed. High strain zones with isoclinally folded gneissic to mylonitic foliations alternate with weakly foliated or relatively undeformed domains with isotropic textures. High strain zones vary from several centimetres to tens of metres in width. Most foliations dip steeply, parallel with the axial surfaces of tight folds in the gneissic and mylonitic bands. In the mafic intrusive complex of the west Anyox Pendant, the transitional zones from low to high strain is commonly less than one metre wide and is characterized by the elongation, rotation, attenuation and grain size reduction of mafic and felsic minerals (Plates 2.9 and 2.10). Evenchick and Holm (1997) described similar transitions involving rock fragments and primary structures within the granitoid, metavolcanic and metasedimentary units. In low strain zones, primary depositional features such as intrusive contacts, sedimentary bedding and randomly oriented volcanic breccia fragments are preserved along with random cataclastite in the granitoid (Evenchick and Holm, 1997). Rhythmic layering of anorthosite and pyroxenite layers in the mafic intrusive complex and compositional banding in the ultramafic rocks are locally preserved within the low strain zones, indicating a complex pre-shear geological history Plate 2.9: Fold hinge in intensely strained, banded mafic intrusive. Plate 2.10: Deformed palgioclase-rich sediment or volcanic rock along the western slope of Mt. Clashmore. 29 for many of the rock units. Structural analyses by Evenchick and Holm (1997) and data from the present study indicate that bedding, foliation and mylonitic foliation have a consistent north-south trend, and reflect steeply-dipping tight to isoclinal folding throughout most of the western pendant. Kinematic indicators from C-S fabrics and down-dip lineations indicate west-side up displacement along several of the shear zones (Evenchick and Holm, 1997). 2.6 METAMORPHISM Metamorphism in the Anyox Pendant is related to both regional deformation and thermal effects from the Hyder Pluton. The grade of metamorphism in the East Anyox Pendant is upper greenschist facies. Volcanic rocks are metamorphosed to fine grained assemblages pf actinolite, chlorite, epidote and fine-grained micas which, in areas of hydrothermal alteration, over print the earlier chlorite- and sericite-rich foliations. A coarsening of this alteration assemblage at the Bonanza Mine may reflect a proximity to intrusive stocks of the Hyder Pluton. In the metamorphic clastic sedimentary rocks, assemblages of chlorite, micas, epidote and rare fine-grained acicular amphibole are common and coarser quartz grains display undulatory extinction. Porphyroclasts of cordierite (often as quartz-chlorite-mica pseudomorphs) and andalusite have been identified in these rocks (Sharp, 1980; Grove, 1986; Fox, 1989; Evenchick and Holm, 1997). Rocks in the Western Anyox Pendant are metamorphosed to upper greenschist facies and at least locally to lower amphibolite facies (Evenchick and Holm, 1997). Hornblende, pseudomorphing primary pyroxenes, occurs in rocks of the mafic intrusive complex and 30 mafic intrusive rocks in the metasedimentary and metavolcanic assemblage. In high strain zones, the hornblende grains are locally attenuated and plastically deformed. A later weakly foliated to non-foliated metamorphic assemblage of actinolite, chlorite and epidote alters both hornblende and plagioclase. 2.7 METALLOGENY The Hidden Creek Mine is the largest of five significant Cu-Zn massive sulphides recognized in the Anyox Pendant (Table 2.1). The deposits consist of massive sulphide lenses comprising pyrite, pyrrhotite, chalcopyrite, lesser sphalerite and minor galena and associated quartz-rich and sulphide bearing stockworks. Massive sulphide mineralization occurs at or near the volcanic sedimentary contact or as in the case of the Eden deposit, within high-angle shears in the basement volcanic suite. Deposits hosted entirely by sediments have been recognized thus far only at the Hidden Creek Mine. Sharp (1980) interpreted the deposits as syngenetic mineralization that formed in a seafloor environment through hydrothermal processes active during the construction of a mafic volcanic pile. Galena from the Hidden Creek Mine has 207Pb/206Pb and 208Pb/206Pb isotopic ratios (Childe, 1997) which lie between the ratios of galena from the lower Middle Jurassic Eskay Creek deposit and the Upper Triassic Granduc deposit. These ratios are also close to those of galena mineralization at the Upper Triassic Windy Craggy deposit (Peter, 1992). These relations reflect the presence an older more evolved Pb source in the Alexander Terrane, which hosts the Windy Craggy deposit, relative to the source in the Stikinia Terrane, which hosts both the Eskay Creek and Granduc deposits 31 (Childe 1997). The Pb isotopic ratios of the Hidden Creek ores are consistent with the Early Jurassic age (-194 Ma) estimated for the volcanic rocks hosting the sulphide mineralization by Smith (1993) and is consistent with a syngenetic mineralizing event. Table 2.1 Grade and Tonnage of Massive Sulphide Deposits in the Anyox Pendant DEPOSIT TONNES GRADE Hidden Creek Production Reserves 21,681,800 13,600,000 1.57% Cu, 0.17g/t Au, 9.25g/t Ag, 0.75% Cu Bonanza Production Reserves 647,904 10,624 2.1% Cu 1.76% Cu, 0.16g/t Au, 13.7 g/t Ag Double Ed Reserves 1,229,235 1.3% Cu, 0.6% Zn Redwing Reserves 164,600 2.0% Cu, 2.7% Zn Eden Reserves 158,757 1.4%Cu, 1.7% Zn Copper-gold quartz vein deposits on the Granby Peninsula, on the eastern side of the Anyox Pendant, and in the Maple Bay area on the western side. They comprise one or more sub parallel veins up to 8 metres wide and 1 kilometre along strike. The veins follow brittle fractures both parallel and cross-cutting stratigraphy in the sedimentary host rocks. Individual veins consist of massive quartz with disseminations, shoots and bands 32 of chalcopyrite and pyrrhotite, minor pyrite, sphalerite and galena (Alldrick et al., 1996; BCMINFILE bibliographies). Small amounts of base and precious metals were extracted from several veins during smelting at Anyox, where the quartz was used for flux (Table 2.2). Table 2.2 Copper-Gold Quartz Veins of the Anyox Pendant DEPOSIT TONNES GRADE Granby Point Production 124,055 1.4 g/t Au, 47.2 g/t Ag Golskeish Quartz Production 47,850 3.1 g/t Au, 17.1 g/tAg Outsider - Star Production Reserves 125,966 18,450 1.9% Cu 1.5% Cu Eagle - May Queen Reserves 1,470,400 1.8% Cu Princess - Anaconda Reserves 32,400 2.14% Cu Primary fluid inclusions from the Granby Peninsula veins are distinguishable from those in footwall volcanic veins at the Hidden Creek Mine by their higher average homogenization temperatures and higher salinities (Sherlock, in Macdonald et al. 1996). The Granby Peninsula inclusions also contain a high-density liquid-gas phase not present in the Hidden Creek veins. Childe (1997) showed that Pb isotope ratios of galena from the Granby veins are more radiogenic than those of the Hidden Creek mineralization, but t> 33 overlap with those of Tertiary vein systems in the Stewart Mining District. It follows that the Granby Peninsula vein systems are probably related to nearby intrusives of the Coast Plutonic Complex. The Molly May-Molly Mac molybdenum-porphyry prospect is located west of Frank Point and immediately south of the contact between the Coast Plutonic complex and sedimentary rocks of the Anyox pendant to the north. The prospect consists of four mineralized zones in a northeast trending, quartz monzonite stock of Eocene age within the Coast Plutonic Complex. The main mineralized zone consists of disseminated pyrite in quartz-veined pegmatite and associated biotite-rich granite. Rock chip samples have assayed up to 0.254 % Mo, 60 g/t Au and 51 g/t Ag (BCMINFILE). The lithological association and a K-Ar date of 48.3 ± 1.9 Ma on biotite from the stock (BCMINFILE) indicate that the Molly May-Molly Mac mineralization is of Tertiary age. 2.8 REGIONAL CORRELATIONS Regional correlation of rock units in the Anyox Pendant is difficult due to the lack of clear marker horizons in the volcanic and sedimentary rocks, limited fossil data from sediments, and the difficulty in obtaining material for reliable U-Pb geochronology from mafic rocks. McConnell (1912) named the metasedimentary rocks of the Anyox Pendant the Goose Bay formation and correlated the volcanic rocks with the Bear River Formation of the Stewart District. Dolmage (1922) used the same terminology as McConnell, but believed that the Goose Bay metasediments were more metamorphosed equivalents of the lower 34 Jurassic Kitsault River Formation exposed along the shores of Alice Arm. In the absence of fossils, these correlations were based entirely on lithological similarities and geographical proximity. Hanson (1935) applied the term Hazelton Group to "rocks of supposed Jurassic age of the Alice Arm district" including the Bear River Formation and Goose Bay Formation of the Anyox Pendant. Grove (1986) retained the term Hazelton Group for calc-alkaline, volcanic and sedimentary rocks of the Unuk River - Salmon River - Anyox areas of probable Jurassic age. He further subdivided the Group into the lower Jurassic Unuk River Formation, the middle Jurassic Betty Creek and Salmon River Formations, and the upper Jurassic Nass Formation. Volcanic rocks of the Anyox Pendant were correlated with the Betty Creek Formation, and the Anyox sedimentary rocks with the Salmon River Formation. Sharp (1980) proposed that the Anyox rocks are better correlated with volcanic and sedimentary rocks of the upper Triassic to lower Jurassic Karmutsen-Maude Assemblage of the Wrangell Terrane. The correlation was based on a lithologic comparison of the Anyox rocks with a stratigraphic section from the Queen Charlotte Islands produced by Sutherland Brown (1968) and chemical similarities between the Karmutsen Formation and the Anyox volcanic rocks. Smith (1993) employed Pb-Pb and Sm-Nd isotope systematics to assign an Early to Middle Jurassic age to volcanic rocks and massive sulphide mineralization in the Anyox Pendant. He further demonstrated that isotopic and lithogeochemical features of the 35 Anyox volcanics are different from those of the Karmutsen-Nikoli Formation, contradicting the correlation suggested by Sharp (1980), but resemble marginal basin volcanics of the Spider Peak Formation in the Methow Terrane. Smith (1993) concluded that the Anyox rocks probably originated in an early to middle Jurassic marginal basin that separated the Insular and Intermontane superterranes. Evenchick and Holm (1997) correlated the eastern Anyox sedimentary package with strata of the Bowser Lake Group in the Alice Arm area on the basis of lithological similarities and a limited amount of fossil data. They tentatively correlated underlying mafic volcanic rocks at Anyox with the Hazelton Group based on a presumed conformable contact between the sedimentary and volcanic rocks. 2.9 SUMMARY The eastern two thirds of the Anyox Pendant are underlain by Jurassic siltstone-sandstone turbidites and pelagic mudstones, Jurassic or possibly Triassic mafic volcanic rocks, and minor relatively undeformed Jurassic or younger dioritic intrusive bodies. Lithologies in the western third of the pendant are more diverse and include sedimentary rocks of age and composition similar to those in the eastern part, as well as associated mafic volcanic rocks and a greater proportion of undeformed mafic intrusives. Cataclasic to mylonitic granitoids of undetermined age and intensely deformed Paleozoic mafic to ultramafic intrusive rocks are also found in the western part of the pendant where they occur in fault-bound panels that have no obvious correlation to the Mesozoic volcanic sedimentary package. 36 Rocks in the Anyox Pendant are metamorphosed to greenschist facies (and locally to amphibolite facies in the western part of the Pendant) and are thermally metamorphosed where adjacent to Tertiary intrusive rocks of the Coast Plutonic Complex. The entire tectono-stratigraphic package is folded around upright to overturned, easterly verging and gently northerly plunging megascopic folds, which are offset along high-angle north-trending brittle faults. Northeast trending folds are identified locally, most notably in the areas of the Hidden Creek and Bonanza mines. Massive sulphide mineralization at the Hidden Creek mine, the Bonanza mine and the Double Ed, Eden and Redwing deposits is believed to represent a Jurassic or slightly older syngeneic event related to construction of the mafic volcanic sequence. Copper-gold quartz veins on Granby Peninsula and in the Maple Bay area can be distinguished from massive sulphide veins by data from fluid inclusions and Pb-isotope features and are probably related to emplacement of the Tertiary Coast Plutonic suite. Weak molybdenum-porphyry mineralization occurs in a small area of Tertiary intrusive rocks along Observatory Inlet. 37 CHAPTER 3: LITHOSTRATIGRAPHY OF THE HIDDEN CREEK MINE 3.1 INTRODUCTION The geology at the Hidden Creek Mine consists of a lower mafic volcanic package and an overlying mudstone-turbidite sedimentary sequence. The ore zones are adjacent to or near the contact between the mafic volcanic and sedimentary rocks, within the hinge zone and overturned easterly limb of the Hidden Creek Anticline (Figure 3.1; Maps 1 and 2 - back pocket). This structure forms part of a broad, north-plunging and south and east-verging fold that dominates the structural style of the area. The Nos. 2 and 3 ore zones consist of stratabound semi-massive and massive sulphide lenses in the upper part of the mafic volcanic package, whereas the Nos. 1, 4 and 5 ore zones consist of strataform lenses in the lower part of the mudstone-turbidite package. Hydrothermal alteration associated with sulphide mineralization forms a broad halo around the volcanic-sediment contact, and is most intense and thickest in the vicinity of the Nos. 1 and 5 ore zones. Altered rocks related to sulphide mineralization are strongly foliated and contain variable amounts of chlorite, epidote, sericite and quartz. Bedded siliceous rocks, up to 75 metres thick, outcrop in the vicinity of the main ore zones, and have been interpreted by Sharp (1980) as exhalative cherts. A non-foliated mineral assemblage of actinolite, red to green amphibole, epidote and biotite, is interpreted as a regional metamorphic overprint of the earlier hydrothermal alteration. 38 Figure 3.1: Distribution of lithologies in the Hidden Creek area. Altered lithologies include chlorite and sericite schist, cherty rocks and quartz-sulphide veins. 39 3.2 MAFIC VOLCANIC ROCKS Mafic volcanic rocks form much of the footwall to the Hidden Creek sulphide lenses. The surface distribution of the volcanic lithologies implies a general stratigraphy comprised of a lower sequence of massive and pillowed flows, sills and minor fine grained gabbroic rocks and an upper sequence of predominantly fragmental volcanic rocks (Figure 3.1). Most of the volcanic rocks weather a pale green colour and vary from dark green to grey on fresh surfaces, while sulphide-bearing and hydrothermally altered volcanic rocks in and near the mineralized zones weather a rust-brown colour. Rare plagioclase phenocrysts are observed and a few samples have coarser-grained to gabbroic textures. However, most of the volcanic rocks near the ore zones are too altered and metamorphosed to allow positive identification of either primary mineralogy or texture. 3.2.1 Massive Volcanic Rocks Massive volcanic intervals, up to 20 metres thick, occur throughout the volcanic stratigraphy and are identified in both drill core and outcrop. In outcrop, these rocks can be traced laterally for tens of metres. Textures that could be used to distinguish these rocks as either flows or sills are rare, perhaps due to subsequent deformation, hydrothermal alteration and metamorphism of the rocks. Where observed, massive volcanic flows are distinguished by distinct chilled and vesicular margins with calcite, chlorite and quartz amygdules. Locally, flow-top breccias are present. Some coarser grained massive rocks may represent sills or portions of thick flows within the volcanic stratigraphy. 40 3.2.3 Pillowed Flows Relatively undefonried pillowed mafic volcanic flows occur in the upper volcanic stratigraphy in the footwall of the No. 4 ore zone, along the western margin of the Hidden Creek map area, and in a NE - SW trending belt extending from the southern edge of the Nos. 2 and 3 pit to the northern margin of the of the No. 6 pit (Figure 3.1). Relatively undeformed pillows are from 10 centimetres to 2 metre in longest dimension, with aspect ratios of about 2:1 (Plate 3.1). Individual pillows are internally massive and cut by radial contraction fractures and joints. Quartz, chlorite and calcite amydules are common along the pillow margins, which are 1 to 4 centimetres thick, aphanitic and darker than the pillow cores. Interpillow cavities are filled by cherty lenses and fine-grained volcaniclastic rock. Cherty lenses are also found in internal cavities in the cores of the pillows. In drillcore, pillows are distinguished by aphanitic, chlorite (-biotite)-rich cuspate pillow margins with cherty lenses in the interpillow cavities Within mineralized areas, pillow margins become increasingly silicified. Fine to coarse disseminated sulphides accompany silicification. On weathered outcrop, chalk-white to rust-coloured ridges of quartz and sulphides mark the outlines of individual pillow forms. 3.2.4 Volcanic Breccias and Fragmental Rocks Interlayered fragmental volcanic rocks and pillowed flows form most of the upper 100 metres of the volcanic sequence in the Hidden Creek Mine area, including the volcanic footwall of the main ore zones, and host most of the major stockwork intersections in the upper volcanic sequence. Fragmental volcanic rocks consist of broken pillow lobes, joint 41 Plate 3 . 1 mafic pillow volcanics in the footwall of the No. 2 ore zone. Note the rusty weathering pillow rims and cherty lenses in the pillow cores. Plate 3 . 2 Surface exposure of pillow breccia in the footwall of the No. 6 ore zone. Pillow forms are defined by rust-weathering, siliceous and sulphide-bearing pillow rinds and indicate that the breccia is in situ and not remobilized. 42 and fracture bounded blocks, a lesser component of fine-grained hyaloclastite and chert lenses. Locally brecciated pillows are defined by near complete, rust weathering, pillow rinds, which suggests that the breccia is in situ and not remobilized (Plate 3.2). Breccia clasts are 5 to 30 centimetres long and are subangular to tear-shaped. Many clasts have chlorite(-biotite)-rich rust weathering rinds and have a similar appearance, on a small scale, to the pillow lavas, but tend to be more deformed with higher aspect ratios. Typically a decrease in pillow or clast size is accompanied by an increase in the volume of finer-grained volcaniclastic material and frequency of cherty lenses. The distinction between the relative components of the fragmental units becomes blurred with increasing deformation. Undeformed volcanic breccias are rare both in outcrops and in drill intersections. In high strain zones, both the volcanic clasts and chert lenses become progressively more attenuated and form 1-4 centimetre thick, irregular bands of chert, and volcanic rock altered to chlorite, biotite and actinolite (Plate 3.3). Competency contrasts in the volcanic bands appear to be due to a mix of larger volcanic clasts and fine-grained volcaniclastic rock in the protolith. Cherty bands, which partially envelop the volcanic clasts, are white to red, <1.5 centimetres thick and commonly appear boudinaged and folded. In drillcore, the irregular and inhomogeneous distribution of volcanic clasts and cherty lenses progressing into banded chert and actinolite, chlorite and biotite rich layers are the most diagnostic features of fragmental units (Plate 3.4). 43 Plate 3.3: Quartz-cemented volcanic breccia in the footwall of the No. 6 ore zone. Each division on the scale card to the lower left of center is 1 centimetre. « Plate 3.4: Banded quartz-chlorite-actinolite schist in drill core. Hole 88-4, from 175 to 186.2 metres. 44 3.2.5 Gabbroic Rocks Several gabbro diorite bodies crop out to the north of the collapsed mine working. The intrusions are medium to coarse grained and are cut by finer grained dykes of similar composition. The gabbro and diorite bodies sit within the mafic volcanic rocks and do not appear to extend into the sedimentary sequence. Although contacts between the northern gabbros and the volcanic rocks are not exposed, the gabbros are chemically similar to the volcanic rocks (see Chapter 4) and are very different than the Tertiary mafic intrusions in the area. Most likely the northern gabbros originated in the same magmatogenetic event that formed the Anyox volcanic rocks. The gabbros and diorites consist primarily of plagioclase and hornblende. Plagioclase is saussuritized but still recognizable; hornblende is interpreted as a metamorphic alteration of clinopyroxene. Sub- to anhedral grains of hornblende enclosing, in whole or in part, smaller euhedral plagioclase crystals and have replaced pre-metamorphic, sub-ophitic pyroxene and plagioclase. Other less voluminous mineral phases include actinolite, chlorite, quartz, pyrite and magnetite. Despite the coarseness of the rock, a weak foliation in the gabbros parallels the main foliations in the volcanic rocks and further distinguishes them from undeformed Tertiary mafic intrusions in the area. 3.3 VOLCANIC PETROGRAPHY The mineralogy of the mafic volcanic rocks varies with increasing hydrothermal alteration. No primary mafic minerals are recognized even in the coarser grained volcanic rocks, regardless of the degree of alteration or metamorphism, and plagioclase is 45 preserved only in mildly to moderately altered rocks. Volcanic rocks that have suffered intense hydrothermal alteration are composed almost entirely of chlorite with lesser epidote and variable amounts of quartz. In moderately altered volcanic rocks, the proportions of quartz, chlorite and epidote decrease and the proportions of actinolite, hornblende and feldspar increase. Rocks that have experienced the lowest degree of hydrothermal alteration are rich in actinolite, hornblende, and feldspar and contain only small patches of chlorite and quartz. Magnetite and rutile are predominant accessory oxides in intensely altered rocks. Pyrite and pyhrrotite, the most common sulphides throughout the volcanic suite, are most abundant in the most hydrothermally altered rocks. In the mafic volcanic rocks, all the primary mafic mineral phases and groundmass have been altered to secondary mineral assemblages of chlorite, quartz, actinolite, hornblende, epidote and biotite (Plate 3.5). Similarly, hyaloclastite and fine-grained volcaniclastic rock in the fragmental rocks or between pillows, have been completely replaced by secondary minerals. Plagioclase, the only surviving primary mineral, is preserved only in mildly to moderately altered rocks, where it is corroded and partially altered to chlorite, quartz, actinolite and epidote. Typically, feldspar is best preserved in the more crystalline rocks such as the fine-grained gabbros. Hydrothermally altered rocks preserve a strong foliation characterized by flattened and commonly crenullated, intergrown mats of fibrous to tabular chlorite or by more acicular grains which anastomose throughout a fine-grained quartz-rich matrix (Plate 3.6). In plane polarized light, chlorite varies from straw yellow to light green to dark green and 4 6 Plate 3.5: Photomicrograph of a moderately altered volcanic rock in the footwall of the No.2 ore zone. Bioite and radiating clusters of actinolite overprint a fine-grained quartz-chlorite-rich matrix. Plane light, surface sample 11-1, width of view=5 mm. Plate 3.6: Photomicrograph of a hydrothermally altered mafic volcanic rock in the footwall stratigraphy. Lath-like fibrous chlorite grains anastomose through a fine-grained recrystallized quartz-rich matrix. Fine to coarse disseminations of pytThotite (black opaque mineral) pepper the rock. Plane light, hole E9, at 176.4 metres, width of view 5 mm. 47 has anomalous brown to blue interference colours in crossed polars, reflecting Fe-rich to Mg-rich varieties respectively (Albee, 1962). Throughout the least altered volcanic rocks, chlorite also occurs in small nonfoliated patches that in some cases may be metamorphic. For the most part however, chlorite appears to have formed as a product of hydrothermal alteration. Fine-grained recrystallized quartz with undulatory extinction is intergrown with other secondary hydrothermal minerals in centimetre-wide haloes along the margins of quartz veins, cherty rims of pillows and volcanic fragments, and around thin fractures in the host rock. Quartz partially replaces plagioclase crystals forming granular-textured aggregates along grain boundaries and within individual crystals. In some thin sections fine-grained recrystallized quartz appears uniformly distributed throughout the altered rock. In more deformed samples, pockets of quartz-rich altered rock are flattened and attenuated forming blue-grey lenses that alternate on the centimetre-scale with green chloritic altered rock. Clinozoisite and zoisite are intergrown with foliated quartz-chlorite assemblages in the altered selvages of mineralized veins and as a minor component of the hydrothermally altered volcanic rocks. Microcrystalline clusters of epidote replace primary feldspars in less altered rocks. In some thin sections, large nonfoliated euhedral epidote grains overprint earlier chlorite-quartz assemblages and are likely the product of metamorphism. The relative proportion of epidote as a secondary mineral phase increases in the least altered rocks. However, individual crystals are commonly too small to allow one to determine whether the epidote is of hydrothermal or metamorphic origin. 48 Amphiboles of the actinolite-tremolite series and hornblende are the most common mafic minerals (up to 70% by volume) in the less altered volcanic rocks and typically form prominent, easily recognizable grains in a finer matrix of epidote, chlorite and feldspar. In thin section, the actinolite-tremolite is pleochroic (colourless to pale yellow to green). Actinolite-tremolite grains are acicular to fibrous and form nonfoliated radiating clusters that overprint earlier foliated quartz-chlorite-rich mineral assemblages and impart a felty texture to the rocks in hand specimen (Plate 3.7). Hornblende is more common in coarser phases of the volcanic suite but is generally less abundant than actinolite-tremolite amphiboles. Hornblende typically forms squat tabular crystals with strong red to green pleochroism that are intimately intergrown with actinolite-tremolite. In some petrographic sections, large amphibole grains have pleochroic hornblende cores and margins comprising finer grained acicular actinolite-tremolite. Biotite occurs as a secondary mineral in about 20% of the volcanic rocks, mainly near the top of the volcanic sequence. Biotite is inhomogeneously distributed in bands and patches throughout the volcanic rocks and is also in the selvages of some mineralized veins. Where abundant, biotite forms mats of intergrown tabular grains that display a thatched pattern in thin section. Elsewhere, biotite is more evenly distributed as nonfoliated aggregates with actinolite-tremolite that overprint foliated chlorite- and quartz-rich mineral assemblages (Plate 3.8). The nonfoliated habit and spatial association with actinolite-tremolite suggest that biotite is the product of metamorphism. Plate 3.7: Photomicrograph of altered mafic volcanic rock. Accicular actinolite grains overgrowing "flattened" mats of chlorite. Surface sample from the footwall of the No. 2 ore zone. Width of view=0.63 mm. Plate 3.8: Photomicrograph of biotite-actinolite metamorphic phases in a moderately chlorite-altered mafic volcanic rock. Footwall of the No. 4 ore zone, hole 93D9, 122.5 metres. Field of view=5 mm. 50 3.4 SEDIMENTARY ROCKS A sedimentary succession of massive to laminated clastic sedimentary turbidites and mudstone overlies the mafic volcanic sequence and comprises the hangingwall of several of the main sulphide lenses at the Hidden Creek Mine. These rocks weather grey to black and are rust brown near mineralized zones. Discontinuous limestone lenses account for <5% of the stratigraphy and are most abundant near the base of the sedimentary sequence. Least altered sediments are quartz and feldspar rich and although some metamorphic recrystallization has occurred, primary sedimentary structures such as graded bedding and rip-up clasts are well preserved and in some cases can be traced into zones of mild to moderate hydrothermal alteration. Chlorite, muscovite and epidote, are the main alteration minerals. Non foliated mineral aggregates of biotite and rare acicular actinolite-tremolite overprint both the altered and least altered rocks and are interpreted to have formed during regional metamorphism. In addition to the altered clastic sediments, the sedimentary package includes locally bedded impure and recrystallized quartz-rich rocks, or cherts, near the contact with the mafic volcanic package. The bedded siliceous rocks are within and adjacent to mineralized zones and are at least in part hydrothermally altered equivalents of the turbidite-mudstone sequence. 3.4.1 Clastic Turbidites and Pelagic Mudstone The clastic turbidites have been deposited as a series of prograding, fining-up cycles, each tens of metres in thickness. Each cycle progresses from interbedded sandstone and siltstone at the base to bedded sandstone-siltstone-argillite turbidites with pelagic 51 mudstone in the middle intervals and massive to laminated pelagic mudstone at the top. Individual turbidite beds are massive and unsorted, rarely graded and ranging from one to tens of centimetres in thickness (Plate 3.9). Near the contact with the mafic volcanic rocks, there is a greater proportion of argillite and mudstone and the clastic turbidites are thinner. On fresh surfaces coarser more phyllitic sediments appear grey and finer grained mudstone-rich layers appear black. The overall grain size and bed thickness of the sedimentary units increases in successive cycles above the mafic contact so that coarse quartzo-felspathic sandstone beds occur in the upper sedimentary sequence (see Section 2.2). Fine-grained sandstone-siltstone turbidites from 0.5 to 30 centimetres thick have sandstone-siltstone bases which grade into mudstone-rich tops. Contacts between beds are sharp and commonly marked by flame and load structures. Fine grained, disseminated sulphides and quartz blebs occur along foliation planes in the silty layers. Thinly bedded to laminated pelagic mudstone and siltstone-argillite turbidites consist of roughly equal proportions of siltstone and mudstone with a lesser component of sandstone and argillite (Plate 3.10). Individual beds tend to be only a few centimetres thick, are generally massive, occasionally cross-laminated and rarely display good grading. Grey biotite- and muscovite-rich argillite beds commonly occur interbedded with siltstone and mudstone. Thick sequences of massive to laminated mudstone are the least abundant type of the clastic sedimentary rocks. The sequences are up to 15 metres thick and are most commonly interbedded with thinly bedded to laminated siltstone-rich turbidites. 5 2 Plate 3.9: Interbedded turbidite-mudstone sequence in the Hidden Creek sedimentary cover located to the north of the collapsed workings of the Nos. 2 and 3 ore zones. In this photo, 0.2 to 0.5 metre-thick siltstone-sandstone turbidites are separated by recessively weathering mudstones. Plate 3.10: Thinly bedded fine sandstone and siltstone turbidites (light gray) and intervening graphitic mudstones (dark) in drillcore. Turbidites range from graded and ungraded. Hole D9, 12.8 metres. 53 Mudstones are black on fresh surfaces, and weather rust brown. Individual mudstone beds, up to 30 centimetres thick, are separated from one another by 0.5 to 2 centimetre thick layers of fine sandstone or siltstone. 3.4.2 Limestones Limestone, recognized in outcrop and drillcore, is composed of coarse calcite with up to 40 % detrital silt- and sand- sized quartz and feldspar grains and fine black mud. In drillcore, limestone beds are usually < 0.5 metres thick, and are interbedded with the graded and laminated sandstone-siltstone-argillite turbidites, but not with thickly bedded mudstone. The limestone beds are grey, coarse grained and often have silicified, biotite and epidote-rich altered selvages that can extend into the host turbidite for several centimetres. In outcrop, limestone occurs as recessive-weathering, discontinuous beds and lenses. Exposed surfaces weather grey and have a mottled appearance due to thin, <0.5 centimetre thick, resistant, sand and silt sized, quartzofeldspathic layers. The quartzofeldspathic layers are commonly folded, suggesting that the limestone lenses may be dismembered fold hinges and boudins within the disrupted sedimentary layers. Although most lenses are <1 metre long, thicker and more continuous layers are recognized in the walls of the collapsed working of the Nos. 1, 5, and 6 ore zones. Calcite in most of the limestones is entirely recrystallized. However in some limestones, with a high quartzo-feldspathic component, calcite forms discrete grains with broken edges and appears to be detrital. Furthermore, such limestone lenses are found 54 exclusively within turbidites and never with just the pelagic mudstones. These limestones may have been deposited as calcareous turbidites in the sedimentary sequence. However, other limestones in the sequence may be chemical precipitates. 3.5 SEDIMENTARY PETROGRAPHY The main detrital components of the least altered sedimentary rocks are subhedral, silt- to sand-sized quartz and feldspar grains, some lithic fragments and black to brown mud and clay (Plates 3.11 and 3.12). Coarser quartz grains display undulatory extinction. Feldspar grains, though mildly saussuritized, are still distinguishable. Some beds contain muscovite and biotite apparently not related to hydrothermal alteration, that may be detrital or metamorphic in origin. Fine to coarse disseminated pyrrhotite is the main accessory sulphide away from the mineralized zones. Recrystallized calcite occurs in several samples. Hydrothermally altered, clastic sedimentary rocks overlie the volcanic sequence and form the footwall to Nos. 1, 4, 5, and 6 ore zones (Plates 3.13 and 3.14). The primary mineralogy of the altered clastic sediments has been obliterated by intense hydrothermal alteration and metamorphism, resulting in the albitization of feldspars in moderately altered rocks, the replacement of feldspar with chlorite and muscovite in more intensely altered rocks, and the recrystallization of hydrothermal and detrital quartz into a fine grained saccaroidal texture. Fine grained euhedral rutile is rare and pyrite, not pyrrhotite, is the predominant sulphide phase. The altered sedimentary rocks vary texturally from schistose to cherty as a function of 55 Plate 3.12: Photomicrograph of a mudstone-siltstone boundary in the Hidden Creek sedimentary cover. The lower sericite-rich layer fines upward to a sharp contact with the more quartz-feldspar-rich silty base of the upper bed. Note that the foliation at a high angle to bedding. Hole E1,420.0 metres. Crossed polars, width of view=5 mm. Plate 3.13: Cherty and sulphidized, bedded clastic sediment on the western edge of the No. 1 pit. Layers are <1 to >10 centimetres thick. Less siliceous, rusty, sulphide-bearing layers separate the whitish siliceous layers. Also present are sulphide-bearing veins which cut bedding at a high angle. Plate 3.14: Three examples of cherty clastic sediment from drillcore. Bone white samples (e.g. left piece of core) contain >80 % Si0 2 but several % A 1 2 0 „ indicating the presence of a clastic component. In places, bedding similar in appearance to that in outcrop (Plate 3.13) can be recognized, with siliceous beds separated by sericite-chlorite altered clastic sediment (e.g. middle piece of core). From left to right, the samples are from hole D l at 43 metres, hole D2 at 124 metres, and hole D1 at 27 metres. 57 quartz content. In both schists and cherts, chlorite- to muscovite- to biotite-rich endmembers are recognized. In the schists, chlorite and muscovite form foliated mats of intergrown platy mineral grains. Chlorite shows slight pale green to yellow pleochroism and is typically grey when rotated from extinction under crossed nicols. Muscovite has colourless to pale green pleochroism and displays high second-order birefringence. Muscovite in some sections has a pink to green iridescence in plane polarized light. Cherts, the most siliceous of the altered sediments, consist of aphanitic quartz in a granular texture with variable amounts of chlorite and mica as intergranular phases. Relatively pure chert is generally white to grey on fresh surfaces and weathers a chalky-white. Chert weathers rusty where sulphides are present, yellowish where they contain significant biotite and sericite impurities, and olive green to white when chlorite is present. Individual beds may be massive and up to several metres thick. More commonly, however, cherty beds vary from less than a centimetre to several centimetres thick and are interbedded with thin, schistose layers (Plate 3.15). Primary sedimentary structures such as graded bedding and rip-up clasts are locally preserved in both the cherts and the schists and layering in the altered sediments mimics primary bedding in the least altered sediments. However, near mineralized zones it is difficult to identify a turbidite-mudstone precursor, as few traces of original bedding remain. Lithogeochemical data presented in Chapter 4 indicates that these cherty rocks contain a significant component of aluminosilicate detritus. Zones of fragmented chert make up a significant portion of the cherty intervals. Chert clasts are up to 10 centimetres long and are blocky to slightly rounded. The clasts are 58 Plate 3.15: Photomicrograph of hydrothermally altered sedimentary rock of biotite and quartz-feldspar layers in the altered sedimentary rock. Hole D9,73.4 metes, width of view 5 mm. Plate 3.16: Photomicrograph of relict bedding in quartz-chlorite-biotite-altered sediment. The lower biotite-rich layer is graded; fining toward the upper chlorite-quartz layer. The biotite-rich interval may be an altered equivalent to AljO,-, K 2 0 - and MgO-rich mud or pelagic bed top in unaltered sediment. Hole D2,96.9 metres width of view=2.63 mm 59 separated by an anastomosing network of 0.2 to 2 centimetre thick bands of biotite-chlorite-sericite schist. Fragmented cherty rocks are spatially associated with mineralization and appear to cut up stratigraphy in at least two areas are interpreted as zones of hydrothermal breccia and veining. Nonfoliated biotite with brown to red pleochroism overprints both chlorite and muscovite and is believed to be related to regional metamorphism. Biotite forms tabular euhedral mineral grains that comprise > 50% of the modal mineralogy of some of the altered sedimentary rocks and commonly form centimetre scale bands and thin seams in the altered sediments. More rarely, the proportion of biotite increases gradually in graded layers which fine toward sharp contacts with coarser quartz-chlorite layers in a way that mimics graded bedding in the unaltered sediments (Plate 3.16). In such cases the biotite-rich interval may be an altered equivalent to AI2O3-, K2O and MgO-rich mud or pelagic bed tops in the unaltered rocks. This interpretation is consistent with the distribution of biotite elsewhere in the altered sedimentary rocks as biotite-rich bands and seams have a similar distribution in the chlorite-quartz-altered sediments to pelagic mudstone beds in the clastic turbidites. 3.5.1 Porphyroclastic Sedimentary Rocks Hydrothermally altered sedimentary rocks with porphyroclastic texture are common within a few tens of metres of the mafic volcanic contact throughout the Hidden Creek area. In outcrop, the porphyroclasts are lighter in colour and are harder than the sedimentary rock in which they are developed and on weathered surfaces appear as 60 embossed spots comprising from 10% to 50% of the rock. Bancroft (1918) noted that spotted sediments also occur near the margins of some larger intrusive bodies. The most common porphyroclasts are grey to white, 0.5 centimetre in diameter, with a waxy luster. Others are red-brown, ovoid and about 1 centimetre in diameter (Plate 3.17). Spotted units are roughly equally distributed between the moderately and intensely altered sedimentary rocks and between the chlorite and muscovite rich phases of the altered sediments. Petrographic examination indicates that the spots are a mosaic of fine-grained recrystallized quartz with abundant muscovite, chlorite and biotite aligned in a planar fabric. Individual porphyroclasts are often difficult to distinguish as they are only slightly more quartz-rich than the host rocks and grain margins are often diffuse. Fox (1989) suggested that the porphyroclasts are cordierite and quartz-muscovite-biotite psuedomorphs after cordierite. In the course of this study, however, cordierite could not be positively identified in hand specimen, petrographically or through x-ray diffraction analyses of several of the spotted sedimentary rocks. Porphyroclasts commonly sit within the foliated chlorite- and muscovite-rich layers in the altered sediment and are characterized by quartz-rich pressure shadows and foliated tails of mica and chlorite. Some porphyroclasts show evidence of rotation whereby the foliation within the porphyroclast is at an oblique angle to and often bends into the foliation of the host rock. In one petrographic section a thin sulphide-bearing quartz vein cuts across a porphyroclast (Plate 3.18). These features indicate that the porphyroclasts grew at the same time or prior to the main phase of deformation in the sedimentary rocks 61 Plate 3.17: Coarse texture in the hydrothermally altered, sedimentary rocks adjacent to the mafic volcanic contact. Plate 3.18: Photomicrograph of rotated porphyroblast in the altered sedimentary rocks, a clockwise rotation of the quartz-chlorite-sericite-rich porphyroclast is indicated by the bending of the foliation in the platey minerals along the margins of the clast. Note the late quartz-sulphide vein cutting the porphyroclast and an earlier foliation. Hole D3,90.5 metres, width of view=2.63 mm. 62 and at least the latest phase of sulphide-rich quartz veining. 3.6 T E R T I A R Y I N T R U S I V E R O C K S A suite of non-foliated mafic to intermediate dykes and rare sills intrude the volcanic and sedimentary rocks in the Hidden Creek area. Fine grained to aphanitic intrusives are dark green to black, can be hornblende-, plagioclase-, or biotite-phyric, and locally have amygdules filled by calcite. Medium to coarse grained intrusives contain variable proportions of subhedral to euhedral feldspar, quartz and hornblende with accessory magnetite and pyrite and vary from dioritic to quartz monzonitic compositions (Plate 3.19). The intrusives are undeformed and relatively unaltered. Chlorite and epidote alteration of the amphiboles and mild saussuritization of the feldspars is consistent with greenschist facies metamorphism of the rocks but does not approach the extent of hydrothermal alteration in the surrounding volcanic and sedimentary rocks (Plate 3.20). Intrusive contacts cut across foliation in the host rocks. Xenoliths of silicified sediment and partially digested clots of pyrrhotite were observed in several of the intrusives. These features indicate that rocks of this suite were intruded after the main stage of sulphide mineralization. Modal compositions, lack of deformation and a distinct trace element chemistry (Chapter 4, this thesis) indicate that the intrusive are unrelated to the mafic volcanic rocks and is probably associated with phases of the Coast Plutonic Complex. Childe (1997) reported an Early Tertiary (53 +5/-7 Ma) U-Pb zircon age from an undeformed mafic dyke in the Plate 3.19: Fine to medium grained plagioclase-homblende intrusive. This intrusion contains xenoliths of chert and clots of sulphide and has well developed chilled margins. Hole D2,84.1 Plate 3.20: Lath-like grains of plagioclase are intergrown with high birefringence hornblende. Hole D2,84.1, with of view=2.63mm. 64 Hidden Creek area. This age is consistent with others reported from eastern margin of the Coast Plutonic Complex (Carter, 1981; Grove, 1986; Evenchick and Holm, 1997). 3.7 S T R U C T U R E At least two phases of folding and two phases of faulting complicate the structure of the Hidden Creek Mine area. The main mineralized zones sit within the Hidden Creek Anticline which forms part of a megascopic northerly trending, south and easterly verging fold system that dominates the structural style of the map area. A northeasterly trending fold system was recognized in the western parts of the map area, this folding, which parallels the southern surface trace of the volcanic-sediment contact may predate the northerly-trending structures (Figure 3.2). Shallow dipping faults are associated with the early folding event and are interpreted as thrusts by Fox (1989) and Tyler (1993). A series of northerly-trending brittle normal faults transect the map area and appear to rotate the earlier fold and fault structures. Deformation is most intense in the vicinity of the orebodies and along the contact between the volcanic and sedimentary rocks and presumably reflects rheological differences between the ore lenses, the hydrothermally altered lithologies and the least altered rocks further away from the contact. 3.7.1 Deformation of the Lithological Units Lack of marker horizons in the volcanic rocks makes it difficult to assess fold styles. A penetrative cleavage developed throughout the entire mafic volcanic package and locally intense shear and flattening fabrics are the dominant expressions of deformation. Strain is commonly accommodated in discrete zones, tens of metres wide, in which pillows and 65 1 • Mafic Volcanic a - Massive and Pillow b - Fragmental and Schist . c • Mixed -JL- Massive sulphide outcrops Figure 3.2: Distribution of major structural elements in the Hidden Creek area. Northeast-trending folds are more evident in the western and southern portions of the mapsheet while north-trending structures dominate the area around the pits. 66 volcanic clasts in the fragmental units are attenuated, elongated and flattened (Plate 3.21). Pillowed and massive units tend to show less evidence of strain than the fragmental rocks. In the fragmental rocks, volcanic clasts are separated by an anastomosing network of 0.2 to 2 centimetre thick cherty, fine-grained recrystallized quartz and volcaniclastic rock altered to chlorite and actinolite. Quartz has recrystallized in pressure shadows and along the margins of the volcanic clasts and locally partially encloses individual clasts. In the most intensely deformed exposures, attenuated vein networks, cherty lenses and inhomogeneously altered volcanic layers have consistent trends over tens of metres, imparting a banded appearance in both outcrop and drillcore. Shearing and clast rotation is common in these zones. The sedimentary rocks lack clear marker horizons and the interpretation of map scale folds is derived mainly from bedding and cleavage measurements (see below) and from the orientation, styles and geometries of minor folds observed in outcrop. Deformation in the sedimentary sequence is expressed as open to tight, upright to recumbent folds with wavelengths on a scale of metres to tens of metres (Plate 3.22). These are particularly noticeable along the walls of all the open pits and probably affect the distribution of the mineralization throughout anticlinal structure that hosts the main orebodies. The sedimentary rocks have been affected by at least two phases of folding. In rare cases refolding of previously folded layers are observed in outcrop and in more schistose sedimentary layers, crenulation cleavages are observed. However, in most outcrops, Si and S2 cleavages could not be positively distinguished and as a result the analyses of the 6 7 Plate 3.21: Flattened pillow volcanics with fine grained volcaniclastic sediment to the west of the collapsed workings of the Nos. 2 and 3 ore zones. These rocks form the transition from relatively pristine pillow volcanics to more intensely deformed quartz-chlorite schist (e.g. Plate 3.4). A syn-volcanic mafic dyke cuts the volcanic sequence along the right margin of the photo. Plate 3.22: Syncline in mudstone-turbidites in the southern structural domain of the Hidden Creek area. The sedimentary sequence is comprised of interbedded siltstone-sandstone turbidites, up to 5 metres thick, interbedded with thinner (10 centimetre thick) pelagic mudstone layers. 68 megascopic structures the sedimentary rocks focuses on the change in the orientation of structural elements from one domain to another throughout the map area. Folds related to the first deformation event are typically tight to isoclinal with a strong, bedding parallel, axial planar cleavage. Fold orientation varies from upright to recumbent. Disharmonic, similar and kink band fold styles are all observed. Asymmetric folds have long normal limbs, narrow hinge zones and shorter overturned limbs and appear reflect the fold style of the Hidden Creek anticline. Parasitic folds occur along the limbs. Where observed in those rare outcrops, folds related to the second deformation event are typically upright, gentle to open parallel folds with a spaced non-axial planar cleavage. The folds are most clearly recognized in the long limbs of the Fi folds and are associated with a crenulation in the Si fabric in the most fissile and schistose layers especially in the hydrothermally altered sedimentary rocks near the contact with the mafic volcanic rocks. Tyler (1993) identified several shallowly dipping thrust faults in the walls of the Nos. 1 and 5 pit that imbricate the volcanic and sedimentary rocks that may account for the thickness of the altered cherty sediments in this area. Although not specifically located, imbrication of the folded volcanic and sedimentary strata along shallowly dipping structures is referred to in Fox (1989). In outcrops mapped as part of this study, inhomogeneous shears cut and imbricate the fold hinges in the most intensely folded sediments and are believed to be contemporaneous with folding. High-angle brittle normal faults cut and displace the contact between the folded volcanic 69 and sedimentary rocks. Most of these faults have a northwest to northeast orientation. Some easterly trending high-angle faults are recognized; one of which follows the volcanic-sedimentary contact in the southern part of the map area. The solid body rotation of blocks between these faults may have resulted in some dispersion of the earlier structural elements (cleavage, bedding and fold axis) from recognized trends, but for the most part earlier fabrics are preserved within the fault bound blocks. Evenchick (pers. comm.) has identified numerous north-trending brittle normal faults throughout the Anyox pendant, some of which cut intrusives of the Coast Plutonic Complex and are therefore Early Tertiary or younger in age. Brittle high-angle faults in the Hidden Creek area are similar in character to those identified by Evenchick are likely the same age. 3.7.2 Fold Analyses The Hidden Creek Anticline and the Gamma Zone Syncline are the major fold structures in the map area (Figure 3.2). These folds are predominately north-trending, east-verging structures but rotate to a more easterly trend in the southern part of the map area. Six structural domains are recognized based on the orientation of major structural elements in each domain (Figure 3.3, Map 2 - back pocket). All structural measurements from the stereographic projections used in the fold analyses were taken by the author. The projections were compared to some data obtained from the Gamma Zone Anticline and the area of the No. 6 ore zone by Peter Lewis during a field visit to Anyox in the summer of 1994. Structural styles and the importance of certain structural elements with respect to predominantly outcrop scale features were also discussed at this time. 70 1 '. : ; • •, } •. ~~~~ fTT c - Mixed \ Contour line Figure 3.3: Structural domains in the Hidden Creek area. 71 The sedimentary rocks are divided into: • The Southern domain, in the area of the No. 6 ore zone. • The Southeastern domain, in the area of the Silica Pit and the Nos. 1 and 5 ore zones. • The Northern domain, north of the pits. • The Gamma domain, in the central part of the map area. The volcanic rocks are divided into: • The Central domain, between the Gamma zone sediments and the pits. • The Western domain, on the west margin of the map area. In the sediments of the North domain, bedding and cleavage trend north-south with northeast and westerly dips respectively (Figure 3.4a,b). Bedding cleavage intersections and axis of small-scale parasitic folds plunge moderately to shallowly toward the north. Dispersion in the data reflects non-cylindrical, open fold geometry and interference by other folding and faulting events. The orientation of the cleavage suggests that the fold system is easterly verging. Similar-type folds styles in the sedimentary strata suggest that both the bedding and cleavage should dip in the same direction. The difference in the dip attitudes between the bedding and cleavage may reflect the box fold geometry of the Hidden Creek Anticline (Fox, 1989; Nelson, 1935; Lewis, pers. comm.) or possibly counterclockwise rotation of the strata around north-plunging axes during folding or block faulting. 72 Southeast Domain So Southeast Domain Scl-F/L • Bedding (So). • Foliation (Sci) + Fold axis (F)/So-Scl (L) intersection lineation Figure 3.4: Orientation patterns for (a) bedding and (b) bedding/cleavage intersection lineations and small scale fold axis in the north domain sediments, and (c) bedding and (d) bedding/cleavage intersection lineations in the southeast domain sediments. Al l plots are lower hemisphere equal area projections. 73 In the Southeast domain (Figure 3.4c,d), the distribution of bedding and cleavage mimic each other, varying from predominantly northerly trending to easterly trending and moderately to steeply dipping, with a strong east to south verging asymmetry. Bedding-cleavage intersections and axes of parasitic folds plunge moderately to steeply to the north and east. This variation records a progressive change in the fold system from gently dipping, open folds in the upright limb of the Hidden Creek anticline, to the north, to tighter folds with more steeply dipping limbs along the hinge zone of the anticline. The orientation of the contact changes from moderately easterly dipping to the North to near vertical in the South domain. The change in the fold style also corresponds with a change in the trend of the contact from north to east along the southern margin of the No. 1 ore zone. Structural elements in the sediments of the South domain generally have a much tighter distribution than those in the North or Southeast domains (Figure 3.5a,b). The distribution of bedding and cleavage mimic each and follow a great circle path on the stereographic projection. Bedding-cleavage intersections and axes of small-scale, parasitic folds tend to plunge shallowly to northeast and southwest. These features define a sub-cylindrical, upright to gently northerly plunging and strongly south-south westerly verging, tight to isoclinal fold system. The structural elements show some dispersion that may be the result of modification by later phases of deformation. Bedding measurements from sediments in the Gamma Zone (Figure 3.5c,d) domain are loosely distributed along a great circle path that trends to the west-southwest and dips moderately northward. For the most part cleavage mimics bedding in distribution. 74 South Domain So South Domain - Scl-F/L Gama Domain So Gama Domain Scl-F/L • Bedding (So) A Foliation (Sci) + Fold axis (F)/So-Scl (L) intersection lineation Figure 3.5: Orientation patterns for (a) bedding and (b) bedding/cleavage intersection lineations and small scale fold axis in the south domain sediments, and (c) bedding and (d) bedding/cleavage intersection lineations in the gama domain sediments. A l l plots are lower hemisphere equal area projections. 75 Bedding-cleavage intersections and axes of parasitic folds plunge northward to varying degrees. The distribution of structural elements in this domain is similar to that in the southeast domain presumably reflecting both rotation of early fabrics and the superimposition of later deformation events. Cleavage measurements from volcanic rocks in the Central domain (Figure 3.6a) have a north-trending, steep westerly dipping orientation that is consistent with an easterly verging fold system. Cleavage measurements from volcanic rocks in the west domain (Figure 3.6b) are loosely distributed along a great circle path with the bulk of the measurements having moderately northwest dipping orientations. The dispersion of the structural elements along a great circle path is similar to that observed in the sedimentary rocks of the Southeast, South and Gamma domains and may be related to the superimposition of later deformation events. 3.7.3 Discussion It is clear from the data presented above that the orientation of major structural elements in the Hidden Creek map area changes from a predominantly east-northeast orientation in the southwestern parts of the mapsheet (in the vicinity of the No. 6 ore zone) to a northerly trend in the northern parts of the mapsheet. Fox (1989) suggests that the north-trending, east verging fold system (Hidden Creek Anticline-Gamma Zone Syncline) was formed during the earliest phase deformation in the area. The rotation of the main structural elements is partially accounted for by the presence of an east-west trending Central Volcanics Sci N S West Volcanics Sci N S • Bedding (So) A Foliation (Sci) + Fold axis (F)/So-Scl (L) intersection lineation Figure 3.6: Orientation patterns of foliations from (a) the central volcanic domain and (b) the west volcanic domain. All plots are lower hemisphere, equal area projections of poles to planes. 77 shear zone located several hundred metres to the south of the No. 6 ore zone. Mapping by the author and Peter Lewis failed to identify this shear zone. This study considers it more likely that the observed map pattern is simply the result of the superimposition of a north-trending, east-verging fold system upon the an earlier east-northeast4rending, south verging fold system. Alternatively, a single north-trending fold system may have had a component of dextral shear offsetting the orientations of the normal and overturned limbs. Each domain samples a different part of the fold resulting in a systematic variability in orientation of the structural elements. 3.8 H I D D E N C R E E K M I N E G E O L O G Y : S U M M A R Y The mafic volcanic package is comprised of a lower portion of predominantly massive and pillowed volcanic rocks, sills and gabbroic phases and an upper portion of predominantly volcanic breccia. Pillows, where discernible, are up to 1 metre in length, with rusty weathering rims. In local shear zones, the pillows are elongated to pancake-like shapes. Reworked volcanic breccias consist of angular clasts 5 to 30 centimetres long, together with lesser fine-grained hyaloclastite, and pockets of cherty infillings. Most volcanic rocks are too altered to allow, positive identification of either primary mineralogy or texture, although some plagioclase-phyric and gabbroic rocks are recognizable. Hydrothermally altered rocks are characterized by fibrous grains of sub-aligned chlorite anastomosing through a fine-grained, recrystallized, quartz-rich matrix. Feldspar grains, where recognizable, are corroded and partially altered. Coarser non-aligned actinolite is superimposed upon the alteration assemblage. 78 Interbedded siltstone and sandstone turbidites with pelagic mudstones overlie the mafic volcanic sequence. Individual turbidites range from one to tens of centimetres in thickness; they are massive and unsorted, with rare grading, and are comprised of subhedral, silt- to sand-sized quartz and feldspar grains, and black to brown argillaceous material. Near the mafic contact, there is a greater proportion of argillite, and clastic turbidites are thinner. Although some metamorphic recrystallization has occurred, original sedimentary textures away from the mineralized zone are well preserved. Recrystallized calcite occurs in several samples, commonly as discrete grains with broken edges, and appears to be detrital in origin Impure limestone beds containing up to 30% clastic material may be in part turbiditic in origin. . The primary mineralogy of the altered clastic sediments has commonly been obliterated by intense hydrothermal alteration and upper greenschist metamorphism which has led to the replacement of feldspar by chlorite, epidote and muscovite, and the recrystallization of hydrothermal and detrital quartz into a saccharoidal texture. Locally a porphyroclastic texture is developed in some of the altered sedimentary rocks. Metamorphic biotite and actinolite overprint both chlorite and muscovite. Bedded siliceous rocks, which occur near the contact with the mafic volcanic rocks are at least in part altered equivalents of the turbidite-mudstone sequence. Non-foliated and relatively unaltered mafic to intermediate dykes and rare sills intrude the volcanic-sedimentary package. The intrusives are feldspar-quartz-hornblende-rich and cut across primary contacts and foliations in the host rocks. A U-Pb zircon age of 53 +5/-7 Ma suggests that the intrusives are contemporaneous with phases of the Coast Plutonic 79 Complex. A penetrative cleavage is developed throughout the entire mafic volcanic package and strain is commonly accommodated in discrete zones of intensely foliated quartz-chlorite schist. Open to tight, upright to recumbent folds with wavelengths on a scale of metres to tens of metres occur throughout the sedimentary rocks. The earliest folds, which are best preserved in the southern and western parts of the map sheet, are tight to isoclinal, east-northeast trending and southerly verging. North-trending and easterly-verging non-cylindrical open folds, which are best preserved in the northern parts of the mapsheet, overprint the earlier folding causing significant dispersion in the orientation of the major structural elements. High angle north-trending brittle faults cut the folded strata, rotate the earlier structures, and in one instance, offset the Nos. 2 and 3 ore zones. 80 CHAPTER 4 : LITHOGEOCHEMISTRY 4.1 I N T R O D U C T I O N For this study, a suite of 45 sedimentary, 61 volcanic, 1 gabbro and 8 late mafic dyke samples were analyzed for major and trace element chemistry by X-ray fluorescence at the Geochemical Laboratory, McGill University. A subset of 10 volcanic and 7 sedimentary samples were analyzed for rare-earth elements by neutron activation at Activation Labs in Ancaster, Ontario. The samples were obtained from surface exposures and drillholes intersecting the footwall and hangingwall of the main ore zones at Hidden Creek. Several volcanic rocks from surface exposures near the Bonanza deposit were also analyzed. A complete list of analytical data and details on sample and analytical quality control are discussed in Appendix A and C respectively. 4.1.1 Trace Element Systematics Hydrothermal alteration and greenschist facies metamorphism have replaced much of the primary mineralogy and changed the bulk rock chemistry of many of the Anyox volcanic and sedimentary rocks. Several studies examining the mobility of elements in altered and metamorphosed rocks found that Al, Ti, P and the high-field-strength elements Zr, Y, Nb and the REE are relatively immobile during hydrothermal alteration and low grade metamorphism (MacLean and Kranidiotis, 1987, MacLean, 1988, Winchester and Floyd, 1976, Cann, 1970). These immobile elements can be used to distinguish between the volcanic, sedimentary and late mafic intrusive rocks in the Anyox area (Figure 4.1a). 81 E a. a. 100 90 80 70 60 50 40 30 20 10 "l i i 1 1 1 r "i 1 1 r Tholeiitic Zr/Y = 2-5 Transitional Zr/Y = 5-7 Calc-alkaline Zr/Y = 7-20 r - - 1 - T ' I I I i i 40 80 120 160 Z r ( p p m ) 200 240 280 Figure 4.1 a: Y vs Zr immobile element plot showing the composition fields for the Hidden Creek volcanic and sedimentary rocks and the Tertiary mafic dyke. Tholeiitic, transitional and calc-alkaline compositional fields after McLean and Barrett (1994) 25 I I I I I I I I i 1 1 1 1 1 t 1 20 Basalt / ^^ ^^ ^^  Mass Gain: Dilution of / ' ^F*8fe&/, Immobile Elements / "^ 7^ *^  Mass Loss: Cone, of — , Immobile Elements i 1 5 / cf < 10 o — / ^' Basaltic andesite 5 — / s I ' / , / • / -0 t s I I l l 1 I I I i 1 i I I i 0 60 120 180 Z r ( p p m ) Figure 4.1b: Schematic explanation of alteration trends observed in the Hidden Creek volcanic rocks. The displacement of an altered sample from the fractionation trend represents the mass change factor, which is one parameter used in calculating elemental mass changes. Concentrations of immobile elements are increased in rocks affected by mass loss, and altered samples will be displaced away from the origin along linear trend. Altered sample move toward the origin with mass gain, indicating a dilution of the immobile elements. 82 During hydrothermal alteration mass gains or losses will dilute or enrich the immobile elements without changing their ratios. On immobile element plots, alteration trends extend towards the origin with mass gain and in the opposite direction with mass loss (Figure 4.1b). Therefore, if the original composition of the protolith is known, lithogeochemical plots using these immobile elements can evaluate changes in bulk rock chemistry resulting from hydrothermal alteration. Incompatible elements (bulk distribution coefficients DSOiid/meit <0.1) monitor the degree of fractionation and the magmatic affinity of the Anyox volcanic rocks. Ti, Y, Zr and P all behave incompatibly in fractionating basalt to basaltic andesite liquids (Pearce and Norry, 1979). Volcanic rocks from the same fractionating series should form linear trends extending away from the origin on binary incompatible element plots. The slope of the fraction trend may change depending on the minerals precipitating. 4.1.2 Least Altered Rocks Selection of the least altered mafic volcanic rocks was based on petrographic examination (low chloritization and silicification), low loss on ignition, and the retention of more or less primary contents of CaO+Na20 (10-14%) and MgO (5-10%). Least altered sedimentary rocks were selected partly on the basis of petrography (abundant feldspar); they also tend to have the highest CaO+Na20 values and the lowest loss-on-ignition and MgO values. Petrographic examination indicates that rocks of the late mafic intrusive suite were not significantly affected by hydrothermal alteration. 83 Table 4.1: Chemical composition of representative least-altered volcanic rocks at the Hidden Creek deposit, Anyox Sample(surface) 74 11-1 48 65 Hole No. E6 E2 E2 E65 82-10 E2 82-4 Depth (m) 68.3 135.1 surface 53.0 83.5 surface surface surface 77.4 195.7 11.4 Series E-MORB E-MORB T-MORB T-MORB T-MORB N-MORB N-MORB N-MORB N-MORB N-MORB N-MORB Si0 2 (%) 47.54 49.33 51.41 47.47 48.56 50.58 50.43 50.53 49.54 48.42 47.84 Ti0 2 2.27 1.23 1.30 2.01 1.37 1.76 ' 1.22 1.87 1.13 1.57 1.24 AljOj 18.08 17.94 15.64 15.49 14.99 14.48 15.47 15.18 15.65 14.84 16.25 FejOj 12.40 9.60 12.42 16.64 11.76 13.35 10.98 14.47 13.02 13.73 9.41 MnO 0.05 0.16 0.15 0.19 0.18 0.21 0.16 0.44 0.35 0.20 0.24 MgO 6.01 6.13 5.78 5.60 8.85 9.40 7.94 8.98 9.71 6.68 10.49 CaO 4.32 9.07 9.35 9.14 11.60 7.72 10.07 6.09 6.15 9.74 9.12 Na20 4.86 3.80 3.19 2.59 1.65 2.13 3.10 2.32 3.41 3.01 2.08 KjO 1.32 0.62 0.34 0.59 0.29 0.05 0.22 0.09 0.28 0.13 1.46 P 2 0 5 . 0.50 0.26 0.19 0.29 0.19 0.17 0.11 0.17 0.10 0.13 0.10 BaO 0.04 0.05 0.02 0.05 0.04 0.00 0.00 0.00 0.02 0.02 0.19 LOI 2.32 1.59 1.15 0.48 0.83 0.79 0.96 0.76 1.53 1.45 2.17 Total 99.79 99.86 101.01 100.61 100.38 100.73 100.75 101.00 100.97 100.00 100.68 Cu (ppm) 83 147 95 65 76 198 144 146 89 105 97 Zn 152 114 118 131 87 131 78 213 196 99 106 Co 26 59 36 50 36 48 51 56 42 55 36 Ni 16 118 30 29 39 49 95 64 86 51 106 Cr2Oj 13 161 39 21 28 53 189 40 162 37 263 V 503 255 286 376 350 365 293 383 289 378 319 Sc 34 37 34 30 42 39 41 39 0 42 0 Zr 145 81 80 140 79 105 73 109 58 88 65 Y 70 32 38 54 34 47 33 49 30 42 31 Nb 11 12 8 9 9 8 7 7 3 7 3 Rb 30 12 4 9 3 0 2 0 7 0 24 Sr 208 190 137 167 236 68 201 64 78 218 61 Ga 25 16 17 21 16 16 17 19 17 19 15 Pb 7 7 11 2 1 7 6 7 2 2 4 Table 4.2: Chemical composition of representative altered volcanic rocks at the Hidden Creek deposit, Anyox. Sample (surface) Hole No. Depth (m) Series D6 52.3 E-MORB E2 138.4 E-MORB D8 60.4 T-MORB D9 122.5 T-MORB 44-5 surface N-MORB 63-2 surface N-MORB 82-10 218.3 N-MORB D9 89.9 N-MORB D9 112.7 N-MORB E6 189.2 N-MORB Si0 2 (%) 47.81 48.85 51.20 39.42 43.08 54.41 47.03 49.23 39.60 52.03 Ti0 2 2.67 1.44. 1.86 1.79 1.24 1.38 0.99 1.67 1.63 1.23 A1203 17.78 20.39 16.80 14.71 18.50 11.71 14.18 16.88 15.88 13.16 Fe 20 3 10.42 9.97 10.75 22.15 18.63 18.05 16.89 12.40 18.21 17.51 MnO 0.11 0.09 0.13 0.14 0.27 0.18 0.15 0.07 0.18 0.24 MgO 8.41 5.65 7.11 11.47 9.72 8.94 13.80 9.71 14.03 9.16 CaO 4.79 3.50 3.31 2.13 3.59 0.73 1.29 3.32 1.36 0.92 Na20 0.70 4.49 3.61 0.08 2.31 0.15 0.17 2.30 1.07 1.43 K 2 0 3.91 3.47 2.65 1.28 0.04 0.03 0.02 0.20 0.44 0.02 P 2O s 0.59 0.33 0.22 0.29 0.10 0.13 0.08 0.16 0.14 0.07 BaO 0.12 0.26 0.12 0.04. 0.00 0.00 0.00 0.03 0.04 0.01 LOI 2.62 1.18 1.84 6.62 3.42 4.96 5.71 4.31 6.98 4.65 Total 100.05 99.70 99.67 100.45 100.99 100.77 100.43 100.37 99.79 100.52 Cu (ppm) 258 90 89 2200 141 425 363 164 1223 372 Zn 224 109 104 518 101 92 144 94 209 73 Co 39 40 50 140 73 34 49 51 40 37 Ni 38 69 44 22 98 31 74 85 42 69 Cr 2 0 3 123 207 77 18 183 77 236 173 333 70 V 503 249 367 365 267 312 266 354 373 189 Sc 41 35 32 29 29 28 0 40 34 30 Zr 182 92 116 189 69 87 52 114 20 67 Y 61 40 47 82 31 38 24 48 40 23 Nb 11 12 10 11 9 7 3 11 8 9 Rb 73 58 94 16 0 0 3 27 6 0 Sr 50 234 132 176 46 22 19 19 56 30 Ga 21 13 19 24 21 19 18 24 20 15 Pb 6 3 12 12 2 6 0 4 1 4 84 4.2 V O L C A N I C R O C K S 4.2.1 Major and Trace Element Compositions Least altered mafic volcanic rocks at Anyox have major element compositions ranging from basalt to basaltic andesite (Table 4.1). Ranges of the major oxides include Si02 from 44 to 52 %, A1203 from 15 to 18%, Ti0 2 from 1.2 to 2.0 %, CaO from 6 to 12 % , and MgO from 5 to 10 %. The K2O content of <0.5% together with REE data (below) indicate that the majority of the mafic rocks are low-K tholeiites. Altered mafic volcanic rocks have greater ranges in Si02, AI2O3, Ti02, and MgO and are on average depleted in CaO and enriched in K 20 (Table 4.2). The major element compositions of the mafic volcanic rocks are also reflected in the trace element compositions. The volcanic rocks plot as basalt to basaltic-andesites in standard classification plots (Figure 4.2) using immobile trace elements. On a Ti-Zr-Y ternary plot (e.g.: Figure 4.2b), the volcanic rocks form a cluster within the ocean floor basalt and low-K tholeiite compositional fields as defined by Pearce and Cann (1973). This tight cluster of data is reflected in individual Ti02 vs Zr and Y vs Zr plots (Figure 4.3) as linear trends with positive slopes and small Y-axis intercepts. The Anyox volcanic rocks have an average (Zr/Ti)1000 ratio of 9.94 and plot mainly in the field of ocean floor basalts (Figure 4.3a). The whole mafic group has an average Zr/Y ratio of 2.37, which is typical of ocean-floor tholeiitic basalts (Figure 4.3b). The positive slopes in the trends are due to the high degree of incompatibility of these elements during crystallization of mafic volcanic rocks. As Zr is more incompatible than either Y or Ti (Sun and McDonough, 1989) in fractionating basaltic magmas, positive y-intercepts can result if the most conserved element of the incompatible a) Winchester & Floyd 1977 (fig 6) » .1 N .01 .001 - i — • fc- And I Rhyodacite/Dacite A sn/Nph: SubAlkaline Basalt ' i .01 .1 1 Nb/Y 10 Ti/100 Pearce&Cann1973 b) Within Plate Basalts: D Ocean FloorBasalts:B Low Potassium Thole 11 tes: A, B Calc-Alkaline Basalts: B,C Zr Y * 3 + <> N-MORB Mafic Volcanics, Unaltered/Altered y y T-MORB Mafic Volcanics, Unaltered/Altered ^ A E-MORB Mafic Volcanics, Unaltered/Altered Figure 4 2- Immobile element plots for the Hidden Creek mafic volcanic rocks (a) Zr/Ti02 vs Nb/Y compositional plot indicting that the volcanic rocks are subalkalme basalt to basaltic andesite. (b) Zr vs Ti/100 vs Y*3 ternary plot. ITie majority of the rocks plot in the field of ocean floor basalts. 50 100 150 200 250 300 Zr (ppm) + O N-MORB Mafic Volcanics, Unaltered/Altered y V T-MORB Mafic Volcanics, Unaltered/Altered A A E-MORB Mafic Volcanics, Unaltered/Altered Figure 4.3: Immobile element plots for the Hidden Creek mafic volcanic rocks, (a) Zr vs Ti02 binary plot. Samples plot mainly in the field of ocean-floor basalts with an average 1000(Zr/Ti) of 9.94. (b) Zr vs Y binary plot. Samples have an average Zr/Y ratio of 2.37. 87 o 12 -8 •• O as O T • • • 25 -20 • 15 • n O CN 10 • < 5 • 0 4 0.1 0.2 0.3 0.4 0.5 0.6 P 2O s Wt% + N-MORB Mafic Volcanics, Unaltered/Altered ^ T-MORB Mafic Volcanics, Unaltered/Altered A E-MORB Mafic Volcanics, Unaltered/Altered Figure 4.4: Variation diagrams for least altered Hidden Creek mafic volcanic rocks, using P 2 O s as a monitor of fractionation. FeO* = total Fe calculated as FeO. Enriched volcanic rocks (upright and inverted triangles) typically have higher A1 20 3, T i 0 2 and K 2 0 values than non-enriched rocks (diamonds). 88 pair (Zr) is on the x-axis. On the basis of the Ti02 vs Zr and Y vs Zr plots, the Anyox rocks would be considered part of the same volcanic suite. However, as shown in the following sections, it is possible to recognize an important subset on the basis of several geochemical criteria, including the P/Ti ratio and REE data. Incompatible elements, such as Zr, are commonly used as an index of fractionation for evaluating the variation of other elements in a fractionating magmatic suite. Least altered samples are used to construct a series of Harker-type fractionation plots for each element. In the present study, P2O5 is employed as the index of fractionation (Figure 4.4), rather than Zr. As shown below, P2O5 more clearly distinguishes between the mafic rock sub-series at Anyox than do more commonly used elements, such as Zr, Y and Ti02. The elemental fractionation trends shown in Figure 4.4 are also used to estimate precursor compositions for the mass change calculations given in a later section. Although P may become mobile under certain conditions of hydrothermal alteration, several lines of evidence suggest that it is generally not mobile. In a study of the Triassic Windy Craggy deposits Peter (1992) found only minor mobility of P in altered mafic metavolcanic rocks. Seawater alteration of basalts on the modem seafloor produces only minor P exchange (Thompson, 1983). Finally in this current study mass change calculations using P lead to the same general results as Al-Ti-based calculations, indicating that P is essentially immobile under the alteration conditions that prevailed in the mafic footwall at Anyox. 4.2.2 Rare-Earth Elements The mafic volcanic rocks can be subdivided into LREE-depleted and LREE-enriched suites (Figure 4.5, Table 4.3). These suites also differ in other geochemical parameters, as shown s CU T3 a cu JS .2 u o s. fi « > oi t> +j • « 2 .-si .2 .is O cu a s-S W o fi cu E cu "<3 I ii i cu * Qi 3 es H vo rn ID Q vo m CN PJ 1 § D O s 1 § S t 3 Ov Q VO t 3 tl 3 ^ 6 § o CO I 1 § 5 Q 4> *s TJ p O 3 S Ov Ov Q Z i» O O O r n O O O V O V I O O O 0 0 t " ~ T t v q c > vo'wScKwS'-—<voo —* m — o o o — o o CN o o Tt ov — — oq v-> Tt rn — O rn o >/•> t— o •/-> t-~ CN Tt — — o o o r- o o o vq 00 [--in ci ol ri d d o o o T j - v o o o o r ^ m o o — oqvqv>rn r s t - l v o t N O O f S O O O O c n O v o m m vo p o ov — Ovr^v-» o m* o m CN ov CN o o oo oo o os vo o O Ov ro o Ov *r> — <N cn — — m* o CN — O O O T t v o O T t C N T t o o r ^ T t i n r N m — vdvS — O O C N O O O O m o o O v o v i O O O r n O v p r ~ ; V " i ^ • n d f i d . H n o o o o «-> o o »0 O CT\ O - » f- oo ^ o i—i vo vo CN O O CN B a. iP 3 cU os a Qi Vi Qi U Cu Qi U o fi O eu £ © fl CU s CU • pfi ts 05 <U ' Qi U & m • .fi cU mm mO ce H O oj Qi m* Qi Qi U u e T3 (U J3 .S CJ o CU - oo s t Q vd < « w u VO i l TJ 00 o o o vo O O .-• Tl- oi * * i Crt CN i i n *- — "S ca c —> i l T J C3 B ^ o. *5 y vo r- o o o — CN CNi !-< o o o — o O O O - H C N O C N O O v o o o v o m ^ j - o q c N CN v d m C N O O i - i O — CN — O O O Tt o o o vi cn — 6 m o m o\ CN m o CN O fN O o o o c N T t o o v r ^ o o -rt »n v~> Tt rn • e t c N O O C N O O C N O o o o » n v o o v o m o o O T t p — vq«o d i - d i n ' - - i f * i o CN m CN O O O C N ~ - O 0 0 C N r ^ o o o o o o w - j c N r n 00 00 — C N O O C N O o o o oo o o r~ — o —i m — ON 00 O Tt m o o cn o B 2 u Z w W 90 Norm: Chondrite (Evenson et al. 1978) 100 i " — 1 — i i—i i i i i i i i i i i Sample P/Ti (ppm) Zr (Ce/Yb)N D9-89.9 0.070 11-1 0.070 48 44-5 120 107 0.066 74 0.059 72 E6-189.2 0.041 72 a) 0.89 0.83 0.70 0.54 0.69 L a C e N d S m E u G d T b Yb Lu 100 r 10 \r I I 1 I I L a C e N d S m E u G d T b 3rv Sample P/Ti Zr (Ce/Yb)N (ppm) E6-68.3 0.160 151 1.36 D9-122.5 0.118 206 1.36 E2-53.0 0.105 142 1.01 E6-83.5 0.102 80 1.10 74 0.106 82 1.18 b) Yb Lu + O N-MORB Mafic Volcanics, Unaltered/Altered y V T-MORB Mafic Volcanics. Unaltered/Altered .4 A E-MORB Mafic Volcanics, Unaltered/Altered Figure 4.5: Rare earth element profiles for representative samples of Hidden Creek mafic volcanic rocks, (a) the LREE-depleted suite, and (b) the LREE-enriched suite. The comparative data on the right indicate that variation in R E E patterns are consistent with variations in other elemental abundances. The R E E data are normalized to chondrite values of Evensen et al. (1978). Gd was not analysed but values were calculated in order to better define Eu anomalies in the R E E patterns. 91 by the comparative data. Samples are arranged from least evolved (bottom) to most evolved (top) which corresponds to an increase in the absolute abundance of the REE, an increase in Zr (representing an index of fractionation), and an increase in P/Ti ratios. The LREE-depleted suite has the characteristic pattern of normal mid-ocean ridge basalt = N-MORB (Sun and McDonough, 1989). Negative Eu anomalies in two altered samples may be the result of either fractionation or alteration of plagioclase. In the LREE-depleted series, rocks with the lowest P/Ti ratios also have the lowest Zr and (Ce/Yb)N values. As P/Ti increases, so do Zr and (Ce/Yb)N, which supports the premise that these rocks are related through fractionation. P and the LREEs are more incompatible than Ti and the HREEs in mafic mineral phases (Sun and McDonough 1989). Therefore, as fractionation proceeds, P/Ti and (Ce/Yb)N should increase systematically. The LREE-enriched suite includes one sample (E6-68.3m) with the characteristic evolved pattern of enriched mid-ocean ridge basalt = E-MORB (Sun and McDonough 1989). The other four samples in this suite have relatively flat to slightly LREE-enriched patterns that appear transitional between N-MORB and E-MORB, and are thus referred to as T-MORB. 4.2.3 Ti02vsP2Os At Anyox, there is a strong correlation between LREE-enrichment and higher P/Ti ratios in the mafic volcanic suite. As a result, P/Ti ratios can be used to subdivide the volcanic rocks into LREE-depleted and LREE-enriched suites. Three suites of rocks are distinguished in the volcanic rocks using a Ti02 vs P2O5 plot (Figure 4.6a). Rocks with P/Ti < 0.075 correspond to the LREE-depleted rocks and are classified as N-MORB. Rocks with P/Ti > 0.150 correspond to the most LREE-enriched rocks and are classified as E-MORB. Rocks with P 2 O e (wt%) + O N-MORB Mafic Volcanics, Unaltered/Altered • V T-MORB Mafic Volcanics, Unaltered/Altered A A E-MORB Mafic Volcanics, Unaltered/Altered Figure 4.6: T i 0 2 vs. P 2 0 5 relations for a) least altered mafic volcanic rocks; and b) all mafic volcanic rocks, Hidden Creek area. This plot (like T i 0 2 vs. Zr) is useful for establishing volcanic trends, but not for assessing net mass change effects in altered rocks because potential alteration lines are near-parallel to the fractionation trends. Alteration effects are instead assessed from A1 2 0 3 vs P 2 0 5 relations. 93 ratios between the N-MORB and E-MORB series are interpreted in this study as the result of mixing between the two end members and are classified as T-MORB. The linear P/Ti trend observed in the least altered N-MORB volcanic rocks (Figure 4.6a) is consistent with similar trends in Ti/Zr plots reflecting the fractionation of olivine, plagioclase and pyroxene from an evolving basaltic liquid (Pearce and Cann, 1973). The two least altered E-MORB samples can be joined by a similar trend line, which extends away from the origin. Because Ti and P are immobile over the spectrum of Anyox compositions, altered mafic volcanic rocks should lie on trends which are parallel to the fractionation trends and as a result can be assigned to one of the three sub-series based on their P/Ti ratios (Fig 4.6b). Several other criteria support the subdivision of the mafic volcanic rocks using P/Ti ratios. Large ion litholphile elements, such as K and Ba, are also incompatible in evolving basaltic liquids which concentrate P and the high field strength elements, Zr, Y and Ti. Both K and Ba tend to be more enriched in both the least altered and altered volcanic rocks with high P/Ti ratios and LREE enrichment (Figure 4.4 and Tables 4.1 and 4.2). Despite the observed trends, the relative mobility of the large ion lithophile elements during hydrothermal alteration makes using K and Ba enrichment suspect as definitive criteria for subdividing the volcanic rock suite. In petrographic section, the majority of the enriched volcanic rocks contain biotite whereas in all but a few of the altered volcanic rocks, biotite is missing from the modal mineralogy of rocks in the non-enriched (N-MORB) suite. The presence of biotite appears to reflect the higher K content of the enriched volcanic rocks and can be used as a reliable petrographic means to distinguish between the enriched and non-enriched suites, especially in the least 94 a^ltered, actinolite-rich volcanic rocks. 4.2.4 Al203 vs P2Os Some of the trends in the TiCh vs P2O5 plot can be further tested using AI2O3 vs P2O5 relations. The AI2O3/P2O5 ratio should also reflect primary rock forming processes and remain constant in hydrothermally altered rocks. Least altered N-MORB samples form a linear trend with a negative slope in an AI2O3 vs P2O5 plot (Figure 4.7a) which correlates with the N-MORB fractionation trend shown by Ti02 vs P2O5 and reflects plagioclase fractionation. Least altered E-MORB samples have distinctly higher AI2O3 and P2Os than can be accounted for by the N-MORB type fractionation and form a separate trend. Samples of T-MORB also lie off the N-MORB trend mainly due to their higher P2O5 values and form a cluster of points between the N-MORB and E-MORB trends. In an AI2O3-P2O5 (or AbOs-Zr) plot, altered samples will lie on alteration lines that intersect fractionation trends at moderately high angles (as opposed to the situation for Ti02-P20s or Ti02-Zr plots). At Anyox, altered N-MORB and E-MORB samples show significant departures from their estimated fractionation trends due to mass loss and gains (Figure 4.7). On the basis of these relations, mass changes can be calculated for the altered volcanic rocks, as discussed below. The first step in this procedure involves relating altered samples back to their initial position on the appropriate fractionation (or mixing) trend in Figure 4.7a. Initial AI2O3/P2O5 ratios and precursor values for the mass change calculations are given in Table 4.2. Alteration of the T-MORB samples is difficult to assess visually in this plot. Furthermore, it should be noted that E-MORB and T-MORB samples with higher AI2O3 values have not necessarily been subjected to higher degrees of mass loss than the N-MORB 25 20 N-MORB E-MORB f 15 MORB 10 Mixing ? Fractionation 0.2 0.4 0.6 0.8 b) 25 N-MORB E-MORB V v T^T-MORB^ ' Schematic alteration effects 0.2 0.4 0.6 P 2O s ( W t % ) 0.8 • O N-MORB Mafic Volcanics, Unaltered/Altered • V T-MORB Mafic Volcanics, Unaltered/Altered A A E-MORB Mafic Volcanics, Unaltered/Altered Figure 4.7: A l 2 0 3 vs. P 2 0 5 relations for (a) least altered mafic volcanic rocks, and (b) all mafic volcanic rocks, Hidden Creek area. In this plot, altered rocks lie along alteration lines which are at moderate angles to fractionation trends (as in an AI 2 0 3 vs. Zr plot). 96 samples, as the E-MORB samples had a higher AI2O3 content to begin with relative to the N-MORB series. 4.2.5 Mass Changes During Alteration Mass balance calculations were performed on the Anyox mafic volcanic rocks in order to quantify the effects of hydrothermal alteration related to mineralization (Table 4.4). The calculations employ a multiple precursor method following MacLean (1990) and MacLean and Barrett (1993), and are based on the fractionation and mixing trends shown in the AI2O3 vs P2O5 plot (Figure 4.7b). After the initial Al203-P205 contents of each altered rock are determined, the initial values for the other major elements were estimated from the individual element versus P2Os fractionation trends discussed earlier (Figure 4.6). The mass changes ( A values) are reported as absolute oxide abundances in weight %. A detailed calculation of this procedure is presented in Appendix B. Similar mass change results were obtained for the N-MORB suite using Al203-Ti02 and Al203-Zr to determine precursor compositions (not shown). This was done as a check to ensure the reliability of P2O5 in these calculations. Furthermore, in the calculations using P2O5, losses and gains of the immobile elements Ti02 and Zr for most of the samples in the N-MORB and E-MORB suites, were <5% of the precursor values (Appendix B). This indicates comparable incompatible and immobile behavior in P, Ti02 and Zr in the unaltered and altered volcanic rocks. Greater calculated changes in Ti02 and Zr were seen in the T-MORB samples. Precursor compositions for this suite were defined by mixing trends which are not as well constrained as the fractionation trends used to calculate the mass changes in the N-MORB and E-MORB suites. 97 Table 4.4: Representative calculated mass changes for volcanic rocks at the Hidden Creek deposit, Anyox Hole Depth (m): 82-10 77.4 Unalt (N) 82-4 11.4 Unalt (N) 82-10 218.3 Alt (N) 82-4 134 Alt (N) 82-4 166.8 Alt (N) D9 89.9 Alt (N) 82-10 164.5 Alt (T) D9 114.2 Alt (T) D6 100.6 AltfE) D6 41.5 Alt (E) Analytical data on LOI-free basis; Fe as FeO 50.52 49.07 50.61 48.79 45.32 51.96 47.90 41.53 48.45 51.66 1.15 1.27 1.07 1.29 1.53 1.76 1.62 1.94 1.38 1.36 15.96 16.67 15.26 15.16 15.40 17.82 14.12 16.08 17.51 17.06 11.95 8.69 16.36 18.05 25.05 11.78 27.41 23.93 14.83 13.78 0.36 0.25 0.16 0.13 0.10 0.07 0.17 0.13 0.07 0.12 9.90 10.76 14.85 13.99 10.08 10.25 5.99 10.77 10.04 12.43 6.27 9.35 1.39 2.13 2.05 3.50 1.74 2.22 4.88 1.50 3.48 2.13 0.18 0.29 0.19 2.43 0.60 1.43 2.28 1,07 0.29 1.50 0.02 0.04 0.11 0.21 0.19 1.55 0.22 0.62 0.10 0.10 0.09 0.11 0.14 0.17 0.23 0.27 0.31 0.31 0.02 0.20 0.00 0.00 0.02 0.03 0.02 0.12 0.02 0.08 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00 156.50 162.50 177.25 141.90 109.38 105.50 61.57 58.88 57.24 54.97 0.144 S i0 2 T i 0 2 A l 2 0 3 FeO MnO MgO, CaO Na 2 0 K 2 0 P2O5 BaO Total Al 2 03/P 2 0 5 ratio N-MORB use the fractionation line y=17.65-12.83x and the above alteration lines y=mx T-MORB use the mixing line y=13.82+9.57x and the above alteration lines y=mx E-MORB use the fractionation line y=l 8.08+1.39x and the above alteration lines y=mx P 2 0 5 (Precusor) 0.104 0.101 0.093 0.114 ' A1 2 0 3 (Precursor) P 2 0 5 Mass Change Factor S i0 2 T i 0 2 A1 20, FeO MnO MgO CaO Na 2 0 K 2 0 P 2 0 5 BaO Total S i0 2 T i 0 2 A1A FeO MnO MgO CaO Na 2 0 K 2 0 P 2 0 5 BaO Total S i0 2 T i 0 2 A1 20, FeO MnO MgO CaO Na 2 0 K 2 0 P 2 O s BaO Total 0.149 0.266 0.280 0.324 0.337 16.3 16.4 16.5 16.2 15.8 15.7 16.4 16.5 18.5 18.5 1.022 0.981 1.079 1.067 1.026 0.883 1.159 1.027 1.058 1.087 Precursor Values 49.55 49.48 49.32 49.76 50.40 50.50 49.69 49.64 49.51 49.47 1.28 1.25 1.20 1.35 1.57 1.60 1.96 2.07 1.51 1.57 16.31 16.36 16.46 16.19 15.80 15.74 16.37 16.51 18.53 18.55 10.88 10.86 10.82 10.92 11.05 11.07 11.59 11.66 11.85 11.91 0.24 0.24 0.25 0.24 0.23 0.23 0.18 0.18 0.16 0.16 8.81 8.85 8.94 8.70 8.35 8.30 6.97 6.80 6.31 6.16 9.98 10.00 10.06 9.91 9.68 9.65 8.80 8.69 8.38 8.28 2.53 2.51 2.47 2.57 2.73 2.75 3.34 3.41 3.63 3.69 0.28 0.28 0.26 0.30 0.37 0.38 0.61 0.64 0.73 0.76 0.10 0.10 0.09 0.11 0.14 0.15 0.27 0.28 0.32 0.34 0.04 0.04 0.04 0.04 0.04 0.04 0.05 0.05 0.05 0.05 100.01 99.98 99.91 100.10 100.37 100.41 99.84 99.96 101.00 100.95 Reconstructed Values: 51.64 48.16 54.59 52.08 46.48 45.89 55.53 42.65 51.27 56.15 1.18 1.25 1.15 1.38 1.57 1.56 1.87 2.00 1.46 1.48 16.31 16.36 16.46 16.19 15.80 15.74 16.37 16.51 18.53 18.55 12.21 8.53 17.64 19.27 25.68 10.40 31.78 24.58 15.69 14.97 0.36 0.24 0.17 0.14 0.10 0.07 0.20 0.13 0.08 0.13 10.12 10.56 16.02 14.93 10.34 9.05 6.94 11.06 10.63 13.51 6.41 9.18 1.50 2.27 2.10 3.10 2.01 2.28 5.17 1.63 3.55 2.09 0.20 0.31 0.20 2.14 0.70 1.47 2.41 1.16 0.29 1.47 0.02 0.05 0.11 0.19 0.22 1.59 0.23 0.67 0.10 0.10 0.09 0.11 0.14 0.15 0.27 0.28 0.32 0.34 0.02 0.19 0.00 0.00 0.02 0.03 0.02 0.13 0.02 0.09 102.22 98.14 107.85 106.74 102.55 88.32 115.91 102.68 105.83 108.69 Mass Changes: 1.76 6.68 2.08 -1.32 5.27 2.32 -3.92 -4.60 5.84 -6.99 -0.10 0.00 -0.05 0.03 0.00 -0.05 -0.08 -0.07 -0.05 -0.09 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 1.34 -2.33 6.82 8.35 14.63 -0.67 20.18 12.92 3.84 3.06 0.12 0.00 -0.07 -0.10 -0.13 -0.16 0.02 -0.04 -0.08 -0.03 1.31 1.71 7.08 6.23 1.99 0.75 -0.03 4.25 4.31 7.35 -3.57 -0.82 -8.56 -7.64 -7.59 -6.56 -6.79 -6.42 -3.21 -6.65 1.03 -0.41 -2.27 -2.27 -2.53 -0.61 -2.64 -1.94 -1.21 -2.53 0.01 1.19 -0.24 -0.26 -0.25 -0.19 -0.40 0.95 -0.50 -0.08 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 -0.02 0.15 -0.03 -0.04 -0.03 -0.01 -0.03 0.07 -0.03 . 0.04 2.21 -1.84 7.95 6.64 2.18 -12.09 16.07 2.73 4.83 7.74 Notes: Unalt=least-altered; AIt=Altered (N)=N-MORB; (T)=T-MORB; (E)=E-MORB 98 The total mass changes in the mafic volcanic rocks, as expressed as the sum of individual oxide changes in absolute weight percent, range from additions of 30% to losses of 25%. It is these net mass changes that are responsible for the dispersion of sample points along the alteration lines in the immobile element plots (Figures 4.6 and 4.7). The largest elemental fluctuations are in Si02 and FeO (total Fe, including sulphides), with significant changes in MgO, CaO, Na20 and K20. A plot of A(CaO+Na20) vs A(MgO+FeO) (Figure 4.8a) illustrates the progressive development of chlorite (gain of MgO and FeO) with breakdown of plagioclase (loss of Ca and Na) during alteration. Gains of MgO+FeO are up to +21%, whereas losses of CaO+Na20 are up to -12%. Variation in Si02 mass changes from -11% to +21% could reflect processes ranging from silica leaching during strong chloritization to silica deposition during formation of hydrothermal quartz veinlets (Figure 4-8b). Net loss or gain of Si02 does not correlate with mass changes in other oxides, possibly due to more than one generation of alteration. Significant gains in K 20 (up to +3.4%), in 5 of the 37 N-MORB samples, account for biotite alteration in rocks which typically lack modal biotite (Figure 4.8b). Strong biotite alteration (30% to 40% of the modal mineralogy) in T-MORB and E-MORB rocks is probably due to K-alteration and differs from least altered enriched rocks where biotite is only a minor mineral phase (5-10%). 4.2.6 Mineralogy Many of the mafic volcanic rocks which have been altered to mineral assemblages of actinolite, chlorite and epidote can be shown to have undergone little chemical change, whereas others with similar mineralogy have experienced significant mass changes as a result 99 ( % » « ) O 3 B N + O B 0 100 of hydrothermal alteration associated with mineralization. Relations between bulk lithogeochemistry and the main mineralogical components of volcanic rocks can be shown using molar proportion plots, for example, MgO vs AI2O3 vs (CaO+Na20+K20) (Figure 4.8c). The minerals shown in this figure were identified petrographically. Least altered mafic volcanic rocks plot in an area between albite and actinolite compositions. Altered equivalents of the samples fall along a sub-horizontal trend extending towards chlorite and biotite indicating that most of the Mg-gain in the volcanic rocks is accommodated in aluminosilicates (e.g., chlorite). Very little Mg-gain occurred through the formation of hydrated oxides and silicates (e.g., talc, brucite) which would have diluted the Al in the rocks and shifted the alteration trend on the diagram towards Mg. Although not quantitative, the changes in molar proportions indicate the degree of Mg addition and alkali loss in the rocks which can be verified by mass changes calculations using trace element data (Section 4.2.5). The molar proportion diagrams are useful in providing a clear link between the modal mineralogy, major element chemistry and trace element chemistry of the volcanic rocks. 4.3 S E D I M E N T A R Y R O C K S The least altered sedimentary rocks and the hydrofhermally altered schists and cherts have both major and trace element compositions that are clearly distinct from the mafic volcanic compositions (Tables 4.1 and 4.5). The sedimentary rocks, both altered and least altered, have higher Si02 contents but generally lower AI2O3, Fe203, MgO and CaO than the volcanic rocks. The trace element compositions of the sedimentary rocks are more difficult to assess due to mechanical sorting of the detrital components which may account for the extremely 101 Table 4.5: Chemical composition of representative altered and unaltered sedimentary rocks at Hidden Creek Hole Dll Dl l El DI D2 D2 D6 D9 DI D3 Depth (m) 23.8 77.1 138.7 19.2 37.2 45.7 88.1 67.9 26.8 31.4 Notes: Unalt Unalt Unalt Alt Alt Alt Alt Alt Chert Chert Si02 (%) 78.19 74.94 78.72 67.70 73.69 78.69 71.92 58.97 90.22 83.45 Ti0 2 0.22 0.46 0.32 0.46 0.28 0.20 0.10 0.55 0.06 0.18 Al2Oj 8.31 9.38 10.33 10.63 7.13 5.49 5.40 16.19 4.23 4.85 Fe2Oj 1.36 5.79 2.75 11.26 10.69 9.03 14.52 10.35 2.70 6.04 MnO 0.09 0.07 0.04 0.06 0.05 0.05 0.05 0.03 0.00 0.05 MgO 0.14 2.20 0.26 2.46 4.19 3.71 2.51 4.02 0.10 2.82 CaO 4.32 1.54 1.06 0.48 0.71 0.75 2.31 0.54 0.03 0.23 Na20 3.65 1.60 5.24 0.00 0.23 0.11 0.00 0.65 0.00 0.37 K 2 0 0.17 1.20 0.10 2.73 0.28 0.09 0.69 4.48 1.26 0.18 P 2O s 0.14 0.12 0.05 0.13 0.18 0.04 0.08 0.07 0.02 0.00 BaO 0.00 0.19 0.00 0.13 0.02 0.00 0.00 0.67 0.05 0.02 LOI ' 3.54 2.71 1.54 4.60 2.64 2.46 2.83 3.41 1.73 1.89 Total 100.16 100.37 100.45 100.69 100.15 100.69 100.63 100.02 100.42 100.11 Cu (ppm) 60 172 72 137 167 216 698 408 35 89 Zn 147 1280 207 54 173 319 1284 185 5 26 Co 30 35 33 25 50 47 57 30 17 37 Ni 5 26 11 84 31 15 19 25 0 14 Cr 20 3 4 8 12 41 16 86 104 15 1 14 V 40 202 65 191 129 35 26 184 40 83 Sc 0 0 0 15 9 3 3 14 5 8 Zr 69 68 103 93 86 73 74 139 53 46 Y 26 33 26 50 28 19 21 48 13 17 Nb 4 • 3 6 9 9 7 7 9 10 10 Rb 1 28 1 52 7 14 12 94 23 5 Sr 242 220 , 208 16 18 31 66 35 7 35 Ga 6 11 ' 9 16 9 8 9 22 8 9 Pb 2 3 2 9 4 3 5 13 2 2 Notes: Unalt=Least-altered; Alt=Hydrothermally Altered Ti/100 Zr Y * 3 Figure 4.9: Immobile element ternary plot of Zr vs Ti/100 vs Y*3 showing a clear separation between mafic volcanic groups and sedimentary rocks. 102 low Ti in the sediments. In a Zr-Ti-Y ternary plot (Figure 4.9), the sedimentary rocks occupy an area that is on average lower in Ti and relatively higher in Zr with respect to Y compared to the volcanic rocks and may reflect a more calc-alkaline composition for the sediments, even though they do not fall strictly within the calc-alkaline field as defined by Pearce and Cann(1973). 4.3.1 Ti02vsZr On a Ti02 vs Zr plot (Figure 4.10), the volcanic and sedimentary rocks form two distinct groups that cannot be related by hydrothermal alteration, or through dilution of a volcanic component by detrital quartz. Least altered sedimentary rocks (black dots) form a loose cluster with Ti02 ranging'from 0.2 to 0.5 %, and Zr from 40 to 110 ppm. Altered sediments display a greater range of values in both Ti02 and Zr, which reflects mass change effects due to hydrothermal alteration. The low Ti but relatively high Zr content of all sedimentary rocks indicates that they cannot contain more than a minor component of mafic volcanic material, but instead must be largely derived from a more felsic terrain, probably continental given the high quartz and feldspar contents of the least altered sediments. 4.3.2 Rare-Earth Elements The REE patterns of five of the seven sedimentary rocks show slight to strong LREE enrichment (Figure 4.11). The two least altered samples (black dots) have moderate LREE enrichment similar to that observed in the mafic volcanic rocks and may reflect a more alkaline or even calc-alkaline affinity of the detrital sedimentary components. Two of altered samples have distinctly lower REE abundances (<10x chondrite) and relative 4 3.5 3 55 2.5 1 2 t N 2 1.5 1 .5 0 » l i — r • Unaltered Sediments I Altered Sediments (Including cherty rocks) * jy is ^ s «-•* / Field of - sedimentary rocks O 50 100 150 200 Zr (ppm) 250 300 Figure 4.10: T i 0 2 vs. Zr relations for Hidden Creek sedimentary rocks. The grey field represents the maximum range of compositions of sedimentary rocks and their altered equivalents. The solid line is the trend of volcanic rocks from Figure 8a. This plot clearly shows that most sedimentary rocks could not contain more than a minor component of mafic material. 100 La Ce Nd SmEu(Gd)Tb Yb Lu Figure 4.11: Rare-earth element profiles for Hidden Creek sedimentary rocks. Least altered samples are shown by black dots. Data are normalized to chondrite values of Evensen et al. (1978). Gd was not analysed but values were calculated in order to better define Eu anomalies in the R E E patterns. 104 depletion in the LREE. These two rocks also have the highest combined contents of S1O2 and Fej03, which probably have diluted the overall REE abundances. Although these two samples show LREE depletion relative to other sediment samples, their immobile element ratios do not distinguish them as a separate group, which suggests that the LREE depletion is related to hydrothermal effects. 4.3.3 Alteration Within the sediment suite, it was not possible to establish a trend in the least altered sediment samples, as is necessary to carry out mass balance calculations. Variable amounts of detrital quartz could be mixed with different types of sediment, and these in turn could have been affected further by variable additions of hydrothermal silica. There are, however, some chemical changes in the rocks which are clearly due to hydrothermal alteration. A plot of (CaO+Na20) vs (MgO+FeO) (Figure 4.12a) shows a trend from least to strongly altered sediments as CaO+Na26 decreases due to plagioclase breakdown, and MgO+FeO increases as chlorite forms. Trends in the chemical changes in the sediments appear similar to the calculated mass changes in the volcanic rocks. 4.3.4 Mineralogy In a plot of molar proportions of MgO vs A1203 vs (CaO+Na20+K20) (Figure 4.12b), least altered sediments cluster near the composition of albite. The majority of altered sediments plot toward the compositions of chlorite and biotite. A second group which trends towards muscovite includes some relatively unaltered samples. This suggests that the sediments contained a K-bearing detrital phase (e.g. illite). Depending on the amounts of Mg, Fe and K added during alteration and the proportions of detrital minerals already present, different 105 a) 0 5 10 15 20 25 30 MgO+FeO (wt%) AI 2O s Muscovite Albite Epidote MgO CaO+Na20+K20 Figure 4.12: Hidden Creek sedimentary rocks, a) Whole-rock values of (CaO+NajO) vs. (MgO+FeO). Unaltered sediments are denoted by the filled circles and altered sediments by the open circles, b) Molar proportion diagram: MgO vs. A1 20 3 vs. (CaO+NajO+KjO). Sample symbols are coded by drillhole. 106 proportions of secondary chlorite (Mg and Fe), biotite (Mg, Fe and K) and sericite (K) can be produced. 4.4 T E R T I A R Y M A F I C D Y K E S Eight Tertiary mafic dykes were sampled and analyzed for comparison with the volcanic and sedimentary suites. Geological relationships and petrographic evidence (Section 3.6, this thesis) indicate that the dykes postdate the main phase of sulphide mineralization and are unaffected by hydrothermal alteration associated with this event. As a result, mass change calculations were not made on this suite of rocks. The Tertiary mafic dykes have dioritic compositions that are not easily distinguished from the mafic volcanic suite based on major element chemistry alone (Tables 4.1 and 4.6). Major element abundances of SiC«2, AI2O3, T i 0 2 in the mafic dykes are similar to those of the mafic volcanic rocks. However, three of the mafic dykes are low in Si0 2 despite extremely high Ti0 2 , Zr and Y values and may be under-saturated (alkaline) with respect to Si0 2. An A F M plot (Irvine and Baragar, 1971) shows that five of the eight mafic dyke samples are calc-alkaline with slightly higher Na 20+K 20, and lower FeO+MgO than least altered volcanic rocks (Figure 4.13). Three samples are more tholeiitic (ferro-magnesian) and overlap with the volcanic suite. 4.4.1 Trace Element Chemistry Trace element and REE chemistry clearly separates the late dykes from the volcanic rocks and sedimentary rocks. On a Zr-Ti-Y plot (Figure 4.14), the late mafic dykes from a cluster that overlaps both the within-plate basalt and calc-alkaline basalt fields as defined by Pearce 107 Table 4-6: C h e m i c a l composition of M a f i c Dykes at the H i d d e n C r e e k Deposit, Anyox Sample(surface) 62 278-1 279-1 281 Hole No. DI D2 D3 D5 Depth (m) 82.3 84.1 82.3 94.8 Si02(%) 40.80 49.08 45.40 46.84 42.69 42.60 49.65 49.42 Ti02 2.46 1.46 2.22 1.91 0.84 1.04 0.72 1.33 A1203 13.35 18.15 17.42 17.02 10.62 14.25 9.96 16.45 Fe203 12.34 10.03 12.14 11.46 21.45 10.23 15.86 8.65 MnO 0.20 0.14 0.19 0.19 0.15 0.13 0.13 0.14 MgO 5.66 5.50 5.85 7.37 10.21 6.36 12.31 3.45 CaO 7.13 8.16 8.65 10.35 5.40 7.42 4.42 6.94 Na20 3.18 3.95 3.76 2.86 1.34 3.65 1.04 3.97 K20 1.43 1.03 0.97 0.58 0,97 1.53 0.74 2.45 P205 0.88 0.49 0.84 0.36 0.36 1.02 0.32 0.80 BaO 0.07 0:06 0.07 0.03 0.07 0.23 0.04 0.08 LOI 3.23 2.54 2.84 1.60 5.53 4.42 4.97 6.20 Total 90.77 100.63 100.40 100.62 100.16 92.93 100.47 99.94 Cu (ppm) 24 14 41 23 3026 38 415 97 Zn 97 107 218 121 143 110 1444 175 Co 41 35 14 35 185 29 77 25 Ni 12 32 19 44 1314 28 671 31 Cr203 48 13 0 74 486 90 359 58 V 161 199 252 243 126 163 155 176 Sc 16 0 0 0 21 6 18 16 Zr 225 168 168 158 128 154 97 187 Y 39 21 23 30 12 24 16 25 Nb . 31 14 20 10 10 16 12 25 Rb 20 22 52 29 27 40 24 46 Sr 727 865 1053 467 458 956 356 490 Ga 18 20 19 18 13 20 14 21 Pb 2 5 8 6 6 10 2 3 La 21.30 55.00 Ce — — — — — — 44.00 109.00 Nd — — — — — — 23.00 50.00 Sm — — — — — — 4.08 7.33 Eu — — — — — — 1.01 2.07 Tb — — — — — — 0.60 0.80 Yb — — — — — — 1.88 2.22 Lu — — 0.28 0.33 108 FeO* Na20 + K20 MgO Figure 4.13: AFM plot of least altered mafic volcanic rocks and Tertiary mafic intrusives at the Hidden Creek deposit, Anyox. Although the two suites overlap, the mafic intrusives (filled squares) tend to plot in the calc-alkaline rocks field. Ti/100 Zr Y *3 Figure4.14: Immobile element plot ofZrvsTi/i 000 vs Y*3 for Tertiary mafic intrusives at the Hidden Creek deposit. Compositional fields for the mafic volcanic and sedimentary rocks at Hidden Creek are shown for comparison. 109. and Cann (1973), but is clearly distinct from the volcanic rocks which plot as low-K tholeiites. A Zr vs Y immobile element plot separates the volcanic rocks and mafic dykes into two suites (Figure 4.15) that cannot be related by fractionation. The mafic dykes have 97 to 225 ppm Zr and 12 to 39 ppm Y. On average, they have lower Y but higher Zr contents than the volcanic rocks. The dykes have Zr/Y ratios of 5 to 11, suggesting transitional to calc-alkaline affinities (cf. McLean and Barrett, 1996). In contrast, tholeiitic mafic volcanic rocks have average Zr/Y value of 2.4. This difference is probably due to greater depletion in Y relative to Zr in fractionating calc-alkaline magmas. 4.4.2 REE Elements REE data for two of the mafic dykes are plotted for comparison with the mafic volcanic suite (Figure 4.16). The mafic dykes show strong LREE enrichment and moderate HREE depletion relative to the mafic volcanic rocks. The steep negative slope of the REE patterns of the dykes is characteristic of calc-alkaline rocks, and clearly differs from the nearly flat REE patterns of the tholeiitic volcanic rocks. 4.5 S U M M A R Y Major and trace element data clearly distinguish between the volcanic and sedimentary and intrusive rocks underlying the Hidden Creek area, and provide a chemical basis for characterizing the nature of hydrothermal alteration. The least altered mafic volcanic footwall rocks are basalts to basaltic andesites of tholeiitic affinity. Subsets of N-MORB, T-MORB and E-MORB volcanic rocks have been identified using P/Ti ratios and REE data. 1 100 r i i i i i i i i I I i i i 90 / / 80 -/ / / — / / ' Tholeiitic Y (ppm) 70 60 50 - y / : | • :;,;:x;. *S?: ( >f? / Zr/Y = 2 - 5 ^ ^ - ' ' Transitional 40 30 x / A * / / * ... /SV/jSKS / ' ^ \ ** / /-T „ L ** ^ ' Zr/Y = 5 -7 / Jits Calc-alkaline /• ,m-~/ Zr/Y = 7-20 20 10 7 / , ^  Anyox - y / / 8«diment} " „ - t> J'" ms _ 0 0 40 80 120 160 200 240 280 Zr (ppm) Figure 4.15: Binary immobile element plot of Y vs Zr for the Tertiary mafic intrusive rocks. Samples have Zr/Y ratios from 5 to 18, reflecting transitional to calc-alkaline affinities (Mclean and Barrett, 1994). They are clearly distinguished from the mafic volcanic rocks which have tholeiitc affinities (Z/Y = 2 to 5). ^ I i \ i i 1 1 1 1 1 1 La Ce Nd Sm Eu Gd Tb Yb Lu Figure 4.16: Rare earth element profiles for Hidden Creek mafic intrusive rocks (squares). They show strong L R E E enrichment and slight L R E E depletion which is characteristic of calc-alkaline rocks. The data was normalized to chondrite values of Evenson et al. (1973). I l l Sedimentary rocks, including both clastic and hydrothermal components, are distinguished from the volcanic rocks by their higher SiC>2 and lower Ti02 contents. Tertiary mafic dykes have dioritic compositions but are more calc-alkaline than the volcanic rocks with, slightly higher NaO+K^O, lower FeO+ MgO and Zr/Y ratios between 5 and 11. Hydrothermal alteration in the volcanic and sedimentary rocks is characterized chemically by loss of CaO+Na20 and gain of MgO+FeO. Petrographically, these chemical changes reflect the breakdown of feldspars to chlorite, sericite and epidote. Gains in K 20 (up to 3.4 wt %) occur in sericite-biotite altered volcanic and sedimentary rocks. Mass changes in Si02 are highly variable and may involve two independent processes with S1O2 lost during chloritization and sericitization but added during silicification and quartz veining. Fe is introduced to the rocks as sulphides, Fe-oxides (magnetite) and chlorite. 112 C H A P T E R 5: MINERALIZATION AND O R E ZONE STRATIGRAPHY 5.1 T H E H I D D E N C R E E K O R E B O D I E S The Hidden Creek Mine remains to this day one of the most significant past producers of copper in British Columbia with over 300,000 tonnes of recovered copper metal during its twenty-one year history (Nelson, 1935). The orebodies formed a number of discontinuous, tabular to sheet-like massive sulphide lenses, peripheral zones of siliceous, semi-massive sulphides and associated vein stockworks whose distribution was controlled by first and second order folds of the Hidden Creek Anticline. The main accumulation of sulphides occurred in the Nos. 1, 2, 3, 4 and 5 ore zones, which accounted for over 95% of the mine production (Figure 5.1). The Nos. 1, 4 and 5 ore zones were hosted in the lower part of the sediment package, whereas the Nos. 2 and 3 orebodies were located near the top of the mafic footwall. The No. 6 ore zone is reported to have straddled the contact, extending from the volcanic footwall into the sedimentary hangingwall (Nelson, 1935). The Nos. 7 and 8 zones represent minor sulphide lenses peripheral to the main ore lenses. These two zones were outlined by drilling and were described as volcanic-sediment contact-type lenses (Nelson, 1935). Records of past production and exploration, and petrographic observations from this present study indicate that the distribution of precious-metals and base-metal sulphides was highly variable. High grade ores contained 1.5% to 3% Cu and accounted for 9.1 Figure 5.1: Generalized geology of the Hidden Creek mine area showing the distribution of ore zones and major structures. The Nos. 7 and 8 ore zones are small subsurface deposits indicated by drilling (after Davis etal., 1993). 50 40 ~ 30 20 AfterGrove(1986) 10 h TT 1 3 (ore body) 10 20 30 40 50 60 SiO,(wt%) Figure 5.2: Chemical composition of processed ore from the five major orebodies mined at Hidden Creek. The data are from Grove (1986) and represent compiled analyses of shipments from the mine. 114 million tonnes of the mineable reserves in September, 1918 (Table 5.1). Low grade ore accounted for 8.4 million tonnes averaging 0.75% copper. Bancroft (1918) reports that the No. 5 ore body had higher than average copper and precious metal contents, and included pockets of ore with up to 12% Cu. High-grade intersections from recent exploration drilling include 1.5 metres averaging 4.1% Cu, 0.98% Zn and 77g/t Ag in hole 93D2, and 6.2 metrres averaging 2.5% Cu, 0.5% Zn, lOOg/t Ag and 1.8 g/t Au in hole 82-9. Table 5.1 Mineable Reserves from September, 1918 (Bancroft, 1918) Ore body High Grade Low Grade Tonnage (Mtonnes) Grade (Cu) Tonnage (Mtonnes) Grade (Cu) 1 3.18 2.17% 3.14 0.80% 2 2.81 2.24% 2.70 0.70% 3 1.21 1.75% 1.67 0.66% 4 0.19 1.71% 0.15 0.70% 5 1.45 3.03% 0.65 0.70% 6 0.28 2.56% 0.11 0.74% Total 9.10 2.20% 8.40 0.73% Mine records show that the orebodies had a variable bulk chemical composition reflecting a systematic change in gangue mineralogy in the ore lenses (Figure 5.2). In the 115 sediment-hosted ores of the Nos. 1, 4 and 5 zones, iron occurred principally as sulphides (mainly pyrite), SiC>2 as quartz and CaO as calcite. In comparison, the volcanic-hosted ores of the Nos. 2 and 3 zones were richer in AI2O3 and MgO, which occurred together with Si02 and CaO as silicates (chlorite, amphibole and epidote). The percentages of FeO and S were lowest in the No. 3 ore bodies, which is reflected in the mineralogy by a preponderance of pyrrhotite over pyrite in the massive sulphide lens. The Nos. 1, 5 and 4 ore zones were reported to contain massive pyrite lenses, with high sulphur and low copper contents, were reported from (Bancroft, 1918). The difference in the bulk composition and gangue mineralogy of the sediment-hosted versus volcanic-hosted ore bodies presumably reflects the interaction of mineralizing fluids with volcanic host lithologies on one hand, or sedimentary lithologies on the other. These differences are also evident in the stockwork veins. 5.1.1 Nos. 1 and 5 Ore Bodies The Nos. 1 and 5 ore bodies formed the single largest accumulation of massive sulphides in the Hidden Creek area, producing over 10.5 million tonnes of ore grading 1.55 % copper over the entire life of the mine (Davis et al., 1992). The distribution of sulphide lenses is roughly crescent-shaped in plan (Figure 5.1). The No. 1 ore body lies within the westerly dipping, overturned limb of the Hidden Creek Anticline and occupies the' southeast margin of the ore zone. The No. 5 ore body occupies most of the fold hinge and extends into the northwesterly dipping upright limb. At the 450 ft level of the mine, the single ore zone is roughly 580 metres long and has a maximum width of 41 metres (Nelson, 1935). 116 5.1.2 No. 4 Ore Body The No. 4 ore body occupied the highest levels of the mine (Nelson, 1935) and occurs within the upright limb of the Hidden Creek anticline. This ore body represents the least siliceous and most carbonate-rich ore (Figure 5.2). Sulphide bodies of the No. 4 zone outcrop along the high spur immediately west of the north end of the No. 5 pit, and extend to the north along the walls of Nos. 2 and 3 pit (Figure 5.1). Mine records indicate that the No. 4 ore body was stratigraphically underlain by the most northerly extension of the No. 5 ore body (Nelson, 1935) which, according to work from this study, is underlain by several tens of metres of altered sediment. However, hole 93D-9 (Section 5.4.3) indicates that at least one of the No. 4 ore lenses sits within 10 metres of the volcanic footwall, leaving a significant interval of sediment unaccounted for. 5.1.3 Nos. 2 and 3 Ore Bodies The Nos. 2 and 3 orebodies are interpreted to have been a single ore lens within the footwall volcanic sequence, but are now separated by a north-south trending, steeply east dipping normal fault that displaces the No. 2 ore body some 60 metres vertically and 90 metres laterally to the south (Figure 5.1). The combined ore lens had a length of 3000 ft along the pitch axis, and consisted of an upper portion of massive sulphide and a stratigraphically lower zone of altered and mineralized volcanic schist (Nelson, 1935). 117 5.2 S E D I M E N T H O S T E D M I N E R A L I Z A T I O N 5.2.1 Massive Sulphide Lenses Thick intervals of sulphides and hydrothermally altered sediments intersected in several diamond-drill holes and exposed in the No. 1, Nos. 2/3 and No. 6 pits are interpreted as lateral equivalents of mined-out, sediment-hosted ore lenses (Plates 5.1 and 5.2). Pyrrhotite and pyrite are the dominant Fe-sulphides and occur in varying proportions throughout the mineralized zones. Chalcopyrite is most commonly associated with pyrrhotite but is locally found with pyrite. Sphalerite is frequently absent, but in places comparatively small portions of the ore are rich in this mineral. Galena is rarely observed as veinlets in massive pyrite. In the thickest massive sulphide intervals, pyrite occurs as fine to coarse recrystallized euhedral grains in a predominantly quartz and carbonate matrix. Both matrix and sulphides have vuggy textures. Pyrite forms cubes up to a centimetre in diameter; commonly with pyrrhotite in the interstices (Plate 5.2b). Pyrrhotite is not as coarsely crystalline as pyrite and forms subhedral highly fractured grains that show evidence of plastic deformation. Fractures, which can show a consistent orientation, locally have the appearance of tension gashes and are typically filled with carbonate and silica, however void space is not uncommon. Chalcopyrite occurs as fine to coarse disseminations between coarse recrystallized pyrite and pyrrhotite grains and as thin veins and seams throughout the massive sulphide intervals. 811 119 Plate 52a) Massive sulphide intersection in hole 93D9, consisting of pyrite-rich lower interval and pyrrhotite-rich upper interval. Carbonate and lesser silica are the gangue minerals. Plate 5.2b): Photomicrograph of a semi-massive sulphide layer hosted in greenish altered sedimentary rock. Chalcopyrite (yellow), pyrite (white) and minor pyrrhotite in a carbonate-rich gangue. Bladed chlorite gangue occurs on the right (amphibole also occurs in the gangue). Hole D3,48 m. Reflected light, width of view=2.6 mm. 120 5.2.2 Marginal Mineralization: Siliceous sulphides Semi-massive sulphides, found in siliceous, hydrothermally-altered clastic sediment along the margins of the massive lenses are commonly referred to in the early literature as siliceous sulphides. Sulphides, predominantly pyrite and pyrrhotite, occur uniformly disseminated throughout the host rock, in cross-cutting veins, or as thick semi-massive ribbon-like bands that coalesce into thicker zones of massive sulphides (Plate 5.3a). Pyrrhotite is disseminated and banded, and is the main sulphide in the cross-cutting veins. Pyrite is disseminated and banded and more rarely occurs in veins. Chalcopyrite occurs as stringers and disseminations with pyrite in the semi-massive bands and with pyrrhotite in the veins. The proportions of gangue to sulphides varies throughout the ore lenses, commonly alternating between semi-massive to massive sulphide bands, from 1 to 10 centimetres thick, to near barren intervals of chert and chlorite-sericite-biotite-schist that mimic primary bedding in less altered sedimentary rocks. The proportions of chlorite, biotite and sericite impurities in the cherty hosts varies considerably throughout the mineralized zones and over short intervals (<1 metre), grades from one alteration facies to another. Near the margins of the siliceous sulphide zones, semi-massive and disseminated sulphides occur in more mildly altered host rocks that are clearly turbiditic in origin. Here, sulphides penetrate and replace coarse sandstone layers in turbiditic host rocks to form bedding-parallel sulphide-quartz-carbonate layers. In thin section, sulphides are intergrown with chlorite, sericite and minor epidote and are 121 Plate 5.3a): Siliceous sulphides from the hangingwall of the No. 1 ore zone. Fine to coarse disseminated pyrite in sericite-quartz altered, bedded mudstone turbidite. Top sample from D4, 120 metres and bottom sample from D4,133 metres. Plate 5.3b): Examples of sulphide replacement of sandy layers in the Hidden Creek sedimentary cover. Locally, as in the drillcore on the left, sulphides are remobilized into cleavage planes in the rocks. 122 flattened and elongated within foliations in the alteration phases (Plate 5.3b). Fine disseminations of quartz-sulphide are distributed along microscopic foliation planes in less altered sedimentary rocks and which in some cases, mimics the distribution of sulphides in massive cherty rocks where cleavage cannot be distinguished. 5.2.3 Vein Stockworks The vein networks in the sedimentary rocks reflect both brittle and non-brittle veining that is probably related to the relative competency of the host rocks. Feathery textured sulphide veins occur in intensely chloritized and sericitized sediment as well as in mudstone-turbidite intervals. The veins, which are typically less than 5 millimetres thick follow primary bedding and fissile partings in the host rock and appear to reflect infiltration of hydrothermal fluids through relatively less competent rock. By contrast, fracture veins with more discrete margins clearly crosscut bedding and therefore appear to have transected more competent (early silicified) sedimentary rocks (Plate 5-4). Partial replacement of wallrock fragments by sulphides is associated with the veining. Pyrrhotite is the main sulphide in most of the vein networks, with pyrite usually subordinate. Chalcopyrite is typically a minor sulphide closely associated with pyrrhotite. Quartz, sericite, chlorite and carbonate occur in the veins and altered selvages. Vein stockworks are not restricted to the sedimentary footwall. Quartz-carbonate-sulphide veins cut massive and siliceous sulphides in the main mineralized intervals and also cut into the relatively unaltered hangingwall sediments. 123 Plate 5.4a): Vein textures in sedimentary rocks. From left to right: Quartz-sulphide cemented hydrothermal breccias incorporate fragments of quartz-sericite-bioite altered wallrock; Silicified margin of pyrite-rich fracture vein with a white silicified (-albitized) selvage in quartz-sericite-bioite altered sediment; Diffuse pyrrhotite-pyrite veins with thin chloride selvages in partially silicified sedimentary rock. Pyrite is recrystallized into coarse aggregates and pyrrhotite is more feathery-textured. Plate 5.4b): Photomicrograph: Chalcopyrite-sphalertite-pyrrhotite in coarse carbonate and actinolite-chlorite gangue in hole D8 at 37.2 metres, width of view=5 mm. 124 5.3 V O L C A N I C H O S T E D M I N E R A L I Z A T I O N 5.5.7 Massive Sulphide Lenses The Nos. 2 and 3 orebodies formed small discontinuous lenses of massive sulphides embedded in the foliation of a 100 metre wide zone of banded quartz-chlorite schist in the footwall volcanic rocks. The ore lenses were attenuated and folded and were distributed along the upright limb of the Hidden Creek Anticline. Surface or pit exposures of the Nos. 2 and 3 orebodies were inaccessible at the time of this study and descriptions of the ore lenses by earlier workers are sketchy (Bancroft, 1918; Nelson, 1935). Sulphide-rich zones occurring along the margins of the Nos. 2 and 3 ore zones and in the footwall volcanic rocks beneath the sediment hosted lenses in the Nos. 1, 5 and 4 ore zones are the best approximation of the morphology and mineralogy of the mined out volcanic-hosted ore lenses. In drill core, some of the richest sulphide intersections occur in banded quartz-chlorite schist and in less deformed zones, quartz-cemented volcanic breccias. Zones of semi-massive to massive sulphides, up to 10 metres thick, punctuate the footwall stratigraphy and may reflect sulphide flooding of the volcanic breccias. Here, pyrrhotite, pyrite, and chalcopyrite are recrystallized and form interlocking aggregates with chlorite, saccharoidal quartz, epidote and more rarely calcite. Intensely chloritzed host rocks envelope the mineralized lenses and can contain up to 5% magnetite. Weakly mineralized volcanic breccias with cherty infillings occur on the fringes of the main mineralized zones. Sulphide stringers with chlorite-epidote altered selvages form along the margins of 125 the cherty lenses, branching into the volcanic host rocks and are typically pyrrhotite-rich with lesser pyrite and chalcopyrite. Vuggy textured quartz, zones of hydrothermal brecciation and the progressive sulphide replacement of altered wall rock were also observed throughout the mineralized zones. 5.3.2 Vein Stockworks Quartz-pyrrhotite-chalcopyrite veins occur in the upper volcanic footwall sequence and are commonly associated with intense chloritization and silicification of the host rock (Plate 5.5a). The veins range from 0.2 centimetres to several centimetres in thickness and form branching networks within the volcanic host. Quartz-rich veins have discrete margins, commonly with chlorite-biotite-altered selvages, up to 4 centimetres thick, and often contain coarse recrystallized quartz and more rarely calcite (Plate 5.5b). Alternatively, feathery textured sulphide veins form networks through more uniformly chlorite-epidote-biotite altered host rock. The margins of these veins are less discrete than the fracture veins and there is often no clear distinction between alteration selvage and hostrock. Within high-grade zones, veins coalesce into bands of semi-massive sulphide, up to several centimetres thick. Pyrite rarely occurs in the vein networks except several zones in the footwall of the Nos. 2 and 3 ore bodies where locally it forms a significant component of the veins. A s seen in the sediment hosted ore zones, mafic hosted vein systems are not restricted to just the footwall of the ore lenses and commonly at least one generation of veining overprints massive and semi-massive sulphide lenses. 1 2 6 Plate 5.5b) Photomicrograph: Epidote-chlorite-altered sulphide vein margin in a quartz-chlorite-altered sediment. Hole D5 at 13 8.7 metres. Width of view=5 mm. 127 5.4 ORE ZONE STRATIGRAPHY Surface mapping reveals that lithological units hosting the mineralization in the Nos. 2 and 3 and Nos. 1 and 5 ore zones plunge to the north exposing a stratigraphy comprised of an upper mudstone-turbidite package, a middle unit of predominantly fragmental volcanic rocks and a lower package of predominantly pillowed and massive volcanic rocks. The surface trace of the contact between the fragmental and more massive volcanic units may be the result of folding of a primary lithological contact with an added component of high angle faulting. Locally, quartz-chlorite schist and fragmental volcanics (breccias) are juxtaposed to massive or pillowed rocks across prominent scarps which may reflect faulting. Post-mineralization, high-angle faults displace the folded strata but may mask earlier syngenetic structures. The missing stratigraphy in the No. 4 ore zone (section x-x) and the thick accumulations of volcanic breccia may be accounted for by block faulting on the sea floor prior to or during the mineralizing event. Recent diamond drillholes across margins of the main historical ore zones (Figure 5.3) provide new information on the host stratigraphy and the distribution of altered rocks associated with sulphide mineralization. From north to south, drillholes 82-10, 82-11, 82-4, 93D6, 93D2, 93D3, 39D4 and 93D1 form a transect across the Nos. 2 and 3, and Nos. 1 and 5 ore zones in which mineralization in both the volcanic footwall and the overlying sedimentary sequence were intersected (Table 5.2). Chlorite-dominated alteration assemblages in the volcanic rocks and lower sedimentary rocks are spatially associated with sulphide mineralization. They pass stratigraphically upward, through a transition zone, into sericite-dominated assemblages associated with semi-massive and massive 128 °-2 • Drillhole and number lithogeochem sample 90 metres Figure 5.3: Close-up of the pit area showing the distribution of drillholes and surface samples used to investigate the ore zone stratigraphy. 129 sulphide lenses into the sedimentary sequence. Primary lithologies, alteration assemblages, mineralization styles and ore grade intersections are summarized in Figures 5.4, 5.5, 5.7 and 5.8. Lithogeochemical sample locations and a comparison of observed chemical trends using the M g O vs AI2O3 vs CaO-Na20-K20 molar proportion diagram and the mass change calculations are also given for each ore zone. Table 5.2 Significant dri l l intersections from 1993 (Davis et al., 1993) Hole Interval Mineralogy Gangue Grade (metres) Cu % Zn ppm Dl 106-118 Py, Po, Cpy Src, Si 1.00 1771 Dl 131-135.5 Po, Py Cpy, Src, Si 0.84 118 Dl 144-146 Po, Cpy Si, Src 0.57 1293 D2 142-143.5 Py, Po, Cpy Cc 4.10 9500 D2 168-173 Po, Py, Cpy Si 0.98 980 D3 47-52 Po, Py, Cpy Cc, Chi 1.04 81 D3 137-138.5 Po.Cpy Src, Bt, Si 0.38 1410 D3 141-149.5 Po, Py, Cpy Si, Src 0.91 293 D4 30-32 Po, Cpy Si, Cc 0.40 2890 D6 113-117.5 Po, Cpy Chi, Si 0.45 132 D6 118-129 Po, Cpy Chi, Si 0.55 35 D7 76-76.5 Po, Cpy Si 0.60 410 D8 35-49 Po, Py, Cpy, Sph Cc, Si 0.73 2816 D9 27-38 Po, Cpy Cc 0.50 620 D9 40-49 Py, Po, Cpy Cc 0.47 324 D9 60-62.5 Po, Py, Cpy, Sph Cc, Si 0.40 6158 D9 132-137 Po, Cpy, Py Qv 1.28 722 Abbreviations Po: Pyrrhotite; Py: Pyrite; Cpy: Chalcopyrite; Sph: Sphalerite Src: Sericite; Si: Silicification; Chi: Chlorite; Bt: Biotite; Qv: Quartz veins; Cc: Calcite 130 5.4.1 Nos. 2 and 3 Ore Zones 5.4.1.1 Stratigraphy - Alteration Diamond drill holes 82-10 and 82-11 intersected the footwall volcanic sequence of the Nos. 2 and 3 ore bodies; the core is representative of the textures and mineralogy of this ore zone (Figure 5.4). Surface mapping and sampling along the western slope of the Nos. 2 and 3 pit supplement the information obtained from the drillholes (Figure 5.3). Underground drilling by C O M I N C O between 1936 and 1938 indicated 20 million tons of low grade C u mineralization hosted by volcanic schists in this area. The footwall is comprised of alternating intervals of massive to fragmental, feldspar-phyric volcanic rocks, with minor amounts of veined and fine-grained disseminated pyrrhotite (Figure 5.4). Sulphide bearing, quartz-chlorite-magnetite schists, sampled at Stn. 63.2 and between 130 and 180 metres in hole 82-10, are the most strongly altered lithologies. Less altered schists (Stns. 63.3 and 65) occur at the margins of this zone, near the contacts with the more pillowed and massive units at Stns. 11-1, 64 and 44-5, and between 0 and 100 metres in 82-10. Biotite alteration between 175 to 200 metres in 82-11 immediately underlies the main mineralized zone. A similar biotite-rich zone occurs in 82-10 between 218 metres and the top of the hole at 270 metres. A second zone of intensely altered schistose fragmental volcanics (Stns. 44-1 and 59-4) occurs to the west of the drill hole collars along the Hidden Creek river bed. Mass change calculations indicate moderate to small losses of Si02, CaO, and FeO and small gains of M g O and K 2 0 for least altered rocks deepest in the volcanic stratigraphy 131 OJ Cl c ro .c U </5 W ro 5 CO UJ z o N 111 tn O CO Q Z < CM CO o o 2 E co o o ro t (rt I n d CM 00 CM CO eo eg in r-<o CO 5 5 2 5 6 ^ CD +42 I i a a' >>>>>> * 218.3 po, cpy py.po.cpy •164.5 cpy. po, (py) ? po. cpy, (py) po, cpy •77.4(1 •54.0(1 mm m >>>>>5>i^>>>>>>>^  •>>>>>>5>>>>>>> 250 m-200 m . 150 m • 100 m . 50 m • c o ulphide s S (rt (Jl to H CO '— CO i u E Mint 1 >>> o ro O O ro' O 3 • Li- 2 • • a o Q. <D II if P" cu o u ra C, 6 B CO t3 ra E T3 > *3 — <2 E ^ •3 I e o c . M J J -u * H c <N CO oo 1 1 > cu • 2 1 1 S -o £ W I 00 co JJ <« " o e E «r >> t '5 •u ,2 --E S i s » u £ I * 1 3 CL c_ M D o 1 " B « -58 co N= E .. 0 s ca co cn u J= -C 60_u N 9 a 5 | f I _ 9 Z 0 T3 co C i-CM .S 'S § 8 " cn o « S o 7 J- — > U ca e U D CB O X) s i I f S.S > o 6 S '•5 o CO •S £ •S ° — c ra 1 U a oa CQ d> • CM » o ° I E | CO ,CD I o c o -if cu cu C | s •SP o cu fi eu s—E w 5cZ 132 and massive to pillowed volcanic rocks on surface (Stns. 65 and 11-1). Moderately altered rocks are characterized by modest gains M g O and FeO and sometimes significant mass loss of Si02 (up to -12.5 wt%). Intensely chloritized mafic volcanic rocks have experienced nearly total loss of CaO and N a 2 0 and sharp increases in FeO and M g O . Mass gains in FeO >6 wt% occur in rocks of both the moderately and intensely altered rocks and is reflected in the modal mineralogy by Fe-chlorite, Fe-sulphide and sometimes magnetite. Mass gains in S i 0 2 (up to +19.4 wt%) occur where quartz veining and cherty lenses are associated with sulphide veins and massive sulphides (e.g. Stn. 63.2). 5.4.1.2 Mineralization The main mineralized section in 82-10 occurs between 130 and 180 metres, and in 82-11 between 210 and 260 metres (Figure 5.4). Mineralized intervals are characterized by a sharp increase in disseminations and stringer veins of pyrrhotite, pyrite and chalcopyrite, which can form sulphide-rich intervals up.to 15 centimetres in thickness. Pyrite is the coarsest vein sulphide. Pyrrhotite and chalcopyrite have a more feathery texture, and tend to anastomose between pyrite grains and chlorite-actinolite-epidote gangue. The host volcanics are intensely chloritized and inhomogeneously silicified. Strongly altered volcanic rocks also contain up to 2% fine-grained magnetite. 5.4.2 Nos. 1 and 5 Ore Zones 5.4.2.1 Stratigraphy - Alteration The footwall volcanic rocks intersected in 82-4 and 93D6 are similar to those encountered in 82-11 and 82-10 and consist mainly of fragmental rocks, but with thinner 1 3 3 OJ c TO .C o w re CD c o N "D C TO •» i- *• to a CO cn o i § O CM N I O i i ra in o I o ro o n o 3 • o CT. S o I ^ CO i f ? " O E i s s i J E ! c -a e ca C3 E 3 o flj w m CD . c+«, SO o m —5 ON CD CD  « 0/j C o o cn 5 '— Cu CN | | | 2 5 «> >>J3 •-• ° H & J3 \ = 4) C 0s s CD «J| o LU Z O N UJ or o in a co O 2 I CM C O If) (O UJ ^ CO o n r o o T- CO cj o T- O T- T- T * OO >>> z a ; <*> <** «> <*t ; o; q; cr, q 7q; c E o o E o ? 1 c o ro I II I I CD > S3 fc< > C co CD fC 8 -g J •J.2 83 £ «* 8 - T w 00 . J f & g O (50 w o 5 ° o N CD Mi - i - i 1 O 25 * £ J= A fi 01.S 5 ° CO P U S « o c M o c S CTJ _ S 01 y W "o " ° i> o ^ S C cq cc nr. I 8 <« g § 2 3 >• CD B cjQ t_ —; ,—. PH C(_| 43 -—, 134 massive intervals (Figure 5.5). Rocks in the lower parts of the volcanic footwall (82-4-11.4 and 82-4-37.5) consist of actinolite and feldspar with minor chlorite and epidote. Chlorite alteration increases up stratigraphy in 82-4 and is most intense within 75 metres of the contact with sedimentary rocks. Moderate to intense chlorite-biotite alteration affects the entire intersected interval of fragmental volcanics («50 metres) beneath the sedimentary contact in 93D6. Rock alteration and sulphide veining is most intense within 75 metres of the sedimentary contact and parts of the upper volcanic stratigraphy are intensely silicified (93D6-41.5, 93D6-52.3). Calculated mass changes for altered and least altered footwall volcanic rocks of the Nos. 1 and 5 ore zone are similar to mass changes seen in the volcanic rocks of the Nos. 2 and 3 ore zone. Intensely chlorite-altered, magnesium-rich rocks are distinguished from more moderately altered rocks on the molar proportion plots. With increasing alteration intensity, samples plot further away from the CaO+Na20+K20 axis on the molar proportion plot and toward more chloritic compositions (Figure 5.6). Altered sedimentary rocks from the Nos. 1 and 5 ores zones display a range of compositions from chlorite to muscovite schist (Figures 5.6b, 5.7). Chlorite, epidote, actinolite and quartz altered sediments immediately overlie the volcanic sequence in 82-4 and 93D6, are intersected in 93D2, 93D3 and exposed on surface at Stn 209. These intersections outline a broad alteration zone in the northern and central footwall sediments that extends for at least 310 metres. Although the exact thickness of the chloritized zone is unknown due to possible repetition by folding, intervals of at least 80 metres were intersected in several drillholes. 135 AIA Muscovite (Sericite) Albite Epidote Chlorite MgO CaO+Na,O+K,0 A l , 0 , Chlorite MgO CaO+Na 2O+K 20 + O N-MORB Mafic Volcanics, Unaltered/Altered Y V T-MORB Mafic Volcanics, Unaltered/Altered A A E-MORB Mafic Volcanics, Unaltered/Altered # O Sedimentary rocks, Unaltered /Altered Figure 5.6: Molar proportion plots of MgO vs A1203 vs (CaO+Na20+K20) for outcrop and drill hole volcanic and sedimentary rocks from (a) the Nos. 2 and 3 ore zones and (b) from the No. 1 ore zone, north portion. Samples range from least altered compositions to chlorite altered. Typically the most altered rocks show the greatest CaO+Na20+K20 depletion (from petrography and mass change results). 136 137 In a similar fashion to the volcanic rocks, the sediments show loss of C a O and Na20 with increasing alteration and are dispersed between chlorite-rich and sericite-rich compositions (Figure 5.6b). Schists and cherts from 93D2 are the most intensely chloritized and MgO-rich of the altered sediments and occur closest to the underlying volcanic contact. Samples from 93D2, 93D3, 93D4, and 93D1 are more sericite altered. Sedimentary rocks from 93D3, which contain varying proportions of sericite and chlorite, record the transition between these two main alteration facies. Weakly altered mudstone-turbidite sediments alternate with intensely sericite-quartz-altered and cherty sediments in the upper stratigraphy of 82-4, 93D2 and 93D3, and comprise the entire intersections in 93D1 and D4 (Figure 5.7, 5.8a). Hole 93D1 provides the best intersection sericite-quartz alteration in the sedimentary cover at Hidden Creek. In this hole, two zones of cherty and sericite-altered sediment are separated by less altered intervals of interbedded mudstone-turbidite («5 metres thick). In 93D4, quartz-sericite-altered sediment alternates with centimetre to decimetre thick intervals of semi-massive to massive pyrite and pyrrhotite in a zone about 30 metres in thickness. This mineralized zone is flanked above and below by weakly altered, mudstone-turbidite beds that merge into unaltered sedimentary rock. Intense biotite alteration occurs at or near the volcanic-sedimentary contact in D D H 82-4 and 93D6, and at the base of the chloritized sediment in D D H 93D2. Biotite occurs in variable amounts throughout the footwall sedimentary rocks in both the sericite and chlorite dominated sediments, commonly forming 3 millimetre seams to 3 centimetre bands subparallel to remnant bedding. The biotite seams and bands are interpreted as 138 CaO+Na2O+K20 A I A MgO CaO+Na2O+K20 + O N-MORB Mafic Volcanics, Unaltered/Altered y V T-MORB Mafic Volcanics, Unaltered/Altered A A E-MORB Mafic Volcanics, Unaltered/Altered # O Sedimentary rocks, Unaltered /Altered Figure 5.8: MgO vs A1203 vs (CaO+Na20+K20) molar proportion plots of volcanic and sedimentary rocks from (a) the No. 1 ore zone, central and south portions; and (b) the No. 4 ore zone. Samples range from least altered compositions to chlorite-altered to sericite-altered. Typically the most altered rocks show the greatest CaO+Na20+K20 depletion. 139 having formed from clay-rich sediments in the original turbidite stratigraphy, either as pelagic beds or as the fine bed tops to the clastic turbidites. These layers would be richer in K and M g (as illite, smectite, etc.) than the quartz-feldspar-rich coarser-grained beds, and would preferentially form biotite during regional metamorphism. 5.4.2.2 Mineralization Vein stockworks and thin semi-massive sulphide lenses occur within chlorite schist, chlorite-quartz schist and silicified volcanic breccias throughout the footwall volcanics (Figure 5.5). As in the Nos. 2 and 3 ore zones, the veins are pyrrhotite-rich with lesser pyrite and chalcopyrite, and have chlorite(-epidote) altered selvages. Sulphides are present along the margins of the cherty lenses and between volcanic fragments and form thin semi-massive bands. Quartz-sulphide veins cross cut the sulphide bands and form networks throughout the chloritized schist. Lenses of semi-massive to massive sulphides occur throughout the sedimentary sequence (Figures 5.5 and 5.7). Low grade mineralization was encountered at 125-137 metres (0.55% Cu) in 39D6, 168-173 metres (0.98% Cu) in 93D2, 47-52 metres (1.4% Cu) and 142.5-151 metres (0.91% Cu) in 93D3 and from 125-145 metres in 93D1 (including 12 metres at 1.0% Cu). These sulphide zones grade, sometimes sharply, from semi-massive, coarse-grained, pyrrhotite-pyrite-rich bands up to tens of centimetres thick, into finely disseminated pyrrhotite (<2%). Chalcopyrite occurs as fine veins and disseminations with pyrite in these semi-massive bands. Chlorite, sericite, quartz, calcite and epidote are the main gangue minerals. High grade mineralization at 143-144.5 metres in 93D2 (4.1% Cu , 0.95% Zn) occurs in a thin pyrite-calcite-rich lens in chlorite-sericite altered sediments. 140 Pyrrhotite is the main sulphide in most of the vein networks. Pyrite is of variable abundance, but in most is not a significant component of the sulphide veins. Chalcopyrite is typically a minor sulphide, and closely associated with pyrrhotite. Sulphide veins both predate and post-date the semi-massive and massive sulphides, and are not restricted to any one part of the Nos. 1 and 5 ore zone stratigraphy, but extend through the main alteration zone and into the relatively unaltered hangingwall sediments. Toward the margins of the main mineralized zones, semi-massive and disseminated sulphides occur in mildly altered host rocks that are clearly turbiditic in origin. In holes 93D2, 93D4 and 93D1, heavily disseminated sulphides occur in siltstone and sandstone beds, typically less than 2 centimetres thick, which are separated by unmmineralized mudstone beds. In these 3 holes, sulphides also occur in more diffuse bands that coalesce into thicker semi-massive layers. 5.4.3 No. 4 Ore Zone 5.4.3.1 Stratigraphy - Alteration Holes 93D9, 93D8 and 93D7 were collared in unaltered mudstone-turbidite sedimentary rocks and drilled down stratigraphy toward the volcanic-sedimentary contact (Figure 5.9). Holes 93D11 and 93D10 intersected hangingwall sediments north and east of the No. 4 ore zone. The stratigraphy in these 5 holes matches the that along the eastern wall of the Nos. 2 and 3 pit, where the No. 4 ore lens is exposed (Nelson, 1935), and also matches unaltered sedimentary rocks which outcrop to the north of the pit. The volcanic footwall was intersected in holes 93D9 and 93D8 (Figure 5.9). The footwall 141 Q co Ol 111 i l l ! III I I E E £ E fi 5 S co Q co CD uuuu/<u/\ LU Z O N LU or o d z LU X I-LL o >• X < a: o i -< Qu-i -to o I — =• Z h h h Q co CD • o C ro o OT OT ro o • IL • Q co CD Q co l l l l l l l l l l l l l l l l l l l l l i 52 s 5 MCL o . • T- ™ cH cn o o > o £ <D O E > o 1- " M -S U Co oo'C B CO a > xi <*_ o o S u a s E co i « cd 3 Q U Os - -a k> c Q rt co o O Q T3 cn 3 cn 1) 00 Q o J 3 T3 § i Ml o S i LU -a ON at) c 'o ra cu cn CD c ra £ " eg U 60 i 1 1 O £ ! ra 5.i5 c o ra a. c/1 C CU > o o . 5 . 5 a. u S 1 l5b-2 !a & co • c t- cn 60 CO e I ra 6< in cu (U «J 60 CJ O o ro LL, fc: cu 142 rocks in 93D9 consist of variably chlorite- and biotite-altered fragmental volcanic rocks with lesser massive and pillowed intervals. Intensely biotite- and chlorite-altered rocks forms a zone -15 metres wide flanking the volcanic and sedimentary contact. The alteration in this zone is so intense that primary lithologies cannot be recognized visually and can only be identified by lithogeochemistry. In 93D8 the footwall rocks consist primarily of pillowed and massive volcanic rocks. Although these rocks are typically more biotite-altered than the volcanic rocks in 93D9, primary volcanic textures such as vesicular pillow margins and plagioclase phenocrysts are still recognizable. Mass change calculations and molar proportion plots indicate that the upper 20 metres of volcanic stratigraphy is less altered than the deeper volcanic rocks of 93D9 (Figures 5.8b and 5.9). Mass losses in Si02, up to -12 wt % , accompany intense chlorite alteration of these rocks (93D9-112.7, 93D9-114.2 and 93D9-122.5). Semi-massive to massive sulphide lenses lie above the volcanic contact in both D D H 93D8 and 93D9. Semi-massive sulphides occur in the last 10 metres of 93D7. In all three holes, the sulphide lenses grade into overlying unaltered mudstone-turbidite sedimentary rocks (Figure 5.9). No significant sulphide mineralization was intersected in either 93D10 o r 9 3 D l l . The massive sulphides in the.sedimentary rocks are cemented by fine-grained to aphanitic silica and coarse recrystallized calcite gangue. Commonly, metre-thick intervals of massive sulphides (<20% gangue) alternate with thinner intervals of semi-massive sulphide or near-barren gangue minerals. The gangue in the semi-massive sulphide zones consists mainly of quartz with lesser carbonate, sericite, chlorite, amphibole and fine-143 grained clastic sediment. The hangingwall sedimentary rocks are comprised of laminated siltstone-mudstone, interbedded with lesser sandstone and limestone. Bedded layers range from <1 to >10 centimetres thick. In D D H 93D10 and 93D11, the sediments fine and thin upward over broad intervals, tens of metres thickness. These sequences are characterized by sandstone- and siltstone-rich lower portions that grade up stratigraphy into more mudstone-rich intervals. Two such cycles are recognized in 93D11. A single cycle showing progressive upward fining is intersected in 93D10. On average, the thickness of the sandstone and siltstone layers decreases with the increased mudstone component in the sediments. 5.4.3.2 Mineralization * Abundant veins of quartz-pyrrhotite-chalcopyrite occur in the upper 10 metres of the volcanic footwall in 93D8 between 55 and 65 metres, and in 93D9 between 105 and 138 metres (Figure 5.9). These veins occur stratigraphically below the massive sulphide intersections and are interpreted as footwall stockwork mineralization. The veins are <0.2 centimetres to several centimetres thick and form branching networks within the host volcanic rocks. The veins contain coarse recrystallized quartz, and locally have thin chloritized selvages. Most of the these vein stockworks contain visible chalcopyrite and are weakly mineralized. Significant mineralization was intersected in a 5 metre interval from 131-136 metres in 93D9 which averaged 1.28% Cu. In holes 93D8 and 93D9, semi-massive to massive sulphide lenses lie somewhat above 144 the volcanic contact, and pass transitionally into stratigraphically overlying mudstone-turbidite rocks which are little altered (Figure 5.9). In 93D8, a 30 metre-thick sulphide interval is zoned from an 18 metre-thick core of massive pyrrhotite with lesser chalcopyrite, to upper and lower margins of semi-massive, pyrrhotite-pyrite-rich sulphides. Low grade mineralization from 40-54 metres (0.73% Cu) in 93D8 includes both the lower portion of the sulphide lens and siliceous sulphide margin. Semi-massive sulphides in the last 10 metres of 93D7 are correlative with the semi-massive siliceous sulphides in 93 D8. The sulphide intersection in 93 D9 lies within the sedimentary sequence, about 10 metres above the volcanic contact (Figure 5.9). It is 40 metres thick and consists of semi-massive to massive pyrite and pyrrhotite, with lesser chalcopyrite, sphalerite and minor galena. The lower 25 metres is rich in pyrite, which passes gradationally into a 15 metre-thick interval of mainly pyrrhotite with lesser chalcopyrite. The upper contact with unaltered siltstone-mudstone rocks is faulted. Significant low grade copper mineralization is encountered at 28-39 metres (0.5% Cu), 40-49 metres (0.5% Cu) and 62-64.5 metres (0.43% Cu) in hole 93D9 and includes almost the entire massive sulphide intersection. 5.5 S U M M A R Y A N D D I S S C U S S I O N At the Hidden Creek Mine sulphide mineralization is hosted in both the volcanic and sedimentary rocks. Pyrite and pyrrhotite are the principle Fe-sulphides and chalcopyrite is the main Cu-sulphide. Mineralized zones can contain minor sphalerite and galena. In drillcore most of the significant sulphide lenses were formed by the infilling and 145 replacement of porous sedimentary layers and volcanic breccias with sulphides, where as siliceous, semi-massive sulphides formed along the margins of these lenses. Vein stockworks in the volcanic and sedimentary footwall rocks are likely the feeder zones to the massive sulphide lenses, but locally overprint earlier massive and semi-massive sulphide lenses. The main ores zones are hosted by a sequence of lower massive and pillowed volcanic rocks, a middle unit of mainly fragmental volcanics and an upper mudstone-turbidite sedimentary package. Folding and faulting have modified the original contacts. In the mineralized zones, chlorite-epidote-actinolite alteration assemblages occur in the footwall volcanics and lower sedimentary strata with sericite-carbonate alteration in the upper sedimentary sequence. Some intensely altered volcanic rocks contain accessory magnetite. Biotite overprints both the chlorite and sericite altered rocks especially near the volcanic sedimentary contact and within the broad north-trending shear zone that hosts the Nos.2 and 3 ore zones. In places, biotite forms bands up to 3 centimetres thick which are subparallel to remnant bedding; these bands may represent original clay-rich pelagic layers in the turbidite-mudstone sequence. The altered sedimentary rocks range from silica-poor chlorite and mica schists to silica-rich impure cherts. There is no direct correlation between the extent of alteration and silicification. Banded silica-rich and silica-poor layers mimic bedding in the unaltered siltstone-mudstone sediments, suggesting that permeability contrasts between different sediment layers have provided a first-order control on the infiltration of silica-rich fluids. Similarly, volcanic breccias are preferentially silicified (cemented) relative to more massive lithologies. 146 C H A P T E R 6: SUMMARY AND DISCUSSION 6.1 STRATIGRAPHY AND ORE ZONE GEOMETRY The ore lenses at the Hidden Creek Mine formed along or near the contact between a tholeiitic, mafic volcanic footwall and an overlying sequence of quartzo-feldspathic turbiditic sediments, plus pelagic sediments (Figure 6.1). Cherty and hydrothermally altered rocks occur discontinuously along the volcanic-sedimentary contact and are thickest in the vicinity of the Nos. 1 and 5 ore zones. The volcanic package is comprised of a lower unit of primarily pillowed and massive rocks and an upper unit of mainly volcanic breccia. The volcanic breccias may have been derived through erosion and mass wasting of seafloor volcanic highs, forming talus aprons adjacent to fault scarps; some of the debris could also represent flow breccias. Massive and pillowed volcanic rocks of the lower volcanic unit are uplifted and exposed in the core of the north-trending Hidden Creek Anticline and a second northeast-trending anticline which runs parallel to the southern volcanic-sedimentary contact. Tongues of more massive volcanic rocksprotrude into the breccias in several places and may reflect parasitic folding in the anticline or alternatively block faulting of the volcanic strata. Sedimentary rocks, exposed along the limbs of the Hidden Creek Anticline and in the cores of prominent synclines (e.g, Gama Zone area), are more deformed in the hinge zones and the steeply overturned limb of the anticline than in the upright limb. Vertical sections, constructed using surface data, drillhole data and level plans from the 147 Metres LEGEND • Massive and Pillowed Volcanic Rocks Breccia and volcaniclastic Mixed Quartz-chlorite Schist Sedimentary Rocks Alteration: chert, chlorite-sericite-bioite schist Ore Zone Antidine/syncline Drillhole Collapsed workings Fault Surface trace volc-sed contact Scale-1:10 000 Figure 6.1: Generalized geology of the Hidden Creek mine, Anyox showing the major lithologies and structures, the distribution of the ore zones, diamond drillhole locations and the positions of cross-sections appearing in Figure 6.2. 148 250 m — 200 m — 150 m — 100 m — 50 m — 0 m — Legend Mudstone -Turbidite Pillow and Massive Volcanics Mafic Volcanic O Breccia 9 Quartz-Chlorite 0 Schist Chi - Chlorite Src - Sericite Sen - Schist Mdst - Mudstone Turb - Turbid He 4-• ®I<D Ore Zone Sulphide Veins Drill Hole Projection with mineralized intercept Surface Sulphide Lenses Fault movement with slip direction Block movement away / toward 200 m 150 m 100 m 50 m 0 m -50 m H No. 1 Ore Zone Mdst-turb Horizontal Scale = 1: 5000 Vertical Exaggeration = 1.32x Figure 6.2: Schematic cross sections through the main ore zones at the Hidden Creek mine. Diamond drillholes are projected on to the sections. Orientations and positions of the sections are shown in Figure 6.1. 149 mine (Nelson, 1935) show the spatial relationships between sulphide mineralization, host lithologies, alteration facies and major structural elements within and around the main ore zones (Figure 6.2). The Nos. 1, 2, 3, 4 and 5 ore zones are distributed along the upright limb, hinge zone and overturned limb of the Hidden Creek Anticline and further modified by second and third order folds and post-mineral faulting. Quartz-sulphide veins, related to deformation, cross-cut earlier syngenetic mineralization; they and are commonly found along fractures and shears and in the hinge zones of the folded sedimentary strata. In the upright limb, the No. 3 ore zone is displaceed up and to the north of the No. 2 ore zone by a 120 metre wide shear which envelopes the No. 2 ore zone, and truncates the No. 1 ore zone at depth in the overturned limb of the anticline. Vein stockworks and small sulphide-rich lenses were intersected in the overturned mafic volcanic footwall of the No . l ore zone, and shear-hosted mineralization beneath the No. 2 ore zone. Chlorite-dominated alteration assemblages in the volcanic rocks and lower sedimentary rocks of the No. 1 ore zone pass up stratigraphy (down section and to the south) into sericite^ dominated assemblages associated with semi-massive and massive sulphide lenses within the sedimentary sequence. In the hinge zone of the Hidden Creek Anticline, thick intervals of weakly altered mudstone-turbidite overlie massive sulphide lenses of the No. 4 ore zone and a weakly mineralized stockwork zone in the footwall volcanic stratigraphy. 6.2 S E A F L O O R S E T T I N G The Nos. 2 and 3 ore zones occur in massive and pillowed flows and breccias within the upper volcanic sequence (Figure 6.3a). Veined stockwork zones up to tens of metres 150 a) Nos . 2 a n d 3 O r e z o n e V o l c a n i c H o s t e d 0 m - 50 m 100m J Unaltered sedimentary cover (turbldlte-mudstone) Upper volcanics Volcanic Breccia Chlorite alteration Velning and sulphide lenses (po-py-cpy-qtz-chl) Pillowed basalts and massive flows b) 100 m 0 m Nos. 1 a n d 5 O r e z o n e S e d i m e n t H o s t e d - 100 m Unaltered sedimentary cover (turbldlte-mudstone) Serlclte-quartz alteration Sulphide lenses and veins (po-py-cpy-qtz-chl) Chlorlte-quartz alteration Volcanic breccia, massive and pillowed flows Figure 6.3: Schematic stratigraphic setting of mineralization and alteration relations at Hidden Creek, Anyox: (a) the volcanic-hosted Nos. 2 and 3 ore zones, and (b) the sediment-hosted Nos. 1 and 5 ore zones. Volcanic-hosted mineralization may have occurred in part under sedimentary cover and at least some portion of the sediment-hosted mineralization occurred as a subsurface phenomena. 151 thick punctuate underlying volcanic stratigraphy, and are interpreted as footwall feeders to massive sulphide lenses in the upper volcanic sequence. Hydrothermal alteration is localized around individual veins (or veined intervals) but forms broader alteration halos around the semi-massive and massive sulphides. The alteration is characterized chemically by loss of CaO and Na20, and gain of M g O and FeO. Mass changes in Si02 do not correlate with changes in other major oxides, which may indicate a two-stage seafloor process whereby Si02 is lost during chloritization of the rock (leaching phase), but is later gained through quartz-sulphide veining (depositional phase). Zones of breccia within otherwise massive and pillowed lavas in the upper volcanic sequence may mark hiatuses in volcanism when the products of hydrothermal activity could accumulate. In the Nos. 2 and 3 ore zones, mineralization may have occurred at a paleo-surface marked by volcanic breccias, prior to the final phase of volcanism. Alternatively, mineralization could represent a shallow subsurface phenomenon with sulphide precipitation taking place in more permeable zones of volcanic breccia. The Nos. 1 and 5 ore lenses occur above the volcanic contact and within the lower sedimentary sequence (Figure 6.3b). These lenses consist of semi-massive to massive pyrrhotite-pyrite with minor chalcopyrite and sphalerite and trace galena. Quartz and calcite are the major gangue minerals. Sulphide lenses and vein networks occur throughout the ore zone stratigraphy in both chlorite- and sericite-altered rocks. Pyrrhotite is the main sulphide in the footwall volcanic rocks and in the chlorite-altered sediments. The relative proportion of pyrite increases in the sericite-altered sediments. Chlorite alteration in the volcanic footwall of the Nos. 1 and 5 ore zones increases up 152 stratigraphy and is most intense within 75 metres of the sedimentary contact. Volcanic breccias in the upper volcanic footwall are cut by numerous quartz and sulphide veins. In the northern and central portions of the Nos. 1 and 5 ore zones, chlorite-epidote-quartz alteration extends from the upper volcanic footwall into the overlying sedimentary rocks. The chlorite-rich core is capped and flanked by sericite-quartz altered sediments. There is no systematic distribution of chert within the ore zone, nor are silica-rich zones uniquely associated with either chloritization or sericitization. Altered and unaltered sediments are interleaved throughout the mineralized areas, which suggests that hydrothermal fluids may have advanced and dispersed laterally as a pulse (or series of pulses) up through the stratigraphic column, partially influenced by primary features such as bedding. If mineralized zones were allowed to cool, later pulses of hydrothermal fluids could develop vein stockworks and mineralized breccias superimposed on earlier infiltration and replacement styles of mineralization. 6.3 C O M P A R I S O N W I T H O T H E R S E A F L O O R D E P O S I T S The stratigraphic setting, alteration and mineralization styles of the Hidden Creek deposit resemble features in both modern and ancient volcanogenic sulphide deposits. Middle Valley, on the spreading axis of the northern Juan de Fuca Ridge is a modern, hydrothermally active volcanogenic environment (Figures 6.4 and 6.5). In this area, there are two zones of hydrothermal fluid upflow, the Bent Hil l zone, which is a fossil upflow conduit, and the A A V , an area of active venting where at least 11 vents are discharging hydrothermal fluids from anhydrite chimneys (Goodfellow and Peter, 1994). Several massive sulphide lenses underlie the Bent Hil l zone, as indicated by recent drilling on Figure 6.4: Map of the Juan de Fuca Ridge system showing the main tectonic elements and the location of Middle Valley at the northern extremity of the ridge (from Goodfellow and Peter, 1994). Figure 6.5: Schematic block diagram of the Middle Valley hydrothermal system showing the inactive hydrothermal fluid upflow zone, related alteration, and associated massive sulphide deposit (from Goodfellow and Peter, 1994). 155 Leg 169 of the Ocean Drilling Project (Shipboard press releases, Y . Fouquet and R. Zierenberg, Oct. 1996). Site 856H on Bent Hil l intersected a 100 metre thick zone of sediment hosted, pyrrhotite-chalcopyrite-sphalerite-rich massive sulphides which passes down stratigraphy into a further 100 metres of pyrrhotite-isocubanite chalcopyrite-pyrite-rich, sulphide-veined siltstone and mudstone of the sulphide stringer zone. Cu-rich banded sulphide-sandstone layers, intersected at the base of the sulphide stringer zone, mimic original sedimentary features and were interpreted by shipboard scientists as sulphide replacement of sandy intervals that mark the base of the turbidites (Y. Fouquet and R. Zierenberg, communications, 1996). The base of the sulphide stringer zone is faulted and underlain by relatively unaltered and unmineralized siltstone-mudstone. At least five diabase sills, each 2-5 metre thick, intrude the sedimentary strata over a 50 metre thick interval, at 430 metres depth. The hole ends at 500 metres below the surface in 20 metres of pillowed basalts and flows interpreted as the mafic volcanic seafloor. A l l the igneous rocks are altered and cross-cut by chlorite-quartz-chalcopyrite-pyrrhotite-calcite-epidote veins (Y. Fouquet and R. Zierenberg, communications, 1996). Earlier drilling by O D P Leg 139 indicated that alteration at the Bent Hi l l conduit is zoned outward from a silicified core to weakly altered sediment at the margins as follows (Goodfellow and Peter, 1994): 1) quartz+Fe-chlorite+muscovite+rutile; 2) albite+Mg-chlorite+muscovite+pyrite; 3) anhydrite+illite+barite+pyrite; 156 4) calcite+illite+pyrite. Textural, mineralogical and chemical zonation around the upflow zone is consistent with precipitation from upflowing and outflowing hydrothermal fluid that mixed with entrained sea water at the margins of the discharge conduit (Goodfellow and Peter, 1994). The Windy Craggy deposit in northern British Columbia is a large (>300 mt) C u - C o - A u volcanogenic sulphide deposit of Upper Triassic age (Figures 6.6 and 6.7). It consists of two main ore zones which are hosted by a volcanic-sedimentary sequence of intercalated mafic pillowed to massive volcanic flows, sills and turbiditic calcareous argillites (Mclntyre 1986, Peter 1992, and Mihalynuk et al., 1993). The ore zones consist of sediment-hosted massive sulphide lenses and underlying vein stockworks which cross cut the volcanic and sedimentary strata. Chert-calcite horizons which cap both ore zones and are interbebdded with the sedimentary and volcanic rocks are interpreted by Peter (1992) as hydrothermal exhalatives. The massive sulphide lenses at Windy Craggy are mineralogically zoned and grade from pyrrhotite-chalcopyrite-rich cores to pyrte-calcite-sphalerite-rich margins. Open-space filling, clastic and replacement textures in the sulphide lenses reflect both seafloor and subseafloor mineralizing processes (Peter, 1992). Stockwork veins are pyrrhotite-chalcopyrite-rich with lesser pyrite and sphalerite. Quartz, chlorite and calcite are the main gangue minerals associated with the massive and veined sulphides. The cores of the stockwork zones are intensely silicified to the point of appearing cherty and grade laterally into intensely chloritized rocks (Peter, 1992). 157 Figure 6 . 6 : Location map for the Windy Craggy massive sulphide deposit in Northern British Columbia. 158 Figure 6.7: Geology of the Windy Craggy deposit from Peter (1992). Large pyrite- and pyrrhotite-™ L T ^ r P h ' d e « ° d i e S Z h ° S t e d b y 3 volcanic-sedimentary sequence o k t e r c ^ d m ^ L and pillowed volcanic flows, sills and turbiditic calcareous argillites. massive 159 Alteration and mineralization in the volcanic and sedimentary sequence at Hidden Creek bear a strong resemblance to alteration and mineralization reported at both the modern Middle Valley and the Triassic Windy Craggy settings. The volcanic rocks around the Nos. 2 and 3 ore zones are intensely chloritized and silicified. A s in Middle Valley and Windy Craggy, pyrrhotite and chalcopyrite are the dominant sulphides in the altered volcanic rocks. Alteration around the Nos. 1 and 5 ore zones at Hidden Creek is zoned outward from a quartz+chlorite+pyrrhotite core to a margin of quartz+sericite+pyrite. Chalcopyrite is spatially associated with pyrrhotite and sphalerite (where present) is found in pyrite-rich lenses. In contrast to Middle Valley, calcite is intimately associated with sulphide mineralization and occurs throughout the altered sedimentary sequence in a manner similar to Windy Craggy. Biotite in the altered Hidden Creek host rocks has probably formed in response to the regional metamorphism of K- and Mg-rich clay minerals, such as illite and smectite. In the Hidden Creek volcanic rocks, these minerals initially may have formed as low-temperature seafloor alteration products, whereas in the sedimentary rocks, they may represent primary (or hydrothermally modified) detrital components. 6.4 PRIMARY LITHOGEOCHEMISTRY Least altered mafic volcanic rocks at Anyox have major and trace element compositions which indicate that they are ocean-floor tholeiitic basalts and basaltic andesites. Normal, transitional and enriched mid-ocean ridge basalts ( N - M O R B , T - M O R B and E - M O R B ) are distinguished using P/Ti ratios and R E E data. Enriched volcanic rocks ( E - M O R B and T - M O R B ) occur in the upper portions of the footwall volcanic stratigraphy and are 160 commonly intensely hydrothermally altered due to the proximity of massive sulphide mineralization. With the available information, one can only speculate as to the origin of the E - M O R B rocks. Workers studying modern ocean rift environments (Reynolds et al. 1992; Thompson et al., 1989; and Perfit et al., 1994) have found that the likely source of E - M O R B lavas are small magma chambers formed as the result of partial melting of an enriched (more alkalic) mantle source or alternatively are the product of small amounts of partial melt from similar source rocks as N - M O R B . Either scenario may cause the incompatible element enrichment which is characteristic of the E - M O R B rocks. R E E patterns for regional mafic volcanic rocks from the Anyox pendant (Smith, 1993) are similar to those of the N - M O R B suite of the present study (Figure 6.8a). Smith's samples were from localities in the lower volcanic sequence, away from the Hidden Creek mineralized zones and the contact with sedimentary rocks. The combined data sets suggest that N - M O R B comprises much of the volcanic sequence in the Anyox pendant, but that E - M O R B was locally erupted as a late magmatic event. Some of these areas of E - M O R B eruption are sites of hydrothermal alteration and mineralization which may be the result of increased hydrothermal circulation around a newly introduced heat source (E -MORB) into a slightly earlier and cooler volcanic package (N-MORB) . E - M O R B has been reported from several modern oceanic spreading environments. Mafic rocks from the East Pacific Rise (EPR) at 11-13°N (Figure 6.8b) and from Middle Valley on the Juan de Fuca Ridge (Figure 6.8c) have R E E patterns and other chemical features which indicate that both N - M O R B and E - M O R B suites were erupted (as at Anyox). The EPR extrusive mafic rocks are from the axial graben and a near-axis seamount (Hekinian 161 et al., 1989), whereas the Middle Valley samples are from sub-seafloor sills that are intrusive into unconsolidated sediments (Goodfellow and Peter, 1994). In both areas, most of the mafic volcanism in the areas of hydrothermal activity are N - M O R B . Peter (1992) has identified the mafic volcanic rocks of the Middle Tats Volcanic (MTV) group that host the Windy Craggy deposit as transitional, subalkaline tholeiites which plot as within-plate basalts on most discrimination diagrams. The volcanic rocks are enriched in the light R E E and the large ion lithophile elements (LILE) but lack Ta and Nb depletions. R E E patterns for the M T V are similar to E - M O R B patterns from Anyox but are more L R E E enriched and H R E E depleted (Figure 6.8d). Mafic volcanic rocks from coeval strata in the regional stratigraphy and post-mineralization dykes from the Windy Craggy area have characteristic arc signatures, that is, L I L E and L R E E enrichment and depletions in high field strength (HFS) elements including Ta (Smith and Fox in Peter, 1992). On this basis, Peter (1992) suggested that the Windy Craggy deposit formed in a back-arc basin environment. Tholeiitic basalts and basaltic andesites found regionally distributed throughout the Anyox Pendant and hosting the Hidden Creek ore bodies lack characteristic arc signatures such as those recognized in mafic volcanic rocks from the Windy Craggy area, and are therefore unlikely to have formed in a back-arc basin environment. Major, trace and rare earth element data from mafic volcanic rocks from Anyox have clear mid-ocean ridge signatures and indicate that the Hidden Creek orebodies were formed in heavily sedimented mid-ocean ridge setting comparable to that of Middle Valley along the Juan de Fuca ridge. 162 CD +•* o O E (0 ro 3 o 2 o <D> > o if) '^Z co 0 5 «•= 5 c s> CO o 0 > ° c O < aiupuoipppoy 111 1 1 1 1—1 r O UJ E CO TJ 0) o xi >-3 LU E CO TJ 0 o CO e}.upuoL|o/>|ooy " <u u E •a CD ? t a w c0 Cu >5 a,-a CO so 10 OS C CD J 3 co £ l C X CO CD 8 "S a I O / - N e ^ CO W . * X I O CO Ul .co CO CO 6 GO 2 CU 2 x f c2 § CO & g • — i CO u T ^ CD CD •B CD CD l_ _2 § ra X ) co X J •§ £ c3 CD CO - £ 5 S.9 J3 CO 0 o T5 CO o p o > a CO a 3 C ° ea > co ao a oo (3 CO CJ ..a co £ c 3 S u u c s § I E 6 a CD • £ « s a >^  CD J O CD 13 3 ^ « <D * 1 9}.upuou,o/>|oo}j 9}upuou,o/>|ooy CD < § I B OO Q § 2 •o P. CD J3 . ^ +-» os . 5 73 <*- 1 +j CD U 60 .1 I CD CD o o a u <o ca OH CD 163 6.5 G E O L O G I C A L H I S T O R Y The geological history of the Hidden Creek deposit can be summarized as follows: 1) Accumulation of a thick mafic volcanic sequence composed of basaltic to basaltic andesite flows, pillowed flows and volcanic breccia. Enriched volcanic rocks ( T - M O R B and E - M O R B ) occur in the upper portions of the volcanic stratigraphy and appear to represent a late phase of volcanic activity in the area. 2) Hydrothermal fluid circulation resulted in the deposition of massive sulphides and associated stockwork mineralization in the upper volcanic pile, with chloritization and local K-alteration (probably sericite) in the adjacent volcanic host rocks. Typical temperatures of the mineralizing fluids ranged from 220° to 270°C and had salinities from 4.6-8.9 wt% NaCl eq (Macdonald et al. 1997). 3) Much of the volcanic seafloor was then covered by a few metres to a few tens of metres of pelagic muds and turbidites. The turbidites are quartzo-feldspathic and were probably derived from a continental source external to the mafic-floored basin. 4) Penetration of the hydrothermal system upward into the sedimentary cover with deposition of massive sulphides at or near the seawater interface, partial replacement of sandier interbeds in the subsurface, and formation of stockwork veins in the sediments, all surrounded by an irregular zone of sericite-chlorite-quartz alteration. 5) Cessation of hydrothermal activity but continued accumulation of the turbidite-mudstone sequence (at least one hundred metres thick). 164 6) Deformation and regional metamorphism resulting in secondary biotite-actinolite assemblages in the mafic and sedimentary rocks (but particularly the former), folding of the ore lenses and post-mineral high angle faulting. 6.6 F U T U R E E X P L O R A T I O N 6.6.1 Features of the Hidden Creek Mine The volcanic-sedimentary contact represents an important paleoseafloor surface within the stratigraphy. The distribution of mineralization and alteration around the contact reflects the crucial role of the contact as a focus for hydrothermal activity and sulphide deposition. As in the past, future exploration should focus on the volcanic sedimentary contact in the east Anyox Pendant, particularly around zones of intense hydrothermal alteration. Complex fault networks modify cross-folded north- and easterly-trending anticlinal structures that expose mineralized volcanic rock at both the Hidden Creek and Bonanza mines. Jackish and Rhodes (1988) report that at Hidden Creek, mineralization was thinner along the fold limbs and thicker and of higher grade in the hinge zones (e.g. No. 5 ore zone). This may be due in part to remobilization of sulphides and precious metals during deformation. Similarly late quartz-sulphide veins follow post-mineral, high-angle shears in the volcanic footwall of the deposit and overprint earlier mineralization. Rheological differences between the massive sulphide lenses, the enclosing altered host rocks and peripheral unaltered rocks, may have localized strain around the ore zones during regional deformation resulting in the complex structures. 165 Banded quartz-chlorite schists, which host sulphides of the Nos. 2 and 3 ore zones. These rocks are interpreted as hydrothermally altered and deformed equivalents of mafic volcanic breccias found elsewhere in the footwall. The breccias are more permeable than the massive or pillowed volcanic rocks and may have enhanced subsurface sulphide deposition by providing paths for migrating hydrothermal fluids and sites for fluid mixing during a mineralizing event. Similarly, sandy layers in the sedimentary strata may be preferential sites for sulphide mineralization The alteration pattern associated with the sulphide mineralization can be used as a guide for mineral exploration. Volcanic and sedimentary host rocks in the footwall of the No. 1 ore zone are intensely chloritized. Previous studies have mistaken chloritized sedimentary rocks for silicified volcanics, however, this study has demonstrated that these rocks can be distinguished lithogeochemically. Toward the margins of the ore zone, chloritization gives way to sericitization. Accessory magnetite is observed in some of the altered volcanic rocks in close spatial association with sulphide mineralization. Chloritized sediments are seen in only a few places and likely reflect the entrainment of magnesium rich seawater to the system or interaction of the sediments with hydrothermal fluids derived from the mafic footwall. In either scenario, there would be potential for significant mineralization in the sedimentary strata above the volcanic contact similar to that of the No. 1 ore zone. The distribution of silicified strata through the ore zones is erratic and not uniquely associated with sulphide mineralization. However, the thickest intervals of chert occurs in the vicinity of the Nos. 1 and 5 ore zones, and free silica was a major component of the 166 sediment hosted sulphide ore lenses (Nelson, 1935, Grove, 1986). Quartz-cemented volcanic breccias, quartz-chlorite schists and cherty sedimentary rocks reflect areas of increased hydrothermal activity and may be proximal to a mineralized portion of the hydrothermal system. Most E - M O R B rocks are hydrothermally altered and occur in proximity to mineralized areas. Although there is no definitive genetic link between the E - M O R B rocks and mineralization, there appears to be at least a spatial association that may be a useful exploration tool. The enriched rocks can be identified chemically by P/Ti ratios > 0.075. It is also possible that some late magmatic activity ( E - M O R B ) may post-date early sediment deposition. Therefore, in the field, it would be useful to search for dykes or sills in the sedimentary sequence which may be manifestations o f such late magmatism. 6.6.2 Mineral Potential of the East Anyox Pendent: There are four other known massive sulphide deposits in the east Anyox pendant, Bonanza, Double E d , Redwing and Eden (Table 6.1). Bonanza was mined during production at Hidden Creek. A l l of these deposits are found within the volcanic sequence, where they are hosted by quartz-chlorite schist. Like the Nos. 2 and 3 ore lenses, three of the four deposits occur within 200 metres of the sedimentary contact. Volcanic hosted massive sulphides in the Nos. 2 and 3 ore zone at Hidden Creek appear to represent the roots of a composite volcanic- and sediment- hosted deposit. Previous exploration programs at Bonanza, Double E d and Redwing and Eden have defined only volcanic hosted mineralization. If Hidden Creek is used as a model for evaluating these 167 other deposits, then there is potential for mineralization in the overlying sedimentary rocks in these latter areas. For example, at Hidden Creek, sediment-hosted sulphide lenses of the Nos. 1 and 5 and 4 ore zones occur from 10 to 100 metres above the volcanic contact, and small sulphide lenses of the No. 8 ore zone appear to extend even further up into the sedimentary stratigraphy. Table 6.1 Grade and Tonnage of Massive Sulphide Deposits in the Anyox Pendant DEPOSIT TONNES GRADE Hidden Creek Production Reserves 21,681,800 13,600,000 1.57% C u , 0.17g/t A u , 9.25g/t A g , 0.75% C u Bonanza Production Reserves 647,904 10,624 2.1% C u 1.76% Cu , 0.16g/t A u , 13.7 g/t A g Double Ed Reserves 1,229,235 1.3% Cu , 0.6% Zn Redwing Reserves 164,600 2.0% Cu , 2.7% Z n Eden Reserves 158,757 1.4%Cu, 1.7% Z n 6.6.3 Future Exploration in the Hidden Creek Area Future work in the area of the Hidden Creek Mine should focus on: 168 1) The distribution of breccias and banded chloritized schists in the footwall volcanic stratigraphy. 2) Areas of intense alteration in the vicinity of the volcanic-sedimentary contact and the distribution chloritization, sericitization, biotization and silicification in the altered host rocks. 3) Identification of late volcanic activity related to the underlying mafic volcanic rocks in the form of dykes and sills within the sedimentary sequence. 4) Systematic sampling of the volcanic footwall (especially feeder dykes) in order to identify late phase volcanic rocks of E -MORB and T - M O R B affinities (P/Ti > 0.075). 5) More extensive exploration of the sedimentary stratigraphy for at least 100 to 200 metres above the volcanic contact, especially in areas of intense chloritization of the sedimentary rocks. 169 REFERENCES A L L D R I C K , D.J., 1986. Stratigraphy and structure of the Anyox area (103P/5). In: Geological Fieldwork 1985. B .C . Ministry of Energy, Mines and Petroleum Resources, Paper 1986-1, pages 211-216. A L L D R I C K , D.J., M A W A N I , Z .M.S. , M O R T E N S E N , J.K. A N D C H I L D E , F . C , 1996. Mineral deposit studies in the Stewart District (NTS 103O/P and 104A/B). in Exploration in British Columbia, B .C . Ministry of Energy, Mines and Petroleum Resources, pages 89-109. B A N C R O F T , J .A. , 1918. Preliminary report on the geology of the Anyox map area, including the Hidden Creek and Bonanza deposits. Unpublished report. Granby Consolidated Mining and Smelting L t d . . C A N N , J.R., 1970. Rb, Sr, Y , Zr, and Nb in some ocean floor basalts. Earth and Planetary Science Letters, volume 10, pages 7-11. C A R T E R , N., 1981. Porphyry copper and molybdenum deposits of British Columbia, B .C . Ministry of Energy, Mines and Petroleum Resources, Bulletin 64, 150 pages. C A R T E R , N . A N D G R O V E , E.W., 1972. Geological compilation map of the Stewart, Anyox, Alice A r m and Terrace areas. B .C . Ministry of Energy, Mines and Petroleum Resources, Preliminary Map No. 8. C H I L D E , F. C , 1997. Timing and tectonic setting of volcanogenic massive sulphide deposits in British Columbia; constraints from U-Pb geochronology, radiogenic isotopes, and geochemistry. Unpublished Phd. thesis, University of British Columbia, 325 pages. C H I L D E , F. C , 1994. Chronology and radiogenic isotopic studies of the Kutcho, Granduc, Anyox and Tulsequah Chief massive sulphide deposits. In: Annual Technical Report of the V M S Project. Mineral Deposit Research Unit, University of British Columbia. D A V I S , J.W., A U S S A N T , C H . and C H I S H O L M , R.E. , 1993. Diamond drilling, geochemical and geophysical report on the Anyox Property, Skeena Mining Division. Internal company report for TVI Copper Inc., 27 pages plus appendices. DAVIS , J.W., A U S S A N T , C H . and C H I S H O L M , R.E. , 1992. Geological, Geochemical and Geophysical Report on the Anyox Property, Skeena Mining Division. Internal company report for TV I Copper Inc., 103 pages. D O L M A G E , V . , 1922. Coast and islands of British Columbia between Douglas Channel 170 and the Alaskan Boundary. Geological Survey of Canada, Summary Report, 1922, Part A , pages 9-34. E V E N S O N , N .M. , H A M I L T O N , P.J. A N D O'NIONS, R.K., 1978. Rare-earth abundances in chondritic meteorites. Geochimica et Cosmochimica Acta., volume 42. pages 1199-1212. E V E N C H I C K , C A . A N D H O L M , K., 1997. Bedrock geology of the Anyox Pendant and surrounding areas, Observatory Inlet (103P/5) and parts of the Hastings Arm (103P/12) and 103O/9 map areas, British Columbia, in Current Research 1997-A, Geological Survey of Canada, pages 11-20. E V E N C H I C K , C .A . , A L L D R I C K , D.J., C U R R I E , L.D., H A G G A R T , J.W., M C C U A I G , S., M C N I C O L L , V . A N D W O O D S W O R T H , G.J. , 1997. Status of research in the nass ?River multidisciplinary geoscience project, British Columbia, in Current Research 1997-A, Geological Survey of Canada, pages 21-30. F O X , J.S., 1989. Structural analysis of the Hidden Creek area, Anyox Property, Observatory Inlet region, B .C . Cominco Ltd./Pospector Airways Co. Ltd., private company report. G O U T I E R , J . , M A R C O T T E , C . and W A R E S , R., 1990. Deformation of the Anyox Massive sulphide deposit, British Columbia. In Geological Association of Canada; Mineralogical Association of Canada, Annual meeting, Program with abstracts, page 50. G O O D F E L L O W , W.D . and P E T E R , J .M. , 1994. Geochemistry of hydrothermally altered sediment, Middle Valley, Northern Juan De Fuca Ridge. In: Mottl, M.J. , Davis, E .E . , Fisher, A . T . and Slack, J.F., editors, Proceedings of the Ocean Drilling Program, Scientific Results, Volume 139, pages 207-289. G R O V E , E.W., .1965. Observatory Inlet, Granby Bay area, in B .C . Ministry of Energy, Mines and Petroleum Resources, Annual report, pages 57-59. G R O V E , E.W., 1986. Geology and Mineral Deposits of the Unik River - Salmon River -Anyox Area; B .C . Ministry of Energy Mines and Petroleum Resources, Bulletin 63. H E K I N I A N , R., T H O M P S O N , G . and B I D E A U , D., 1989. Axial and off-axial heterogeneity of basaltic rocks from the East Pacific Rise at 12°35'N-12°51 ' N and l l o 2 6 ' N - l l ° 3 0 ' N , Journal of Geophysical Research, volume 94, pages 17,437-17,463. IRVINE, T .N . A N D B A R A G A R , W.R.A. , 1971. A guide to the classification of common volcanic rocks. Canadian Journal of Earth Sciences, volume 8, pages 523-548. 171 M A C D O N A L D , R.W.J., B A R R E T T , T .J . A N D S H E R L O C K , R.L. , 1996. Geology and lithochemistry at the Hidden Creek massive sulphide deposit, Anyox, west-central British Columbia. Exploration and Mining Geology, volume 5, no. 4, pages 369-398. M A C D O N A L D , R. W. J . , 1996. Geology o f the Hidden Creek Deposit, Anyox West-Central British Columbia, in Annual Technical report, Year 3, V M S Project, M D R U , University of British Columbia, section 5, pages 1-58. M A C L E A N , W.H . , 1988. Rare-earth element mobility at constant inter-REE ratios in the alteration zone at the Phelps Dodge massive sulphide deposit, Matagami, Quebec. Mineralium Deposita, volume 23, pages 231-238. M A C L E A N , W.H. , 1990. Mass changes in altered rock series. Mineralium Deposita, volume 25, pages 44-49. M A C L E A N , W . H . and B A R R E T T , T .J . , 1993. Lithogeochemical techniques using immobile elements. Journal of Geochemical Exploration, volume 48, pages 109-133. M A C L E A N , W . H . and KRANIDIOTIS, P., 1987. Immobile elements as monitors of mass transfer in hydrothermal alteration: Phelps Dodge massive sulphide deposit, Matagami, Quebec. Economic Geology, volume 82, p. 951-962. M C C O N N E L L . R .G. , 1912. Portions of Portland Canal and Skeena Mining Division, Skeena District, British Columbia, Canada Geological Survey Memoir, 32, p. 73-95. M c I N T Y R E , D.G. , 1984. Geology of the Alsek-Tatshenshini Rivers area; in Geological Fieldwork 1983, B .C . Ministry of Energy Mines and Petroleum Resources, Paper 1984-1 pages 173-184. M A C I N T Y R E , D .G . A N D A S H , C A , 1994. Skeena-Nass digital geology compilation, Open File 1994-14, B .C . Ministry of Employment and Investment. M A H A L Y N U K , M .G . , S M I T H , M.T. and M c I N T Y R E , D.G. , 1993. Tatshenshini Project, Northwestern British Columbia (114P/11, 12, 13, 14; 1140/9, 10, 14, 15 & 16); in Geological Fieldwork 1992, Grant, B. and Newell, J .M . , Editors, B .C . Ministry of Energy Mines and Petroleum Resources, pages 189-229. M C K I N L E Y , S.D., 1996. Volcanic stratigraphy and lithogeochemistry of the Seneca Zn-Cu-Pb Prospect, southwestern British Columbia, Unpublished MSc . thesis, University of British Columbia, 195 pages. N E L S O N , H.E. , 1935. The Hidden Creek ore-bodies. Canadian Institute of Mining and Metallurgy Bulletin, Number 280, pages 349-357. 172 P E A R C E , J .A. and C A N N , J.R., 1973. Tectonic setting of basic volcanic rocks determined using trace element analyses, Earth and Planetary Science Letters, volume 19, pages 290-300. P E A R C E , J .A. and N O R R Y , M.J., 1979. Petrogenetic implications of T i , Zr, Y and Nb variations in volcanic rocks, Contributions to Mineralogy and Petrology, Volume 69, pages 33-47. PERFIT, M.R., F O R N A R I , D.J., SMITH, M.C. , B E N D E R , J.F. , L A N G M U I R , C H . A N D H A Y M O N , R.M. , 1994. Small-scale spatial and temporal variations in mid-ocean crest magmatic processes. Geology, volume 22, pages 375-379. P E T E R , J .M. , 1992. Comparative Geochemical Studies of the Upper Triassic Windy Craggy and Modern Guaymas Basin Deposits: a Contribution to the Understanding of Massive. Sulphide Formation in Volcano-Sedimentary Environments. PhD thesis, University of Toronto. R E Y N O L D S , J R . , L A N G M U I R , C .H . , B E N D E R , J.F., K A S T E N S K .A . A N D R Y A N W.B.F . , 1992. Spatial and temporal variability in the geochemistry of basalts from the East Pacific Rise. Nature, volume 359, pages 493-499. R H O D E S , D, A N D J A C K I S H , I., 1988. Annual Project Report, Geology and drilling of the Anyox property, Skeena Mining Division. Unpublished report for Cominco Ltd. S H A R P , R.J., 1980. The Geology, Geochemistry and Sulphur Isotopes of the Anyox Massive Sulphide Deposits; M.Sc. thesis, University of Alberta, 211 pages. SMITH, A . D . , 1993. Geochemistry and tectonic setting of volcanics from the Anyox Mining Camp, British Columbia; Canadian Journal of Earth Sciences, volume 30, pages 48-59. S T A K E S , D.S. and F R A N K L I N , J .M. , 1994. Petrology of igneous rocks at Middle Valley, Juan De Fuca Ridge. In: Mottl, M.J. , Davis, E .E . , Fisher, A . T . and Slack, J.F. , Editors, Proceedings of the Ocean Drilling Program, Scientific Results, Volume 139, S U T H E R L A N D B R O W N , A . , 1968. Geology of the Queen Charlotte Islands, British Columbia. B .C . Ministry of Energy Mines and Petroleum Resources, Bulletin 54. S U N , S.S and M C D O N O U G H , W.F. , 1989. Chemical and isotopic systematics of oceanic basalts: Implications for mantle composition and processes. In: Magmatism in the Ocean Basins, Saunders, A . D . and Norry M.J. Editors, Geological Society Special Publication, Number 42, pages 313-345. T Y L E R , P. A . , 1993., Summary report on results of the 1993 drill program in the vicinity 173 of the Hidden Creek mine, Anyox, B .C . Unpublished report for T V I Copper Inc., 27 pages, plus maps. T H O M P S O N , G . , 1983. Basalt-seawater interaction. In: Hydrothermal Processes at Seafloor Spreading Centers, Rona, P.A., Bostrom, K., Laubier, L. and Smith Jr., K .L . Editors, Nato Conference Series, Series IV: Marine Sciences, Volume 12, pages 225-278. W I N C H E S T E R , J .A. and F L O Y D , P.A., 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology, volume 20, pages 325-343. W I N C H E S T E R , J .A. and F L O Y D , P.A., 1976. Geochemical magma type discrimination: Applications to altered and metamorphosed basic igneous rocks. Earth and Planetary Science Letters, volume 28, pages 459-469. A P P E N D I X A L I T H O C H E M I C A L D A T A it* A total of 115 samples were collected and analyzed for major and trace elements by X -ray fluorescence at the Geochemical Laboratory, McGi l l University, Montreal. A l l major elements and C u , Zn, N i , Cr, V , and Sc were analyzed using glass beads. The trace elements Zr, Y , Nb , Rb, Sr, Ga and Pb were analyzed using pressed pellets. A subset of 17 samples were analyzed for rare-earth and trace elements at Activation Labs in Ancaster, Ontario. Most of the rock samples used in this study were obtained from drillcore and surface exposures from the Hidden Creek mine area. Several volcanic and Tertiary intrusives, collected from the Bonanza Mine area, and two rock samples from the Granby Peninsula were also included in the data set (Figures A l and A2). Complete lists of the major, trace and rare-earth element data are presented in Tables A l and A2. Surface samples are indicated by a single station number (e.g.: 44-1) while drillcore samples are indicated first by drillhole number (e.g.: D9, E6 , 82-10, 88-4) and then by depth down hole given in metres (e.g.: 114.6). Abbreviation used in the following tables are: (E) = E - M O R B (T) - T - M O R B (N) = N - M O R B Alt = Altered O H o o « IT) o CM cu O 2 o CM « Z o a U 03 O 5? _ 60 B cu o I S o - 8 * CM CQ u o cu E •5 cu CA T3 e CB CA 3 o CU 8* ro wo Os Os m 00 wo r-r- CN SO SO Tf O O p Tf 00 SO Tf so CN SO OS m CN ro so o Tf O O o OS CN SO m Tf Os Tf o Tf OS O OS ro Tf 00 SO O 00 ro p OS 00 ro p d o o O O © o o o © Os © o O © d o O o d o d o d o ro 00 d o o d o d o ,o d o d o Tf 00 •n 00 o d o Os Os d o d o d o O d o o Os o CN Tf SO Os CO CN SO OS in r--00 Tf SO m CN o Os Tf O o t-; SO SO Os Tf m Tf 00 m 00 OS o SO Tf 00 00 Tf Tf 00 ro wo CM r~ r~ CN o Os Tf r-oq r-o Tf ro d Tf ro Tf" ro ro © d ro CN d Tf CN CN CN Os Os " ~ wo wo CN ro wo w-i CN o in -a Xi T3 Xl O O o o o o C -O •a XI O o T3 X> o o CN o o o o O o o o SO O O m o CN o ro O o o Tf O CM o CN o o o OS Tf O o o o SO o O d o © o d d d d d d d d d d d d d d d d d d d d d d d d CO Tf o ro OO OO ro Os O 00 t-» Os >n O Os o in o m o OS Tf Tf 00 OS o so ro ro SO o CM 00 o o o o ro — o O d o © © © o O d d d d d d d d d d d d d d d d d d d d d d d d m <N wo o O Tf o CN CN ro © CO Tf ro O oo p ro O Os o Tf ro Os ro ro o SO OS >n CN 00 ro O Os Tf in SO ro 00 m o CN m so oo CN CM o SO Tf CN CO Tf o © CN © O © o O O © © d d d d d d d —~* d d d d d d d d *" 1 d d d d in t- ro 00 Os ro © wo <N 00 wo SO CN SD Tf CM ro Os 00 so 00 ro CM CN o m in Os so m c- 00 SO 00 Tf ro c~ o ro ro Tf wo wo 00 o C N CM CN 00 o CN CM O CN ro © ro o CN CM CN ro CN Tf d CO d CO CO d CN CN d ro ro d d CN ro d d d in rt CN 00 Tf OS in C-o ro ro ro r- wo SO Os O wo ro ro OS 00 ro OS O SO 00 so CO CN Tf SO m so Os SO O m ro SO m CN Tf wo Os wo OS CM CN Tf 00 Os Os OS oq CN o ro o ^ o CN ro SO Os d d m d d CO 00 d Os d Os ro I-" ro Tf so Os SO m Os o Tf Tf Os rN r- Tf OS CN >n SO SO Tf OS wo Os Tf CN 00 OS 00 C~- Os Tf Tf 00 OS Tf Tf so Os •n o m wo 00 m 00 00 ro CN SO 00 o SO oo Tf o oq Os Tf wo in Os O ro CN r-Os © Os o wo 00 00 © CO in d CN ^ - in •n Tf Os d d Os <> wo CO d d ro Os CN o ro CN ro ro t--CN SO o ro o CN 00 CO ro o Tf Tf Tf m Os ro O Tf O m 00 »n Tf Os 00 00 Os m SO ro so r-ro wo ro so wo Tf CN CM CO CM Os O Tf O © O d © O o © © d d d d d d d d d d d d d d d d d d d d d d d d d o o m CO c~ in ro SO oo Os SO o ro m o CN Tf ro SO r-Tf CN Tf o «n CN CN 00 o so so Os 00 CN CO o Tf oq Os in so Tf CN o so t-^  Tf ro CM O Os 00 Os 00 Tf wo Os r- Os so CN O ro © CN od d so* CM CM 00 »n in Tf CN d ro ro d - 00 d CN wo - Tf ro CO CN SO Os d 00 wo CM SO o CM 00 Tf SO O O wo Tf CN m ro r-~ ~ 00 wo oo Tf sq Tf m o 00 <n CN so o C N ro so in CN Tf oo Os oq CN o m ro 00 ON SO CM in SO CO Os 00 wo CN Os CM CN SO Os Tf Tf 00 wo in ro C-" i-" in m' i> Os ro " in ' od Tf in l> Tf CO in WO CM Tf so SO Tf Tf wo m so Tf Tf Tf CN CN CN r-Tf SO Tf 00 ro ro >n Os r~ oo o ro Tf Os Tf ro Tf ro O in ro p SO Tf CN C N CN cs ro OS o CN ro ^ H m SO ro 00 Tf Os Os Tf CM o CM CN Tf r~ co d d d d c-i ' ' —"1 d d d " d o SO 00 >n 00 Tf 00 p ro Tf r-ro o 00 Tf Os so so CO wo Tf Tf SO CN m Tf CN o r-m 00 o o Tf CN Tf OS o Tf 00 CO ro so p ro Tf WO SO oq CO o Tf 00 CM Tf SO SO Tf oq wo wo o m Tf CO Tf O in © Tf d Tf Tf wo 00 Tf Tf Tf d m m SO Tf 00 CN Tf Os Tf CN m Os Tf in Tf t~ Tf OS Tf sd Tf ro CM d wo Os Tf CO Tf Tf Tf Tf wo Tf Tf B O CA O a. 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"2 P. vi m ro m os V ) 00 Ov rt l l l l CN SO CN CN w w w w rt t> os • CN CN — c* rn t--rtrtrOrtOOCNOOOv ^ l l l l l i l l H H H N N « H C l l f l Q H Q Q Q Q O Q Q 3 O 2 i H 5 PB •I © « _^ B Z J : •» 5 "° B 1_ L . C U s .a T 3 St o C J U rt ._ — a cs OJ oa II A P P E N D I X B M A S S C H A N G E C A L C U L A T I O N Introduction Mass change calculations on the Anyox mafic volcanic rocks employed a multiple precursor method following McLean (1990) and McLean and Barrett (1993). This method uses immobile major and trace elements to determine pre-alteration (precursor) compositions of the rocks. A mass change factor is used to reconstruct the compositions of the altered rocks to eliminate effects of closure. The difference between these two values is the mass change in the rocks. Below, is a step by step procedure for calculating the mass changes in altered volcanic rocks. This is followed by a sample calculation (Figure Bl) and a complete list of the calculated mass changes for the volcanic rocks used in this study (Table Bl) . Note that in Table B l , negative values represent mass loss during alteration and positive values represent mass gain. Step 1: Data Conversion Raw lithogeochemical data is normalized to 100 mass units (100 wt %) on a LOI free basis with Fetotai reported as FeO*. Step 2: Determination of Fractionation Trends Using binary element plots, binomial equations for fractionation lines are determined for all element oxides considered in the mass change calculations. In this study P2O5 was used as the index of fractionation (see Figure 4.4). Zr and Y were also calculated as a check on the reliability of the mass change calculations using P2O5. For the immobile elements, AI2O3, Ti02, Zr, and Y, three different fractionation lines, representing N -MORB, T-MORB and E-MORB were identified and calculated. In most cases only two fractionation lines, representing the N-MORB suite, and the suite of enriched volcanic / S T r rocks ( T - M O R B and E - M O R B ) could be identified and calculated for the mobile elements (S i0 2 , FeO, M g O , M n O , CaO, N a 2 0 , K 2 0 and BaO). It should be noted that, in this study, the trend in the T - M O R B samples is thought to result from mixing of N-M O R B and E - M O R B sources and is not strictly a fractionation trend. Step 3: P2O5 (precursor) Calculation Pre-alteration (precursor) values for P2O5 and AI2O3 were calculated by using the intersection of the AI2O3-P2O5 fractionation line for each suite and the alteration line y=mx for each sample (slope (m) given by the AI2O3/P2O5 ratio). The fractionation line for N-MORB: y=17.65-12.83x; The mixing line for T-MORB: y=13.82+9.57x The fractionation line for E-MORB: y= 18.08+1.39x A P2O5 mass factor (P2O5 (precursor)/P20s (altered)) was determined for each sample. This ratio is used to calculate the reconstructed values for each element in the mass change calculation. Step 4: Calculation of Precursor Values Precursor values for all elements were calculated using the fractionation (or mixing) line for each element (determined in Step 2) and the P2O5 (precursor value). These values represent the pre-alteration composition of the rock. Step 5: Calculation of Reconstructed Values Reconstructed values were calculated using the normalized elemental oxide compositions and the P2O5 mass factor. The mass factor is a ratio between the concentration of an immobile element in the precursor and its concentration in the altered rock, and is lit f~ calculated as follows: R C = (IM p r e c u r s o r/IM a l ,ered) x wt % componental tered where R C = reconstructed composition and I M = immobile element monitor (in this study P2O5) (Mclean, 1990). The reconstructed composition represents the net mass of an altered rock that has gained or lost mobile components. Step 6: Calculation of Mass Change Values Mass change values (reconstructed composition - precursor composition) were calculated for each element and are reported as wt % oxide. Negative values represent mass loss while positive values represent mass gain. The net mass change for the entire rock was then calculated by summing the losses and gains in each element. This way of reporting the mass changes differs from other mass balance methods which typically report % elemental change with no reference to net changes on the whole rock. is 1 r Appendix B - Sample Mass Change Calculation Raw Data: Sample Number 82-4-134.0 Rock Type Alt Volcanic (N) Si02 45.66 Ti02 1.21 AI203 14.19 FeO 16.89 MnO 0.12 MgO 13.09 CaO 1.99 Na20 0.27 K20 0.04 P205 0.10 BaO 0.00 LOI 5.49 Total 99.07 Zr 60.00 Y 34.00 P/Ti (ox) 0.08 P/Ti (ppm) 0.06 AnhyFact 1.07 Step 1: Anhydrous+Fe as FeO: Step 2: Fractionation line equations for element Sample Number 82-4-134.0 oxides, Zr, and Y Rock Type Alt Volcanic (N) Si02 48.79 Si02 = 47.31+20.95x Ti02 1.29 Ti02 = 0.528+7.23x A1203 15.16 AI203 = 17.65-12.83x FeO 18.05 FeO = 10.41+4.44x MnO 0.13 MnO = 0.28-0.36x MgO 13.99 MgO =9.99-11.379x CaO 2.13 CaO = 10.73-7.29x Na20 0.29 Na20 = 2.00+5.01x K20 0.04 K20 = 0.07+2.04x P205 0.11 P205 BaO 0.00 BaO = .03+0.07x Total 100.00 Total Zr 64.12. Zr = 17.83+509.56x Y 36.33 Y = 18.03+156.4 lx AI203/P205 141.90 Step 3: Using the fractionation line y=I7.65-12.831x and the above alteration lines; P205(Prec) = x 0.11 A1203 (Prec) = y 16.19 P205 Mass Factor 1.07 (precursor/altered) Step 4: Precursor Values: Step 5: Reconstructed Values: Sample Number 82-4-134.0 Sample Number 82-4-134.0 Rock Type Alt Volcanic Rock Type Alt Volcanic (N) (N) Si02 49.76 =47.31+20.95(0.11) Si02 52.08 = 48.79(1.07) Ti02 1.35 =0.528+7.23(0.11) Ti02 1.38 = 1.29(1.07) AI203 16.19 = 17.65-12.83(0.11) A1203 16.19 = 15.16(1.07) FeO 10.92 = 10.41+4.44(0.11) FeO 19.27 = 18.05(1.07) MnO 0.24 =0.28-0.36(0.11) MnO 0.14 = 0.13(1.07) MgO 8.70 =9.99-11.38(0.11) MgO 14.93 = 13.99(1.07) CaO 9.91 = 10.73-7.29(0.11) CaO 2.27 = 2.13(1.07) Na20 2.57 =2.00+5.01(0.11) Na20 0.31 = 0.29(1.07) K20 0.30 =0.07+2.04(0.11) K20 0.05 = 0.04(1.07) P205 0.11 P205 0.11 . . . BaO 0.04 = .03+0.07(0.11) BaO 0.00 = 0.00(1.07) Total 100.10 Total 106.74 . . . Zr 75.95 = 17.83+509.56(0.11) Zr 68.44 = 64.12(1.07) Y 35.87 = 18.03+156.41(0.11) Y 38.78 = 36.33(1.07) Step 6: Mass Changes: (reconstructed composition - precursor composition) Sample Number 82-4-134.0 Rock Type Alt Volcanic (N) Si02 2.32 = 52.08-49.76 Ti02 0.03 = 1.38-1.35 AI203 0.00 = 16.19-16.19 FeO 8.35 = 19.27-10.92 MnO -0.10 =0.14-0.24 MgO 6.23 = 14.93-8.7 CaO -7.64 =2.27-9.91 Na20 -2.27 =0.31-2.57 K20 -0.26 = 0.05-0.3 P205 0.00 =0.11-0.11 BaO -0.04 = 0-0.04 Total 6.64= — Zr -7.51 =68.44-75.95 Y 2.91 =38.78-35.87 0 so o r- — co O O ro O rs O O © T f so ~ H O © C\ "^ J- (N o ^ vo q to o o —- o o o 9 ' £ «n < o *7 o T > IS 00 (S ro O v> ro o o ro r- so o T f oo ro fS (S o o * CN] O O O O O ' S O r~- <"N O © © s© ^ - O O f N O ^ - O O O O O f J o > © <N O © so vo <N o o —< «—« so r -o O © —* © Tf' O O O O N fN V . <N O O I f ) ' ' o o o o CN o o r o o r o o o r o © ~ O ©" CN © — - ( N - c> O r- oo rr — o 5 -1 o V~) T f — 00 1 S2 3 £ ^ 7 5 n un iri in p - m o < s r — o o ^ D r -( N O p o q o p ^ f S ' v S o o ^ o o r ^ o d t N O O O t ^ oo o o T f CN — r-o - o n ^ n «• N 6 6 O - • ro •-• O © © «S s i o o o —i o o — vO ro —' T f <N C- O n - t > N vo n o :> so © © © T f O CN —' © © © CN ro O O — ro O C N — C N v i ro © O ro O O O ^ h w TJ-o > ro sO Os O —^  © O sO O so oo so r» ro so cN <— © r-^  © o o © t-m oo O O CN © O Os r- T f © O —" O O O O O O O O O OO o o VO (S in N vo M CN O V i so ro o" © ro od CN o" o rt- o\ o m o o m cs v , © CN © r-o o o o o © o o o T 2 - 3 o > o o v , T f r N < N O T t T r O m O N T t r o p p V ) 0 < S C ^ < N O O O ( S ro Os O O ro r-O O O O O ro O O © O © O © •—« fN ro _ T f — O O © © o ©' o T f ro ro — o > o v» — — oo Os CN O T r o — o co oq ro CN o p o T r ' o o s o d o o d T f CN O CN —< — «">. os O Tr © v i o o c N . s c r o p p o — d r 4 — o ' o o ' o •5 c -o > o T f © v> o c N O O O s o r o t - ^ — o o t-o i n o o d d Wi oo T f o — d o o o o o ro c*\ so — o o ro 6 6 * •5 O ft .cs © © T r o d VO 0O -< O VO >t od — o - - « o - n t — •/-. — o o m 1 r ~ o o < N v . . ~ ^ ^ c o © © © © T T ,  V"|  © © T t ' o ' o r s o c N o d o d o o o s© o c N © o r ~ r o o r - - o o © O T f r ~ r ~ ^ Z so —• © T f o Tr —; —. o p e n ^ <5 o — o o — o r ^ c s ' c N o o o o o i ~ - • I I I 1 rs 2 t « r j r o o O O O O O " C O O O CJ c M I I N M O « S , N « « o o o o o o a O O O « e u « n rl 2 6 0 H E = a E « I ,2 v SO O v ^ m o o o r - T t m o o r - - f S f o r - -o \ > o o o \ t N < Y ) N " ^ f r j 0 ^ o e N " 1 S 2 P ? 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SS s cj a.a g « (2 XI >, B H z g B a (A c s c s c n o O O O O O S O 0 0 0 . 4 i B M O J C S C S O £2 to g S 0 cs BH S S! o 1 ^ 3 OL:? — "5 > hi 2 P o > " J o in T) P O N O ta > 2 P 5 I* M H O Q o y P V? 3 i i Q > 2 P O a H w o tf OO O N SO CN - H SO o o so od —' o CN o os ro *-« so o oo — oo vn r- so O so O sO O O O O N n oo r s o O s o s o ^ O s O s T j -c N V " » p T f p p p © ^ o I o ' o r s i O T i : r o « — ' O o O O O — T j - o o o o — — O Os O OO r f o —- o ro © © —«" ©' os r- o <N T f Os O O Os p so © ©'^  CN © r- v~> cn o O —< OS CN —' o o ro T f m o o v> in cN T f i n CN T f O N O N Tf" SO ^ O O N CO O SO CN O — i o o O O r- <NI r- >n CN O O SO O CN o o o O s O N O ^ C N T f o o r O ^ O C S O s C N r O O T f p o o ^ r o s q r ^ c N O O S o r o - ^ r ^ o o r s i o T f v S c N o ' o o i r i c ^ O O T f r o s o r O T f O N O r o o r -o ^ c N o r - p p o o c N < N p p i r ) C N o o o c N - o > n c N - 7 p o o ' T t T f OO O OO (N ro Os oo o o — o o r-^  u o o o ' o o o ' s p r N s o o c i I- c i —< TT O O O — 1 d d © so N N W O O O O O O S O 0 0 0 « C M « r ^ f s O « 3 3 5" S O O w > s 3 I r j > 1 ? f f M ^ "? < 2 T <3 so o o > « 2 M © 0 o < o SO > a iri "3 & m 43 « • " • S o <s > w 2-glS 2 2 P ok > w• « ? c so a G t- 5 i i O S > w eg Q, B .H z g C L E so ro © O N CN t - CO T f CN p OO O N CN ro O O CN — O O ON o o o o N s o o o r - r - -^ - O s o O T f r o V i T f O © ' c o © ^ " v " i © c s i o 00 o 00 ~-o —< t- 1 1 © © <S* r- -H o —• CO p O CN CN © © CO © so ro v i 0 — 0 so ~ H ^- o *n so T f OO O O t " ; Tf ' CN O © fN O s o m m v o c o o o o O O O r o s o m O O O r o o r ^ s o ' r N p ' o SO V~i O T f OO r— o © 00 © r-K O © CO ©" ^ ^- o co CN CN «n T f ro ^ © l A O O l N l N ' A t ^ N O O H O © © o r - © s O » n » n p p © c s ^ 0 © C N © © 0 © © © © * T * —. O O CN m © © ~* o o © O ^ - T j - T f f N O O C N O C N C N O O O p © © CO sO O N OO n O O ( N O ( N O O ( N O O © N© © ro O N © T f —- © 00 © © ~ H rO so CO co r* ro © 00 r-- Tf ro CO © 00 (N O © © CN — 1 CN S J 2 S O O O O O O S O « O O O *» fi M es N N O « a si o H A P P E N D I X C Q U A L I T Y C O N T R O L •Ms •:; ; Several M D R U in-house standards were used to examine the accuracy of the analytical data used in this study. Three in-house standards were used: A L B - 1 - Ajax albitite, P-l -Porteau Cove granodiorite, and QGRM-100 - gabbro. Standards were submitted at different times with various batches of samples, and in most cases duplicate samples were included in each batch. In this way the precision of a given measurement could be compared to analyses from within each batch of samples and between batches. The data were compiled, and mean values, standard deviations and percent errors calculated for each element. Table C l compares the measured values from this study to the accepted values for the standards in the MDRU-compiled database (as reported in McKinley 1996). It is significant that all the previous analyses of the standards were carried out at a different laboratory ( X - R A L , Don Mil ls, Ontario) than the one used for this study (McGil l University). A s a result, these standards provide only an approximate guide to the accuracy of the analytical data. In general, the standards used in this study showed little analytical variation between duplicates in a single batch and between different batches. Percent error in the major elements was typically < 5% and measured values showed an excellent correlation to the accepted values from the MDRU-compiled database (Figures C l to C3). Analytical error was greater in the trace elements, particularly in Cu , Pb, Zn , and Co, where percent error for significant concentrations of an element (> 20 ppm) was as high as 50%. In standard A L B - 1 , analytical variations in both the measured and accepted trace element values were very high, and may reflect a problem in the sample preparation. In the remaining two standards, percent error was low (< 7.2%) for the trace elements used in this study (Zr, Y , Rb and Sr). In contrast to the major elements, measured values for the trace elements showed a much poorer correlation to the accepted values and although the data from this study had generally lower analytical variations than those for the accepted MDRU-compi led data, one cannot say which data set is more accurate. •s * 3 i 0 s CL OJ 00 00 00 00 00 00 00 00 00 00 Os m so p so so to cn so r -T t vo 00 o o m CN rt T t o © T t O © o VO so O o o © cn O r -*-H fN O © o CN o o o O © o o o o © © Os m T t in OS 00 00 o o p 00 T t cn 00 OS O 00 o CN T t O T t cn © rt1 rn rr, CN o o o o v o v o v o w o v o v o v o v o v o v o v o v o r -00 r~ r -t-; o Os cn T t CN T t cn CN 00 r - VO VO vo vo vo Os t-; cn vo vo O 00 o CN CN p cn Os VO cn T t T t CN VO — CN rt1 VO "> oS m . o SO o T t rt rt CN OS CN CN T t T t OS OS T t SO rt T t CN CN rt CN SO 00 C N cn C N T t vo os so r- C N ° ° K -t -VO 00 vo CN T t T t oo T t T t I--; CN 00 cn cn SO rt CN T t o cn o T t 00 vo CN rt T t »—i 00 SO vo CN T t OO o OS OO cn T t Os v o so v o so VO oo 00 Os r - C N OS 00 v o C N 00 r - O O C N cn v o v o r - C N VO T t o T t — T t C N C N C N cn C N 00 o o Os r~ 00 OS 00 00 v o c N o t ~ - o c N o o o s r - o o s s o m O r t O O O O O O O O v o o o o o o o o c s o o o o CN OS Os O OS m vo Os r -T t t - ; o rt V O O O o T t o T t cn o rt r n T t CN o o Os Os O T t CN cn rt 0 0 VO rt SO o S o< vo r-VO VO VO vo VO Os m SO SO o o so 00 Os T t cn VO o T t OS T t cn T t o o r~ CN T t so 00 © CN VO • 1 . cn m rr oo vo cn m t-CN vo 00 oo t- rt cn VO rt CN vo o O o vo vo CN o 03 T 3 a cd Q s <rt o CO CD CO ~3 •a m S Z s 3 rt <» A --J cj E •a s» CJ ° s- > < 2 i pa o Z "5. E .rt 0 3 •s oo oo 00 oo 00 oo 00 00 00 00 00 .00. VO vo o o SO cn 00 o CN cn vo SO cn o OS oo cn oc T t OS oo cn 00 O rt o cn cn rt o CN o rt CN o SO O S r t r ^ V O r t T t O O T t r t r t O O V O rtOrtOOOOrtOOOTt o o o o o o o o o o o o T t O vo T t SO vo CN VO rt o T t SO P so o OS 00 cn cn O OS — O CN o vo o o cn o o T t T t T t T t T t T t T t T t T t T t T t T t o t — o o r - t - - v o v o v o v o T t OO SO so vo V O T t T t so CN p T t T t rt OS Os 00 cn o 00 V O m CN CN rt1 VO vo r - vo VO T t 00 00 VO 00 T t cn CN CN o CN cn Os cn CN i-H rt VO O OS so o OS rt o O OS o <^  O rt T t CN Os SO rt CN cn 00 Os 00 r -T t VO m oo rt 00 T t *-H cn o v - i OS CN CN oo rt vo rt o OS r -so CN vo 00 vo Os vo CN cn SO o o T t rt cn CN CN vo o r~ CN T t SO * T t 00 SO OS V O o T t T t T t T t T t T t T f T t - * T t T t vo o cn T t V O SO T t f -— r-O rt — CN O rt 00 CN O 00 T t CN T t 00 CN OS vo o o r t r t r t v o ' r t s d o o cn CN rt rt T t vo T t 00 O so so CN CN ^ SO VO so vo 00 CN cn OS SO CN SO o VO VO cn T t VO T t CN T t cn so VO CN oo CN o CN o o T t o m oo o so o o o CN 00 v o o o o" o' o o o o o o o o SO r - ^> VO CN cn cn \Z T t f~- CN cn OS T t • CN CN CN CN 1 T t rt rt rt V O CN T t cn CN P 00 00 Os 00 cn o CN OS CN T t cn CN t~ cn o OS SO SO O 00 T t 00 cn Os o 00 — o CN o VO o o CN O m SO Os T t vo rn |-~ rt OS OS SO CN Os CN •—I CN rt 00 8 s a * oo CN CN r6 o so o oo o o «*! 2 » 0 0 f ~ c? — rt C N g; -t i 88 C/3 H t i s s * * s? . S S u z s? ^ it o S 2 2 tl 5 € S E E E E s E a a a a a I o. Cb CL CL CH CL CH CL s c o c o i - ^ u " - ^ U N U « U > S l > - r t |_ | | I I g. a. £ CL g t » 0- z z o E E CL O. CL CL 1-T3 § Q o Crt CD GO "c3 c o _cu Q 2 -^ r . E o Z OJ E « o o o o o o o o o o o o o o o o o o o o o o o o 0 \ o o o o w o 0 r o o o t - - o o o > - * r o c N t - ^ M v o p O N T f o o t - ^ p T f T f o o o ' o o o o w o o o o o Tf T f c N T f O O W O T f O v — O CN ro . . — p p © - « p p p T f o o o o o o o ' o ' o o o ' o — o o o — r— wo •—• o — o o r o o t — C N O C N W O W O V O C O V O C T V O —< —' C N fO (N VO « - O N V O t ^ v O O T f O r o O C N l s : 0 ^ m C t ; t N ' t " f ^ oo wo T f oo T f C N wo — n- o vo m t - T f © o o o r-. o C N H o «o vo m « - o s - r - c e m c e o \ O C N V O WO T f — — O wo oo ro — O o — o oo vo T f ~ H O T f v O T f f - v O c o v o wo o in T f ro C N r~ C N C N — C N r o wo CO CO r-T f VO T f wo r o 00 WO T f 00 wo CN T f ON CN VO r o CO WO r-r~- T f o p Ov T f © o p CN 00 ro vo r o f - CN 00 wo O ~* ^ CN CN CN T f CN od wo o" od WO w-i od VO CN CO Os CN ro o Os vo CN CO o r o CN CN CN O o T f o r-o WO o O o VO o CO wo CO p CN 00 T f 00 vo vq OS o o Os wo T f VO T f t -wo VO 00 o © © ' o O o o o © o © © o 00 wo CN T f T f WO CN o 00 o od CN ro VO 00 Os WO T f © Ov o vq wo ro 00 p o CN i-H CN r-o wo r~ VO Os CN o 00 wo wo 00 Os wo wo 00 ro ro ca e ca a ca a 00 T f *~1 w-i w-i o w-i 00 CN o O OV Os Os r~ o V0 WO w-i CN CN CN 00 w-i ro CN CO wo w-i CN wi ro CN ro CN CN i N 0s-t i So t i s s < & S? 5 5 5? 5 5 vc 5? O o S U * i * z 2 2 tl i—i « O « E E E E E c Q. Q. O. Q. O. B o. a. a. n. a. g, 3 e o w i- °" i_ U N U ffl U > N E E [ E a. 5- o, a. °- a. A . „Q . H ^ | E a rs Q. Q. E E o. a. a a. ea-O 1 ^ ALB-1 Major Elements Accepted Values wt% ALB-1 Trace Elements 0 50 100 150 200 250 300 Accepted Values ppm Figure C - l : Comparative analyses of measured vs accepted values for M D R U standard A L B - 1 . Measured values, from this study, were analyzed at McGill University while accepted concentrations were measured at X - R A L . Error bars are +/- 1 standard deviation. P-1 Major Elements 0 10 20 30 '40 50 60 70 80 Accepted Values wt% P-1 Trace Elements 50 100 150 200 250 Accepted Values ppm Figure C-2: Comparative analyses of measured vs accepted values for MDRU standard P-1. Measured values, from this study, were analyzed at McGill University while accepted concentrations were measured at X-RAL. Error bars are +/-1 standard deviation. QGRM-100 Major Elements 0 10 20 30 40 50 Accepted Values wt% QGRM-100 Trace Elements Accepted Values ppm Figure C-3: Comparative analyses of measured vs accepted values for M D R U standard QGRM-100. Measured values, from this study, were analyzed at McGil l University while accepted concentrations were measured at X - R A L . Error bars are +/-1 standard deviation. 

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