Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Geology of the Snip Mine, and its relationship to the magmatic and deformational history of the Johnny… Rhys, David A. 1993

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-ubc_1993_fall_rhys_david.pdf [ 50.73MB ]
831-ubc_1993_fall_rhys_david_figures.pdf [ 5.45MB ]
Metadata
JSON: 831-1.0052894.json
JSON-LD: 831-1.0052894-ld.json
RDF/XML (Pretty): 831-1.0052894-rdf.xml
RDF/JSON: 831-1.0052894-rdf.json
Turtle: 831-1.0052894-turtle.txt
N-Triples: 831-1.0052894-rdf-ntriples.txt
Original Record: 831-1.0052894-source.json
Full Text
831-1.0052894-fulltext.txt
Citation
831-1.0052894.ris

Full Text

 GEOLOGY OF THE SNIP MINE, AND ITS RELATIONSHIP TO THE MAGMATIC AND DEFORMATIONAL HISTORY OF THE JOHNNY MOUNTAIN AREA, NORTHWESTERN BRITISH COLUMBIA  By David A. Rhys B.Sc., The University of British Columbia, Vancouver, B.C., 1989  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN THE FACULTY OF GRADUATE STUDIES (Department of Geological Sciences) We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA OCTOBER 1993 ©DavidAlnRhys,193  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.  (Signature)  Department of  Gledcy0.‘1^Ciepc.e S ,  The University of British Columbia Vancouver, Canada  Date ^Cc.4.oiNer-  DE-6 (2/88)  i3  j  93  ii  ABSTRACT  The Snip mine consists of an auriferous southwest-dipping shear vein system in a north-dipping Triassic greywacke-siltstone sequence altered with abundant veinlet and pervasive biotite. The deposit, termed the Twin zone, is the largest of numerous shear veins in the mine workings. It contains just under 30 tonnes of gold.  The Twin zone is composed of four ore types that are mineralogical end members of two distinctive styles of mineralisation. They are: (i) carbonate and (ii) chlorite-biotite ore consisting of laminated schistose veins of calcite, chlorite, biotite and pyrite, which display textures indicative of an origin, at least partially by, wall rock replacement; and (iii) dilatant quartz veins and (iv) dilatant pyrite-pyrrhotite sulphide veins. Alteration comprises pale calcite-K-feldspar-silica envelopes surrounding black biotite envelopes adjacent to the veins. A post-ore biotite-altered mafic dyke intrudes the zone.  Geologic relations in the Snip mine indicate that the mineralised veins were emplaced progressively in a dynamic tectonic environment characterised by semi-brittle deformation. Numerous kinematic features in the zone record normally-directed simple shear parallel to a westerly plunging elongation lineation. Deformation was heterogeneous and confined mainly to the shear veins. Galena Pb-Pb isotopic signatures suggest an Early Jurassic age for the veins. Abundant shallow easterly-dipping quartz-calcite extension veins formed during a later, probably Tertiary, event.  The Red Bluff porphyry, an elongate K-feldspar megacrystic plagioclase porphyritic quartz diorite to tonalite stock, intrudes the greywacke sequence 300-800 metres northeast of the Twin zone. Two successive, intense hydrothermal events are centred on the porphyry and are associated with subeconomic Au and Cu concentrations. These are: (i) early quartz-magnetite-sericite-K-feldspar-biotite (potassic) alteration associated with abundant quartz-magnetite-hematite veins, overprinted by (ii) sericite-pyritequartz (phyllic) alteration characterised by pyrite veining. Intrusion, semi-brittle deformation, and  111  alteration and mineralisation within the large hydrothermal system of the Red Bluff porphyry were closely related spatially and temporally. A genetic relationship is supported by: similarities in structural fabrics and alteration histories in the Twin zone and the porphyry, alteration and metal zoning of vein systems distributed concentrically around the porphyry, and apparently concordant Early Jurassic zircon U-Pb age from the porphyry with galena Pb-Pb signatures from the Twin zone and surrounding vein systems. Two significant structurally-controlled Au deposits in the area, Inel and Stonehouse, have similar age, mineralogy, structure, alteration and spatial relationships to Early Jurassic intrusions. They represent contemporaneous, possibly genetically related, hydrothermal systems.  iv  Table of Contents ABSTRACT TABLE OF CONTENTS^  iv  LIST OF TABLES^  vii  LIST OF FIGURES^  viii  LIST OF PLATES^  ix  ACKNOWLEDGEMENTS CHAPTER 1: INTRODUCTION 1.1.1 Introduction^ 1.1.2 Location and access^ 1.1.3 Previous studies^ 1.1.4 History^ Development of the Snip Mine Other significant deposits in the Johnny Mountain area  1 1 4 5  CHAPTER 2: GEOLOGIC SETTING 2.1.1 Regional Geology^ 2.1.2 Lithologies of the Johnny Mountain area ^ Lower Sequence Upper sequence Intrusive rocks 2.1.3 Structure of the Johnny Mountain area ^ 2.1.4 Metallogeny of the Stewart - Iskut River Area ^ The Texas Creek plutonic suite and regional metallogeny Mineralised structures in the Johnny Mountain area Galena Pb-Pb isotopic data from veins on Johnny Mountain Bronson skarn  9 9  21 23  CHAPTER 3: GEOLOGY OF THE SNIP MINE 3.1 INTRODUCTION^  37  3.2 MINE GEOLOGY^ 3.2.1 The greywacke sequence at Snip^ Alteration and metamorphism 3.2.2 Dykes^ Plagioclase porphyritic dyke Lamprophyres Biotite spotted unit 3.2.3 Geochronology^ K Ar dates U-Pb zircon data Galena Pb-Pb isotopic data  37 37  -  54  60  ^ 3.2.4 Structural features Shear veins Foliation Quartz stockwork (130 haulage level south) Calcite-chlorite-biotite-pyrite veinlets Extension veins Faults  61  3.3 THE TWIN ZONE SHEAR VEIN SYSTEM^ 3.3.1 Introduction^ 3.3.2 Composition of the Twin zone: Mineralogy and ore types ^ Carbonate ore and chlorite-biotite ore Sulphide ore Quartz ore Biotite and chlorite composition Gold occurrence in the Twin zone 3.3.3 Alteration and vein paragenesis ^ 3.3.4 Structural style of the Twin zone and related veins ^ Twin zone Footwall vein Internal structure of the Twin zone 3.3.5 The 150 vein and other shear veins ^ 150 vein Other major veins 3.3.6 Relationship of stratigraphy to the Twin zone^  147  3.4 ORE TYPE, MINERAL AND METAL DISTRIBUTION IN THE TWIN ZONE 3.4.1 Introduction^ 3.4.2 Ore type distribution in the Twin zone^ 3.4.3 Mineral distribution in the Twin zone ^ 3.4.4 Gold distribution in the Twin zone^  152 153 169 172  3.5 DISCUSSION^ 3.5.1 Structural history of the Snip mine^ Temporal relationships of structures at Snip Relative timing of deformation in the Twin zone Structural history and relationships to structural events on Johnny Mountain 3.5.2 Deformation processes within the Twin zone ^ Deformation mechanisms Fluid pressure cycling and ore type distribution Strain softening and the localisation of deformation to the Twin zone Shear sense indicators and effects of heterogeneous deformation Morphology, structural style and displacement on the Twin zone  84 84 88  107 116 140  173 173  179  CHAPTER 4: THE RED BLUFF GOLD-COPPER PORPHYRY SYSTEM 4.1 INTRODUCTION^  199  4.2 THE RED BLUFF GOLD-COPPER PORPHYRY SYSTEM ^ 4.2.1 The Red Bluff porphyry^ Modal composition and texture 4.2.2 Dykes within the Red Bluff porphyry^  199 199 201  vi  4.2.3 Alteration related to the Red Bluff porphyry Potassic alteration Sericite-pyrite-quartz alteration Quartz-hematite-sulphide veins Chlorite-calcite veins Quartz-calcite-chlorite extension veins  205  4.2.4 Structure of the Red Bluff porphyry Faults 4.2.5 Metal distribution within and adjacent to the Red Bluff porphyry Metal distribution within the porphyry Cu and Au grades in greywackes adjacent to the Red Bluff porphyry Molybdenite compositions  219  4.3 DISCUSSION Early Jurassic intrusions and the origin of secondary biotite on Johnny Mountain Relationship of the Red Bluff porphyry system to the Twin zone and other veins on Johnny Mountain Depth of emplacement of the Red Bluff porphyry and implications Development of the Red Bluff porphyry system Comparisons to other porphyry systems  226  233  CHAPTER 5: OTHER GOLD DEPOSITS IN THE JOHNNY MOUNTAIN AREA  5.1.1 Introduction^ 5.1.2 Inel^ 5.1.3 Stonehouse^ 5.1.4 Discussion^ Implications for exploration CHAPTER 6: SUMMARY AND CONCLUSIONS  244 244 252 259 ^  265  Geologic history of the Johnny Mountain area  REFERENCES CITED  ^  269  APPENDICES Appendix 1: List of sample locations, with northing, easting and elevation on the^276 Snip grid system  vii List of Tables Page Table 2.1^Radiometric dates obtained in the Johnny Mountain area ^ 21 Table 2.2^Examples of gold deposits in the Stewart-Iskut River region associated with ^25 known and probable Early Jurassic (Texas Creek) Intrusions Table 2.3^Showings and deposits, northern Johnny Mountain and Snippaker Ridge ^29 Table 2.4^Metal content and metal ratios of some mineralised structures, Johnny Mountain ^30 Table 2.5^Summary of zoning of mineralised structures on Johnny Mountain and^30 Snippaker Ridge Table 2.6^Galena lead isotope analyses for the Johnny Mountain area, northwestern B.0 ^35 Table 3.1^Stratigraphic units and associated alteration at the Snip mine^ 47 Table 3.2^Dykes in the Snip mine^ 59 Table 3.3^Common structures in the greywacke sequence at the Snip mine^62 Table 3.4^Geochemical analyses obtained from ribboned stockwork veins^63 75 Table 3.5^Geochemical analyses obtained from extension veins^ Table 3.6^Twin zone mineral species^ 89 Table 3.7^Classification criteria and abundance of ore types in 456 intersections of the^90 Twin zone Table 3.8^Percentage abundance of common minerals in Twin zone ore types ^90 Table 3.9^Occurrence of gold in the Twin zone ^ 106 Table 3.10 Alteration and paragenesis, Twin zone and related shear veins, Snip mine ^115 Table 3.11 Intersection points of unit 3 with the Twin zone ^ 149 Table 3.12 Mineral distribution and associations in the Twin zone^ 171 Table 3.13 Sequence of formation of structural features at the Snip mine^179 Table 3.14 Deformation processes affecting common minerals in the Twin zone^185 Table 4.1^Distribution and paragenesis of minerals in the Red Bluff porphyry ^217 Table 4.2^Veins in the Red Bluff porphyry^ 219 Table 4.3^Red Bluff drill hole composite assays^ 227 Table 4.4^Molybdenite compositions^ 232 Table 5.1^Common structures, listed from oldest to youngest, in the Johnny Mountain mine ^259 (Stonehouse deposit) Table 6.1^Geologic history of the Johnny Mountain area ^ 267  viii  List of Figures Page Figure 1.1 Location of the Snip mine and the project area ^ 2 Figure 1.2 Geographic features of the Johnny Mountain area, with insets ^ 3 Figure 2.1 Geology of the Johnny Mountain area^ 10 Figure 2.2 Geologic setting of the Snip mine, 1:5,000 scale^ (in pocket) Figure 2.3 Deposits on northern Johnny Mountain ^ 32 Figure 2.4 Lead-lead isotopic plots of galena from mineral deposits in the Stewart-Iskut ^36 River area Figure 3.1 Schematic section from the Twin zone to the Red Bluff porphyry^38 Figure 3.2 Cross-section through the Twin zone and stratigraphy on section ^(in pocket) 4550 East Figure 3.3 Equal area projections of bedding in the Snip mine workings ^ 44 Figure 3.4 Geology of the 130 haulage level, Snip mine ^ (in pocket) Figure 3.5 Extract from figure 2.2 showing workings, Snip mine grid and location of ^45 Figures 3.1 and 3.2 Figure 3.6 Equal area projections of structural features in the Snip mine workings ^66 Figure 3.7 Cross-sections through the Twin zone and related veins ^ 85 Figure 3.8 Twin zone long section showing the locations of plans and sections and ^86 distribution of veins Figure 3.9 Twin zone long sections showing drill hole pierce points and fault restoration^87 Figure 3.10 Twin long section with contoured dip angle^ 118 Figure 3.11 Geology of the 4055/4061 stope undercut ^ (in pocket) Figure 3.12 Geology of the 3852/3860 stope, lift 5 stope ^ (in pocket) Figure 3.13 Geology of the 3852/3860 stope, lift 1 stope and the 150 vein sill drift ^(in pocket) Figure 3.14 Geology of the 3451 stope undercut and 3049 stope, lift 5 ^ (in pocket) Figure 3.15 Geologic sections through 2647 and 3049 stopes^ (in pocket) Figure 3.16 Internal structure of the Twin zone, drawn from photographs ^ 119 Figure 3.17 Equal area projections of Twin zone structural features^ 120 Figure 3.18 Equal area projections of 150 vein structure features ^ 141 Figure 3.19 Structure of the 150 vein, drawn from photographs ^ 142 Figure 3.20 Geologic map of the 130 vein, 430 level^ 146 Figure 3.21 Intersection of the mixed greywacke-siltstone package (unit 3) with the Twin zone 150 Figure 3.22 Calculation of the displacement of unit 3 on the Twin zone^ 151 Figure 3.23 Contoured vertical long section plots of ore types in the Twin zone ^154 Figure 3.24 Hand contoured plots of true ore type thickness, central Twin zone ^157 Figure 3.25 Twin zone long section relating structural features to thickened areas of quartz ^165 and sulphide ore Figure 3.26 Contoured vertical long section plots of visually estimated mineral percentages ^166 in the Twin zone Figure 3.27 Hypothetical morphology of the Twin zone during deformation^ 196 Figure 4.1 Geologic map of the Red Bluff porphyry in the 130 haulage level ^(in pocket) Figure 4.2 Map of northwestern Johnny Mountain showing the distribution of biotite ^214 Figure 4.3 Equal area projections of structural features in the Red Bluff porphyry, 130 ^222 haulage level Figure 4.4 Au versus Cu scatter plots for selected Red Bluff drill holes^ 230 Figure 5.1 Geology of the AK drift, Inel deposit^ 250 Figure 5.2 Geology of the Discovery drift, Inel deposit^ 251  ix  List of Plates Page Plate 2.1.^Aerial view of Johnny Mountain^ 12 Plate 2.2.^Lithologies of the Johnny Mountain area^ 15 Plate 2.3.^A: Red Bluff cliffs, Snip mine area^ 19 B-D: K-feldspar megacrystic intrusive rocks, Johnny Mountain area Plate 3.1.^Clastic units, Snip mine^ 40 Plate 3.2.^Photomicrographs of clastic units, Snip mine ^ 42 Plate 3.3.^Greywacke alteration, Snip mine^ 49 Plate 3.4.^Greywacke alteration, Snip mine^ 51 Plate 3.5.^Biotite spotted unit and other dykes, Snip mine^ 56 Plate 3.6.^Biotite Spotted Unit (BSU), Snip mine^ 58 Plate 3.7.^Shear veins, Snip mine^ 71 Plate 3.8.^Veins and veinlets, Snip mine^ 73 Plate 3.9.^Extension veins, Snip mine^ 79 Plate 3.10. Extension and shear veins and their structural associations and characteristics, ^81 Snip mine Plate 3.11. Faults, Snip mine^ 83 Plate 3.12. Carbonate ore, Twin zone, Snip mine ^ 95 Plate 3.13. Chlorite-biotite ore, Twin zone, Snip mine ^ 97 Plate 3.14. Sulphide ore, Twin zone, Snip mine^ 99 Plate 3.15. Ore type relationships and character in various veins from the Snip mine^101 Plate 3.16. Quartz ore, Twin zone, Snip mine^ 103 Plate 3.17. Gold occurrence in the Twin zone, Snip mine^ 105 Plate 3.18. Alteration in the Twin zone, Snip mine ^ 110 Plate 3.19. Alteration in the Twin zone, Snip mine ^ 112 Plate 3.20. Photomicrographs of chlorite-biotite relationships in the Twin zone and shear ^114 veins, Snip mine Plate 3.21. Photomicrographs of deformation fabrics in the Twin zone and shear veins, ^129 Snip Mine Plate 3.22. Deformation textures in the Twin zone, Snip mine ^ 131 Plate 3.23. Structural features of the Twin zone, Snip mine ^ 133 Plate 3.24. Mesoscopic folds in the Twin zone, Snip mine ^ 135 Plate 3.25. Shear bands and oblique foliations, Twin zone and 150 vein, Snip mine ^137 Plate 3.26. Twin zone, shear sense indicators in thin section, Snip mine^139 Plate 3.27^Structure of shear veins at the Snip mine^ 144 Plate 4.1.^Character and alteration of the Red Bluff porphyry^ 204 Plate 4.2.^Alteration of the Red Bluff porphyry^ 211 Plate 4.3.^Alteration of the Red Bluff porphyry^ 213 Plate 4.4.^Photomicrographs of alteration, Red Bluff porphyry ^ 216 Plate 4.5.^Deformation of the Red Bluff porphyry, Snip 130 portal area ^224 Plate 5.1.^Inel deposit^ 247 Plate 5.2^Stonehouse deposit^ 255  x  ACKNOWLEDGMENTS  This study would not have been possible without the generous assistance of Cominco Metals and Cominco Explorations Ltd. The work and ideas presented benefited greatly from numerous invaluable discussions with, and assistance from Cominco geologists Al Samis, Terry Hodson, Bruce Coates, Earl Masarsky, Ken Donner, Nick Callan, Ian Paterson and Jim McLeod. I thank Merlyn Royea and Ray Merrifield of Cominco Metals for their hospitality, and permission to work and stay at the Bronson camp. Dale Craig of Cominco is also thanked for his help in logistical support. Special thanks go to Bruce Coates and Terry Hodson for their play by play descriptions of new developments in mine geology over the last year. Cominco Metals generously provided food, accommodation and logistical support for the author for 148 days between June and September 1991 and 1992.  Colin Godwin, Peter Lewis, Al Sinclair, James Macdonald and John Thompson advised on the work, kept the project on track and significantly improved the text with their edits and ideas. I would also like to thank David Yeager of Skyline Gold Corp., Victor Jaramillo and Bob Gifford of Gulf International Minerals, and Paul Metcalfe, Art Ettlinger and James Moors at The University of British Columbia for important discussions and the sharing of their ideas and information. Arne Toma expertly and artistically drafted several of the figures. Kika Ross provided much needed encouragement and moral support. Thanks are also extended to my parents, John and Pat Rhys, who have been considerate and helpful.  Funding for this study was provided under the Mineral Deposit Research Unit project "Metallogenesis of the Iskut River Area", which is supported by thirteen mining companies, the Science Council of British Columbia and a Natural Science and Engineering Council CRD grant.  CHAPTER 1: INTRODUCTION  1.1.1 Introduction  The Snip mine, owned jointly by Cominco Ltd. (60 percent) and Prime Resources Group Inc. (40 percent), commenced production in January, 1991. It is currently the largest gold producer in British Columbia. The deposit is a vein filled shear zone, named the Twin zone, that contAins a diversity of ore types, all of which have high grade gold values. The mineralised zone is spatially associated with the tabular subeconomic Red Bluff Au-Cu porphyry deposit, 800 metres to the northeast. Numerous precious and base metal showings, and the past producing Skyline Gold mine occur to the south, within six kilometres of Snip.  Research was undertaken to document the geology of the Snip mine and its relationship to the geologic history of the area, and to compare and contrast the various styles of mineralisation in the Johnny Mountain area. The study is based on two summers of fieldwork (1991 and 1992 seasons), during which detailed (1:500 scale) underground mapping, extensive core logging and sampling were completed at Snip. In addition, surface mapping of the area was carried out at 1:5,000 and 1:20,000 scale in conjunction with other workers (Peter Lewis and Paul Metcalfe). Thin section examination of mineralogic relationships and structural features in oriented samples has corroborated the field information. The study was greatly augmented by geologic mapping, drilling and geochemical information from Cominco Ltd. and Skyline Gold Corporation that was obtained during the course of exploration and mining in the area.  1.1.2 Location and Access  Snip mine is 85 kilometres east of Wrangell, Alaska, and 110 kilometres northwest of Stewart, British Columbia. The mine is on the south side of the Iskut River, two kilometres south of its confluence with  2  III Jurassic Intrusions  ^  km ^ 0^100^200 300  Lower to Middle Jurassic Hazelton Group (volcanic rocks, dominantly calc—alkaline) Bowser Lake Group (sedimentary rocks)  Modified from G.S.C. Map 1712A, Wheeler and McFeely, P., 1991.  Figure 1.1: Map of northwestern British Columbia showing the location of Figure 1.2 and the Snip mine. Jurassic intrusions (including the Texas Creek plutonic suite), volcanics (Hazelton Group) and Jurassic Bowser Lake group sediments are shown.  3  Figure 1.2: Location map of the Johnny Mountain area showing the location of the Snip mine, Stonehouse deposit, Inel deposit, Figure 2.2 and geographic features mentioned in the text.  4  Bronson Creek (Figures 1.1 and 1.2). It occurs at the northwest end of Johnny Ridge. Mine workings range from 130 to 500 metres above sea level, and comprise nine levels. The mill site and accommodation are within the Bronson Creek valley 1.5 kilometres northeast of the deposit and 120 metres above sea level.  The local terrain is extremely rugged, with many local peaks above 1900 metres in elevation. Glaciers are common, locally extending to low elevations (400-800 metres) in the valleys. The area is thickly vegetated with a forest of mountain hemlock and Sitka spruce. Steeper slopes and gullies are commonly covered with thickets of slide alder and devils club, which make traversing extremely difficult.  A 1600 metre long landing strip at the mine provides access. Freight is brought to and from the mine by hovercraft on the Iskut river from Wrangell, Alaska. DC-3, DC-4, Hercules and Bristol transport aircraft are also used. Central Mountain Air provided regular passenger service during the study from the airstrip to several British Columbia destinations.  1.1.3 Previous studies  No systematic detailed geologic descriptions of the Snip mine or the Johnny Mountain area have been undertaken, except for an unpublished review of the geology of northwestern Johnny Mountain by Atkinson et al., 1991. Regional mapping projects in the Iskut River region, including an overview of the geology of the Snip mine area, are documented in Kerr (1948), Britton et al. (1990) and Metcalfe and Moors (1993). Published regional maps include Souther et al. (1979), Alldrick et al. (1990), Lefebure and Gunning (1989), and Fletcher and Hiebert (1990). Galena Pb-isotope data for showings and mineral deposits in the Iskut River region are reported in Godwin et al. (1991). Exploration and brief descriptions of Snip geology are documented in Nichols (1987, 1989). A series of short unpublished company petrographic reports by McLeod (1987a-e, 1989a,b, 1991a,b, 1992) address specific mineralogic aspects of Snip geology. Read (1990) presents the results of a primarily stratigraphic study  5  of lithologies adjacent to the orebody. Preliminary descriptions of some of the findings of this project are presented in Rhys and Godwin (1992), and Rhys and Lewis (1993).  The Red Bluff porphyry deposit is described mainly in exploration reports. These include geologic overviews of surface mapping and drilling, and are contained within Pedley (1950), Mawer (1965), Nagy (1966), Parsons (1966a,b,c) and Metcalfe (1988). A petrographic study of samples collected during 1965 exploration by Cominco Ltd. is contained in Harris (1966). Macdonald et al. (1992) describe U-Pb zircon geochronometry of several plutons in the region, including the Red Bluff porphyry intrusion.  1.1.4 History  The Stikine River, into which the Iskut River flows, was used as a major access route to the Cassiar (1873-75) and Klondike (1896-1900) gold rush fields. International Boundary survey crews travelled through the lower Stikine-Iskut areas during these periods, and named several topographic features, including Johnny Mountain (Annual Report, B.C. Department of Mines, 1911). Apart from this, there is little historic record of travel in the lower Iskut until the early twentieth century.  Claims were first staked in the area of the Snip mine in 1907 by the Iskut Mining Company, based in Wrangell, Alaska. The initial claim group, the Iskoot claims (9 claims), covered the west side of Bronson creek on Johnny ridge three kilometres southeast of the present Snip workings (Annual Report, B.C. Department of Mines, 1907, p. L54). The Red Bluff claim group (five claims), 1 kilometre east of the present mine workings, was staked in 1909. Between 1908 and 1911, several short adits were started on various showings in both claim groups, and some trenching was done. One ton of selected material from a series of foliation parallel sulphide veinlets in schistose greenstone (Annual Report, B.C. Department of Mines, 1919, pp. N83-84) was shipped from one of the showings for a smelter test at Ladysmith in 1909. This yielded approximately 1.9 grams Au, 44.2 ounces Ag and 12.4% Cu (Annual Report, B.C. Department of Mines, 1911, p. K63). This material was taken from the upper claim group (Iskoot  6  claims: Annual Report, B.C. Department of Mines, 1919, pp. N83-84) in the vicinity of the current Bonanza showings on ground presently held by Skyline Gold Corporation. Only minor work was done by the Iskut Mining Company on the Iskoot and Red Bluff claim groups between 1911 and 1929 (Annual Report, B.C. Department of Mines, 1929, p. 114). Both claim groups were Crown granted during this time. The Bronson Creek area was regionally mapped in 1929 (Kerr, 1948).  Cominco Limited had 42 claims staked in 1929 around the Iskoot and Red Bluff claim groups. These were examined subsequently by Cominco geologists (Castle, 1929), but nothing of interest was found and the claims were abandoned. No further exploration activity was carried out on Johnny Mountain until 1949, when Kennco Exploration Company (Canada) Ltd. ran a brief prospecting program on Bronson Creek and the lower Crown grants (Pedley, 1950).  The Tuksi Mining Company acquired the Crown grants (Red Bluff and Iskoot) in 1964. In the same year, Jodee Explorations Company, Cominco Ltd. and Copper Soo Mining Company staked claims around these grants. Cominco personnel examined all of these the claim groups that year and in 1965 mapped the area. Eight holes were drilled totalling 341 metres on optioned ground on the Red Bluff grants (Annual Report, B.C. Department of Mines, 1965, p. 43; Parsons, 1966). During 1965, Ted Muraro (Cominco) discovered a 1.5-3 metres wide, south dipping, vein filled shear zone containing visible gold at approximately 630 metres elevation on the steep north end of Johnny Ridge (Parsons, 1965). In 1966, some trenching was done by Cominco in the vicinity of the 1965 diamond drill holes to test the continuity of copper mineralisation, with limited success. The gold showing (future Snip orebody) was exposed for 25 metres and channel sampled. It returned values as high as 224 ppm Au over 1.2 metres (Nagy, 1966). However, high values such as this were attributed to weathering concentration, since fresher sulphide rich material returned lower assays (17 ppm). In addition, the vein was estimated to contain between 2,000 and 3,000 tonnes--a figure too small to warrant further development (Nagy, 1966).  7  Development of the Snip Mine  Cominco Ltd. re-staked the area covering the 1965-66 gold showing with the Snip claim group in 1980. Between 1980 and 1986, soil sampling, mapping and trenching was carried out in the vicinity of the gold showing. A joint venture agreement was signed with Delaware Resources Corporation in 1986. Twelve drillholes totalling 1494.2 metres and surface trenching located four gold bearing structures, the largest and most continuous of which was the Twin zone (Nichols, 1987). In 1987, an airstrip and a 40 man camp were constructed beside Bronson Creek to provide access and accommodation. Seventy-three more surface drill holes (13,857 metres) outlined the Twin zone on 50 metre centres. The Twin zone was intersected by underground advance on the 300 level in 1988, and underground and surface drilling (6,827 metres) was continued. During 1989 and 1990, the drill hole spacing was decreased to 12.5 metres to enable more confident ore reserve calculation and stope definition. By late 1990, a reserve of 936,000 tonnes grading 28.6 ppm Au was delineated entirely within the Twin zone (A. Samis, personal communication, 1991). Delaware Resources, incorporated into Prime Resources Group Inc., had by this time earned a 40% interest in the property by funding exploration between 1986 and 1990. Production began in January 1991 at a rate of 350 tonnes per day and has since been increased to 450 tonnes per day. Mining is by both conventional and trackless mechanised cut and fill, and by shrinkage stoping. Approximately 30 percent of the gold is recovered by a gravity circuit, and the rest by a sulphide flotation concentrate. Production during 1991 was 123,000 tonnes grading 30.4 ppm Au (3.7 tonnes Au total), and during 1992, 165,000 tonnes grading 31.7 ppm Au (5.2 tonnes Au total), for a total gold production up to 1 January 1993 of 8.97 tonnes (just over 288,000 ounces; T. Hodson, personal communication, 1993). New reserves have been added during 1991 and 1992 as a result of development on several veins in the foot wall of the Twin zone, primarily the 150 vein that contains new reserves of approximately 70,000 tonnes.  8  Other significant deposits in the Johnny Mountain area  The Stonehouse deposit (Johnny Mountain mine), discovered originally by Hudsons Bay Mining and Smelting Company in 1954, preceded development of Snip mine. This deposit is 6 kilometres south of Snip on Johnny Mountain (Figure 1.2). The Johnny Mountain mine produced 2.91 tonnes of gold, 4.56 tonnes of silver and 973 tonnes of copper from 207,058 tonnes mined between August 1988 and its closing in September 1990 (D. Yeager, personal communication, 1993).  Between 1987 and 1992, intensive exploration was carried out throughout the area by several companies. Numerous showings south of the Snip mine that were trenched and drilled by Skyline Gold Corp. and joint venture partners during this period include: the Red Bluff porphyry, SMC, Bonanza, CE, C-1, C-2, C-3, Road and Mike showings. Other significant exploration projects include Inel (Gulf International Minerals Limited; Figure 1.2), 11 kilometres southeast of Snip, and the Rock and Roll (Black Dog deposit, owned by Eurus Resource Corp. and Thios Resources Inc.), 10 kilometres to the northwest. Keewatin Engineering Inc. carried out exploration on the Handel and Chopin claim groups to the east of the Red Bluff porphyry between 1988 and 1991 on behalf of the property owners, Solomon Resources Limited.  9  CHAPTER 2: GEOLOGIC SETTING  2.1.1 Regional Geology  The Iskut River region is within the Intermontane Belt on the western margin of the Stikine terrane. Three distinct stratigraphic elements are recognised in the western portion of the area (Anderson, 1989): (i) Upper Paleozoic schists, argillites, coralline limestone and volcanic rocks of the Stikine Assemblage, (ii) Triassic Stuhini Group, and (iii) Lower to Middle Jurassic Hazelton Group volcanic and sedimentary arc related strata. Intrusive rocks in the Iskut River region comprise four plutonic suites (Anderson et al., 1993; Macdonald et al., in preparation): (i) Late Triassic (Stikine plutonic suite) calc-alkaline intrusions that are coeval with Stuhini Group strata; (ii) Jurassic Copper Mountain, (iii) Texas Creek, and (iv) Coast Plutonic Complex. These plutonic suites are variable in composition but are roughly coeval and cospatial with Hazelton Group volcanic strata. Tertiary elements of the Coast Plutonic Complex are represented by predominantly granodioritic to monzonitic Eocene intrusions of the Hyder plutonic suite, exposed 12 kilometres south of the Snip mine (Britton et al., 1990).  2.1.2 Lithologies of the Johnny Mountain area  Strata in the Johnny Mountain area are defined here as a lower sequence and an upper sequence, probably correlative with the Triassic Stuhini and Jurassic Hazelton Groups, respectively. The sequences are separated by a regional, flat lying to gently dipping unconformity, which is exposed at the break in slope east of the Skyline Gold Corporation Stonehouse camp (Figure 2.1; Plate 2.1). This unconformity is mapped, but not exposed, at the 1,800 metre level on Snippaker Ridge (Pegg and Travis, 1991; Metcalfe and Moors, 1993). All of the rocks have been affected by lower greenschist facies metamorphism with the development of chlorite in clastic units and chlorite and epidote in volcanic units. A broad zone of secondary biotite development occurs at the northwest end of Johnny Mountain and along its southwest margin, the significance of which is discussed in succeeding chapters.  Stratified Rocks LOWER SEQUENCE (Triassic Stuhini Group) Greywacke, slltstone, mudstone and minor conglomerate AndesRic breccia to volcanic conglomerate  UPPER SEQUENCE (Jurassic Hcrzetton Group) Daclte - Andeslte flows, breccia, tuff  IA  Rhyolite flows, welded lapilli tuff Basalt flows, epiclastic rocks  Plagioclase phyric andesite  Intrusive Rocks Jurassic  Triassic  K-feldspar megacrystic porphyry  Diorite  Diorite, plagioclase porphyry  4111%tit  Late steep fault  DI fold axial surface trace  No.^Si foliation  Glacial Ice  S2 foliation  x  Bedding  X Mineral deposit  U-Pb zircon Isotopic date  FIGURE 2.1: Geology of the Johnny Mountain Area, Northwestern British Columbia.  0  11  Lower sequence  The strata below the regional unconformity, here termed the lower sequence, consist of poly-deformed and moderately to weakly metamorphosed feldspathic turbiditic greywackes with subordinate interbedded siltstones, mudstones, volcanic conglomerate and rare dolostone and/or limestone. This sequence underlies most of northwestern Johnny Mountain and western Snippaker ridge, and it hosts the Snip mine and Inel deposit (Figure 2.1; Plate 2.1). The stratigraphy exposed in the Snip workings is described further in Chapter 3.  Lack of exposure over much of the area and complication by folding and faulting have hindered construction of a stratigraphic column for the lower sequence on Johnny Mountain. Neither the stratigraphic top nor bottom is exposed, so the true thickness is unknown. The exposed section has a minimum true thickness of between 900 and 1200 metres, measured from the northeast end of the Snip workings south to Sky Creek. Strata composed primarily of fine to medium grained feldspathic and lithic turbiditic greywacke comprise most of the sequence. Subordinate graded beds of siltstone and black mudstone occur throughout the sequence, but are most common at the base of the exposed section along Sky Creek and along the northeastern part of Johnny Flats (along the northernmost anticlinal trace in Figure 2.1; Plate 2.1). The greywackes are massive to crudely bedded, with local graded beds up to 10 metres in thickness. Individual graded beds may have sharp scoured basal contacts with siltstone or mudstone rip up clasts (Plate 2.2A). Fine grained porphyritic pebble to cobble sized mafic to felsic volcanic clasts are common in coarser beds or at the base of thick graded beds. Interbedded monolithic to polylithic volcanic conglomerates, biotite rich plagioclase porphyritic tuff or flow units, and felsic crystal tuff are common in the highest exposed portion of the section on Johnny Mountain west of the Stonehouse deposit. K-feldspar megacrystic and medium to fine grained equigranular intermediate to felsic sills intrude the sequence in this area.  12  Plate 2.1: Aerial view of Johnny Mountain, northwestern British Columbia. The photograph, looking southeast, was taken approximately 1 kilometre northwest of the Snip camp. Important geologic and topographic features referred to in the text are marked in the accompanying sketch. Volcanic rocks of the Jurassic upper package (Jr) occurs at the crest of the ridge, unconformably overlying folded Triassic clastic sediments (Tr). A prominent anticline traces across Johnny flats (upper centre) and plunges gently towards Sky Creek (right). The Red Bluff porphyry (+ +) intrudes the northeast edge of the mountain (left, bottom). The Twin zone runs through the lower centre of the picture, dipping to the southwest. It is intersected by a northwest-dipping fault near the bottom of the photograph (squiggly lines). Sky Creek runs along a southwest-dipping fault. Photograph courtesy of Cominco. The photo was taken in 1986 before mine development.  13  Several thin lenses of massive recrystallised limestone and dolostone, and crinoidal limestone occur sporadically throughout the lower sequence on Johnny Mountain. A small northeast trending body of recrystallised limestone associated with a diopside-garnet skarn that occurs just north of the Snip mine camp (Figure 2.2) is probably part of this sequence.  On Snippaker Ridge eight kilometres southeast of Snip (Figures 1.2, 2.1), the greywacke sequence is paraconformably overlain by polymictic pebble to cobble conglomerate with interbedded greywacke (Pegg and Travis, 1991; Metcalfe and Moors, 1993). Calcareous greywacke at the top of this unit east of Snippaker Peak has yielded Norian corals and ammonoids (Nadaraju and Smith, 1992), thus providing a minimum age of Upper Triassic for the lower sequence. The lower sequence is thus assigned to the Triassic Stuhini Group. No fossils have been found elsewhere in the sequence. Two samples, one of crinoidal limestone collected south of the Stonehouse deposit, and a second of calcareous mudstone from a drill hole on the northeast flank of Johnny Mountain (Skyline hole 975, 270.2-270.9 metres) failed to yield microfossils (R. G. Anderson and G. Nadaraju, personal communication, 1992).  Plagioclase + hornblende + pyroxene phyric andesitic volcanics, including tuffs and flows, occur to the northeast of Snip at low elevations on the south side of the Iskut River interbedded with greywacke (Pegg and Travis, 1991; Figure 2.1). These rocks are attributed to the Triassic Stuhini Group by Alldrick et al. (1990). They lie below the clastic lower sequence that forms most of Snippaker Ridge. No contact relations are described in Pegg and Travis (1991) or Britton et al. (1990), but if the contact is stratigraphic, then they indicate a vertical thickness for the clastic lower sequence on Snippaker Ridge of 1.6 kilometres up to the Jurassic unconformity at the ridge top.  Upper Sequence  Flat lying Early Jurassic felsic to intermediate volcanic sedimentary, pyroclastic and flow rocks, probably of the Lower Hazelton Group, are exposed to the south and east on Johnny Mountain and  14  Plate 2.2. Lithologies of the Johnny Mountain area, northwestern British Columbia. The coin is 2.4 centimetres in diameter and the knife is 8.5 centimetres long. A: Graded turbidites with basal scour surfaces and mudstone rip-up clasts from the lower sequence (Triassic) on eastern Johnny mountain. Skyline Gold Corp., Bonanza drill hole DDH 975: 298.1 metres. B: Bronson stock west of Monsoon Lake. Biotite-rich dark grey medium to fine-grained equigranular diorite (left) containing a rounded xenolith of plagioclase porphyritic diorite. Sample is DR-193. C: K-feldspar megacrystic plagioclase porphyritic mafic dyke intruding a schistose biotite-rich portion of the Bronson stock 400 metres northwest of the Snip camp. A laminated calcite > chlorite + epidote + pyrite shear vein with an epidote alteration envelope occurs along the margin of the dyke. Both dyke and shear vein cut foliation in the wallrocks.  4  4.!•  •  ^rk^14! •^diki •  16  Snippaker Ridge unconformably overlying the greywacke sequence and the Norian greywacke (Metcalfe and Moors, 1993; Britton et al., 1990; Figure 2.1; Plate 2.1). Gold bearing veins of the Stonehouse deposit at the Johnny Mountain gold mine occur at the base of this sequence. These strata form three lithologically distinct units that are present on Johnny Mountain, and for the lowest unit, on Snippaker Ridge (Atkinson et al., 1991; Metcalfe and Moors, 1993; Rhys and Lewis, in preparation). Lowest rocks of the upper sequence are andesitic to dacitic, medium to dark greenish grey ash to block tuff and tuffaceous sediments approximately 300 metres in thickness. Tuffaceous components are plagioclase phyric and poorly to moderately bedded. The age of the dacite-andesite and the basal unconformity is constrained to Latest Triassic to Early Jurassic by: (i) Norian fauna in the underlying succession on Snippaker Ridge (Nadaraju and Smith, 1992), (ii) a U-Pb zircon age of 194 ± 3 Ma from a plagioclase phyric dyke that cuts tuffs in the lower part of the unit in the Stonehouse deposit (M.L. Bevier, personal communication, 1993; Table 2.1), and (iii) a U-Pb zircon age of 192.9 ± 1.3 Ma (preliminary minimum age only) obtained from massive plagioclase + hornblende phyric dacite 3.5 kilometres southeast of Snippaker Peak (P. Metcalfe and J. Gabites, personal communication, 1993). Conformably succeeding the andesitic to dacitic sequence on Johnny Mountain is a 350 metre thick dacitic to rhyolitic tuffaceous volcanic interval comprising variably welded tuff and tuff breccia and massive flow banded sections (Atkinson et al., 1991; Rhys and Lewis, in preparation). U-Pb zircon analyses of the flow banded rocks yield an age of 192 ± 3 Ma (M.L. Bevier, personal communication, 1993; Table 2.1). Uppermost rocks of the sequence comprise dark green clinopyroxene + plagioclase-phyric basaltic flows. The lithologic character, thickness and age of the upper sequence at Johnny Mountain compares closely to regional Hazelton Group successions of the Iskut River and Stewart areas, which currently are being reviewed (P.D. Lewis, personal communication, 1993).  Intrusive rocks  Triassic to Tertiary dykes and stocks, including the Red Bluff porphyry, intrude the Triassic and Jurassic rocks of Johnny Mountain. A heterogeneous medium grained equigranular plagioclase + clinopyroxene  17  ± amphibole phyric diorite stock lies immediately north of Monsoon Lake, separated from the greywacke sequence at the Snip mine by a strong northeast trending lineament and possible fault (Figures 2.1 and 2.2). This unit, with deformed and biotite rich southern margins, was previously mapped as andesite (Lefebure and Gunning, 1989); however, the equigranular medium grained texture in relatively undeformed areas suggests instead that it is intrusive. Brown biotite, pale green amphibole and accessory magnetite commonly replace pyroxene grains; plagioclase is saussuritised. Biotite abundance decreases northward. The unit contains common resistant weathering rounded xenoliths of a coarse plagioclase and clinopyroxene porphyritic andesite (Plate 2.2B). These comprise up to 30% of the outcrops in some areas, and commonly range from 4 to 30 centimetres in diameter; they are locally >1 metre across. A UPb zircon date was obtained from an K-feldspar, plagioclase phyric monzodiorite within this unit (Macdonald et al., 1992; sample location is on Figure 2.1); the age is poorly constrained between 225 (Late Triassic) and 197 Ma (Early Jurassic). The contacts of this unit with an K-feldspar megacrystic, plagioclase phyric monzodiorite intrusion straddling the Iskut River to the north are poorly defined (Figure 2.1). The two units have been mapped previously as one (e.g. Britton et al., 1990). A further complication are the different names applied to the collective unit. It is proposed (Figure 2.1) here that the northerly K-feldspar megacrystic unit be called the Iskut River stock, as suggested by Kerr (1948), and that the southern dioritic unit be termed the Bronson stock following Lefebure and Gunning (1989).  The Red Bluff porphyry is an elongate stock that intrudes the northeast end of Johnny Mountain (Figures 2.1, 2.2; Plates 2.1, 2.3A). The porphyry is a K-feldspar megacrystic, plagioclase porphyritic quartz diorite to tonalite body (Plate 2.3B) that is overprinted by a porphyry Au-Cu system. A sample obtained from foliated porphyry in the Snip 130 portal returned a U-Pb zircon age of 195 ± 1 Ma (Macdonald et al., 1992; Table 2.1; sample site on Figures 2.1 and 2.2). The porphyry and its associated hydrothermal system is described in detail in Chapter 4.  18  Plate 2.3. A: Red Bluff cliffs, Snip mine area, northwestern British Columbia. Photograph is taken looking west. The cliffs are composed of the Red Bluff porphyry, a tabular steeply-dipping quartz + magnetite + sericite altered K-feldspar megacrystic quartz diorite to tonalite intrusion that is approximately 250 metres thick. The southwestern contact of the intrusion runs along the break in slope behind the top of the cliffs and continues above the lower cliffs to the far right. The northeast contact runs just below the cliff base. The prominent gully in the lower right corner is a steeplydipping northwesterly-trending gouge-filled fault zone. Snip camp is just out of the lower right hand corner of the photograph. B D: K feldspar megacrystic intrusive rocks, Johnny Mountain area. The coin is 2.4 centimetres in diameter. -  -  B: Red Bluff porphyry. The sample is potassically altered with sericite and K-feldspar replacing plagioclase and matrix. K-feldspar megacrysts (tan colour) are intact. Disseminated and veinlet-controlled magnetite comprises 5-10% of the samples. Quartz veins with magnetite (banding and selvage in the sample) are common. Top sample is from Skyline DDH 964: 48.2 metres; bottom is from Skyline DDH 944: 74.1 metres. Drill hole locations are marked on Figure 2.2. C: Sample from the centre of a 15 metre wide dyke northeast of Monsoon Lake. K-feldspar megacrysts containing grey quartz grains are in a matrix of sericite-altered plagioclase. Sample is DR-186. D: Sample from a sill 1.5 kilometres west of the Stonehouse deposit. Kfeldspar megacrysts are in a matrix of sericite altered plagioclase porphyry. Sample is DR-370.  20  Orthoclase megacrystic dykes with moderate to steep southwesterly dips intrude the Bronson stock one kilometre north of the Snip camp (Figure 2.2; Plates 2.2C, 2.3C). These dykes are similar mineralogically and texturally to the Iskut River stock and Red Bluff porphyry. They range from 10 centimetres up to 15 metres in thickness. The thickest have fine grained chilled margins with medium grained porphyritic cores. Phaneritic dykes consist of between 5 to 10% orthoclase phenocrysts in a matrix of medium grained plagioclase porphyry. Accessory apatite is common. Magnetite, occurring interstitially and as thin stringers, is common in some dykes. The stringers are typically subparallel to the margins of the dyke. The dykes contain foliated xenoliths of the biotitic Bronson stock, indicating that they postdate foliation.  Several small stocks, sills and dykes of unknown age and intermediate to mafic composition intrude the western side of Johnny Mountain. These include several northeast trending locally K-feldspar megacrystic plagioclase porphyritic felsite sills, dykes and small stocks that occur between two and five kilometres south of Snip (Figure 2.1; Plate 2.3d). North dipping plagioclase porphyritic, locally Kfeldspar megacrystic, dykes in the Stonehouse mine workings have returned a U-Pb zircon age of 194 ± 3 Ma (M.L. Bevier, personal communication, 1993; Table 2.1). On the Inel property to the southeast, a small quartz-feldspar porphyritic felsite stock (Inel porphyry) intruding elastic rocks probably correlative with the lower sequence on Johnny mountain returned a U-Pb zircon age of 190 ± 3 Ma (Macdonald et al., 1992).  The relative ages (Table 2.1) of Jurassic volcanic rocks of the upper sequence (Snippaker Ridge dacite and Johnny Mountain rhyolite) and the Early Jurassic intrusions (Red Bluff porphyry, Inel stock and Stonehouse feldspar porphyry dykes) suggest that the intrusions are subvolcanic. They are probable feeders to the overlying volcanic units.  21  Table 2.1: Radiometric dates obtained in the Johnny Mountain area. Locations of dates are on Figures 2.1 and 2.2. Material dated  Location  Age (method)  References  Clinopyroxene-plagioclase diorite  Bronson stock, north of Snip  Between 197 and 225 Ma (U-Pb zircon)  Macdonald et al., 1992  Foliated K-feldspar porphyritic intrusion (Red Bluff porphyry)  Snip 130 level, near portal  195 + 1 Ma (U-Pb zircon)  Macdonald et al., 1992  Plagioclase porphyritic dyke  Johnny Mountain mine (Stonehouse)  194 + 3 (U-Pb zircon)  M.L. Bevier, personal communication, 1993  Plagioclase + hornblende phyric dacite  Snippaker Ridge, 3.5 km southeast of Snippaker Peak  192.9 + 1.3 Ma (U-Pb zircon; preliminary minimum age)  J. Gabites and P. Metcalfe, personal communication, 1993  Flow banded rhyolite  Johnny Ridge  192 + 3 (U-Pb zircon)  M.L. Bevier, personal communication, 1993  Inel stock: Quartz-feldspar porphyry, aphanitic matrix  Inel camp site  190 + 3 (U-Pb zircon)  Macdonald et al., 1992  Anomalous green biotite from a quartz vein in the Twin zone  Snip, 300 level west  51.9 + 1.8 Ma (K-Ar, biotite separate)  R.L Armstrong, U.B.C., personal communication, 1991  Biotite lamprophyre dyke  Snip, 300 level east  32.0 + 1.1 Ma (K-Ar whole rock)  R.L Armstrong, U.B.C., personal communication, 1991  2.1.3 Structure of the Johnny Mountain area  Megascopic folds are abundant in the Triassic succession on northwestern Johnny Mountain. The folds have north-northwest trending subhorizontal axes, tight profiles and steep limb dips. Moderate southwest vergence is defined by northeasterly dipping axial surfaces and locally inverted southwest limbs. Two major fold pairs with wavelengths of 1-3 kilometres are defined by facing direction and bedding dip changes. The largest of these, an anticline that extends through the northern portion of Johnny Mountain (Figure 2.1), separates northeasterly facing strata at the Snip mine and along Bronson Creek from northwesterly facing strata exposed west of Sky Creek and the Stonehouse deposit. Folds are truncated by  22  the flat lying largely unfolded angular unconformity at the base of the Jurassic sequence. Folding in the upper sequence is limited to broad warps of bedding attitude.  A moderately to steeply northeast dipping penetrative flattening fabric (SI) forms a regionally persistent foliation in the lower sequence. It is most strongly developed as a pervasive phyllitic flattening fabric defined by the alignment of sericite and biotite west of Sky Creek and the Stonehouse deposit on the southwest flank of Johnny Mountain. The foliation is parallel to the axial surfaces of megascopic folds. Si forms small to moderate angles to bedding depending on position to the major folds, but to the southeast where it is most intensely developed it is subparallel to bedding. Here it locally contains a strong linear fabric defined by clast or phenocryst elongation. Elongation fabrics plunge moderately to the west-northwest, and fabric asymmetry indicates a large component of oblique (sinistral + normal) simple shear associated with fabric development.  All of the previously described structures and the entire Triassic - Jurassic sequence, were subject to a later deformation resulting in a shallowly dipping to subhorizontal foliation (S2). It is best developed in fine grained rocks such as siltstone or mudstone. This foliation is parallel to axial surfaces of tight, shallowly northwest plunging folds and crenulations of the earlier foliation, and is developed as a spaced cleavage defined by preferred dimensional orientation of sericite. In regions of phyllitic to schistose rocks, such as on the southwest flank of Johnny Mountain, S2 forms a flat crenulation cleavage. Well developed crenulation lineation here plunges shallowly to the northwest. Jurassic rocks above the unconformity contain a single foliation, which in most cases dips moderately to the northeast or southwest. This foliation is best exposed above the Stonehouse deposit where it is subparallel to S2 in the lower sequence.  Abundant shallow dipping extension veins cut the SI and S2 fabrics on Johnny Mountain. Moderate to steep northwest dipping and southwest dipping fault sets cut all other lithologies and structures in the area.  23  North and west of Monsoon Lake in the southern portion of the Bronson stock (Figure 2.1), the earliest formed foliation (phyllitic) dips moderately southeast to south. It is pervasive, is defined by biotite alignment and is well developed in the southern portion of this unit. The foliation rotates to variable southwest and northeast dipping bedding subparallel orientations west of the stock in metasedimentary rocks of the lower sequence. Elongate biotite-magnetite blebs and a parallel striation on the foliation surfaces define a lineation in the Bronson stock that is subhorizontal to gently plunging west-southwest or east-northeast. The significance of the foliations in this area is uncertain. Crenulation of the southwest dipping foliation in metapelites west of the Bronson stock by flat lying S2, however, indicates that the southwest dipping fabrics predate the S2 forming event. The changes in orientation imply folding of the foliation about northwest trending fold axes, a feature not observed to the south on Johnny Mountain. The area is separated from rocks to the south on Johnny Mountain by a northeast trending fault that runs through Monsoon Lake.  2.1.4 Metallogeny of the Stewart Iskut River region -  The Texas Creek Plutonic suite and regional metallogeny  The age, mineralogy and texture of the Red Bluff porphyry suggest that it belongs to the metallogenetically important, Early Jurassic, Texas Creek plutonic suite (Alldrick, 1985, 1991; Brown, 1987). Plutons of this suite are widespread in the Stewart-Iskut River region and range in age from 196 to 185 Ma (Anderson and Bevier, 1990; Macdonald et al., 1992, and in preparation). The two largest exposed, the Texas Creek pluton (west of Stewart) and the Lehto batholith (20 kilometres east-southeast of Snip), are predominantly calc-alkaline medium grained biotite-hornblende granodiorite to quartz monzonite and quartz diorite (Smith, 1977; Britton et al., 1990). Both have K-feldspar porphyritic, generally megacrystic, marginal phases and crosscutting dykes, classified as hornblende monzodiorite to monzonite or andesite, which are texturally and mineralogically similar to the Red Bluff porphyry  24  (Grove, 1971; Britton et al., 1990). Prismatic hornblende and common, widespread alteration of mafic minerals and plagioclase to chlorite and epidote are characteristic of the Texas Creek intrusions (Anderson and Bevier, 1990). Isolated calc-alkaline to sub-alkaline stocks and plutons are of either equigranular hornblende granodiorite to monzodiorite (e.g. Summit Lake stock, and Inel stock) or Kfeldspar phyric varieties (e.g. McLymont Creek pluton, Iskut River stock and the Red Bluff porphyry).  The Stewart-Iskut River area contains many significant gold deposits and showings spatially associated with Texas Creek intrusions, a relationship that has been noted previously (e.g. Buddington, 1929; Alldrick, 1991; Brown, 1987). Examples include the Premier mine, Snip mine, Eskay Creek deposits, Red Mountain deposits and Sulphurets Snowfield zone. All of these contain published reserves or have produced greater than 25 tonnes of gold. Deposits in the area that have Pb-Pb isotopic data consistent with a Lower Jurassic age are hosted by, follow contacts of, or are proximal to (within 500 metres of) Early Jurassic intrusions and dykes of the Texas Creek plutonic suite (Alldrick et al., 1987; Godwin et al., 1991; Alldrick, 1991; Alldrick et al., 1993; Macdonald et al., 1992; summarised in Table 2.2) suggesting that intrusion and mineralisation are broadly coeval. Such deposits include auriferous sulphide-quartz-carbonate veins (Twin zone, Scottie Gold, Stonehouse, Marc zone, Inel and Salmon River veins), epithermal style Au-Ag base metal veins (Premier and Hank), porphyry Au-Cu stockworks (Kerr, Sulphurets, Red Bluff, Khyber Pass and Sericite Ridge) and skams (Snippaker Creek).  25  Table 2.2: Examples of gold deposits in the Stewart-Iskut River region associated with known and probable Early Jurassic (Texas Creek) intrusions. Deposit name and Production (P) or ^Description references^Reserves (R) 1 Snip (Twin zone)  ^  936,000 tonnes  Red Bluff porphyry: strongly altered Kfeldspar-megacrystic plagioclase porphyritic quartz diorite to tonalite  (U-Pb zircon)  207,058 tonnes grading 14.1 ppm Au, 22.0 ppm Ag, and 0.47% Cu (P, 19881990)  Steep north dipping quartzsulphide veins obliquely cut andesitic dykes; strong Kfeldspar alteration  Early Jurassic dacitic to andesitic volcanics  Steep north dipping plagioclase phyric andesite dykes  194 + 3 (U- Pb zircon)  AK zone, 57,600 tonnes grading 11.7 ppm Au (R, 1991)  AK zone: southwest dipping pyritic breccia adjacent to a Kfeldspar phyric andesite dyke Discovery zone: phyllonitic sulphide, calcite, chlorite veins and shear veins, southwest and northeast dipping  Triassic feldspathic greywacke and siltstone  Inel stock: quartz monzodiorite, 500 m west; K-feldspar megacrystic andesite and diorite dykes are associated with both zones  190 + 3 Inel stock (U -Pb zircon)  4.3 million tonnes grading 14.3 ppm Au and 304 ppm Ag (13 , 19191992)  Crescent shaped epithermal quartz-sulphide vein stockworks and breccia zones enveloping steep dipping northeast and southwest trending porphyry dykes  Hazelton group andesitic and dacitic volcanics  Premier porphyry: Kfeldspar megacrystic, plagioclase porphyritic andesite dykes forming elliptical plugs and pipes  197,522 tonnes grading 16.5 ppm Au, 16 ppm Ag (P, 1981-1985)  Northeast dipping pyrrhotite quartz-calcite veins and stockworks in shear zones  Hazelton group andesitic volcanics  Summit Lake stock: coarse grained hornblende granodiorite; <500 m west of veins  zircon)  N/A (approx. 1 million ounces)  Densely disseminated to massive and stringer pyrite lenses along the brecciated south dipping contact with the Goldslide intrusion  Goldslide intrusion and Hazelton andesitic volcanics  Goldslide intrusion: Hornblende-plagioclase porphyritic granodiorite to diorite  Between 200 and 160 (K- Ar)  N/A  Pyrrhotite veins within the periphery of, and marginal to, the Texas Creek intrusion  Texas Creek pluton, border phase; Hazelton volcanics  Texas Creek pluton: border phase; Kfeldspar megacrystic hornblende granodiorite  (U Pb  N/A  Veins pods and irregular masses of calcite, pyroxene, garnet, amphibole, epidote, quartz and chlorite skarn, commonly with magnetite, pyrite, chalcopyrite and sphalerite  Variable; mainly calcareous Triassic volcanic sediments  Lehto batholith: Kfeldspar megacrystic and equigranular quartz diorite phases  N/A  Potassic and sericite-pyrite alteration zones with auriferous quartz-magnetite veins; adjacent to a large eastsoutheast striking shear zone  ?Early Jurassic intermediate to mafic volcanics  Northwest trending K-^Undated feldspar megacrystic diorite dykes  (Yeager and Metcalfe, 1990; Bevier, pers. comm., 1993)  Inel (Rhys and Lewis, 1993; Macdonald et al; 1992)  Silbak Premier (Brown , 1987)  Scottie Gold (Alldrick, 1991)  Red Mountain (Marc zone) (Vogt et al., 1992; Schroeter et al, 1992)  Salmon River veins; Alaska Star (AUdtick, 1991)  ^  and Ray, 1991)  ^  (H. Marsden, pers. comm., 1993)  195 + 1  Triassic feldspathic greywacke sequence  Johnny Mountain (Stonehouse)  Khyber pass  Intrusion age (Ma)2  Phyllonitic southwest dipping shear vein system, calcitequartz-sulphides-chloritebiotite  (Rhys and Godwin, grading 28.6 ppm ^ 1993; Macdonald Au (R, 1990) et al., 1992)  Snippaker Creek skarns (Webster  Host rocks^Associated intrusion  194.8 ± 2  (U Pb -  zircon)  192.8 ± 2  (U Pb -  195 + 2 -  zircon)  Undated  26  Table 2.2 (continued)  Zoned potassic and sericitepyrite alteration zones with auriferous quartz-magnetite and pyrite vein stockworks  ?Early Jurassic sediments and volcaniclastic rocks  K-feldspar megacrystic^Undated diorite dykes; adjacent to the Strip Mountain diorite to monzonite stock  ^ tonnes at 0.62% (Bridge and ^ Cu and 0.27 ppm Godwin, 1992)  Quartz, Fe-oxide, sulphide and gypsum vein stockworks in quartz-sericite-pyrite and propylitic alteration zones  Dykes, intermediate volcanics and sediments  Intermediate to mafic pm- syn- and postmineral dykes, including late synmineral K-feldspar megacrystic varieties  Sulphurets  West zone: steep-dipping  Hazelton group intermediate volcanics and sediments  Sericite Ridge^N/A (H. Marsden, pers. comm., 1993)  Kerr  ^  127.5 million  Au (R, 1992)  (Roach and Macdonald, 1992: Macdonald, 1993);  Hank  ^  West zone: 750,000 tonnes at 15.4 ppm Au and 644 ppm Ag (R, 1992) 245,000 tonnes  ^ (Kaip and grading 4 ppm Au McPherson, 1993; (R, 1992) J. Gabites, pers. comm. 1993)  northwest trending Au-Ag quartz-sulphide shear veins Snowfield zone: porphyry style pyritic propylitic alteration zones Epithermal phyllic and argillic alteration zones with auriferous quartz-carbonate stockworks surround a weakly altered K-feldspar megacrystic stock  Triassic volcanics and sediments overlain by Jurassic clastics  195 ± 1.5 (U Pb -  zircon; Kfeldspar megacrysti c dyke)  Bald Bluff stock: K- ^185 + 3 ^ feldspar megacrystic (U Pb ^ hornblende phyric zircon) ?andesite -  1 P=production; R= reserves; N/A=not announced 2 Early Jurassic galena Pb-Pb isotopic signatures have been obtained from all of the deposits except for Red Mountain (Marc  zone), the Snippaker Creek skarns, and Salmon River valley veins, which have not been analysed. K-feldspar from alteration at Hank returned an Early Jurassic Pb-Pb signature (A. Pickering, personal communication, 1993).  Mineralised structures in the Johnny Mountain area  Mineralised veins, shear veins and shear zones in the Bronson Creek area are abundant in a northwesterly trending belt from five kilometres northwest of Snip on the north side of the Iskut River, to Inel and Khyber pass, 13 kilometres to the southeast. Geologic descriptions, mineralogy, associated alteration and metal contents for many of the deposits located on northwestern Johnny Mountain are summarised on Table 2.3; locations are shown on Figure 2.3. The structures include isolated veins and sets of tabular dilatant sulphide-quartz veins (e.g. the Stonehouse deposit, Silver Dollar showing), layered calcitesulphide-chlorite-biotite shear veins (e.g. Snip, Sky Creek veins), and pervasive sulphide disseminations and veins in phyllonitic shear zones (e.g. SMC, C-3, Evermore and Blue Grouse). The veins lack textures typical of epithermal systems, such as vuggy crustiform banded or comb quartz. With the  27  exception of the Stonehouse veins in the Jurassic volcanic package and shear veins in the Bronson stock, all of the veins on northwestern Johnny Mountain are hosted by the folded Triassic clastic sequence. Mineralised structures are commonly crenulated and folded by the S2 foliation.  The structures have two common orientations, both with moderate to steep dips: southwest dipping and north to northeast dipping. Southwest dipping orientations predominate, usually cutting bedding obliquely to orthogonally. Northerly and northeasterly dipping orientations generally are controlled by pre-existing structural features. On the east and west sides of Johnny Mountain in the Snip workings, Bonanza zone, and at the SMC showing, north and northeasterly dipping mineralised structures are commonly parallel to bedding. Similarly, veins of the Stonehouse deposit obliquely cut or are subparallel to north dipping plagioclase porphyritic dykes. The most continuous set of structures occurs along the northeast side of Johnny Mountain, and includes the Twin zone, and to the southeast, the CE contact and Bonanza zones (Figure 2.3). These define a set of southwest dipping veins that is continuous over a 6 kilometre strike length. Mineralised structures are abundant within 1-2 kilometres west of the Red Bluff porphyry in the Snip mine workings (see Chapter 3).  Mineralised structures on Johnny Mountain and Snippaker ridge display zoning of both alteration mineralogy and metal abundance. West and southwest of the Red Bluff porphyry, relatively Au-Cu enriched structures with potassic alteration envelopes occur over an area of approximately 8 square kilometres (Figure 2.3; Table 2.5). These include the Twin zone, abundant shear veins throughout the Snip workings, Monsoon north shear veins, Sky Creek veins, Road showing, shear veins in the Bronson skarn, Mike, O.S.C. and Boundary. They consist of laminated calcite-biotite-chlorite-quartz or massive pyrite ± pyrrhotite ± magnetite with or without envelopes of biotite and/or K-feldspar. The veins are relatively Cu and Au rich but Zn poor; Zn:Cu ratios are usually less than 5 (Table 2.4).  Zn-Pb enriched structures with sericite-quartz-pyrite ± chlorite alteration envelopes and assemblages occupy an area of greater than 35 square kilometres east and southeast of the porphyry, and south of the  28  previously described region (Figure 2.3). The structures include: (i) sericitic shear zones with pervasive sulphide dissemination, such as SMC-Tillerman, Evermore, C-3, Blue Grouse and Chopin showings, and (ii) pyrite-sphalerite-quartz veins and shear veins, including Silver Dollar, Cottonwood, Windsock, Boundary and Silvertip (Table 2.3). The structures are Zn and Pb enriched, but Cu and Au poor, although locally high Au grades occur. Zn/Cu and Ag/Au ratios are usually greater than 15 and 5, respectively (Table 2.4). White to pale grey, locally K-feldspar megacrystic, felsite stocks, dykes and Si parallel sills are spatially associated with several of these showings, including SMC-Tillerman, Evermore, C-3 and Silvertip. The intrusions are commonly mineralised and altered, indicating that they predate the mineralising event.  Veins of the Stonehouse deposit define a second region containing Au-Cu enriched veins with potassic alteration assemblages (Figure 2.3; Tables 2.4, 2.5). Mineralised boulders of vein material similar to the Stonehouse veins occurring in till at the toe of the Johnny Mountain (McFadden zone till) indicate that veins with similar metal contents and mineral assemblages lie to the south under the glacier.  29  Table 2.3: Major characteristics of showings and deposits, northern Johnny Mountain and Snippaker Ridge, northwestern B.C. Locations are shown on Figure 2.3. Showing or^Description^ deposit name'^  Veinj or shear zone^Alteration mineralogy2^ mineralogy2  Twin zone^Southwest dipping shear vein system with quartz-sulphide CA, QZ, CL, BI, PY, PO ^Potassic: BI, KSP veins^ Bonanzab^Southwest dipping sulphide rich shear veins and shear^PY, CA, QZ, PO, SP, CL, SER, CL (BI, SER) zones^ BI, GL, CPY CEa^Southwest and northeast dipping shear zone and veins;^QZ, PY, SP, SER^QZ, SER also broad zones of pervasively disseminated sulphides without associated structures SMC - Tillerman^Folded north dipping shear and alteration zones with^SER, QZ, PY, SP, GL, CPY, CA, QZ, SER, PY, pervasively disseminated and vein sulphides; also older^Fe-carbonate^ KSP, CA, Fesubordinate pyrite-calcite-chlorite-biotite veins and^ carbonate; veinlets with biotite + magnetite envelopes Mikes^Subvertical north striking pyrite vein ^ PY, CL, GL, CPY Sky Creek^North dipping laminated shear veins^ CA, QZ, CL, BI, PY^Potassic (?) (veins) Sky Creek^Pyrite-sericite alteration zone with sulphides disseminated SER+PY > CPY^SER, PY (disseminated)^and in veinlets Blue Grouse^Sericitic southwest dipping shear zone in dolostone ^QZ, PY, SP, GL^? Silver Dollar^Subvertical to steep north dipping en echelon sulphide^PY, QZ, SP, GL^? veins in dolostone Road Showing^Subvertical vein, strikes 130 degrees^ QZ, CA, PY, CL, BI^KSP, CA Chopin^Variable, but predominantly southwest dipping sericitic ^SER, QZ, CA, PY, SP^SER, PY, clays showings e^shear zones with quartz-calcite lenses; sulphides disseminated Cottonwooda^Southwest dipping quartz sulphide veins and stringers^QZ, PY, SP, GL, ASPY^CL Bronson skarn^Diopside-garnet skarn with south dipping sulphide- ^CA, EP, CL, PY, MAG, MO^DI, GN, CA, carbonate shear veins. Retrograde quartz-calcite-epidote-^ QZ, EP, CL, molybdenite veinlets^ TR Monsoon Lake^Southwest dipping shear veins^ north  CA, CL, BI, QZ, PY, CPY ^BI  11 Oz a  Southwest dipping sulphide vein^  PY^  Copper Queen a  North dipping shear zones^  QZ, SER, CL, PO, PY, SP^QZ, SER, CL  oPa  Southwest and northeast dipping veins and altered shear^PY, CPY, SP, GL, QZ, SER^QZ, SER zones  Stairway Creek a  Subvertical to northeast dipping shear zone hosted^QZ, PY^ sulphide vein striking 120 degrees  QZ, SER  QZ, SER  30  Table 23 (continued)  Ladder Creeka^North dipping shear zone hosted breccia vein ^QZ, PY Evermore ^  Northeast dipping to vertical shear zone ^PY, SP, GL, QZ, SER  SER, QZ SER, QZ, PY, Fe-carbonate  Blackcata^Shallow northeast dipping sulphide vein^PO, SP, GL, CPY Windsock (Zinc^Steep north dipping veins and pervasive pyrite trench)a^disseminations in greywacke  ^  PY, PO, SP  SER, PY, QZ  Two Barrela^Pervasive sulphide disseminations and veins in greywacke PY, SP Two Bita  Vertical sulphide veins and pervasive disseminations striking 110  PO, PY, SP, GL  Stonehoused  Steep north dipping quartz-sulphide dilatant veins  QZ, PY, CL, CA, CPY^KSP, BI, CL  Boundarya  Subvertical northwest striking sulphide vein  PY, QZ, SP, GL^KSP  0.S.C.a  Subvertical north striking breccia vein  QZ, PY, CPY^KSP  CE Contacta  Abundant southwest dipping sulphide veins  PO, SP, CA^SER, PY  C-3  Moderate northeast dipping shear zone with pervasive sulphide dissemination  QZ, KSP,SER, CL, CA, PY, PO, KSP, SER, CA, SP, CPY, Fe-carbonate^QZ, Fecarbonate  Silvertipa  Moderate northeast dipping sulphide vein^PO, QZ, SP, GL  Bernie  Lensoidal northeast dipping quartz extension veins that ^QZ, PY, SP, GL, SER, BI obliquely cut regional foliation, disseminated sulphides also occur  C-1  Northeast dipping quartz >calcite veins containing^QZ, CA, PY, GL disseminated sulphides  SER, QZ, PY  'Information sources: a Unpublished Skyline data; bAtkinson, 1990, cPegg and Travis, 1991; dYeager and Metcalfe, 1990. 2Abbreviations: QZ=quartz; CA=calcite; SER=sericite; BI=biotite; CL=chlorite; KSP=K-feldspar; DI=diopside; GA=garnet; EP=epidote; PY =pyrite; PO=pyrrhotite; MAG=magnetite; SP=sphalerite; GL=galena; CPY=chalcopyrite; MO=molybdenite; ASPY =arsenopyrite.  31 Table 2.4: Metal content and metal ratios of some mineralised structures, Johnny Mountain, northwestern B.C. Showings and deposits are located in Figure 2.3. Calculated from unpublished exploration data to 1993. Showing or  Ni  deposit name  Au ppm Ag ppm Cu ppm Pb ppm Zn ppm (Au x 100)/Cu  Zn/Cu  Ag/Au  (Ag x 10)/ Cu  836 ddh  61.5  23.1  1028  605  2719  5.98  2.64  0.38  0.23  Bonanza  17 ddh  0.4  26.1  600  7900  38500  0.06  64.2  65.25  0.43  SMC  60 ddh  3.7  22.5  1319  3893  33650  0.28  25.51  6.08  0.17  Cottonwood  12 ddh  0.84  25.5  324  1947  5890  0.25  18.18  30.36  0.79  Stonehouse2  production data  14.04  22.03  4700  N/A  N/A  0.29  N/A  1.6  0.47  CE Contact  18 ddh, tr  0.65  36.7  575  2710  57538  0.11  100.1  56.5  0.63  Twin zone  1 N=number of analyses; abbreviations refer to data source for analyses: ddh=diamond drilling, tr=trenching. 2 D. Yeager, personal communication, 1993. N/A = not available.  Table 2.5: Summary of the distribution of mineralised structures on Johnny Mountain and Snippaker Ridge, summarised from Tables 2.3 and 2.4 and from Figure 2.3. Location  ^  Examples  ^  Predominant^Predominant vein alteration^mineralogy mineralogy  ^  Zn/Cu Ag/Au  <5^<2  North, west and southwest of the Red Bluff porphyry, over a 8 km 2 area  Twin zone, minor shear veins throughout the Snip workings, Monsoon North veins, Road showing, Sky Creek veins, Bronson Skarn shear veins 1  Biotite-Kfeldspar +chlorite  Laminated calcite + biotitechlorite-quartz or massive pyrite + quartz + pyrrhotite veins and shear veins  East, south and southeast of the Red Bluff, and south and west of the zone described above  SMC - Tillerman, C-3, Evermore, Bonanza, CE veins; Blue Grouse, Silver Dollar, Cottonwood, Blackcat, Windsock, Silvertip, Chopin showings  Sericite-quartzFe-carbonatepyrite + chlorite  Massive pyrite+sphalerite +^> 15^> 5 quartz + calcite + chlorite veins, and pervasive pyrite + sphalerite dissemination in sericitic shear zones  • IA/ems of the Stonehouse deposit would also fit into this category based on alteration and metal ratios (see text).  ^  32 ^X^I^/ -\, 1^- -^/ --  _ -/‘ /^  I^I 1, • BRONSON SKARN  / •^' MONSOON NORTH I - 4  \ \ \ \ \ \  \  \ \ \ \ \ \ \^\ \ \ \ \ \^\ \ \  SKYLINE  _  SIOtIEHCUSE COLD  N \ C-1  `1^N  ^1  LEGEND  BURNIE PROSP CT \ 1.3 KM^LT  SERICITE-PYRITE ALTERATION, RUSTY WEATHERING  RED BLUFF PORPHYRY  ZONE CONTAINING Au-Cu MINERALIZED STRUCTURES WITH BIOTITE ±K-FELDSPAR  /  / ^/  BRONSON STOCK  ±CHLORITE ALTERATION LOWER SEQUENCE (TRIASSIC)  ZONE CONTAINING Zn-Pb MINERALIZED STRUCTURES WITH SERICITE ± CHLORITE ALTERATION • CE  UPPER SEQUENCE (EARLY JURASSIC)  SHOWING OR DEPOSIT NAME MINERALIZED VEIN, SHEAR VEIN OR SHEAR ZONE  %.•••• %.■•••  FAULT ROAD  0  2 Kilometres  CREEK  Figure 2.3: Showings and deposits in the northwestern Johnny Mountain area, northwestern British Columbia. See Figure 1.2 for location.  33  Galena Pb-Pb isotope data from veins on Johnny Mountain  Pb-isotope ratios from mineral deposits and showings in the Stewart-Iskut River area plot in two distinctive clusters (Figure 2.4; Alldrick et al., 1987; Godwin et al., 1991). The clusters define two distinct, short lived but regionally extensive metallogenic events, defined as Tertiary and Early Jurassic by Alldrick (1991) based on stratigraphic information, and K-Ar and U-Pb zircon dates of related alteration and intrusions.  Samples from 15 different showings and deposits on northwestern Johnny Mountain and three deposits within 10 kilometres southeast of Johnny Mountain (Inel, Khyber Pass and Sericite Ridge) have been analysed (Table 2.6; Godwin et al., 1991; A. Pickering, personal communication, 1992). These consistently plot in either the Jurassic or the Tertiary clusters. Early Jurassic data were obtained from southwest and northeast dipping sulphide rich shear zone hosted veins and shear veins on Johnny Mountain associated with potassic alteration, as described in Table 2.3. These include the Twin zone, several veins associated with the Stonehouse deposit, SMC, Silver Dollar, Blue Grouse, CE zone, Bonanza, Boundary, C-3 and Two Barrel. Samples from veins within broad alteration zones defining the Inel, Khyber Pass and Sericite Ridge deposits returned similar ratios (Table 2.6). Samples which plot in the Tertiary Pb-isotopic cluster from Johnny Mountain come from southeast and northeast dipping lensoidal blocky to fibrous quartz-calcite ± chlorite extension veins with disseminated galena, sphalerite and pyrite (Table 2.6). The veins have no associated alteration. They are discontinuous (the largest at C-1 are 5-10 metres long), and they cut foliation associated with shear zones and veins with Jurassic Pb-Pb signatures. Samples were from the Bernie and C-1 showings, and extension veins within the Knob Hill stock and Stonehouse mine workings (Johnny Mountain). All are from the southwestern area of Figure 2.3. One sample from a vein at Khyber Pass also returned a Tertiary Pb-Pb signature, but no information is recorded about the setting of the vein or its characteristics in The University of British Columbia LEADTABLE database.  34  Extension veins with Tertiary Pb-Pb signatures cut veins of the Stonehouse veins, with Early Jurassic galena Pb-Pb isotope signatures, corroborating the potential age relationship. The lack of spread between the two clusters, close spatial relationship of some deposits with contrasting Pb signatures--as at Stonehouse (above) and Big Missouri in the Stewart camp (Alldrick, 1991)--and different structural and mineralogic characteristics of each type suggest that only two discrete mineralising events occurred in the area.  Bronson Skarn  A small pyroxene-garnet skarn (80 by 60 metre exposure) occurs at the southwestern end of the pod of recrystallised limestone north of the Snip camp adjacent to its contact with foliated biotitic Bronson stock (Figure 2.2). Irregular veins and bodies of epidote-quartz-calcite ± actinolite ± chrysotile with molybdenite cut massive green pyroxene + brown garnet and appear to be a retrograde feature. Several 10 to 30 centimetre wide moderately south dipping pyrite + calcite + chlorite > biotite + magnetite + actinolite + epidote shear veins occur in coarse grained marble at the north end of the skarn Coarse actinolite and subordinate epidote commonly overgrow foliated chlorite in the shear veins and contain foliation parallel pyrite inclusion trails. This suggests that the shear veins and associated foliation formed before the termination of skarn metasomatism.  Orthoclase megacrystic felsite dykes intrude the Bronson stock within 100 metres of the skam (Figure 2.2; Plate 2.2C). A laminated calcite-chlorite-biotite-epidote-pyrite shear vein similar to those in the skarn occurs along the contact of one of the dykes and has a 0.5-4 centimetres wide epidote with subordinate calcite alteration envelope within the dyke (Plate 2.2C). This suggests that the dykes were emplaced before the formation of the shear vein. Since the similar shear veins in the skarn predate the termination of metasomatism, it is inferred that the dykes also predate epidote + actinolite formation in the skarn.  35  Table 2.6: Galena lead isotope analyses for the Johnny Mountain area, northwestern B.C. Sample numbers refer to the listing in the University of British Columbia LEADTABLE file (Godwin et al., 1988). Data is from Godwin et al., 1991, and A. Pickering, personal communication 1992. T.Z. = Twin zone.  Pb/ ° Pb  Pb^Lat.^Long. Pb^2°6Pb^north^west  Lab^Showing or deposit ^Pb^Pb number ^2 °4 Pb^2°4Pb Shooing6' and deposits with Junissie plena 30629-001 Sericite Ridge (Tami) 15.610 18.857 Two Barrel 30813-001 15.595 18.837 Two Barrel 30813-002 18.860 15.614 30814-001 Stonehouse 18.848 15.605 Stonehouse 30814-001 18.855 15.611 30814-003 Stonehouse (Gold Rush vein) 18.842 15.591 30814-005 Stonehouse (16 vein) 18.853 15.603 30891-002 Khyber pass 18.842 15.611 Khyber pass 30891-002 18.846 15.611 30891-002 Khyber pass 18.862 15.630 30989-001 Stonehouse (south veins) 18.838 15.588 31002-001 Snip, T.Z., discovery showing 18.847 15.606 31002-002 Snip. T.Z.. UG-505, 45m 18.809 15.598 31002-003 Snip, T.Z., UG-505. 53m 18.865 15.611 31002-004A Snip, T.Z., 3852 u/cut 18.835 15.592 31002-004B Snip, T.Z.. 3852 u/cut 18.840 15.598 31002-005 Snip, T.Z., 2640 raise 18.831 15.584 31002-006 Snip, 150 vein, 400 level 18.842 15.592 31002-007 Snip, shear vein 300 level 18.865 15.606 31002-008 Snip, T.Z. FW vein. 3852 lift 1 18.813 15.606 31025-001 CE zone 18.819 15.624 31045-002 Bonanza 18.808 15.601 Bonanza 31045-004 18.808 15.604 31048-001 C-3 18.867 15.614 31049-001 Boundary 18.827 15.588 31053-001 P-13 18.859 15.617 31054-001 Inel. AK drift 18.876 15.606 31054-002 Inel, Discovery drift 18.837 15.627 31099-001 SMC 18.853 15.602 31100-001 Silver Dollar 18.832 15.604 31103-001 Blue Grouse 18.816 15.605  38.456 38.399 38.465 38.427 38.450 38.403 38.430 38.448 38.47 38.526 38.370 38.429 38.393 38.450 38.382 38.404 38.355 38.387 38.431 38.415 38.465 38.406 38.410 38.459 38.372 38.466 38.443 38.486 38.429 38.425 38.414  0.82781 0.82788 0.82788 0.82797 0.82796 0.82746 0.82762 0.82854 0.82835 0.82620 0.82747 0.82802 0.82931 0.82752 0.82784 0.82792 0.82755 0.82755 0.82727 0.82956 0.83021 0.82951 0.82965 0.82759 0.82799 0.82811 0.82676 0.82962 0.82760 0.82858 0.82937  2.0394 2.0384 2.0395 2.0388 2.0393 2.0381 2.0385 2.0406 2.0413 2.0425 2.0368 2.0390 2.0412 2.0382 2.0378 2.0384 2.0368 2.0374 2.0372 2.0420 2.0439 2.0420 2.0422 2.0385 2.0382 2.0397 2.0366 2.0432 2.0384 2.0404 2.0145  56.58 56.62 56.62 56.62 56.62 56.62 56.62 56.60 56.60 56.60 56.63 56.67 56.67 56.67 56.67 56.67 56.67 56.67 56.67 56.67 56.63 56.65 56.65 56.66 56.66 56.62 56.61 56.61 56.77 56.65 56.65  130.88 131.07 131.07 131.07 131.07 131.07 131.07 130.97 130.97 130.97 131.07 131.10 131.10 131.10 131.10 131.10 131.10 131.10 131.10 131.10 131.07 131.06 131.06 131.08 131.09 131.06 130.84 130.84 130.98 131.06 131.05  Showings and deposits with lerliaiy zalena 30814-002 Stonehouse (extension vein) 30814-002 Stonehouse (extension vein) 30891-001 Khyber pass 30991-001 C-1 30991-002 C-1 31046-001 Bernie 31046-002 Bernie 31046-003 Bernie 31106-001 Knob Hill. extension veins 31106-001 Knob Hill. extension veins  38.562 38.586 38.585 38.634 38.646 38.591 38.575 38.593 38.604 38.618  0.81952 0.81956 0.81610 0.81466 0.81456 0.81930 0.81898 0.81916 0.81332 0.81316  2.C238 2.0239 2.0166 2.0147 2.0142 2.C234 2.0225 2.0235 2.0114 2.0110  56.62 56.62 56.60 56.62 56.62 56.60 56.60 56.60 56.63 56.63  131.07 131.07 130.97 131.08 131.08 131.08 131.08 131.08 131.08 131.08  2 4  -  19.054 19.065 19.134 19.176 19.187 19.023 19.073 19.073 19.193 19.203  15.615 15.625 15.615 15.622 15.629 15.626 15.620 15.624 15.610 15.615  36  206Pb/204Pb 18.5^18.7^10.9^19.1^19.3^19.5 39.0 a  38.8  38.6  38.4  38.2  15.8  15.7 • 0 0 3  15.6  15.5 18.5  18.7  ^  18.9^19.1  ^  19.3  ^  19.5  206Pb/204Pb  Figure 2.4: Lead-lead isotope plots of galena from mineral deposits in the Stewart-Iskut River area from Godwin et al., 1991. The data plot in two clusters. Circles represent early Jurassic, gold-silver and base metal mineralization that is coeval with the Texas Creek plutonic suite. Triangles represent Tertiary, silver-lead-zinc + molybdenum deposits associated with Coast Plutonic Complex granitic intrusions. Dots represent analyses that cannot be assigned or are of poor quality. Mineralized veins of the Snip, Inel and Stonehouse deposits and data from extension veins on Johnny Mountain plot in the Early Jurassic cluster and Tertiary clusters, respectively (Table 2.6).  37  CHAPTER 3: GEOLOGY OF THE SNIP MINE  3.1 INTRODUCTION  The geology of the Snip mine was investigated through underground mapping and drill core logging. At surface, although the slopes are steep, outcrop generally is limited to creeks and is obscured elsewhere by colluvium and vegetation. The local Snip surface geology and workings are shown on Figure 2.2.  This chapter is organised into several sections that first describe lithologies and structures of the Snip workings, and then describe several aspects of the geology of the Twin zone. A discussion of the structural history of the mine and Twin zone geology follows. The Red Bluff porphyry, described in Chapter 4, is not addressed here.  3.2 MINE GEOLOGY  3.2.1 The greywacke sequence at Snip  Rocks exposed in the Snip mine workings comprise a stratigraphically intermediate position in the clastic lower succession of Johnny Mountain (Figure 2.2). Between 700 and 850 metres of true thickness in the sequence has been intersected by the Snip underground workings and drilling, measured from west of the 130 portal adjacent to the Red Bluff porphyry to drilling in the south central end of 180 level (south of the 300 level portal on Figure 2.2). Bedding throughout the workings dips moderately to steeply north to northwest (Figures 2.2, 3.1, 3.3). Laminated graded beds of siltstone and greywacke are upright and face north. Dips in the mine workings range from 60 to 80 degrees north on 180 level to shallower dips of between 30 and 50 degrees on the 230 to 340 levels (Figures 3.1, 3.2, 3.3A, 3.3B). Bedding dips are variable but generally steeply north to northwest dipping above 340 level and on surface above the workings (Figure 3.3C).  EARLY JURASSIC: RED BLUFF PORPHYRY 'V •  Altered Foliated K—Feldspar Megacrystic Intrusive Abundant Quartz—MagnetiteHematite Veins  to...0001""'"  Biotite Spotted Unit  unffillr2151". Vein  TRIASSIC: LOWER SEQUENCE (STUHINI GROUP)  SW A  Massive Feldspathic Greywacke  Fault  Interbedded Greywacke and Siltstone  Bedding Trace  Massive Greywacke with Volcanic Clasts  NE A  NORTHING (metres)  '  500  - 400  - 300  200  +•  4.  •  •  4. /  Xi • + • *• ••;1 t;/ '' 1 ,  •  .4 +^/^/^/ 1 / / • / •••■ / f+ • 1;/;;4; ' ?'  f • .•  Figure 3.1: Schematic section from the Twin zone to the Red Bluff porphyry, Snip mine. Section,  viewed looking northeast, intersects the Twin zone on section 4550 metres east. The section is located on Figure 2.2.  N  100  39  Plate 3.1.  Clastic units, Snip mine, northwestern British Columbia. The coin is 2.4 centimetres in diameter. Sample location coordinates are listed in Appendix 1.  A: Graded medium-grained feldspathic greywacke (dark grey) and siltstone (pale grey). Grading and scour marks in this unit indicate that bedding faces to the north at Snip. Sample is DR-280, from 130 haulage level at station 292 + 75 metres SW. Sample location is shown on Figure 3.5. B: Coarse-grained lithic greywacke with framework grains of mudstone, siltstone and fine-grained porphyritic volcanic in a medium-grained feldspathic greywacke matrix. Note the green epidote alteration of the larger clasts in the lower core. Sample is from DDH UG-686: 49-50 metres. Scale is in centimetres. C: Subrounded plagioclase porphyritic andesite or basalt clast in a feldspathic greywacke matrix. Note the abundant disseminated pyrite in both the clast and the matrix (approximately 1-2%). The sample is from DDH UG-33: 74.7 metres. D: Right: Matrix supported volcanic conglomerate. Matrix is a medium- to coarsegrained feldspathic greywacke. Clasts are of biotised aphanitic to plagioclase porphyritic volcanic fragments. Left is massive medium-grained poorly sorted lithic greywacke with biotite (top) and pyrite + calcite (bottom) altered angular clasts. Biotite content, approximately 2%, is confined mainly to altered lithic grains. Right sample is from DDH UG-4: 96.95 metres, and left sample is from DDH UG-32: 112 metres.  'm1111;1111;11111, Lt^c!  41  Plate 3.2.  Photomicrographs of elastic units, Snip mine, northwestern British Columbia. Long field of view is 5 millimetres in all samples; nichols are crossed. Sample location coordinates are listed in Appendix 1. A: Fine-grained poorly sorted feldspathic greywacke with abundant interstitial disseminated biotite. Most of the framework grains are plagioclase (>60%) and quartz. Sample is DR-16, 130 haulage, station 275 + 63 metres southwest. Sample location is on Figure 3.5. B: Medium-grained feldspathic greywacke with abundant angular plagioclase grains, including the large grain at right centre. Biotite (brown) is both disseminated and fracture controlled. The sample is DR-248. Sample location is shown on Figure 3.5. C: Anastomosing spaced foliation in fine-grained greywacke defined by biotite. Foliation is subhorizontal. Sample is DR-141, collected on the main ramp at 300 level. D: Biotitic siltstone, with bedding cut by a shallow-dipping foliation (S) defined by trails of aligned biotite. Note both the pervasive and fracture controlled distribution of biotite. Sample is AJM-ISK90-290, 130 haulageway, which was collected near sample DR-280 (Plate 3.1D). Sample location is on Figure 3.5. Sample was collected by James Macdonald.  42  43  The rocks consist primarily of grey weathering massive fine to medium grained poorly sorted feldspathic to lithic greywacke (Plates 3.2A, 3.2B). Laminated and graded beds of siltstone and mudstone comprises between 3 and 15% of the sequence (Plates 3.1A, 3.2D). Massive coarse grained greywacke comprising 5-10% (Plate 3.1B) and less abundant matrix supported volcanic conglomerate (1-2%; Plate 3.1D) also occur throughout. Greywacke framework grains consist of, in decreasing order of abundance, plagioclase (mainly albitic), quartz, K-feldspar, siltstone/mudstone and volcanic rock fragments. The coarser grained greywackes and the lithic greywackes often contain 0.5-10 centimetre wide subrounded plagioclase ± biotised mafic minerals ± K-feldspar porphyritic intermediate to mafic volcanic clasts, and clasts of tan coloured siltstone or dark grey mudstone (Plates 3.1C, 3.1D). Clasts constitute generally less than 10% by volume. Graded bedding, lack of any other sedimentary structures, clast type and angularity, poor sorting and abundance of sandstone suggest that these rocks formed as turbidites proximal to a volcanic source. Abundant subhedral and angular plagioclase framework grains in some units suggest that there may be waterlain or reworked crystal tuffs in the sequence (Plate 3.2B).  A true stratigraphic thickness of 400 metres was examined through logging of 28 drill holes on Snip cross-section 4550. An attempt was made to construct a stratigraphic section for the clastic sequence at Snip (Figure 3.2). This section was chosen because it is relatively unfaulted, and contains drill hole S-72, which provides an excellent cross-section of stratigraphy. The information was obtained mainly from the footwall of the Twin zone adjacent to the orebody, where most of the underground development and drilling has been completed. Four stratigraphic divisions, recognised in this section (Figures 3.1, 3.2; Table 3.1), are described in the following:  Unit 1: The stratigraphically lowest part of the section consists of volcanic clast rich medium grained greywacke containing 1-5% clasts in a massive medium grained greywacke matrix. This lithology is interbedded with laminated graded siltstone and mudstone, and massive fine to medium grained clast free greywacke. Unit 1 has a minimum thickness of 80 metres and extends off the section to the south.  Figure 3.3: Equal area projections (lower hemisphere) of poles to bedding in the Snip mine area, northwestern B.C. A: All measurements, both underground and on surface. Bedding dips primarily north, but a range to northwest, northeast and southwest dips is also present. The poles roughly plot on a single plane (dashed line) which may indicate folding about a northwesterly-plunging axis at point 1. B: Poles to bedding measured underground in the foot wall of the Twin zone on 180-230 levels (+) and 230 to 340 levels (•. Bedding dip angle shallows from 180 to 340 level. C: Poles to bedding (o) measured on surface above 340 metres level in the immediate hanging wall of the Twin zone. Note that dips are generally steep.  45  /  , X , ‘ / ---^----^/^\ \ BRONSON STOCK \ ^V 1 X 1 /^/ \ N^  Figure 3.5: Map of the Snip mine area extracted from Figure 2.2. The location of the Figures 3.1, 3.4, 4.1 and the Snip mine grid are shown. The mine grid is in metres. See Figure 2.2 for a legend of map symbols.  46  Unit 2: Overlying Unit 1, Unit 2 consists of 60-80 metres of massive fine to medium grained greywacke. Unit 3: A mixed package (80 metres thick) of massive fine to medium grained greywacke interbedded with laminated graded siltstone/mudstone beds and 5-10 metre thick beds of massive coarse grained granular greywacke occurs above Unit 2. Unit 4: Stratigraphically the highest, is a thick package of massive fine to medium grained greywacke with subordinate coarse grained greywacke. This package is at least 200 metres thick, and it extends above and north of the section. Most individual beds within the packages are laterally discontinuous, even between closely spaced drill holes, and many are probably lensoid in shape. Nevertheless, the overall proportion of different rock types and thicknesses of units is relatively consistent.  Mapping in the 130 haulage level (Figure 3.4) north of the section crosses a package of massive fine to medium grained greywacke with only minor (<30 metres true thickness) siltstone and mudstone over its entire length (a total of approximately 600 metres of stratigraphy). However, this section is not directly correlative with the 4550 section because it is separated from it by a 3-12 metre wide gouge filled fault zone (Figure 3.4). The fault and its probable direction and magnitude of offset are further described in section 3.24. Drilling on cross-sections 4725 and 4800 to the northeast encountered a similar sequence to that observed in the 130 level, but these sections also are separated laterally from the 4550 section by a series of faults that offset the eastern portion of the Snip orebody.  A study completed by Read (1990) defined stratigraphy in the hanging wall and the footwall of the Twin zone between the 180 and 300 metre levels on 9 sections from 4400 to 4500 metres east. Read recorded a 50-90 metre thick package of interbedded fine to coarse grained greywacke, siltstone, mudstone. He divided this into three units based on bedded and massive portions of the package (units B-5, U-6 and B6 in Read, 1990). When plotted on mine plans, this package is the lateral equivalent of unit 3. Comparison of the sections indicates that individual siltstone/mudstone units within the package are seldom traceable for more than 25 to 40 metres laterally (over 2 to 3 sections), but the package maintains  47  its overall mixed lithologic character throughout the sections that were examined. Unit 3 is offset by the Twin zone in all of Read's sections and on Figure 3.2. It may play an important role in the geometry of the Twin zone, a relationship described further in section 3.51.  Table 3.1: Stratigraphic units and associated alteration in the Snip mine workings, northwestern British Columbia. Stratigraphic units are listed from lowest (unit 1) to highest (unit 4). Refer to Figures 3.1 and 3.3 for cross-sections.  Stratigraphic Description unit  ^  Thickness Alteration  Unit 1  Fine to medium grained feldspathic^>80 greywacke with volcanic clasts ^metres interbedded with laminated graded siltstone and mudstone and coarse grained greywacke  Unit 2  Massive fine to medium grained feldspathic greywacke  60-80^Disseminated to veinlet controlled biotite metres^+ pyrite + calcite + chlorite  Unit 3  Massive fine to medium grained feldspathic greywacke interbedded with graded laminated siltstone and mudstone and subordinate coarse grained greywacke  80 metres  Unit 4^Massive fine to coarse grained feldspathic greywacke  Disseminated, veinlet controlled and patchy biotite + pyrite ± epidote + calcite ± amphibole; volcanic clasts are commonly altered to epidote + calcite + biotite + pyrite  ^  Disseminated to veinlet controlled biotite + pyrite + calcite + chlorite; finer grained beds have predominantly veinlet controlled alteration while disseminated alteration is common in coarser beds  ^ >200 Disseminated to veinlet controlled biotite ^ metres + pyrite + calcite + chlorite; zones of pale grey textureless greywacke may be altered to K-feldspar + quartz + albite + sericite + calcite  Alteration and metamorphism  The style and distribution of alteration is described below and summarised in Table 3.1. It is most obvious as abundant disseminated and fracture controlled brown to black biotite that occurs throughout the elastic sequence at Snip. Biotite commonly comprises 3-15%, and in restricted areas 20-40%, of the rock by volume (Plate 3.2). The biotite imparts a brown purple colour to samples. Rough broken surfaces appear to have a higher than actual biotite content because the breaks usually occur along biotitic fractures.  48  Plate 3.3.  Greywacke alteration, Snip mine, northwestern British Columbia. The coin is 2.4 centimetres in diameter. Sample location coordinates are listed in Appendix 1.  A: Top: Fine-grained greywacke with abundant biotite + pyrite veinlets. Bottom: Fine-grained greywacke with biotite veinlets subparallel to the core axis. The veinlets join biotite > pyrite patches. Calcite veinlets are oblique to (some join) the biotite veinlets. Top is from DDH UG-641: 45.5 metres, and bottom DDH UG-652: 116.2 metres. The scale is in centimetres. B: Brown to black biotite veinlets cutting fine-grained carbonate ± silica-K-feldspar altered greywacke and siltstone. Veinlets in the bottom core have pyritic centres. Note the abundant calcite veinlets that form a high angle with the biotite and biotitepyrite veinlets. The calcite stringers are developed only in areas of calcite alteration and low biotite content; they are cut by the biotite veinlets. Top is from DDH UG33: 17.6 metres; bottom is from DDH UG-315: 11.9 metres. C: Veinlets in fine- to medium-grained greywacke. Top: Epidote-calcite veinlets with biotite envelopes in medium-grained biotitic greywacke. Sample is from 340 level ore pass. Bottom: Pyrite veinlet with an inner biotite envelope and outer bleached carbonate ± quartz envelope. Sample is from UG-655: 21.2 metres. D: Pyrite-calcite-chlorite veinlets with wide biotite envelopes (black) in fine-grained carbonate and K-feldspar altered fine-grained greywacke (pale brown to pink). Note the localisation of calcite stringers in the carbonate-K-feldspar altered greywacke. Top is from DDH UG-659: 24.4 metres; bottom is from DDH S-68: 116.8 metres.  50  Plate 3.4.  Greywacke alteration, Snip mine, northwestern British Columbia. The coin is 2.4 centimetres in diameter. Sample location coordinates are listed in Appendix 1. A: Biotite patches and veinlets in fine-grained greywacke containing calcite veinlets. Sample is from DDH UG-10: 13.4-13.6 metres. B: Strongly K-feldspar altered greywacke with veinlets of biotite (brown) + sericite (high birefringence) veinlets. Note the albite grains. Photomicrograph, crossed nichols. Field of view is 4 millimetres. Sample is DR-324, collected from an altered greywacke sliver within the 150 footwall vein, 385 level at the main ramp. The sample location is shown on Figure 3.13. C: Calcite-biotite-epidote altered feldspathic greywacke. Elongate to spherical patches of calcite + epidote ± pyrite occur both surrounding and adjacent to foliation parallel biotitic fractures (e.g. in left core below the coin) or disseminated with no apparent relation to fractures (right core). Internal fractures within the patches are perpendicular to foliation (centre). Pervasively disseminated biotite forms approximately 15% of the rock. Left is from DDH UG-656: 107.9 metres; centre is from DDH UG-656: 109.4 metres; and right is from DDH UG-656: 107.0 metres.  52  Biotite distribution, from disseminated to veinlet controlled, varies with the grain size of the rock. Veinlet controlled biotite is common in fine grained greywacke, siltstone and mudstone, and altered greywacke (Plates 3.3, 3.4B). The veinlets (0.3-5 millimetres wide) commonly have biotite + pyrite + chlorite + calcite cores and 0.2-2.5 centimetre wide bleached envelopes (Plates 3.3C, 3.3D). Alteration mineralogy associated with the bleaching is variable, but commonly includes: calcite, K-feldspar, quartz, and subordinate sericite and albite (Plate 3.4B). Calcite altered envelopes are often associated with closely spaced 1-3 millimetre wide calcite veinlets, which are formed usually at a high angle to the biotite veinlets (Plates 3.3B, 3.3D). Irregular 1-4 centimetre wide patches of brown biotite with lesser pyrite occur in some areas, closely bounded by fractures (Plate 3.4A).  Fine to coarse grained greywacke contains predominantly disseminated biotite that is often associated with disseminated pyrite + calcite ± epidote and rarer pyrrhotite + chalcopyrite. Microscopically, the biotite is interstitial to framework grains (Plates 3.2A, 3.2B), and often has a preferred orientation defining a weak to well developed foliation (Plate 3.2C). It occurs with pyrite and/or pale orange to yellow calcite in 0.5-2 millimetre wide irregular shaped blebs that interlock giving a microfractured appearance to the rock. The biotite also occurs in face controlled pressure shadows around pyrite with calcite and quartz. There is a complete continuum between both styles of biotite distribution; disseminated and veinlet controlled biotite mostly occur together (Plates 3.2B, 3.2D). Alteration may be locally intense, almost completely replacing the greywacke with calcite, biotite, sericite and pyrite. These intensely altered areas can be 10 to more than 25 metres wide, and have gradational boundaries into less altered wallrock; they generally have no apparent relation to veins.  In the lowest parts of the sequence at Snip, particularly in greywackes containing abundant volcanic clasts within unit 1, disseminated and veinlet controlled biotite with subordinate epidote is locally abundant and comprises 15% or greater of the rock volume (Table 3.1). Calcic clinoamphibole is also common in some samples, and sphene was identified by Nichols (1989). In thin section, pale brown Kfeldspar replaces plagioclase framework grains in strongly biotite altered samples. Volcanic clasts are  53  often partially to wholly altered progressively from fine grained felted biotite to calcite + epidote + pyrite + chlorite + sericite (Plate 3.1D). Calcite-epidote and/or pyrite altered clasts are commonly rimmed by biotite envelopes. In these units, epidote + chlorite + calcite + pyrite may also be veinlet controlled with biotite envelopes (Plate 3.4C). Siltstone and mudstone clasts alter to K-feldspar, biotite, or calcite + pyrite. Spots of calcite ± epidote ± pyrite + biotite alteration that resemble clasts are also common in some units (Plate 3.4C, at right).  Wide intersections of massive, pale grey, fine grained rock resembling siltstone often occur in drill core, commonly with >30 metres true thickness. However, this lithology is seldom traceable between even closely spaced drill holes, unlike the unit 3 package described above. The massive grey texture is interpreted to be an alteration feature that obliterates greywacke clastic textures. In some cases, this style of alteration can be attributed to overlapping alteration envelopes around biotite veinlets, but elsewhere rock of this texture has no apparent relationship to vein density. Staining with sodium cobaltinitrate indicates that pervasive K-feldspar, usually with veinlet controlled biotite, comprises a significant portion of the rock in many areas. However, other visually identical samples contain no K-feldspar. Petrographic work suggests that these latter samples are altered with quartz, calcite, sericite and albite; although individual minerals are difficult to identify due to the microcrystalline nature of much of this rock. Like the biotite veinlet envelopes above, pervasive calcite altered samples usually have calcite veinlets, which are developed at a high angle to biotite veinlets where present. Strongly pervasively K-feldspar altered samples usually have a waxy lustre and a tan to pale brown colour.  The abundance of biotite, K-feldspar and sericite, and their association with pyrite, are unlikely to reflect thermal metamorphism of a potassium rich greywacke. The mineralogy is more compatible with potassium introduction during hydrothermal alteration.  54  3.2.2 Dykes  Plagioclase porphyritic dyke  A plagioclase porphyry dyke is intersected by several holes drilled in the footwall of the Twin zone (Nichols, 1989; B. Coates, personal communication, 1993). It is not exposed on surface or in the underground workings. The dyke is a variably altered fine to medium grained massive plagioclase + quartz porphyritic rock. Plagioclase and subordinate quartz phenocrysts, comprising 2-10% of the rock, are typically set in a pale green sericite + quartz + pyrite ± K-feldspar altered fine grained matrix with plagioclase phenocrysts (10-30%) and fine grained matrix. Mafic minerals (1-5%) are altered to pyrite + biotite. The rock is cut by biotite + calcite + pyrite veinlets, some of which have bleached envelopes.  Biotite spotted unit (BSU)  A southwest dipping unmineralised basic biotitic dyke, termed the "Biotite Spotted Unit" (BSU; Nichols, 1989), intrudes the Twin zone, and commonly obliquely cuts veins in the zone (Figures 3.7, 3.11, 3.14). The dyke is invariably moderately to strongly altered to the assemblage biotite + calcite + pyrite ± quartz ± sericite + chlorite. Biotite content typically ranges from 5 to 20% as disseminations, veinlets and irregular fracture fillings with pyrite and calcite. Mafic minerals, altered to felted black biotite ± pyrite spots 0.5 to 4 millimetres long, typically comprise 5 to 15 volume percent in a fine grained matrix of intergrown plagioclase with biotite and subordinate sericite. The least altered samples of the dyke consist of an equigranular intergrowth of albitic plagioclase (approximately An,„; grain size is typically 0.05-0.3 millimetres long; Plate 3.5B). A pervasive phyllitic to schistose foliation defined by the parallel preferred orientation of biotite parallels the dyke contacts (Figure 3.6A; Plates 3.5C, 3.6C). Elongation of the biotite spots plunges west (Figure 3.6B, Plate 3.5C). In several stopes, primarily 3860 and 4061 (Plate 3.6C), the margins of the biotite altered dyke are gradational with adjacent schistose biotitic Twin zone. Elsewhere, however, contacts are pristine and intrusive, sometimes  55  Plate 3.5.  Biotite Spotted Unit and other dykes, Snip mine, northwestern British Columbia. The coin is 2.4 centimetres in diameter. Sample location coordinates are listed in Appendix 1.  A: Biotite lamprophyre, 300 level east. Euhedral biotite and clinopyroxene phenocrysts are in a fine-grained plagioclase + devitified glassy matrix. Sample is DR-264. Crossed nichols. Field of view is 5 millimetres. B: Photomicrograph of the Biotite Spotted Unit (BSU). Tightly intergrown plagioclase grains comprise approximately 80% of the photograph. The remainder is biotite (brown) and opaques (pyrite). Sample is DR-245, from 4055 stope undercut. Sample location is shown on Figure 3.11. Crossed nichols. Feld of view is 5 millimetres. C: Phyllitically foliated BSU dyke. Biotite spots in a fine-grained biotitic matrix define a lineation which plunges down dip with a westerly rake in the Twin zone. Sample is DR-217 from 300 level west.  cm c\  57  Plate 3.6.  Biotite Spotted Unit (BSU), Snip mine, northwestern British Columbia. The coin is 2.4 centimetres in diameter. Sample location coordinates are listed in Appendix 1.  A: Left: Foliation defined by black biotite spots in the dyke is obliquely cut by laminated calcite > > chlorite veins. Right: Calcite veinlets, some with biotite envelopes, are subparallel to foliation. Left sample is from DDH UG-369, 49.9 metres; right is from DDH UG-462: 28.9 metres. B: Biotite spotted mafic dyke from the Red Bluff porphyry west of the 130 portal. Sample is DR-97. Sample location is marked on Figure 3.5. C: Foliated BSU. Top left of photo is the calcite-quartz-chlorite hanging wall vein of the Twin zone. The dyke is strongly foliated and deformed within 30 centimetres of the Twin zone hanging wall vein (note the disaggregated quartz and calcite veinlets). Below this, the dyke is blocky and less deformed; quartz + calcite veinlets are continuous. 3860 stope lift 5, looking west-northwest. Photo location is shown on Figure 3.13. Field of view is 1.5 metres. D: BSU-greywacke intrusive contact. The BSU is at the left and greywacke at the right in both photographs. Top: The BSU has a narrow pale tan coloured finegrained chilled margin. Note the small size of the biotite spots at the contact with respect to the rest of the dyke. Biotite-pyrite veinlets are common in the greywacke at the right, and some extend into the dyke. Bottom: An unusual tan coloured intersection of the BSU, which may be a result of near surface weathering. Banding in the dyke occurs adjacent to the contact, and is possibly flow banding or chilling. Calcite veinlets (here acid etched) cross the contact. Top sample is from DDH UG188: 53.5 metres; bottom sample is from DDH S-42: 5.0 metres.  58  59  with bleached and flow banded, tan coloured chilled margins (Plate 3.6D). Foliation parallel calcite veinlets with minor chlorite are commonly occur in the dyke where foliation is strongly developed (Plate 3.6A, 3.6C). Southeast dipping extension veins cut the dyke and its associated foliation (Figure 3.61). The BSU is texturally and mineralogically similar to biotite spotted dykes within the Red Bluff porphyry (Plate 3.6B; also see Chapter 4). The BSU is distinct from the biotite lamprophyre dykes, described below, because the latter lack foliation or alteration and have euhedral biotite and pyroxene phenocrysts.  Table 3.2: Dykes in the Snip mine workings. Dyke^Location/orientation  ^  Phenocrysts^Matrix^Alteration  Lamprophyres East end of the Twin zone and in the 130 level; steep northwest dipping; often intrude faults  Euhedral biotite (20%) and pyroxene (10%)  Fine grained pyroxene, plagioclase and opaques in a devitrified glassy matrix  None  Biotite Spotted Intrudes the Twin zone; Unit (BSU)^Southwest dipping  Mafic phenocrysts (210%) now altered to a fine grained biotite  Equigranular fine grained plagioclase  Abundant veinlet and disseminated biotite with pyrite, calcite, sericite and chlorite  ^ ^ ^ Plagioclase Intrudes greywackes in the Plagioclase + quartz Aphanitic, altered Pervasive sericite + ^ porphyritic footwall of the Twin zone; (2-10%) and pyrite + ^ quartz + pyrite + K^ ^ dyke^orientation is not known biotite altered mafic feldspar and veinlets of ^ minerals (1-5%) biotite + calcite + pyrite  Lamprophyres  Several steeply northwest dipping, 020 to 050 striking, 10-80 centimetre wide biotite lamprophyre dykes occur at the east end of the 300 metres level between sections 950 and 1000 metres, and at the surface directly above. The dykes are fresh and unaltered, and they cut shear veins (see section 3.2.4). They contain phenocrysts of euhedral dark brown biotite (20%), up to 2 millimetres long and 0.4 millimetres wide, and pyroxene (10%). The matrix to the phenocrysts contains fine grained plagioclase, pyroxene  60  and opaques in a devitrified glassy matrix (Plate 3.5A). The dykes are parallel to, and locally intrude gouge filled faults. Two lamprophyre dykes were identified in the 130 haulage level (Figure 3.5).  3.2.3 Geochronology  K-Ar dates  A biotite separate from a quartz vein within the Twin zone on 300 level west returned a K-Ar age of 51.9 ± 1.8 Ma (Table 2.1). The biotite is a dark green colour in thin section, atypical of other biotite in the Twin zone that is brown to red. It resembles the green biotite occurring in extension veins. Late extension veins commonly occur in quartz veins within the Twin zone (e.g. Plate 3.24C), so the sample could have contained at least some extension vein material. A second date from a biotite lamprophyre dyke on 300 level east returned a K-Ar whole rock date of 32.0 ± 1.1 Ma (Table 2.1). Coordinates of the K-Ar sample locations with respect to the Snip mine grid are listed in Appendix 1.  Both of these K-Ar dates correspond to thermal events in the Stewart area, 80-100 kilometres to the south, which are described by Alldrick (1991). The biotite age from the Twin zone quartz vein corresponds to the 55-45 Ma range of dates from the Coast Range intrusions of the Hyder plutonic suite. Hornblende and biotite K-Ar data from the Early Jurassic Texas Creek pluton are reset to between 62 and 45 Ma presumably because of this intrusive event. The Twin zone thus may also be reset by intrusions of the nearby Coast complex. The K-Ar whole rock date obtained from the biotite lamprophyre at Snip is typical of the 25-35 Ma range for biotite lamprophyre dykes in the Stewart area. This, coupled with its pristine condition, imply that the date represents the age of its intrusion and crystallisation.  61  U-Pb zircon data  The only U-Pb zircon date obtained from the Snip workings came from the Red Bluff porphyry (195 ± 1 Ma; Table 2.1; located on Figure 3.5). Approximately 20 kilogrammes of material from the BSU (sample DR-245; coordinates listed in Appendix 1) was crushed for U-Pb dating, but no datable minerals were found (J. Gabites, personal communication, 1993).  Galena Pb-Pb isotopic data  Five samples of galena from the Twin zone, one from the 150 vein and one from a shear vein on the main ramp at Snip have been analysed at the Geochronology Laboratory at The University of British Columbia (Table 2.6). All returned data that plot in the Jurassic clusters on Figure 2.4 (Godwin et al., 1991; A. Pickering, personal communication, 1992). No galena was obtained from extension veins in the Snip workings.  3.2.4 Structural features  Mesoscopic structural features in the Snip mine include shear veins, shallow dipping foliation, calcitechlorite-biotite veinlets, extension veins and brittle faults (Table 3.3). The spatial distribution of many of these structural features within the 130 haulage level is shown on Figure 3.5. A discussion of the relationships and relative timing of the structures follows in section 3.5.  Quartz stockwork (130 level south)  A stockwork of quartz veins and veinlets occurs at the south end of the 130 haulage level between 2100 and 2220 metres north (Figure 3.4). The veins are composed of sugary translucent quartz tinted pale green by disseminated sericite. Fine grained disseminated pyrite forms up to 1% of the vein volume.  62 Table 3.3: Common structures, listed from oldest to youngest, in the greywacke sequence at the Snip mine, northwestern British Columbia. Structure  Vein BD  Orientations  Associated fabrics  Dimensions/ Abundance  Quartz stockwork veins (130 haulage)  Granular quartz with fine grained sericite  Variable  None  Veins 0.5 to 10 cm^None wide are discontinuous and form closely spaced stockworks in the 130 haulage drift  Shear veins  Laminated calcite + chlorite + biotite + quartz + pyrite; also quartz and sulphide veins  Mainly moderate southwest dipping, but range to northwest dipping  Schistose internal foliation parallel or oblique to shear zone boundaries; subhorizontal external foliation  Typically 2-30 cm wide, and <20 m long; spaced 1-2 per 20 m. Twin zone and related veins are much larger  Biotite and/or bleached ± calcite + Kfeldspar + quartz ± sericite envelopes  Biotite-pyrite veinlets  Biotite ± pyrite > + chlorite + calcite  Variable  Biotite is parallel or oblique to veinlet walls  Usually <2 mm, but continuum with shear veins; may form dense networks  Bleached envelopes; similar mineralogy to shear veins  Calcitebiotitechloritepyrite veinlets  Calcite + biotite + chlorite + pyrite, often laminated  Variable, but most commonly shallow dipping  Alignment of micas parallel to vein walls; veins are often parallel to flat foliations adjacent to shear zones  1-5 mm wide, 2 to 15 cm long; widespread but only locally abundant, commonly spaced > 10/m  Some have thin biotite envelopes  Extension veins  Blocky to fibrous quartz + calcite + chlorite + epidote + Fe carbonate; biotite in some  Shallow to moderate southeast and northeast dipping; southeast dipping veins are youngest and most common  None  Abundant lenticular, 0.5-4 cm thick and 0.2 to 1.5 m long; form sigmoidal arrays  None usually, some epidotic veins have epidotic envelopes  Faults  Usually filled with clay gouge; many contain vuggy quartzcalcite-pyrite veins  Predominantly moderate to steep northwest and southwest dipping; widest faults dip northwest  None  Gouge filled zones 0.5 cm to >1 m wide; often remobilise shear zones.  Bleached envelopes up to 2 m wide  Alteration  Veins typically range from 0.5 to 6 centimetres wide and 0.6 to 3 metres long; larger veins are up to 35 centimetres wide. There is no associated foliation or alteration. The veins are commonly ribboned with slivers of greywacke. Orientations are variable but locally consistent (Figure 3.6F; Plate 3.8B). Shear veins, extension veins and faults cut the stockwork. The veins are commonly folded and offset about the spaced subhorizontal foliation. The upper plate commonly has offsets of <0.3 to 2.5 centimetres that are consistently to the southwest (Plate 3.8B). Four samples of the veins were analysed at the Cominco  63  Research Laboratory for 7 elements (Table 3.4). Metal values are low, except for Au which is higher than 0.1 ppm in two samples. Table 3.4: Analyses of stockwork vein samples from the southern end of the 130 haulage level. The samples were analysed at the Cominco Research Laboratory, Vancouver, B.C. Cu, Pb, Zn, Ag As and Mo were analysed by aqua regia digestion with an inductively coupled plasma finish. Gold was analysed by fire assay. Sample locations are shown on Figure 3.5 and coordinates listed in Appendix 1.  Sample #  Cu (ppm)  Pb (ppm)  Zn (ppm)  Ag (ppm)  Au (ppb)  As (ppm)  Mo (ppm)  DR-132 DR-134 DR-135 DR-001  93 273 40 90  6 5 <4 5  17 48 14 36  <0.4 0.8 <0.4 <0.4  98 430 180 <10  <2 14 13 11  <2 <2 3 2  Shear veins  The dominant structural feature within the greywacke sequence at the Snip mine is a series of gold bearing shear veins which include the Twin zone and its splays. They have variable thickness but usually range from 2 to 80 centimetres, excluding the Twin zone. The veins are abundant throughout the mine workings and are often closely spaced. For example, shear veins occur 7 to 15 metres apart on the 130 haulage level over a distance of nearly one kilometre (Figure 3.4). Moderately southwest dipping orientations predominate, but range to northwest and north dipping (Figure 3.6C). Branching veins with splays of different orientations indicate that this orientation range is not caused by folding of the veins (Plate 3.7C). Northwesterly dipping orientations are particularly common on 340 level (Figure 3.14). The shear veins, apart from the Twin zone and related veins, typically carry 0.2 to 5 ppm gold (Figure 3.4).  The veins are composed primarily of laminated calcite + chlorite + biotite ± pyrite (Plates 3.7C).  3.7A,  Sulphide and quartz veins are also common. Alteration envelopes are sporadically developed, and  often the transition from vein to wallrock is abrupt with no visible alteration envelope. Where developed, envelopes are like those of the biotite + pyrite veinlets throughout the greywacke sequence. They generally consist of a 0.5 to 2 centimetres wide felted black biotite envelope that is commonly internal to  64  a 0.5 to 10 centimetres wide outer bleached envelope of calcite ± K-feldspar ± quartz ± sericite. Biotite envelopes are particularly common around pyrite and chlorite veins (Plate 3.8A). Grey calcite completely replaces greywacke adjacent to some veins (Plate 3.7D).  Oblique internal and external foliations, down dip verging folds (Plate 3.7B), sheath folds, synthetic shear bands, asymmetric augen, rotated quartz and pyrite porphyroclasts, and oblique subhorizontal foliations (Plate 3.7D) are common to both the Twin zone and other shear veins in the Snip workings. They indicate an oblique normally directed shear sense parallel to a southwesterly plunging striation lineation developed on foliation surfaces (Figure 3.6D). A subhorizontal cleavage is locally present over a distance of <0.2 to several metres into the hanging wall and/or footwall of some of the shear zones. The foliation rotates to parallel the shear vein boundaries adjacent to them. Shear veins may be boudinaged, with boudin interstices filled locally by blocky calcite and quartz (Plate 3.10B).  The internal structure, geometry, mineralogy and alteration associated with the Twin zone are documented in detail in sections 3.3 and 3.4.  Foliation  A subhorizontal to shallow southwest dipping foliation is erratically developed in the clastic sequence at Snip; it is subparallel to the shallow foliation developed adjacent to shear veins (Figure 3.6E; Plates 3.2C, 3.2D, 3.7D). However, most of the sequence is massive on an outcrop scale. Foliation occurs in all rock types; siltstone and mudstone units are not preferentially foliated. The foliation is defined by: a preferred orientation of biotite ± sericite in blebs or pervasively in strongly altered greywacke, biotite, quartz and calcite pressure shadows around pyrite, and discrete closely spaced subparallel anastomozing biotitic foliation surfaces. Corroded quartz and plagioclase greywacke framework grains are truncated against the discrete foliation surfaces suggesting that it is a pressure solution fabric (Plate 3.2C). The foliation is best developed at the south end of the 130 haulage level, on portions of the 180 metres level,  65  at the base of the 150 vein on the main ramp at 300 metres level, and sporadically for up to 10 metres into the footwall of the Twin zone. Rocks with a high biotite ± calcite content are the most intensely foliated, and locally form biotite schists.  A moderate to steep north to northwest dipping foliation occurs in some locations in the 130 haulage level. In the siltstone package in the centre of the level it is developed as a spaced pressure solution cleavage defined by trails of opaque minerals. In fine to medium grained greywacke, a locally developed steep northwest dipping phyllitic foliation defined by alignment of sericite is crenulated by the shallow south dipping fabric. The north dipping foliation is cut by southwest dipping shear veins.  The shallow dipping and north dipping foliations observed at Snip probably correspond with the S2 and S1 foliations, respectively, that are observed elsewhere on Johnny Mountain (see section 2.13).  Calcite-chlorite-biotite-pyrite veinlets (calcite veinlets)  These veinlets are abundant throughout the mine workings. They are composed of granular calcite with laminae and blebs of chlorite + biotite + pyrite (Plate 3.8C). The veinlets are discontinuous, and are typically 2 to 15 centimetres long and 1-5 millimetres wide. They have locally consistent orientations, often 2 or 3 at any one location, but overall their orientation is variable. However, orientations cluster around horizontal (Figure 3.6G). Where foliation is developed, the veinlets are parallel to it, especially in biotite rich areas. The veinlets are generally closely spaced where abundant (up to 25/metre), but some areas are nearly devoid of them. They are commonly developed within bleached calcareous envelopes of shear veins and biotite veinlets (e.g. Plates 3.3B, 3.4A, 3.8A). Where subhorizontal to shallow southwest dipping foliations are developed adjacent to shear zones, the calcite veinlets are foliation parallel (Plate 3.8B). They are cut by extension veins and brittle faults.  66  Figure 3.6 A M (above and following pages): Equal area projections (lower hemisphere) of structural features in the Snip mine workings, northwestern British Columbia. A: Poles to foliation in the Biotite Spotted Unit (BSU). Foliation is southwest dipping and parallel to the walls of the dyke. B: Lineation of biotite spots on foliation surfaces within the Biotite Spotted Unit. C: Poles to shear veins in the Snip mine workings, excluding the Twin zone. Note the range of orientations from southwesterly (predominant) to northwesterly dipping. D: Slickenside and elongation lineation developed on shear vein foliation surfaces, excluding the Twin zone. -  67  Figure 3.6 (continued): E: Poles to foliation within the greywacke sequence external to shear veins. The crenulated north to northeasterly dipping foliation observed on the 130 level is not included in this plot (see text). Note the range in orientations from subhorizontal to shallow and moderate southwest-dipping. F: Poles to quartz veins in the stockwork at the south end of the 130 haulage level. Attitudes are variable. G: Poles to calcite-chlorite-biotite-pyrite veinlets developed in the greywacke sequence. The veins cluster around an approximately horizontal orientation. H: Poles to quartz-calcite-chlorite extension veins developed throughout the greywacke sequence. Note the two clusters with moderate to shallow southeast (predominant) and northeast dipping orientations.  68  Figure 3.6 (continued): I: Poles to extension veins developed within the Biotite Spotted Unit. These have similar orientations to extension veins developed in the greywackes (Figure 3.6H). J: Poles to epidote bearing extension veins developed on the 130 haulage level. These have easterly dips that are intermediate between the two clusters defined in Figure 3.6H. K: Poles to the central plane of southeast-dipping en echelon extension vein arrays in the 130 haulage level. The arrays dip east-northeast and west-southwest. L: Poles to gouge filled faults with greater than or equal to 10 centimetres of gouge. Moderate to steep northwest dipping orientations predominate.  69  Figure 3.6 (continued): M: Poles to gouge filled faults of all thicknesses, including those in Figure 3.6L. Note the range in orientations that is similar to that of the shear veins (Figure 3.6C). N: Slickensides on gouge filled faults. Orientations are variable, but generally plunge to the west.  70  Plate 3.7.  Shear veins, Snip mine, northwestern British Columbia. The hammer is 32.5 centimetres long and the coin is 2.4 centimetres in diameter. Sample and photograph location coordinates are listed in Appendix 1.  A: Schistose laminated southwest-dipping calcite-chlorite-biotite shear vein, 180 level south, looking southeast. B: Asymmetric down-dip verging fold in a south-dipping laminated calcite-quartzchlorite-biotite shear vein, 130 haulage level at survey station 279, looking west. Photo location is shown on Figure 3.5. C: 150 footwall vein, 385 level, looking southeast. The vein bifurcates with southwest dipping (left) and northwest dipping branches (right). Oblique foliation, shallower than the dip of the zone, is visible in the upper left corner of the photo. Shallow dipping calcite veinlets are common in the right hand side of the photo. Photo location is shown on Figure 3.13. D: Schistose laminated calcite-biotite-chlorite shear vein in an oriented sample. Note the oblique foliation within the zone (right), subhorizontal foliation outside the zone (bottom, parallel to bar), and ptygmatically folded calcite vein (left of centre). The pale area under the coin is strongly calcite altered greywacke. Sample is DR-22, from the 130 haulage level 13 metres northeast of survey station 286. Sample location is shown on Figure 3.5.  72  Plate 3.8. Veins and veinlets, Snip mine, northwestern British Columbia. The hammer is 32.5 centimetres long and the coin is 2.4 centimetres in diameter. A: Pyrite vein with an inner chlorite envelope (chl), biotite envelope (bio) and outer carbonate-K-feldspar altered greywacke envelope (pale brown-grey) with calcite veinlets. Sample is DR-278 from 3852 stope, lift 5 access. Sample location is shown on Figure 3.12. B: Three generations of veins, 130 haulage 20 metres south of survey station 274, looking east. Quartz veins of fine-grained sugary quartz with minor disseminated pyrite (quartz veins forming a subparailel set dipping to the right = 1) are cut successively by foliation parallel shallowly dipping calcite veinlets (parallel to the bar at 2) and later northeasterly dipping quartz-calcite-chlorite extension veins (dipping to the left = 3). The extension veins cut both of the other vein sets and the foliation. The earliest quartz veins are offset on the foliation consistently with the upper plate offset to the south. Photo location is shown on Figure 3.5. C: Subhorizontal calcite > pyrite + chlorite + biotite veinlets in fine-grained biotitic greywacke. Sample is DR-121 from 340 level northeast. Sample location is shown on Figure 3.14.  73  74  Extension veins  Two orientations of extension veins with moderate northeast and southeast dipping orientations occur abundantly throughout the greywacke sequence (Figure 3.6H; Plate 3.9). They cut shear veins (Plate 3.10A, 3.10B, 3.10C), the flat foliation developed external to shear veins, calcite-chlorite-biotite-pyrite veinlets, and the 130 level quartz stockwork (Plate 3.8B). The veins are composed primarily of blocky to fibrous quartz and calcite with subordinate chlorite. Iron carbonate, pyrite and epidote are also common vein constituents. Usually there is no alteration associated with the extension veins. However, wallrock fragments are sometimes chloritised, and some epidote bearing extension veins have green epidote envelopes. Typical veins are lenticular, 0.2 to 2.5 metres long and 0.5 to 4 centimetres wide. Spacing is variable, but commonly 0.5 to 2.0 metres. Quartz and calcite fibres are generally perpendicular to the vein walls where observed, indicating extensional opening. Chlorite and subordinate green and brown biotite comprise between 2 and 10% of the vein volume and occur in 0.5 to 5 centimetre wide clots, usually with pyrite, spaced through the veins. Microscopically, the colour of biotite in extension veins is variable; proximal to sulphide grains and/or biotitic wallrock, the biotite is brown and has a gradual 0.31 millimetre wide transition to more distal straw green.  Crosscutting relationships indicate that the southeast dipping extension vein set, which is also the most abundant, is younger than the northeast dipping set. Fibrous epidote bearing extension veins, developed only in the 130 haulage level, have east dipping orientations intermediate between the northeast and southeast dipping sets (Figure 3.6J). These epidote bearing veins cut the northeast and southeast dipping veins, and sometimes form through-going veins that cut the centre of en echelon arrays developed by these veins.  Both northeast and southeast dipping extension vein sets frequently form en echelon arrays (Figure 3.6K; Plate 3.9). Two array orientations are common for each type of vein. Southeast dipping veins commonly are developed in moderate west to southwest dipping (Plate 3.9B) and shallow east to northeast dipping  75  arrays (Plate 3.9A). Varying degrees of sigmoidal folding of the veins are indicative of a reverse sense of shear on the moderate westerly dipping arrays (Plates 3.9B, 3.9C), and an upper plate south directed sense of shear on the shallow easterly dipping arrays. Arrays associated with northeast dipping extension veins have similar orientations and sense of shear. Moderate north dipping en echelon arrays of extension veins were observed in some areas.  The extension veins commonly are boudinaged, with subhorizontal linear boudin axes striking southsoutheast (Plate 3.10D). Although they cut shear veins, the extension veins are often offset in a normal sense along them (Plate 3.8A). The veins cut folds within shear veins, indicating the extension veins postdate this style of deformation. However, extension veins commonly are strongly developed adjacent to and terminate against shear veins (Plate 3.27). Table 3.5: Analyses of chloritic extension veins from the Snip mine workings. The samples were analysed at the Cominco Research Laboratory, Vancouver, B.C. Cu, Pb, Zn, Ag As and Mo were analysed by aqua regia digestion with an inductively coupled plasma finish. Gold was analysed by fire assay. The samples were collected selectively so that each contained 30-60% chlorite + pyrite + green biotite. Sample locations are shown on Figure 3.5; coordinates are listed in Appendix 1.  Sample  Location  Cu (PP01 )  Pb (PPni)  Zn (1)Pm)  Ag (13Pni)  Au (PPb)  As (1)13m)  Mo (Wm)  DR-99 DR-100 DR-I01 DR-103 DR-136 DR-137  130 level (SS 271 + 8m SE) 130 level (SS 292 + 39m SE) 130 level (275 + 29m SE), sigmoidal array 130 level (SS 279 + 3m SE) 130 level (SS 274 + 18m NE) 130 level (SS 268 + 19m NE) Ramp below 380 level (SS 220 + 5m NE) Ramp, 410 level Ramp below 380 level (SS 211 + 30m W) 340 level east (SS 384 + 21m SE) 340 level undercut, adjacent to the Twin zone footwall  229 42 29 57 37 17 246 357 125 110 153  <4 8 5 <4 10  8 105 105 29 30  <0.4 <0.4 <0.4 <0.4 <0.4  <10 376 24 38 24  6 25 13 22 <2  3 2 <2 10 <2  4  9  <0.4  <10  7  <2  <4 15 30 <4 50  48 69 270 42 66  0.7 4.5 0.4 <0.4 1.7  714 1452 56 380 578  35 88 19 21 44  <2 3 2 3 2  DR 98 -  DR-105 DR-109 DR-115 DR-I19  Clots of chlorite with subordinate pyrite and green biotite and attached quartz + calcite vein material collected selectively from 11 chloritic extension veins throughout the Snip workings were analysed at the Cominco Research Laboratory, Vancouver, B.C., for seven elements (Table 3.5). Only Au has relatively  76  anomalous values in the data set, with several samples returning values > 500 ppb. However, the grades reflect the metal concentrations primarily in the chlorite clots, which comprise only 10-30% of the veins, so the overall grade of the entire vein may be different. Samples collected further away from the Twin zone in the 130 haulage level have generally lower Au, Ag, Pb, Cu and As values than those collected closer to the Twin zone on the main ramp and on 340 level, implying that metal zonation around veins may be useful in exploration.  Faults  Gouge and vein filled brittle faults cut all other structural features in the mine (Plate 3.11A). Moderate northwest dipping orientations predominate and include the thickest faults (faults with > 10 centimetres of gouge; Figure 3.6L), but southwest dipping orientations are also common (Figure 3.6M). Many southwest dipping faults reactivate pre-existing shear veins. Faults are filled with 0.5 centimetres to more than 2 metres of rusty to white clay and rock flour gouge. 2-50 centimetre wide vuggy quartz-calciteankerite-pyrite veins are common in many of the faults (Plates 3.11B, 3.11D), especially those with northwest dipping orientations. The faults have bleached envelopes 0.1 to 2 metres wide of sericite + clays + Fe-carbonate + quartz ± pyrite (Plates 3.11A, 3.11B, 3.11C). Biotite and chlorite are altered to pale green sericite adjacent to faults. Subvertical north-south striking calcite veinlets are developed in the alteration envelopes of some faults. Sampling indicates that the fault gouge and veins do not carry gold, except where they intersect mineralised shear veins (A. Samis, personal communication, 1991).  Slickensides have variable orientations (Figure 3.6N), and in some cases two directions on a single fault plane can be observed. The displacement of several faults that cut the west and east portions of the central Twin zone has been determined from displaced markers within and associated with the Twin zone. These include: (i) offset of the base of the orebody, (ii) the relative position of the BSU to the Twin zone, and (iii) continuity of ore types and mineral trends across the faults. For faults at the western end of the central orebody (Figure 3.9) this corresponds to a net offset of approximately 110 metres of  77  oblique right lateral and reverse movement parallel to slickensides on the fault. Faults on the east side of the main block of the Twin zone (Figure 3.9) offset the zone by 30 to 45 metres in an oblique right lateral and normal sense. Deflected foliation and slickensides on a large northeast trending fault that intersects the Red Bluff cliffs (Plate 2.3A) indicate a right lateral displacement with a small reverse component (Metcalfe, 1988). Thus, overall the faults have right lateral displacement, but individual slivers of rock that they separate may have rotated during displacement resulting in both reverse and normal offset components. Alternatively, the conflicting sense of vertical displacement may result from multiple phases of movement.  78  Plate 3.9. Extension veins, Snip mine, northwestern British Columbia.  The hammer is 32.5 centimetres long and the coin is 2.4 centimetres in diameter. A: En echelon northeast-dipping calcite-quartz-chlorite extension veins form a subhorizontal array. Photo is of 4055 stope undercut access looking southeast; its location is shown on Figure 3.11.  B: En echelon arrays of southeast dipping quartz-calcite-epidote extension veins fold graded sandstone and siltstone beds with a reverse sense of motion. Bedding faces north (left). Photo, located on Figure 3.5, is taken looking southeast, 130 haulage level, 82 metres southwest of survey station 292. C: Sample taken just to the right of the hammer head in Plate 3.9B, but looking the opposite direction (northwest). Note the localisation of folds around the extension vein array. The hinges of the folds point to the direction of offset for the respective sides of the array. The presence of both folded (sigmoidal) and unfolded veins indicates that folding was synchronous with, and continuous throughout, the formation of the veins. Sample is DR-2. Sample location is shown on Figure 3.5.  79  80  Plate 3.10. Extension and shear veins and their structural associations and characteristics, Snip mine, northwestern British Columbia. The hammer is 32.5 centimetres long. A: Folded southwest dipping quartz-calcite shear vein (shr) is cut by shallow southeast-dipping quartz-calcite-chlorite extension veins (ext). The shear vein is folded about a weak subhorizontal axial planar cleavage. The extension veins are undeformed and cut the cleavage, indicating that they are younger than both the shear vein and the folding. View is to the southeast (140 degrees). Main ramp at 410 metres elevation. Photo location coordinates are listed in Appendix 1. B: Boudinaged southwest dipping calcite-pyrite-chlorite shear vein (shr). Quartzcalcite fill occurs between boudins and is joined by southeast-dipping extension veins (ext). 4055 stope access looking southeast. Photo location is shown on Figure 3.11. C: Southwest-dipping calcite-chlorite-biotite-pyrite shear veins (shr) cut by southeastdipping extension veins (ext). The extension veins change their orientation within the shear vein at the left either as a result of refraction or because of late movement on the shear vein. Photo, located on Figure 3.11, is of the 4055 stope access looking southeast, approximately 2 metres northeast of Figure 3.8B. D: Boudinaged shallow southeast dipping quartz-calcite extension vein. Photo, located on Figure 3.5, is of the 130 haulage level 35 metres southeast of survey station 279, looking southeast.  8i  82  Plate 3.11.  Faults, Snip mine, northwestern British Columbia.  The hammer is 32.5 centimetres long and the coin is 2.4 centimetres in diameter. Sample and photo location coordinates are listed in Appendix 1. A: Rusty gouge-filled fault with a bleached argillic envelope. Photo is taken from the 180 level southwest drill drift, looking northeast. B: Alteration and veining associated with the brittle faults. Top: Fracture controlled bleached argillic alteration envelopes an irregular calcite vein. Bottom: Vuggy calcite vein with drusy calcite growth in vugs is from within a fault zone. Top sample is from DDH UG-639: 8.9 metres; bottom is from DDH UG-652: 47.4 metres. C: Bleached alteration of Twin zone vein material adjacent to a 4 centimetre wide gouge-filled fault. The top of the photograph is approximately 5 centimetres from the fault. Unaltered Twin zone vein (bottom) is composed of calcite + chlorite + quartz. Calcite + chlorite are altered to Fe-carbonate, sericite and clays in the altered material above. Biotite is typically altered to pale green sericite in fault alteration zones. Sample, located on Figure 3.14, is DR-127, from the 340 level west. D: Calcite-pyrite vein from a gouge-filled fault. The calcite, and some of the pyrite, shows drusy growth. Sample is DR-110 from the 340 level northeast. Sample location is shown on Figure 3.14.  ^  70^71^72^73^14^75^16^  '11111^'  77^78^19  84  3.3 THE TWIN ZONE SHEAR VEIN SYSTEM  3.3.1 Introduction  The Twin zone shear vein system strikes 120 degrees and dips 30 to 60 degrees southwest (Figures 2.2, 3.7). It is the largest shear vein at the Snip mine and has been traced by drilling for 500 metres horizontally and vertically. Thickness varies to a maximum of 13 metres and averages approximately 2 metres. In the eastern and lowest parts of the mine, the zone dies out in a series of discontinuous pyrite veins and veinlets. Several smaller shear veins occur below its lower termination in an en echelon geometry. Erosion has removed the westernmost and top parts of the zone.  The Twin zone was investigated through extensive core logging and underground mapping. During the summer of 1991, 456 drill intersections of the Twin zone containing 837 assay intervals were logged by the author. This comprised most of the existing intersections of the zone at that time. Each of the intervals considered contains Twin zone vein material, and most also contain varying amounts of greywacke. Holes with missing core, or those which did not cross the entire width of the zone were not logged. Evaluation of mineral distribution is based on visual estimations of the percentage of minerals logged in the 837 intervals. Visual estimates were made of 12 common minerals, including calcite, quartz, pyrite, chlorite, biotite, pyrrhotite, sphalerite, arsenopyrite, chalcopyrite, magnetite, galena and molybdenite. The relatively coarse grained nature of most of the minerals (usually > 0 2 millimetres diameter) in veins made core logging relatively easy; thus, visual mineralogical estimates often totalled 100%. Thicknesses of four discrete ore types were also measured and their mineral contents were estimated visually.  The geochemical database from the Twin zone consists of the concentrations of 13 elements that were determined in all 837 intervals. During exploration (1986-1990), the intervals were analysed for Au, Ag and Cu at the Cominco Research Lab in Vancouver. During 1992, the sample pulps were analysed for  85  S 420 —  N Figure 3.7A: Snip Mine Section 4475 East  — 420  380 380  340  LEGEND  300 —  — 300  NEI Calcite - Chlorite-Motile and/or Quartz-Sulphide Veins EMI BSU  1=1 Unit 3  Interbedded Sillstone and Greywacke  i=1 Massive Grey's/oak. 260 —  260  Drill Hole MA Underground Workings  220 — — 220  180 —  140 — 140  S  S 460 —  Figure 3.7B: Snip Mine Section 4525 East  N  300 —  260 —  Figure 3.7: Cross-sections through the Twin zone and related veins, looking northwest (toward 300  degrees azimuth). The cross-sections are located on Figure 3.8. Sections are along 030 degrees azimuth. A: Section 4475 East. The Twin zone steepens near its base from approximately 40 degree dips above 320 metres elevation to >50 degrees below this level. The Biotite Spotted unit (BSU) intrudes the zone and intersects veins below it. The mixed greywacke-siltstone package (unit 3) is shown (based on information from Read, 1990); it is offset in a normal sense. Note that the Twin zone steepens where it intersects unit 3. B: Section 4525 East. Note the Footwall vein, the 150 Footwall vein and the 130 vein; each in turn occurs progressively deeper into the footwall of the Twin zone. These veins have generally steeper dips that the Twin zone. Unit 3 was not located on this section by the author or Read (1990), so it is not shown.  86  tmi 0  450  Figure 3.11 Figure 3.12 I Figure 3.13  400  350 Figure 3.14 300  250  ■•■•••■,"■11./^) Figure 3.15 •  Easting (m)  Figure 3.8: Twin zone vertical long section showing the locations of plans and sections and  the distribution of the 150 and Footwall veins. Looking north-northeast (030 azimuth). The eroded top and structural base of the Twin zone are marked as dashed lines. Faults bounding the central block of the orebody are squiggly lines. Underground stope maps of the Twin zone and 150 vein are marked as thick continuous and dashed lines, respectively. Cross sections through the entire zone are vertical dotted lines. The distribution of the 150 vein projected to the section is stippled. The areal distribution of the Footwall vein is hatched (inclined straight lines) and its structural base is marked (continuous line at its base).  4.30  ^  4 .40  ^  4.50  ^  4.60  ^  4.30  ^  4.40  ^  4.50  ^  4.60  Figure 3.9A (left): Twin zone vertical long section looking toward 030 azimuth (north-northeast). The central pierce point of the 365 intersections used in the spatial distribution plots are shown as rectangles. The bounding faults are drawn from mine plans and sections. The line below the drill intersections indicates the base of the continuous Twin zone (stippled outline) defined from cross-section. Although mineralised veins continue below this level, they either do not line up with or are separated from the main Twin zone because they represent discrete, separate veins. The continuous line is the ground surface. Faults define three blocks: western, central and eastern blocks. The central block contains the majority of the current mine reserves. Compare to restored long section in Figure 3.9B. Figure 3.9B (right): Twin zone vertical long section, with fault offsets restored. West of the central block, intersections have been lowered by 50 metres elevation and moved 60 metres to the west (-60 metres easting). The block to the east has been dropped by 25 metres elevation and shifted 5 metres west (subtracted 5 metres from the easting). Restoration is based on fault slickensides, separation of the dyke from the Twin zone and offset of the base of the Twin zone. Arrows show vector and amount of fault restoration. This plot is the base for Figures 3.10, 3.24 and 3.27.  88  Fe, Mo, Pb, Zn, As, Co, Cd, Cr, Ni and Mn, and reanalysed for Cu and Ag for a total of 13 elements. Gold was determined by fire assay; all of the other elements were determined by aqua regia digestion with an inductively coupled plasma spectroscopy finish. The geochemical and mineralogical data set forms the basis of a companion study describing mineral and metal distribution in the zone, some preliminary results of which are summarised here (Rhys, 1993; Rhys, Sinclair and Godwin, in preparation).  Detailed 1:200 scale underground maps and sections of several stopes on the Twin zone and 150 vein by the author and Cominco geologists E. Masarsky, K. Dormer, B. Coates and A. Samis are presented in Figures 3.11-3.15. The locations of these plans and the spatial distribution of the Twin zone are shown on vertical long section in Figure 3.8. Drill hole intersections of the zone, on which the ore type, mineral and metal distribution plots are based, are shown on Figure 3.9.  3.3.2 Composition of the Twin zone: mineralogy and ore types  Although twenty-six mineral species and three native metal species have been identified in the Twin zone (Table 3.6), more than 90% of the Twin zone is composed of only five minerals (Table 3.8): calcite, quartz, pyrite, chlorite and biotite. Calcite is the most abundant mineral in the zone, followed by quartz and pyrite. Other gangue minerals noted in thin section include muscovite (sericite), K-feldspar, calcic clinoamphibole (actinolite or hornblende) and Fe-carbonate. Several tellurides and sulfosalts have been identified in sulphide rich vein material by J. McLeod using a scanning electron microscope/energy dispersive X-ray (SEM-EDX) system (McLeod, 1987a, 1987b, 1989).  The vein material has a pronounced layering of four different ore types, which in order of abundance are: (i) carbonate ore (42% of the zone), (ii) sulphide ore (24%), (iii) quartz ore (19%), and (iv) chlorite/biotite ore 15%. All carry gold. Individual drill intersections of the Twin zone consist of one or more of the ore types. The criteria defining the four ore types used during core logging and their relative  89  Table 3.6: Mineral species identified in the Twin zone, Snip mine, northwestern British Columbia. PHASE' PHASE'  COMPOSITION  Sulphides  Pyrite Pyrrhotite Chalcopyrite Arsenopyrite  FeS2 FeS i _ x CuFeS 2 FeAsS  Sphalerite Galena Molybdenite^4:, TellurobismuthiteJ Hessite (h ) Aguilarite 6i P Volynskite (h) Altaite®  ZnS PbS  Fe304  Native Elements Gold^,I .., Bismuth" Hi Electruma i,ii0  M°S 2  Bi 2 Te3 Ag2Te Ag2(S,Se)  Au Bi Ag0 . 3Au 0.7  Gangue Minerals Quartz Calcite Biotite Chlorite K-feldspar Muscovite Albite Carbonate  PbTe  Pb-Bi-S Ag SbS Cu 3 Sb 3 S 12 4 13  'Superscripts refer to minerals identified by (ii) McLeod, 1987b; (iii) McLeod, 1989.  Oxides  Magnetite  Sulfosalts Cosalite 00 PyrargyriteClii? ... TetrahedriteCil ' u O  COMPOSITION  Si02 CaCO 3 K(Mg,Fe)3(A1Si30 10)(OH) 2  (Mg,Fe)3 (Si,A1)40 10(OH)2(Mg,Fe)3 (OH)6  Amphibole  KAISi 3 O 8 ICAl2(A1Si30 10)(OH)2 NaAISi 3 O 8 Probably Fe carbonate Actinolite or hornblende  Epidote  Ca2(A1,Fe)Al20(SiO 4)(Si 2 0 7 )0H  J. McLeod at the Cominco Research Laboratory by SEM-EDX: (i) Mcleod, 1987a;  abundances are in Table 3.7. Visually estimated mineral contents of each ore type and the entire Twin zone are shown on Table 3.8.  The pronounced compositional layering of the Twin zone enabled a fairly easy division of these ore types in drill core. Individual drill intersections contained anywhere from one to all four ore types, each of variable thickness and mineral content.  90  Table 3.7: Classification criteria and abundance of ore types in 456 intersections of the Twin zone, Snip mine, northwestern B.C. Carbonate ore^Chlorite-biotite ore^Sulphide ore^Quartz ore^Total Twin zone  Criteria for^>50% calcite + Fe-^>30% chlorite +^>30%^>50% quartz and classification^carbonate, and <30%^biotite^sulphides^<30% sulphides sulphides or quartz^ or phyllosilicates 388  278  318  287  456  Cumulate tree thickness (m)  309.5  111.0  178.4  139.5  737.4  % Twin vein material  42.0  15.1  24.1  18.9  100  Number of intersections where ore type is present  Table 3.8: Percentage abundance of common minerals based on visual estimates from 456 intersections of ore types in the Twin zone, northwestern B.C. Percentages are weighted averages of true ore type thickness for each intersection.  Mineral  Sulphide ore  Chlorite-biotite ore  Carbonate ore l  Quartz orel  Total Twin zone  4.4 4.3 17.4 0.9 0.3 2.6 0.04 0.1 0.1 0.03 0.06 0.3 0.004 0.008 0.005 0.3 0.3 0.5 0.4 0.3 0.5 0.006 0.02 0.01 4.7 74.2 18.5 1 69.81 8 24.8 37.7 Calcite 12.9 9.2 8.0 Chlorite 4.4 39.9 12.4 1.7 21.8 5.5 3.0 Biotite 6.6 'Petrographic work indicates that: (i) approximately 10% of the material visually logged as calcite in carbonate ore is fine grained quartz pervasively disseminated with the calcite, and (ii) some of the material logged as chlorite ( <5%) in carbonate, chlorite-biotite and quartz ore is green amphibole (actinolite or hornblende), sericite and/or green biotite intergrown with chlorite. Pyrite Pyrrhotite Chalcopyrite Magnetite Molybdenite Arsenopyrite Sphalerite Galena Quartz  58.5 9.2 0.3 1.1 0.001 1.4 1.0 0.01 7.4  3.9 0.7 0.07 0.06 0.012 0.002 0.07 0.003 4.6  Carbonate ore and chlorite - biotite ore are two end members of the same ore type; they display a complete compositional gradation. Although their separation is subjective, the two were treated independently during core logging, because of the significant variation in biotite and chlorite content with respect to calcite (Table 3.7), and the occurrence of discrete calcite rich or chlorite-biotite rich  91  veins. Veins transitional between the two end members (i.e., within the error of visual estimation criteria) were treated as carbonate veins. Carbonate ore (Plate 3.12) is generally compositionally layered with alternating laminae of  schistose calcite and chlorite-biotite. Calcite occurs as bands of massive to foliated granular calcite and averages approximately 70% of the ore type (Table 3.8). Laminae of chlorite and biotite usually comprise 2 to 20% (Plate 3.12C), but elsewhere veins of almost pure calcite occur (Plate 3.12A). Sulphide content averages approximately 5%, occurring as pervasive disseminations and bands. Quartz occurs as rounded sub-millimetre scale porphyroclasts, veinlets, and fine grained disseminations (mainly <10%) forming up to a total of 20% of the ore type (Plate 3.12B). Fe-carbonate occurs abundantly in some intersections, and green calcic clinoamphibole (actinolite or hornblende) was identified in several samples intergrown with calcite and chlorite. Bleached and carbonate + quartz + K-feldspar altered slivers and blocks of greywacke are associated with many carbonate veins. Some veins have indistinct 5 to 10 centimetre wide transitional margins with greywacke that record progressive replacement of wallrock by calcite. Chlorite-biotite ore (Plate 3.13) consists of schistose chlorite + biotite (averaging approximately  60%) and calcite. Some drill hole intersections are almost pure chlorite (Plate 3.13C, bottom) or biotite (Plate 3.13A, bottom left). Quartz is locally abundant as augen or foliation parallel veinlets. Total sulphide content, mainly pyrite and minor pyrrhotite, averages approximately 4%. A gradual transition, 3 to 25 centimetres wide, from weakly foliated biotitic greywacke to nearly pure schistose biotite ore occurs in some drillholes. Here, remnant carbonate and/or K-feldspar altered greywacke grains and elastic textures are often visible in chlorite or biotite rich sections (Plate 3.13C, top right). These observations suggest that chlorite-biotite ore, like carbonate ore, may have formed largely by progressive wallrock replacement (see section 3.33). Veins and/or laminae of pink calcite are common in chlorite rich areas of chlorite-biotite and carbonate ore (Plate 3.13C). Pink carbonate commonly occurs at the transition from biotite rich ore or vein selvages to chlorite rich shear veins. It appears represent alteration of biotite altered wallrock to chlorite and calcite. In thin section, the pink colour correlates with the amount of disseminated biotite.  92  Molytxlenite and visible gold are spatially associated with pink carbonate in upper levels of the mine (340-420 metre levels; Table 3.9).  Sulphide ore (Plate 3.14) contains a diversity of sulphide minerals. Sulphides occur in discrete  foliation parallel veins of predominantly pyrite that are 5 centimetres to more than 1 metre thick (Plate 3.15A). Massive pyrrhotite occurs locally. Layers and fragments of other ore types or minerals are common, giving a stratified texture to some veins (Plates 3.14B, 3.14D). Other significant sulphides include, in decreasing order of abundance, arsenopyrite, sphalerite, chalcopyrite and galena. Disseminated to laminated magnetite occurs in some pyrite veins, with or without disseminated pyrrhotite (Plate 3.14B). Both biotite and chlorite are associated with the sulphides, but seldom exceed more than 10 volume percent of the vein. Calcite is interstitial to sulphide grains in most veins. Quartz eyes and medium to coarse grained euhedral pyrite cubes and pyritohedrons are common in pyrrhotite rich ore (Plates 3.14A, 3.14C). Both chalcopyrite and fine grains (<0.1 millimetre) of visible gold commonly are associated spatially with the quartz (Plate 3.14C). Sphalerite occurs in a limited number of sulphide veins. It generally occurs with arsenopyrite, and is common in discrete veins and veinlets that obliquely cut other ore types (Plate 3.15C) and foliations (Plate 3.15D), suggesting that it is late. Sulphide veins commonly are interlayered with quartz veins in multiple sets (Figure 3.16B).  Quartz ore (Plate 3.16) consists of foliation parallel milky white quartz veins containing the  same sulphide species as the sulphide veins. The sulphide content is mostly less than 8% (Plate 3.16A). The relative abundance of pyrite is generally less than that in sulphide ore. Other sulphides, notably pyrrhotite and chalcopyrite, are proportionally more abundant. Chlorite, and less abundantly biotite, commonly comprise 5-15% of the quartz veins (Plate 3.16D), but locally form up to 50 percent of the vein. Bladed quartz-chlorite intergrowth is common in veins with abundant chlorite (Plate 3.16; Figure 3.16B). Most quartz veins are fractured. The fractures are filled with calcite and/or iron carbonate, resulting in a carbonate content of 1 to 4 percent. Chlorite and sulphides may also occur as fracture fill (Plate 3.16D, top left).  93  Progressive increase in sulphide content over distances of 1 to 2 metres commonly produces a gradation from quartz to sulphide veins, implying a genetic relationship between these two ore types. The usual discrete nature of quartz and sulphide veins with respect to carbonate ore, chlorite-biotite ore and greywacke, and the bladed intergrowth of chlorite and quartz in quartz veins suggests that these two ore types represent open space fill (dilatant) veins (Plates 3.12D, 3.13D, 3.15A, 3.15B).  Biotite and chlorite composition  Chlorite in the Twin zone has been erroneously described as annite (Fe-biotite) in previous literature (Nichols, 1987; Rhys and Godwin, 1992). To assess their compositions, a suite containing phyllosilicate rich samples from the Twin zone (11 samples) and shear veins throughout the workings (6 samples) was analysed during 1991 using the Cameca SX-50 electron microprobe at the Department of Geological Sciences, The University of British Columbia. Analyses were obtained by K. Wilks. The results are being investigated currently (Wilks and Rhys, in preparation), but some preliminary information is summarised here. Multiple analyses of grains from each sample indicates that Twin zone biotites have Fe to Mg ratios between 1.8 and 3, corresponding to a composition within the biotite field and transitional between phlogopite (K2Mg6[Si6Al2020](OH)4) and annite (K2Fe6[Si6Al2020](OH)4; Deer et al.,1966). The biotite is red and brown, and more rarely, green in some quartz veins where it occurs with and is subordinate to chlorite. Chlorite returned ratios of Fe to (Fe+Mg) between 0.5 and 0.9 and Si content (4.5 and 5.4 silicon atoms per formula unit) consistent with classification as a thuringite or pseudothuringite chlorite (Deer at al., 1966). Similar results were obtained from X-ray diffraction analysis of a further 7 samples from the Twin zone. Green biotite occurs in the two sets of extension veins, some of which cut Twin zone veins.  94  Plate 3.12. Carbonate ore, Twin zone, Snip mine, northwestern British Columbia. The coin is 2.4 centimetres in diameter and the hammer is 32.5 centimetres long. Sample location coordinates are listed in Appendix 1.  A: Grey calcite veins with biotite-pyrite-chlorite altered wallrock fragments (top) and disseminated biotite and minor pyrite with wisps and fracture fillings of biotite (bottom). Top is from DDH UG-238: 63.9 metres; bottom is from DDH UG-33: 126.5 metres. B: Top left: Laminated schistose calcite-chlorite-biotite with quartz eyes. Top right: calcite with disseminated pyrite and chlorite showing relict clastic texture. Bottom left: Calcite vein with quartz eyes enveloped in sphalerite (sp). Bottom right: Calcite > chlorite + biotite + pyrite vein. Top left is from DDH S-58: 37.6 metres; top right DDH UG-150: 71.6 metres; bottom left DDH UG-89: 60.6 metres; bottom right DDH UG-195: 45.7 metres. C: Laminated calcite > chlorite + biotite + pyrite shear vein, typical of much of the Twin zone ore. The pink tint of the calcite is from finely disseminated biotite. Note the oblique foliation (top part of picture) giving a clockwise sense of rotation (right lateral shear sense) and the folded white calcite vein. Sample DR-328, 3852 stope lift 5 west. Sample location is shown on Figure 3.12. Sample, cut parallel to the stretching lineation and perpendicular to foliation, is viewed in the XZ plane of the finite strain ellipsoid. Bulk shear sense is shown (arrows). D: Asymmetrically folded laminated calcite > chlorite + biotite + pyrite (carbonate ore, above) and quartz (below) veins in a thin portion of the Twin zone. Note the localisation of folds above an irregularity in the footwall of the zone. The fold vergence suggests a normally-directed shear sense. The fold axis is approximately perpendicular to the lineation in the zone. 4061 stope undercut west, looking northwest. Photo location is shown on Figure 3.11. Bulk shear sense is shown with arrows.  , C) t.J1  96  Plate 3.13. Chlorite-biotite ore, Twin zone, Snip mine, northwestern British Columbia. The coin is 2.4 centimetres in diameter and the hammer is 32.5 centimetres long. Sample location coordinates are listed in Appendix 1. A: Schistose biotite (black) with flattened foliation parallel pyrrhotite (po) and chalcopyrite (cpy) and disseminated magnetite (mag). Shear zone boundary parallel pyrite (py) + chlorite (chl) > calcite veins occur in the central and upper parts of the photo. Foliation, here visible as preferred orientation of pyrrhotite and pyrite, is oblique to the zone (shallower dipping). Sample is cut parallel to lineation and perpendicular to foliation. Sample is DR-129, from 3451 undercut. Location is shown on Figure 3.14. The bulk shear sense is shown with arrows. B: Top: Apophyses of biotite (black) with calcite (white) in a matrix of chlorite. Bottom: Black biotite cut and partially replaced (below coin, along fracture) by chlorite-pyrite-calcite veins. Top is from DDH UG-408: 35.7 metres; bottom is from DDH UG-470: 46.9 metres. C: Top left: chlorite> calcite+biotite vein with disseminated and veinlet-controlled pyrite. Top right: chlorite > > calcite + pyrite + biotite vein with relict clastic (granular) texture. Bottom: chlorite vein with disseminated pyrite, minor magnetite (mag)--bottom left with free gold (au)--and a patch of pink calcite coloured by finegrained biotite (bottom centre). Top left is from DDH UG 398: 32.3 metres; top right is from DDH UG-451: 4.54 metres; bottom is from DDH UG-370: 50.2 metres. D: 4061 stope undercut west, Twin zone, looking northwest. Schistose biotitic ore (bio) with oblique shallow-dipping foliation that is parallel to deformed quartz veins. The Twin zone boundary is parallel to the grey sulphide vein (sulph) in the upper left of the photograph. Photo location is shown on Figure 3.11.  97  98  Plate 3.14. Sulphide ore, Twin zone, Snip mine, northwestern British Columbia. The coin is 2.4 centimetres in diameter. Sample location coordinates are listed in Appendix 1.  A: Top: Quartz eyes and coarse pyrite in a matrix of magnetic pyrrhotite with minor chalcopyrite. Bottom: Laminated calcite-chlorite and quartz vein fragments in a pyrrhotite matrix. Top is from DDH UG-420: 72.4 metres; bottom is from DDH UG-257: 33.2 metres. B: Top left and top right: Pyrite veins with disseminated pyrrhotite (approximately 5%) and bands of magnetite (dark grey = mag) and chlorite (green). Bottom: Pyrite vein with fragments of calcite > chlorite + quartz vein adjoining a laminated calcite > chlorite + pyrite vein containing minor sphalerite. Top left is from DDH UG538: 47.2 metres; top right is from DDH UG-417: 67.7 metres; bottom is from DDH UG-459: 59.2 metres. C: Pyrrhotite (po) vein with quartz (qz) and biotite (black) fragments. Chalcopyrite (cpy) is concentrated adjacent to some quartz fragments, but pyrite (py) is disseminated throughout the pyrrhotite matrix. Sample is DR-91, 150 vein, 400 level west access (sample location is shown on Figure 3.12). D: Pyrite vein with an attenuated folded quartz > chlorite vein fragment. Dark reddish brown bands of sphalerite (sp) occur at the top of the sample to the right of the coin. Oblique foliation, defined by laminated calcite-chlorite-pyrite in the calcite layer in the upper portion of the photograph, suggests a right lateral sense of shear (normal motion). Sample is DR-215, 3852 stope, lift 1 east. Sample is cut parallel to lineation and perpendicular to foliation.  100  Plate 3.15. Ore type relationships and character in various veins from the Snip mine, northwestern British Columbia. The hammer is 32.5 centimetres long and the coin is 2.4 centimetres in diameter. A: 385 sill drift, 150 vein, looking down on the vein in the floor (looking southsouthwest). A massive pyrite > pyrrhotite + quartz vein occurs in the basal portion of the vein below a calcite + biotite > chlorite + pyrite vein. The black patches are completely biotite altered wallrock fragments. Photo location is shown on Figure 3.13. B: 3242 stope lift 2 west, looking northwest. Calcite > pyrite + quartz vein in laminated biotite + calcite + chlorite shear vein. Note the oblique shallow-dipping foliation in the shear vein, dipping approximately 20 degrees shallower than the shear zone boundary. A quartz > chlorite extension vein cuts the calcite vein, but it is deflected in the shear vein. The fabrics indicate a component of normally directed simple shear on the zone. The bulk shear sense is shown with arrows. Field of view is 1.6 metres. Photo location is shown on Figure 3.14. C: Footwall vein, 9 metres into the footwall of the Twin zone. Quartz + arsenopyrite vein (1, above hammer), calcite > chlorite + biotite vein (2, at hammer head), and massive pyrite > arsenopyrite + quartz vein (3, at base of photograph). A dark brown sphalerite vein (sp) runs through the centre of the photograph and obliquely cuts the contact with the sulphide and carbonate veins (at left of the photograph it is in the sulphide ore and from left of centre it is in carbonate ore). Photo is taken looking northwest, 3852 stope lift 5 access, footwall vein. Photo location is shown on Figure 3.12. D: Sample from a 5-10 centimetre wide calcite + quartz + chlorite > biotite + pyrite shear vein with compositional layering cut by a purple-brown sphalerite > pyrite veinlet. Sample is DR-220, 300 level access at survey station 154, 20 metres into the foot wall of the Twin zone. Sample coordinates are listed in Appendix 1.  101  102  Plate 3.16. Quartz ore, Twin zone, Snip mine, northwestern British Columbia. The coin is 2.4 centimetres in diameter and the hammer is 32.5 centimetres long. Sample location coordinates are listed in Appendix 1. A: Quartz vein containing chlorite + pyrite + sphalerite in a laminated calcite + chlorite + biotite vein (top and bottom of picture). Sample is DR-279, 3852 stope, lift 5 west. Sample location is shown on Figure 3.12. B: Layered quartz (qz), sulphide (sul) and laminated calcite + chlorite veins (carb). Note the bladed chlorite and quartz intergrowth in the central quartz vein. 4055 stope undercut, looking up the vein to the northeast. The photo location is shown on Figure 3.11. C: Irregular contact between a quartz vein and laminated calcite > chlorite + biotite + pyrite vein. Truncation of the lamination by the quartz indicates that it must have formed before the quartz vein. Sample is from DDH UG-527: 38.8 metres. D: Typical quartz veins with chlorite ± pyrite ± biotite fracture fillings. The sample at bottom left contains disseminated chlorite flakes. Calcite and Fe-carbonate filled fractures occur in all of the samples (white and yellow) and often cut the chlorite. Top left is from DDH UG-377: 49.55 metres; top right is from DDH UG-318: 10.8 metres; bottom left is from DDH S-63: 58.9 metres; bottom right is from DDH UG173: 34.3 metres.  104  Plate 3.17. Gold occurrence in the Twin zone, Snip mine, northwestern British Columbia. The coin is 2.4 centimetres in diameter. Sample location coordinates are listed in Appendix 1. A: Native gold (au) with chalcopyrite (cpy) filling a fracture in pyrite. The sample is photographed in reflected light; lateral field of view is 0.5 millimetres. Sample is from DDH S-3: 57.8 metres. B: Euhedral native gold grain enclosed in pyrite. The sample is photographed in reflected light; lateral field of view is 0.33 millimetres. Sample is from DDH S-8: 5.6 metres. C: Native gold (au) associated with a grey telluride (tb), probably tellurobismuthite (McLeod, 1987), filling fractures in arsenopyrite. Sample is photographed in reflected light; lateral field of view is 0.58 millimetres. Sample is from DDH S-45: 61.9 metres. D: Native gold (au) mantled by molybdenite (black = mo) in a calcite vein with disseminated brown biotite (pink carbonate). Both reflected and transmitted light were used in this photograph to enhance the outline of the molybdenite, because its poor polish precluded a clear photograph. Sample is DR-116 from 3242 stope, August 1991. The sample location is shown on Figure 3.14. Lateral field of view is 0.5 millimetres. E: Coarse native gold occurring in foliation parallel trails in a calcite > chlorite shear vein. Note that the gold occurs in an area of mottled calcite-chlorite intergrowth, and not in the well laminated vein material to the left of the white calcite vein. Sample is from the 3049 development raise. F: Coarse native gold in a mottled chlorite> calcite matrix. The folded pale green calcite contains disseminated sericite. The gold orientation defines a flattening fabric that is axial planar to the minor folds. Sample is DR-84, taken from the 150 vein at its junction with the Twin zone, 4061 stope undercut access. Sample location is shown on Figure 3.11.  Plate 3.17A  4 Plate 3A 7R  106  Gold occurrence in the Twin zone  Gold in the Twin zone occurs mainly as relatively pure native metal. Silver content is generally low and rarely reaches 15% (McLeod, 1987a). Gold is predominantly free, and its occurrence is variable depending on the ore type and minerals present (Table 3.9).  In sulphide ore, gold occurs as 10 to 50 micron grains free in gangue but spatially associated with pyrite, filling fractures in sulphides (Plates 3.17A, 3.17C), or completely enclosed in pyrite (Plate 3.17B), and less commonly, arsenopyrite. It is commonly associated or intergrown with: chalcopyrite (Plate 3.17A), various tellurides (e.g. tellurobismuthite, hessite: Plate 3.16C) sulfosalts (tetrahedrite, pyrargyrite), and native bismuth (McCleod, 1987a,b). Silver may be contained in electrum, tellurides, sulfosalts or chalcopyrite (McCleod, 1987a, 1989). Sulphide ore generally has gold grades of >70 ppm.  Gold is associated with, or enclosed in sulphides and chlorite as fine, free gold in quartz ore. It also occurs as disseminations in unfractured quartz. Gold grades typically range from <30 to 60 ppm.  Table 3.9: Occurrence of gold in the Twin zone, Snip mine, northwestern British Columbia. Ore type  ^  Sulphide ore  Mineral association  ^  Pyrite, chalcopyrite, pyrrhotite, magnetite, arsenopyrite, chlorite, biotite, tellurides, sulfosalts, native bismuth  Quartz ore^Pyrite, chalcopyrite, pyrrhotite, chlorite  Carbonate and chlorite-biotite ore  Gold occurrence Enclosed in, within fractures or rimming sulphide grains; also free in gangue with chlorite or biotite. Often intergrown with tellurides, native bismuth, tetrahedrite or chalcopyrite Rimming, contained by, or spatially associated with these minerals, but less commonly occurs without them free in quartz  Pink carbonate with fine grained biotite;^Streaked on chlorite foliation surfaces; or as coarse flakes chlorite, molybdenite; associated with alteration^and seams spatially associated with pink carbonate. of biotite to chlorite, calcite and rarer actinolite ^Commonly intergrown with or rimmed by molybdenite  In carbonate and chlorite-biotite ore, gold is most abundant (commonly > 100 ppm) and coarse in the pink carbonate vein material and in chlorite rich ore spatially associated with pink carbonate (Plates 3.17E, 3.17F). The gold is associated with molybdenite (Plate 3.17D), which may rim, or is intergrown  107  with, the gold. Elsewhere, in carbonate ore and biotite rich ore gold, grades are lower (usually <30 ppm) and visible gold is associated with pyrite, chalcopyrite and magnetite.  3.33 Alteration and vein paragenesis  A well developed, visible alteration envelope is normally not observed in wallrock adjacent to the Twin zone at outcrop scale or in drill core. Thus, the transition from vein to biotitic greywacke generally is abrupt. Where alteration is best developed, commonly around chlorite and pyrite rich veins, mineralogy defines a consistent alteration sequence that may extend from wallrock well into the veins. The entire sequence, summarised on Table 3.10 and on Plate 3.18, consists of 5 stages involving primarily chloritebiotite and carbonate ore types. The outermost alteration (1 in Table 3.10) consists of the bleached greywacke envelope described above. Where it is calcareous, it is associated with calcite veinlets that occur at a high angle to the vein. Internal to the bleached envelope, felted to schistose biotite often with minor pyrite, pyrrhotite and/or magnetite replaces greywacke and occurs at the transition from wallrock to vein (2 in Table 3.10). The biotite may form narrow (0.2-5 centimetres) vein selvages, or in some areas, comprises schistose biotitic shear vein up to 1 metre wide that form biotite rich chlorite-biotite ore (Figures 3.7). In distal portions of this facies, at the transition with the bleached vein envelope, the biotite separates thin (<0.3-1 millimetre wide) wallrock slivers defining a shallowly dipping spaced cleavage (Plate 3.18A). Internal to the biotite selvage, a 0.5-1.5 centimetre wide layer of sugary brown to pink calcite tinted by fine grained biotite is commonly developed (3 in Table 3.10). Boundaries are sharp (Plates 3.18A, 3.18B). This material may also form veins up to 80 centimetres wide. Minor pyrite and molybdenite are common. The pink carbonate is developed adjacent to chlorite rich vein material (4 on Table 3.10), and forms a sharp transition zone between biotite and chlorite rich vein material (Plate 3.18). The chlorite, associated with variable quantities of calcite, forms chlorite rich chlorite-biotite ore or carbonate ore, commonly comprising zones of >70% phyllitic to schistose chlorite. Pyrrhotite is common (1-4%) where the chlorite content is high. Chlorite rich vein material is succeeded by massive granular to crudely layered calcite + pyrite + chlorite (5 in Table 3.10). Pyrite content commonly varies  108  from <2 to 60%, and is commonly 5-10%. Pink carbonate alteration often is associated spatially with visible gold (Plate 3.19C).  Boundaries of these alteration zones are remarkably sharp (Plate 3.18), and their mineralogy is consistent and relatively simple Alteration zones (3) to (5) in Table 3.10 and above comprise replacement vein material, which entirely replace the wallrock or the mineralogy of the previous, more distal, adjoining alteration zone. Where alteration is developed, the entire sequence described above is rarely developed. Bleached envelopes and biotite vein selvages are the most commonly developed. Pink calcite is the rarest. Various stages of the sequence can be missing, but the mineralogic sequence is still consistent. For example, the sequence may proceed from biotite directly to calcite ± pyrite (Plate 3.19C, top). Finger like foliation parallel pods of chlorite or calcite (Plate 3.19D), or veins of chlorite + pyrite + calcite (Plates 3.13A, 3.13B, 3.19C), some with nebulous outer pink calcite replacement zones (Plate 3.19A) commonly replace biotite in biotite rich shear veins. Some calcite-chlorite-biotite shear veins have only calcite altered envelopes, and lack other alteration types (Plate 3.7D). The paragenetic sequence is developed at all scales of vein, from shear veins in the Twin zone (Plates 3.18-3.20) to biotite-chloritepyrite veinlets developed throughout the greywacke sequence (Plates 3.3, 3.4). Alteration breccias occur in some areas of the Twin zone (Plate 3.18C). Biotite commonly is altered to chlorite in shear veins (Plates 3.19A, 3.20A, 3.20B, 3.23B). However, randomly oriented brown biotite overgrows the chlorite in some samples (Plate 3.20C).  Carbonate rich veins commonly contain greywacke fragments altered to quartz, K-feldspar and/or carbonate, commonly with a pale greenish to yellow tint probably caused by the presence of fine grained chlorite or sericite. The quartz flooded wacke is often finely granular and translucent with up to 5% disseminated pyrite.  109  Plate 3.18. Alteration in the Twin zone, Snip mine, northwestern British Columbia. The coin is 2.4 centimetres in diameter. A: Progressive Twin zone alteration, Twin zone footwall vein, 3852 stope lift 5 west. Sample is DR-352, taken the opposite side of the sample in Plate 3.18B. Note the spaced foliation defined by biotite in altered greywacke to the right of the coin and the oblique foliation developed within the shear vein suggests a right lateral sense of shear. The sample is cut parallel to the lineation on the schistosity and perpendicular to foliation. Refer to 3.18B and Table 3.10 for a description of the alteration zones. B: Well developed progressive alteration, 3852 stope lift 5 west, Twin zone Footwall vein. Sample is DR-352, taken the opposite side of the sample in Plate 3.18A. Alteration facies are as follows, from outer to inner: (1) bleached silica-carbonate-Kfeldspar altered greywacke with biotite veinlets (below coin), (2) black biotite vein envelope, (3) pale brown to pink calcite > biotite, (4) chlorite + quartz ± amphibole, and (5) pyrite > calcite in the core of the vein. Sample is DR-352; sample location is shown on Figure 3.12. C: Alteration breccia in the footwall of the Twin zone. Progressive alteration of greywacke fragments to biotite (1), pink and cream calcite coloured by biotite (2) and chlorite (3). Sample is DR-126, 3242 stope, lift 1 (sample location is shown on Figure 3.14).  111  Plate 3.19. Alteration in the Twin zone, Snip mine, northwestern British Columbia. The coin is 2.4 centimetres in diameter. Sample location coordinates are listed in Appendix 1.  A: Biotite (bio) vein with disseminated magnetite (mag), and elongate chalcopyrite (cpy) and pyrrhotite (po) is altered to pink/brown calcite (cal) > biotite + chlorite with a pyrite (py) + chlorite (chl) core. Sample is DR-129, 3451 stope undercut, footwall Twin. Sample location is shown on Figure 3.14. B: Top: Calcite vein with an inner biotite envelope and outer tan coloured carbonate envelope. Bottom: Pyrite + calcite vein with inner chlorite and outer biotite envelopes. Top sample is from DDH UG-271: 44.6 metres; bottom is from DDH UG-399: 34.6 metres. Core is 3.6 centimetres in diameter. C: Chloritic vein material with abundant coarse free native gold. This is the same sample shown in Plate 3.16F. Note the brown patch of calcite + biotite. Sample is DR-84, 150 vein at its junction with the Twin zone, 4061 stope undercut access. Sample location is shown on Figure 3.11. D: Calcite-chlorite veins with irregular margins and biotite envelopes suggestive of progressive wallrock replacement. Note the chlorite at the interface between calcite and biotite altered greywacke in the bottom sample. Top is from DDH UG-418: 53.0 metres; bottom is from DDH UG-185: 35.9 metres.  113  Plate 3.20. Photomicrographs of chlorite-biotite relationships in the Twin zone and shear veins, Snip mine, northwestern British Columbia. A: Chlorite (green) replacing biotite (brown) in a matrix of twinned calcite crystals. Note the indistinct boundaries between the chlorite and the biotite. Plane polarised light. Field of view is 0.63 millimetres Sample is DR-65, from the Twin zone, 4055 stope undercut. Sample location is shown on Figure 3.11. B: A compositional layer of biotite (brown) is replaced by chlorite (pale green) along the upper boundaries of the layer and along a fracture in the centre of the picture. Plane polarised light. Field of view is 5 millimetres. Sample is DR-22, from a shear vein in the 130 haulage level. Sample location is shown on Figure 3.5. C: A chlorite blade (single fibre; not a vein) in a quartz vein consisting of finely intergrown chlorite (dark green-black) is overgrown by high birefringent biotite (yellow, green and red). The quartz matrix is unstrained and has polygonal grain boundaries. Crossed nichols. Field of view is 5 millimetres. Sample is DR-77, from the Twin zone, 4055 stope undercut. Sample location is shown on Figure 3.11.  114  115 Table 3.10: Alteration zonation and character, Twin zone and related shear veins, Snip mine, northwestern British Columbia. ^ ^ Location with^Width Description Alteration type ^ respect to vein (equivalent ore type) 1. Bleached envelope  Outer envelope within greywacke  0.3-4 cm^Pale grey to tan calcite ± silica ± K-feldspar > ± sericite + albite bleaching, often with biotite > pyrite veinlets. 0.3-3 mm wide calcite stringers are common in carbonate rich envelopes, usually at high angles to the shear vein  2. Biotite selvage (biotite rich chloritebiotite ore)  Inner envelope, transitional between vein and wallrock  0.2-5 cm, usually less than 1 cm, but may comprise the bulk of some veins  Felted black biotite, often with disseminated calcite, quartz, pyrite, pyrrhotite and/or magnetite. Weakly to strongly foliated, commonly with shallow dipping oblique foliation to the shear vein boundary. Replaces wallrock fragments and slivers within veins  3. Pink/brown calcite (pink carbonate veins of carbonate ore)  Within outer portions of veins, or as laminae throughout  0.5-1.5 cm, but may be up to 60 cm  Red brown to pink sugary calcite tinted by fine grained disseminated biotite. Replaces biotite altered wallrock fragments within veins  4. Chlorite+calcite (chlorite rich chlorite-biotite ore)  Central vein  <0.1 to >1 m wide  Chlorite + calcite> + pyrite + pyrrhotite. Chlorite is often > 70%. Amphibole occurs in some veins. Comprises schistose chloritic cores to many veins and chlorite rich Twin zone ore  5. Calcite-pyrite (carbonate ore)  Central vein^Variable^Massive sugary calcite with <2 to 60% disseminated pyrite. Chlorite and sphalerite may also occur in this zone  The textures described above suggest that chlorite-biotite and carbonate ore types and veins formed at least partially by replacement processes. Many of the laminated calcite-chlorite-biotite-pyrite shear veins at Snip display evidence for portions of the paragenetic sequence described in Table 3.10, even if they lack progressive alteration zoning. For example, on Plate 3.12C, individual vein laminae consist of biotite, brown calcite, chlorite-calcite, and calcite-pyrite, which are the same mineralogic associations described in the alteration zones above. The consistency of these mineral associations suggests that veins such as this one may represent deformed veins that originally had well developed paragenetic zoning.  116  Thus, individual alteration zones may be disarticulated and strung out into laminae along foliation slip surfaces.  Most quartz and sulphide veins do not fit into the paragenetic scheme defined above. They typically have sharp boundaries (Plates 3.13D, 3.15A, 3.15B), which may obliquely cut laminations in the carbonate veins (Plate 3.16C); some have bladed mineral growth, indicating a dilatant origin (Figure 3.16). Pervasive disseminations of pyrite occur, however, in some carbonate and/or chlorite-biotite veins in sufficient quantity (>30%) for classification as sulphide ore (e.g. (5) in Table 3.10). Such pyrite occurrences may represent either: (i) the sulphide rich stage in the alteration sequence outlined above (Table 3.10), or (ii) deformed sulphide veins with vein boundaries obscured by deformation processes. Pyrite disseminations comprise less than 30% of sulphide ore.  White calcite veins 1-40 centimetres thick, many with coarse grained grey calcite (grains up to 2 centimetres in diameter), and sphalerite veinlets (0.5-4 centimetres thick) appear to be the youngest vein types in the Twin zone. Both late vein types obliquely cut boundaries of all ore types (Plate 3.15C), cut laminae in carbonate-chlorite-biotite veins (Plates 3.12C, 3.15D), and commonly have sharp boundaries suggesting that they are dilatant veins. Many are also deformed (Plate 3.12C). The late veins are commonly auriferous, but grades are usually significantly lower than in adjacent ore types. Foliation parallel white calcite veins, 0.5-4 centimetres wide, occur within the BSU dyke (Plate 3.6A). No sphalerite veinlets occur within the dyke.  3.3.4 Structural style of the Twin zone and related veins  The Twin zone consists of a southwest dipping, closely spaced set of subparallel lensoidal shear veins of the four different ore types (Figure 3.7). The dip of the Twin zone steepens with depth from an average dip angle of less than 45 degrees and strike of 125 to 140 degrees in the upper portions of the mine (above 300-320 metres elevation) to between 60 and 90 degrees dip and 120 degrees strike in the lower  117  portions of the mine (Figure 3.7). The inflection point between the areas of different dip plunges to the west at an angle of approximately 20 degrees (Figure 3.10). The change in the orientation of the zone also corresponds with a change in the dip angle of the internal foliation (Figure 3.17).  The veins define a schistose shear zone in which southwest dipping foliation is confined. A southwest dipping foliation, defined by pervasive alignment of phyllosilicates or closely spaced chlorite-biotitecalcite-pyrite sheeted veinlets, is commonly developed external to the veins for several metres into the hanging wall or footwall of the zone. Subhorizontal to shallow south dipping pervasive foliation may also be developed, as described in section 3.24.  In the lower mine levels (e.g. 2647 and 3049 stopes; Figures 3.14, 3.15) the veins commonly bifurcate around tabular blocks and slivers of biotitic greywacke. Sulphide veins in particular, commonly have irregular, anastomozing non-planar morphology. Individual veins splay primarily into the hanging wall and maintain overall southwest dips (Figure 3.15). Above 340 metre level, veins are more localised and parallel, generally confined to the margins of the BSU dyke, thus defining a more discrete zone (e.g. Figure 3.13). At the bottom and lower eastern portions of the central orebody (between sections 4500 and 4650 metres east), the Twin zone ends in a series of subparallel pyrite veins and veinlets, many of which are en echelon (Figures 3.14, 3.15). Further to the east, between sections 4700 and 4800 metres east and above elevations of 450 metres, the zone splits into several widely spaced (10-40 metres apart) 0.5-3 metres wide lensoidal veins that are developed over a 60 metre width. The BSU dyke is continuous throughout this area. It runs through the centre of the zone of veins and extends to elevations below them to the limits of drilling.  Individual veins within the Twin zone have variable continuity and width. They are seldom traceable for more than 25 metres horizontally or vertically through stopes, although some may be as long as 60 metres (e.g. quartz vein in the Footwall vein on Figure 3.11). Typical widths are between 0.1 and 1 metres. Stacked sets of quartz and sulphide veins are common, and comprise the thickest of these veins  5.00  Twin zone, dip angle (degrees)  (measured from the top of the zone) ^••.  4.00  • cl:r •  8' is  Mean = 43.9 Standard deviation = 15.8 N=365  .^ ./ • 8^ / 3.00  • •  .410111WIAINI  ^ 11811-1X11fflOW , AnusuAl.wt-WaOMMO amMOUP mwrammw U! IIMUmm .111m ,  2.00  4.40  4.50  4.60  Figure 3.10: Contoured Twin zone vertical long section of true dip angle of the top of the zone. View looking north-northeast (030 azimuth). Units are in degrees. The mean is the thick black contour line. Stippled areas lie between the mean and +0.75 standard deviations; black areas are from 0.75 to 1.5 standard deviations above the mean, and hatched areas > 1.5 standard deviations above the mean. Contours below the mean are: (i) a thin continuous line at -0.75, and (ii) a short dashed line at -1.5 standard deviations below the mean. The structural base and erosional top of the Twin zone are shown as long dashed lines. Faults bounding the central block are shown for reference. Blocks east and west of the faults have been moved to restore fault displacement (see Figure 3.9).  119  Figure 3.16: Internal structure, drawn from photographs, of the Twin zone, Snip mine, northwestern British Columbia. Sulphides are stippled. The scale bar is 20 centimetres long. Drawing locations are shown on Figures 3.11 (A and B) and 3.14 (C and D). A: 4055 stope undercut, looking southeast. Folded and attenuated quartz vein in a matrix of schistose laminated chlorite and calcite-biotite. B: 420-level undercut west pillar, looking north. Alternating quartz and massive pyrite veins. The quartz veins exhibit a coarse bladed intergrowth of chlorite and quartz. C: 340-level undercut access, east wall, looking north up the dip of the vein. West verging folded quartz veinlet in a band of black biotite ore. Pyrite veins and footwall greywacke appear in the upper and lower portions of the picture, respectively. D: 340-level undercut access, west wall, looking northwest. A synthetic shear band normally offsets a large quartz augen in a matrix of schistose black biotite > chlorite + calcite. Bottom of sketch is greywacke.  120  Figure 3.17 A-F (above and following pages): Equal area projections (lower hemisphere) of Twin zone structural features, Snip mine, northwestern British Columbia. A: Poles to foliation in the Twin zone, measured in stopes throughout the mine. B: Slickenside and elongation lineation on foliation surfaces within the Twin zone. Lineation plunges moderately west-southwest, parallel to lineations developed on foliation surfaces in the Biotite Spotted Unit (Figure 3.6B) and shear veins (Figure 3.6D). C: Poles to foliation in the Twin zone, measured at different levels in the mine. The plots show a steepening of foliation from shallow to moderate southwest-dipping from the 4055/4061 stope undercut (410 metres elevation, left), tha 2647 stope upper levels (lifts 7-12: 285-300 metres elevation; center), and the base of the 2647 stope and the Twin zone (lifts 1-6: 260-280 metres elevation, right). Data for the right plot (2647 lifts 1-6) was taken from stope maps made by Cominco geologists.  121  Figure 3.17 (continued): D: Axes of folds in the Twin zone. Most of the folds are asymmetric. E: Poles to southwest dipping shear foliation that is parallel to the vein walls (+) and equivalent shallowly dipping oblique foliation (.) developed within the shear veins adjacent to the shear foliation. The data are from the Twin zone and other shear veins. F: Slip direction calculated from 3.17E. The points are 90 degrees from the intersection of the oblique and shear foliations measured along the plane of the shear foliation (Figure 3.17E). These calculated points are compatible with the slip direction in the zone (Figure 3.17B).  122  shown in the stope maps (Figures 3.11, 3.13; Plate 3.16B). Sulphide and quartz veins are often closely related, and individual veins may be sulphide rich in one area and quartz rich elsewhere (Figure 3.15).  Chlorite-biotite and carbonate veins are treated together on all of the stope maps. Although together they comprise most of the Twin zone, their abundance on the maps suggests that they are subordinate to quartz and sulphide ore. This is partially an artefact of both mapping and stope distribution. They commonly occur as 2-10 centimetre wide veins between quartz and sulphide veins, as lenses within these other vein types, or on the margins of other veins where their thickness is too small and distribution too complex to show on the scale of the stope maps. In addition, most of the stopes are centred on sulphidequartz rich areas because these areas typically have high gold grades. These veins are most abundant at the western ends of 4055 and 3852 stopes (Figures 3.11, 3.12).  Foliation parallel brittle faulting affects the zone in many stopes, and is commonly localised to the margins of the BSU dyke. The faults are <2-15 centimetres wide and are filled by rusty gouge. The vuggy calcite-quartz-pyrite veins and bleached alteration associated with larger northwest dipping faults developed elsewhere in the mine are not usually developed in the Twin zone. Offset is variable. Generally there is no discernable or only minor displacement (Figure 3.15). More rarely, ore types and the dyke do not line up across the faults. Displacement is minor compared to the northwest trending faults that offset the west and east portions of the central zone.  The BSU dyke intruded the Twin zone above 280 metres elevation (Figure 3.7). Where the Twin zone steepens below 300 level, the dyke diverges into the hanging wall and continues at a relatively constant 50 degree dip to the limits of drilling (Figure 3.7A). Stope mapping indicates that the BSU cuts ore types within the zone without significant offset (e.g. Figures 3.13, 3.15). Ore types obliquely truncated by the dyke line up on both sides of it in many stopes.  123  Twin zone Footwall vein  The Twin zone Footwall vein is a 1 to 3 metre wide parallel splay of the Twin zone, which is best developed between 370 and 450 metres elevation and 4480 and 4600 metres easting (Figure 3.7B). The vein splays from the Twin zone between 420 and 450 metres elevation and continues at a distance of 3 to 7 metres into its footwall (Figures 3.11, 3.12, 3.13). Several moderate to steeply west dipping veins, striking 110-130 degrees, trend across the greywacke block separating the Footwall vein from the Twin zone in 4055 and 3852 stopes (Figure 3.11, 3.12, 3.13). These cross structures are typically high grade, and generally contain more than 200 ppm Au.  A shallow west plunging open synclinal fold at the base of the Footwall vein joins portions of it to the Twin zone (Figures 3.11, 3.12; Plate 3.27C). The significance of this structure is not understood, but is discussed further in section 3.53. The folded vein material consists mainly of quartz and subordinate sulphide ore, while the remainder of the vein contains a mixture of all four ore types. Footwall shear vein material continues east of the fold in 3852 stope (Figure 3.12), but the width of the vein is greatly diminished (<25 centimetres). At higher levels in 4061 stope (Figure 3.11), the folded quartz vein is separated from the main portion of the Footwall vein to the west by an interval containing only narrow veins and veinlets. Here the fold occurs in a structurally complex zone at the convergence of the 150 vein (see below) and the Twin zone (Figure 3.11).  Internal structure of the Twin zone  Evidence for deformation is abundant in all types of veins in the Twin zone at all scales of observation. Microscopically, laminated calcite-chlorite-biotite veins (carbonate and chlorite-biotite ore types) are heterogeneous and display a wide variety of deformation textures that vary with mineralogy and grain size. Calcite in nearly pure veins or in compositional layers commonly consists of approximately 0.05 to 0 1 millimetre equigranular grains that often define a shape fabric that is parallel or oblique (10 to 35  124  degrees shallower dipping) to the vein walls. Deformation twinning is extremely common, and in many thin sections nearly all grains are twinned. Where chlorite or biotite form thin lamellae in the calcite veins, shape fabrics are most pronounced and elongate calcite grains commonly terminate against the phylosilicates (Plate 3.21A). Elsewhere, microcrystalline calcite ± quartz forms thin layers in veins of coarser grained calcite. Rounded and lensoidal polygonised quartz aggregates or pyrite grains (porphyroclasts) are common in these fine grained areas. Fine grained quartz rich layers in calcite veins may be deformed quartz veins.  Compositional layers of chlorite and biotite are common in carbonate veins. Internally, chlorite and biotite display a strong preferred orientation that defines the foliation. In some chlorite or biotite layers, however, chlorite and biotite form radiating fibres (Plate 3.21B). In such cases, the foliation forms parallel to anastomosing surfaces that separate and truncate lensoidal aggregates of these minerals (Plate 3.21B). Kink banding of phyllosilicate layers is commonly observed in such areas and may be partially responsible for such textures (see section 3.5.2).  In thin section, quartz veins commonly have undulose extinction, display incipient subgrains (Plate 3.21D), have deformation lamellae and are fractured (Plate 3.16D). Where most highly deformed, quartz ribbons with aspect ratios of up to 20:1 are common, often with marginal subgrains (Plate 3.21C). Solid and fluid inclusion trails are parallel to the boundaries of some ribbon grains (Plate 3.22A). Overall, there is a marked reduction in grain size from relatively undeformed quartz veins with coarse crystals and only undulose extinction to fine grained (microcrystalline) equigranular quartz aggregates containing sparse coarser grains. Some quartz veins are annealed, however, and consist of untrained polygonal grains (Plate 3.20C).  Pyrite grains occur in all ore types. The grains are commonly fractured, and other sulphides (pyrrhotite, chalcopyrite, sphalerite and/or galena) or fibrous quartz, calcite, chlorite or biotite filling the voids between fragments (Plates 3.22B, 3.25C). In some sulphide rich carbonate veins, pyrite grains are  125  rounded or tabular. Interpenetrating pyrite grains occur in some samples. In sulphide veins, pyrrhotite, sphalerite, chalcopyrite and galena form a finer grained matrix to pyrite and arsenopyrite grains, which may be euhedral. Grain shapes of these other sulphides are commonly irregular, and in some samples they form weak preferred orientations parallel to the vein walls. Pyrrhotite rich sulphide veins commonly have cuspate undulose margins with shallowly dipping axes. In some stopes, these undulations form cuspate apophyses that project up to 1.5 metres into the wallrock (Figures 3.19B, 3.15). Cleavage in adjacent biotite or carbonate ore curves around these cusps, itself defining folds. Similar structures have been documented in several deposits by Maiden et al. (1986), who termed them cusp and piercement structures, and suggest an origin related to the competency contrast between the pyrrhotite rich sulphide veins and the enveloping wallrock.  The Twin zone and shear veins contain a remarkable diversity of consistent and well developed internal shear sense indicators developed mainly in laminated carbonate and chlorite-biotite ore types. These internal structures indicate that the shear veins formed as dilatant shear zones with an oblique westerly directed normal sense of shear. They include:  (1) A mineral elongation and striation lineation (Figure 3.17) with moderate southwesterly plunge is defined by striations, aligned elongate biotite and chlorite grains, and streaked pyrite, molybdenite and gold on schistose foliation surfaces throughout the Twin zone (Plate 3.22D). The lineated biotite spots in the BSU dyke and lineation on other shear veins at Snip are parallel to this lineation (Figure 3.6, Plate 3.5C).  (2) Oblique shallow dipping foliations occur throughout the Twin zone and shear veins on both mesoscopic (Plates 3.13A, 3.13D, 3.15B, 3.23A, 3.23B) and microscopic (Plate 3.21C, 3.22A, 3.23B) scales. Mesoscopically, oblique foliations commonly occur in wedge shaped to lensoidal blocks within areas dominated by foliation parallel to shear vein walls (Plate 3.23A). Isoclinal folds with axes parallel to the shallow dipping foliation may be localised within the wedges (Plate 3.27D).  126  In some shear veins, foliation is 15-30 degrees oblique to the shear vein boundaries across the entire width of the vein. Quartz and sulphide veins may dilate the foliation in these areas (Figure 3.19). Microscopically, calcite or quartz shape fabrics in polycrystalline aggregates or deformed veins are oblique to shear vein boundaries (Plate 3.21C). Oblique foliations in chlorite-biotite veins may be segmented by slip surfaces parallel to shear vein walls (Plate 3.23B). These have a similar morphology to C-S fabrics (C = foliation parallel to the shear zone boundary; S = flattening foliation oblique to the C fabric) normally developed in quartzo-feldspathic shear zones. However, they probably represent closely spaced shear bands (asymmetric extensional crenulation cleavage; see below) because of their similarity to shear bands developed in the Twin zone.  A plot of the mesoscopic oblique foliations measured during stope mapping and adjacent shear foliation (parallel to shear vein walls) for each is shown in Figure 3.17E. The intersection line of these two sets of planes should be perpendicular to the lineation on the Twin zone foliation if the oblique fabrics and lineation are coeval. The calculated slip direction from the intersection (measured 90 degrees from the intersection of the oblique and shear foliations along the plane of the shear foliation), shown on Figure 3.17F, corresponds well with the measured lineation on the zone.  (3) Asymmetric folds occur in all Twin zone ore types (Plates 3.12D, 3.24A, 3.24B, 3.24C, 3.24D). Fold amplitudes range from 2 centimetres in chlorite-biotite and carbonate ore (Plate 3.24A) to 20-70 centimetre folds in more competent quartz veins (Plate 3.24C). Most fold axes are either subhorizontal or southeasterly plunging, but a range of intermediate plunge directions exists (Figure 3.17). Folds with subhorizontal axes verge down dip, and are common in all ore types. A parallel, shallow dipping crenulation lineation is developed by the intersection of closely spaced fold axial planes in some areas. Intrafolial folds with southwesterly plunging axes verge both east and west, and are common in the chlorite-biotite and carbonate ore types. The dual west and east vergence of folds developed in the relatively incompetent carbonate and biotite ores, with fold axes parallel to the elongation lineation (slip direction), suggests the presence of sheath folds, formed through  127  progressive deformation of initially rectilinear fold axes (Plate 3.23C, 3.23D). Mesoscopic folds occurring at the top of the Twin zone may significantly incre-2ce its width for many metres up dip. These folds commonly are localised above a foliation parallel decollement that has imbricated vein material, resulting in thickening of the zone by up to one metre (Plate 3.24D).  (4) Asymmetric extensional shear bands are common in chlorite-biotite and carbonate ore (Figure 3.16D; Plate 3.25), and locally are associated with minor folds. These structures are discrete slip surfaces that are closely related to synthetic Riedel shears in more brittle environments. They offset and have a 5-25 degree steeper dip than Twin zone shear fabrics (Plate 3.25). These structures cut phyllosilicate compositional layering or quartz veins within carbonate ore, and are commonly between 1-5 centimetres in length with rare examples up to 40 centimetres in length (Figure 3.16D). These slip surfaces are not associated with the development of preferred mineral orientations, except where shear vein parallel foliations are rotated into parallelism with the bands adjacent to them. Displacement varies from up to 6 centimetres of apparent offset on some of the longer shear bands to 0.2-2 millimetres on the smaller ones.  (5) Quartz aggregates and pyrite porphyroclasts with asymmetric and rotated quartz, calcite and/or chlorite pressure shadows (Plates 3.26A, 3.26B, 3.26C) record a sense of movement compatible with the previously discussed kinematic indicators. The pressure shadows comprise recrystallised mineral trails of the porphyroclast (Plate 3.26B), chlorite (Plate 3.26A), biotite (Plate 3.22C), or rotated calcite and quartz fibres (Plate 3.26C).  (6) Asymmetric lensoidal quartz augen have the same geometry as the pressure shadows and indicate a compatible shear sense.  (7) Asymmetric kinking of calcite deformation lamellae occurs in some samples (Plate 3.26D). Shear sense is compatible with all of the other indicators described above.  128  Plate 3.21. Photomicrographs of deformation fabrics in the Twin zone and shear veins, Snip Mine, northwestern British Columbia. All photos are viewed under crossed nichols. A: Strong shape fabrics in calcite (high birefringence). The dark lateral lines mark where calcite grains terminate against chlorite laminae Field of view is 5 millimetres. Sample is DR-22, from a shear vein in the 130 haulage level. Sample location is shown on Figure 3.5. B: Chlorite (vertical grains) in lensoidal aggregates that are separated by foliation planes. Subordinate highly birefringent biotite is intergrown with the chlorite. Field of view is 0.63 millimetres. Sample is DR-38, from the Twin zone, 2242 stope. Sample location coordinates are listed in Appendix 1. C: Quartz ribbon grains (grey and white) intergrown with subordinate calcite. Note the fine-grained subgrains on the margins of individual ribbons and the fine-grained equigranular quartz matrix. The long axes of the ribbons is oblique to the shear zone boundary parallel foliation (parallel to the top and bottom of the photo) developed outside the photograph, indicating an apparent left-lateral bulk shear sense. Field of view is 5 millimetres. Sample is DR-147, from the Twin zone, 4061 stope undercut. Sample location is shown on Figure 3.11. D: A large quartz grain with blocky undulose extinction resulting from subgrain development. Field of view is 5 millimetres. Sample is DR-38, from the Twin zone, 2242 stope. Sample location coordinates are listed in Appendix 1.  129  130  Plate 3.22. Deformation textures in the Twin zone, Snip mine, northwestern British Columbia. A: Quartz ribbon in a quartz aggregate. The matrix is fine-grained calcite (brown) and quartz. A line of fluid inclusions runs through the centre of the quartz ribbon. Two slip surfaces (poorly developed shear bands?) cut the foliation defined by quartz shape fabrics. Crossed nichols. Field of view is 2.3 millimetres. Sample is DR-69B, from 4055 stope undercut. Sample location is shown on Figure 3.11. B: Fractured and segregated pyrite grain (opaque) in a matrix of fine-grained foliated calcite with chlorite aggregates (green) and quartz (pale grey). Voids between pyrite fragments are filled with fibrous calcite. Crossed nichols. Field of view is 2.3 millimetres. Sample is DR-69A, from 4055 stope undercut. Sample location is shown on Figure 3.11. C: Pyrite grain (opaque) in a matrix of foliated biotite (red and blue) with grey quartz grains. Note the face-controlled fibrous biotite pressure shadow on the pyrite grain. Crossed nichols. Field of view is 0.63 millimetres. Sample is DR-129, from 3451 stope undercut. Sample location is shown on Figure 3.14. D: Elongation lineation on schistose chlorite foliation surface defined by streaked native gold (yellow = au) and intergrown molybdenite (pale grey = mo). Sample is DR-116, 3242 stope, lift 1. The sample location is shown on Figure 3.14. The coin is 2.4 centimetres in diameter.  131  132  Plate 3.23. Structural features of the Twin zone, Snip mine, northwestern British Columbia.  The hammer is 32.5 centimetres long and the coin is 2.4 centimetres in diameter. The bulk shear sense is indicated with arrows in samples A, B and C, which are viewed in the XZ plane of the finite strain ellipsoid (i.e. the samples are cut parallel to lineation and perpendicular to foliation).  A: 3852 stope, lift 5 west, looking northwest. Photograph is of laminated calcite + biotite + quartz + chlorite + pyrite shear vein with oblique internal subhorizontal foliation above massive biotitic greywacke. Note the wedge shape of the block containing the oblique foliation. The fabrics indicate a component of normally directed simple shear on the shear zone boundary parallel foliation that dips to the right. The photo location is shown on Figure 3.12. B: Photomicrograph (plane polarised light), looking southeast, of pervasive Twin zone shear foliation (parallel to the bottom of the photograph) defined by platy alignment of chlorite and biotite cut by spaced shear bands (extensional crenulation cleavage). Slip has been accommodated along the inclined shear bands and the shear fabric is rotated sympathetically into parallelism with the shear bands as it joins them. These structures have a similar morphology, but different origin to C-S fabrics. Sample is DR-152, from 260 level undercut west. Lateral field of view is 4 millimetres. C and D: Schistose biotite vein with foliation parallel pyrrhotite (po) trails, disseminated magnetite (mag) and calcite (cal) > pyrite + chlorite + biotite veins. Sample is DR-129 from 3451 stope undercut at access. Sample location is shown on Figure 3.14. C: Cut parallel to lineation and perpendicular to foliation, showing linearity of the calcite veins. Note the oblique foliation in the centre of the picture suggesting a right lateral sense of shear. The sample is oriented, and the view is to the southeast within the Twin zone. Foliation asymmetry indicates a normallydirected sense of shear. D: The same sample as A, but cut orthogonally to it and perpendicular to lineation developed on foliation surfaces. The calcite veins in this section are asymmetrically folded and folds verge to the right (east). Thus, the fold axes are parallel to the lineation, suggesting the presence of sheath folds.  133  134  Plate 3.24. Mesoscopic folds in the Twin zone, Snip mine, northwestern British Columbia. The bulk shear sense is indicated by the fold asymmetry (arrows). The hammer is 32.5 centimetres long. The coin is 2.4 centimetres in diameter.  A: Asymmetrically folded quartz > chlorite + calcite veins with radiating chlorite growth (top, centre) above isoclinally folded brown calcite > biotite + chlorite vein material. Folding intensity is greatest in the theologically weaker calcite rich vein material than in the more competent quartz veins. Fold vergence indicates the bulk shear plane (arrows). Sample is DR-162, 300 level west. Sample location coordinates are listed in Appendix 1. The sample is cut parallel to lineation and perpendicular to foliation (i.e., it is observed in the XZ plane of the finite strain ellipsoid). B: Folded pyrite > quartz veins verge down dip in a block of biotitic greywacke within the Twin zone. A southeast dipping quartz + calcite > chlorite extension vein cuts and offsets pyrite veins in the upper part of the picture with apparent reverse displacement. Subhorizontal calcite veinlets occur in the greywacke to the right of the hammer, parallel to a weak spaced biotitic foliation. 3451 stope undercut southeast, looking northwest. Photo location is shown on Figure 3.14. C: Folded quartz > chlorite + calcite vein above a pyrite vein. Shallow southeastdipping quartz > chlorite + calcite extension veins cut the folds within the quartz vein. The folding is developed above a decollement at the base of the sulphide vein and above foliated biotite altered greywacke. 3451 stope undercut at the access, looking northwest. Photo location is shown on Figure 3.14. D: A large fold terminates a 1.5 metre wide hanging wall portion of the Twin zone. The fold and the tabular block of vein material are separated from the calcite + chlorite + biotite Twin zone vein material below by a shear zone boundary parallel decollement surface as marked. 4055 stope, lift 2 looking northwest. The lateral field of view is 3.5 metres (spacing between the yellow paint marks is 1 metre. Photo coordinates are listed in Appendix 1.  135  136  Plate 3.25. Shear bands and oblique foliations, Twin zone and 150 vein, Snip mine, northwestern British Columbia.  All of the samples are cut parallel to lineation and perpendicular to foliation (i.e., the samples are observed in the XZ plane of the finite strain ellipsoid). The coin is 2.4 centimetres in diameter. The bulk shear sense is indicated with arrows.  A: Interlayered quartz, pyrite and calcite > quartz + chlorite veins. An asymmetric extensional synthetic shear band crosses the compositionally layered calcite > quartz + chlorite vein in the centre of the picture, indicating a left lateral shear sense. Oblique foliation in the pressure shadow of a rounded quartz porphyroclast in the upper centre indicates a compatible sense. The in situ shear sense in the oriented sample is normally directed. Sample is DR-328, 3049 stope lift 5 east. Sample location is shown on Figure 3.14. B: Photomicrograph (plane polarised light) of a asymmetric extensional synthetic shear band in compositionally layered biotite-calcite > quartz-opaques (pyrrhotite + pyrite) shear vein. The shear sense is left lateral, corresponding with an in situ normally directed shear sense. Sample is DR-129, from 3451 stope undercut at access. Sample location is shown on Figure 3.14. The field of view is 5 millimetres. C: Photomicrograph (crossed nichols) of fractured pyrite with displaced segments indicative of right lateral shear. Voids between the fragments are filled with fibrous quartz, which records the displacement history. The deformed grain is associated with a short, discontinuous shear band. Sample is DR-223, 4061 stope undercut, from a schistose portion of the BSU dyke. Sample location is shown on Figure 3.11. The field of view is 5 millimetres.  LIT  138  Plate 3.26. Twin zone, shear sense indicators in thin section, Snip mine, northwestern British Columbia. Samples are cut parallel to lineation and perpendicular to foliation (i.e., the samples are observed in the XZ plane of the finite strain ellipsoid). The bulk shear sense is indicated with arrows. A and B: Photomicrograph (crossed nichols) of quartz porphyroclasts with asymmetric rotated chlorite (3.25A, green) and quartz + chlorite (3.25B) pressure shadows. Sample is DR-69, 4055 stope undercut west. The sense of rotation is anticlockwise (left lateral shear), corresponding to a sense of normally directed shear in the oriented sample. Both views are to the northwest. Sample location is shown on Figure 3.11.The field of view is 2.6 millimetres in 3.25A and 5 millimetres in 3.25B. C: Photomicrograph (plane polarised light) of a pyrite grain with rotated fibrous calcite pressure shadows in foliated calcite > quartz + biotite + pyrite shear vein. The sense of rotation is clockwise (right lateral shear), corresponding to a sense of normally directed shear in the oriented sample. Sample is DR-152, from 260 level west. The view is looking to the northwest. Sample location coordinates are listed in Appendix 1. The field of view is 5 millimetres. D: Photomicrograph (crossed nichols) of asymmetric kinking of calcite deformation twin lamellae. The sense of rotation is clockwise (right lateral shear), corresponding to a sense of normally directed shear in the oriented sample. The view is to the northwest. Sample is DR-152, from 260 level west. Sample location coordinates are listed in Appendix 1. The field of view is 2.63 millimetres.  139  140  3.3.5 The 150 vein and other shear veins  Several shear veins in the footwall of the Twin zone also comprise ore at Snip. The largest and most significant of these is the 150 vein. No significant veins occur in the hanging wall.  The 150 vein  Like the Twin zone, the 150 vein consists of a closely spaced set of subparallel to anastomozing veins of variable ore types, but it is dominated by sulphide veins. The vein is present above the 300 metres level. It diverges from the folded Twin zone Footwall vein at its east end between 4600 and 4625 metres east in 4061 stope (Figure 3.11). The 150 vein does not join the Twin zone, but the structures converge to within 5-15 metres between 380 and 430 levels. Thickness varies up to 3.5 metres, but is usually 0.5-1.5 metres. The vein is longest laterally between the 350 and 400 metre levels, where it can be traced 100120 metres horizontally (Figure 3.13). The vein arcs from a 190 to 160 degree strike at its eastern end to a 125-145 degree strike at its western end. The dip (>50 degrees) is steeper than the Twin zone. Internal foliation orientation varies with vein orientation, but is generally slightly shallower than the vein itself (Figure 3.18A). Mineral lineation on the foliation plunges west (Figure 3.18B). At the basal termination of the 150 vein on the main ramp below 300 level, the greywackes have a schistose subhorizontal biotitic foliation.  The 150 vein consists primarily of massive pyrite + pyrrhotite and quartz veins. Subordinate schistose biotite rich chlorite-biotite ore and/or laminated carbonate ore commonly occur adjacent to the sulphidequartz vein on the margins of the zone (Plate 3.15A). Overall, the vein exhibits evidence for more dilatant opening than the Twin zone. In some stopes (Figure 3.13), schistose chlorite-biotite and carbonate ore are most common where the vein has an azimuth of 120-140 degrees, whereas dilatant sulphide-quartz veins are abundant at azimuths greater than 140 degrees. Thus, the character of the vein changes from shear vein to dilatant vein with increasing strike azimuth. The shear vein character of the  141  Figure 3.18: Equal area projections (lower hemisphere) of 150 vein structure, Snip mine, northwestern British Columbia. A: Poles to foliation, measured on 350, 375, 385, 400 and 420 levels. Foliation is moderately west to southwest dipping. B: West-southwest plunging slickenside and elongation lineations measured on foliation surfaces on the same levels as above.  •.1.1.-wmr.„. . ■ . •••".ries`, 4-;*".. t." IL •^AvV4  ,Figure 3.19: Structure of the 150 vein, drawn from photographs, Snip mine,  northwestern British Columbia. Scale bars are 1 metre long. A (above): 385 sill drift, looking north (up the vein). Massive pyrite + pyrrhotite > quartz veins (stippled) in a matrix of schistose biotite > calcite + chlorite form a 20 degree oblique angle with the boundaries of the zone. The obliquity between foliation and the veins suggests a left-lateral shear sense in this view, which would be right lateral in plan view. The location of this drawing is shown on Figure 3.13. B (left): 400-level west access, looking southeast. Two massive pyrite-pyrrhotite veins are separated by strongly biotite-altered greywacke. Note the undulose margin of  the sulphide vein on the left side of the picture, and the tongue of sulphide that joins the two veins. The location of this drawing is shown on Figure 3.12.  143  Plate 3.27 Structure of shear veins at the Snip mine, northwestern British Columbia. A: 130 vein, 430 level, looking southeast. Laminated calcite > chlorite + biotite + quartz shear vein (right) with two subvertical footwall splays. The grey vein material immediately to the right of the hammer has gradational contacts with the greywacke and consists of strong carbonate wallrock alteration. Note the extension veins (dipping to the left) in the hanging wall of the zone that are orthogonal to it, and the boudinage of the shear vein where they are most abundant. The photo location is shown on Figure 3.20. The hammer is 32.5 centimetres long. B: 150 vein, 385 sill drift southeast, looking east and upward (up vein dip). Massive pyrite + pyrrhotite > quartz vein offset by a southwest-dipping laminated calcite > chlorite + biotite + pyrite shear vein. The base of the massive sulphide vein follows the yellow line. The viewpoint makes the sense of offset misleading, giving an apparent reverse sense; however, lineation on the shear vein indicates that the slip direction plunges shallowly toward the viewer, and that the true sense of offset is oblique normal with a right-lateral component. See Figure 3.13 for the location of this picture and the plan view. The view is 1.7 metres wide. C: Folded quartz > chlorite + pyrite vein between the Twin zone Footwall vein (to the right of the photo) and the Twin zone (left of the photo). View is looking west. Note the extension vein (moderate dip to the left = ext) that cuts the left limb of the folded vein. 3852 stope, lift 5 at access. See Figure 3.12 for the location of this picture and the plan view. Lateral view is approximately 2 metres wide. Photograph by B. Coates, October 1992. D: Flat isoclinal folding in a wedge shaped block of calcite-chlorite-biotite vein. The block is bounded by slip surfaces that are parallel to southwest dipping foliation in surrounding laminated calcite-chlorite-biotite-quartz vein material (top and bottom, partly covered in brown mud). View is to the northwest. Twin zone, 4055 stope undercut. See Figure 3.11 for the location of this picture. The view is 0.6 metres wide.  145  western end of the vein on 385 level is illustrated in Figure 3.19. Here lensoidal sulphide veins are parallel to, and are controlled by, an oblique and moderately southeast dipping foliation. Obliquity indicates a predominantly right lateral sense of shear with an oblique normal component consistent with the lineation direction (Figure 3.18B). The eastern end of the 150 vein on 400 metres level ends in a horsetail like structure bounded by two 160-200 degree striking, west dipping quartz-sulphide veins that bound and join several 120-135 degree striking, moderately southwest dipping veins (Figure 3.12). These dual vein orientations are similar to the changing orientations of the 150 vein on lower levels (Figure 3.13), and the orientations of the Twin zone and cross veins in 4055 stope (Figure 3.11). Sulphide rich sections of the 150 vein, striking 150-180 degrees, are cut and offset by 4-15 centimetres wide southwest dipping laminated calcite-chlorite-biotite-pyrite shear veins on 385 metres level (Figure 3.13; Plate 3.27B).  Other major veins  No other veins with similar size to the Twin zone or 150 vein are currently known at Snip. However, several smaller veins (usually <60 centimetres wide) have high gold grades (commonly > 100 ppm) which are sufficient for mining over a minimum mineable width (e.g. reserves in the 150 Footwall vein are approximately 20,000 tonnes grading 20 ppm Au). All occur within 120 metres of the Twin zone in its footwall, and are either parallel to, or have steeper southwest dips than the Twin zone. These include the 130, 150 Footwall and 2639 structures. The 130 and 150 footwall structures are of similar size and character, and may represent upper and lower extensions of the same structure. The 130 structure occurs 120 metres into the footwall of the Twin zone between 4550 and 4650 East in the upper levels of the mine (above 400 level, Figure 3.20, Plate 3.27A). The 150 Footwall structure is at lower levels (360-400 levels), and occurs 20 metres into the footwall of the northwestern end of the 150 vein (Figure 3.13; Plate 3.7C). The 130 and 150 Footwall veins comprise a mixture of all four of the ore types in a closely spaced set of branching and anastomozing veins, 10 to 50 centimetres in thickness (Plate 3.27A). Veins are commonly in en echelon arrangement (Figure 3.20). Highest gold grades occur in sulphide veins,  Figure 3.20: Map of the 130 vein, 430 level, Snip mine, northwestern British Columbia. The vein is composed primarily of laminated calcite + chlorite + biotite (dashed pattern) in a matrix of massive feldspathic greywacke (stippled). Slickenside lineations are shown as arrows. Note the en echelon arrangement of veins.  147  which may grade in the hundreds of ppm gold. On 380 level (Figure 3.13), the bounding of the 150 vein by the 150 Footwall vein to the north and by the Twin zone to the south is geometrically similar to the bounding of cross structures in 4055 stope by the Twin zone and Footwall vein (Figure 3.11).  The 2639 structure occurs in the footwall of the western faulted part of the Twin zone west of section 4450 and below 340 level. It is parallel to the Twin zone. The structure is a 20-40 centimetres wide replacement vein comprising pink calcite and chlorite. Gold values can be spectacular (several hundred ppm Au), but are erratic. Similar to veins in the Twin zone, gold is coarse and free, and commonly occurs with molybdenite. Other pink calcite/chlorite veins also occur in this area.  Below 220 metres elevation, beyond the base of the Twin zone, several more veins have been intersected, some of which are en echelon with the Twin zone (Figure 3.7A). These veins are discontinuous, and are generally not traceable for more than 50 metres. Although they are mineralogically similar to the Twin zone, gold grades, even in sulphide veins, are mostly low (<10 ppm Au). As described in section 3.24, laminated calcite-chlorite-biotite shear veins also occur well into the footwall and hanging wall of the Twin zone. Like the veins below the Twin zone, gold grades are low (usually <1 to 5 ppm Au). The intensity of veining is different in the hanging wall and footwall of the Twin zone. In the footwall, over 750 metres (2000-2750 metres north along the 130 haulage level) measured perpendicular to the Twin zone, 66 shear veins (<0.05 to 80 centimetres thickness) were mapped (one per 11 metres). Whereas, in the hanging wall on the 180 level south (1700-1900 metres north) only 9 shear veins were encountered over 200 metres (one per 22 metres).  3.3.6 Relationship of stratigraphy to the Twin zone  Intersection points of the top and bottom of the mixed greywacke-siltstone-mudstone package (unit 3 from section 3.21) with the Twin zone were measured using stratigraphic cross-sections generated by Read (1990) (4387.5 to 4500 east; Figure 3.7A) and during this study (4550 east, Figure 3.3). Data are  148  in Table 3.11 and are plotted on Figure 3.21. The top and bottom of the unit are defined as the first and last appearances of siltstone or mudstone in the sections (Figures 3.3, 3.21). The intersection line of the Twin zone and unit 3 undulates across the plane of the Twin zone with a shallow westerly plunge (Figure 3.21). Consistent morphology and parallelism of the lines and the relatively constant thickness of the unit, both in the hanging wall and the footwall, suggest that the points accurately define its outline.  Displacement of bends in the intersection line of the hanging wall and footwall allow unique determination of the magnitude and direction of offset on the Twin zone. The magnitude of displacement is calculated in Figure 3.22. Several assumptions are made for this calculation: (1) The average strike of the Twin zone is 120 degrees, which is parallel to the vertical long section. (2) Average dip of the zone is 44 degrees, the mean value in Figure 3.10. (3) The contoured peak in Figure 3.22A represents the average orientation of the lineation on foliation surfaces within the Twin zone (250/35 orientation).  The average Twin zone lineation defined by contouring (peak in Figure 3.22A) lies within one degree of the trace of the 120/44 trace of the Twin zone defined above. The orientation corresponds with a rake to the lineation of 58 degrees on the Twin zone surface at the closest point to the lineation peak (Figure 3.22B). The plunge of the lineation on the vertical long section is determined in Figure 3.22B. The lineation projected to the long section is the intersection line of a vertical plane that both contains the lineation and is perpendicular to the foliation. This equates to a 48 degree westerly plunge to the lineation on the long section. Projected to Figure 3.21, this orientation closely approximates the displacement direction of unit 3. Thus, in the displacement calculations this plunge is assumed to be the true displacement direction. Measured parallel to this line, apparent net slip on Figure 3.21 ranges between 60 and 90 metres. Calculation of the true net slip, strike slip and dip slip components of the offset on the southwest dipping Twin zone is solved in Figure 3.22C. The calculations establish that: (i) true net slip is 75-114 metres oblique normal, (ii) true dip slip is 64-97 metres, and (iii) true strike slip is 40-61 metres.  149  In addition to the displacement on the Twin zone, several more important observations can be made from Figure 3.21: (1) The inflection point between the upper shallowly dipping portion of the Twin zone and the steeper lower portion of the zone coincides with the upper intersection line of unit 3 in the Twin zone footwall in Figure 3.10 (i.e., the Twin zone steepens its dip angle upon intersecting unit 3). (2) The base of the Twin zone is roughly parallel to and coincides with its intersection with unit 3. (3) Offset of unit 3 continues beyond the base of the Twin zone. These points are discussed further in section 3.5.  Table 3.11: Intersection points of unit 3 (mixed greywacke-siltstone-mudstone package; see section 3.21) with the Twin zone, Snip mine, northwestern British Columbia. Data are measured from sections constructed by P. Read (sections 4387.5-4500 east: Read, 1990; Figure 3.7A). Section 4550 was examined as part of this study (Figure 3.3). The points are plotted on Figure 3.21.  Section (Easting) 4387.5 4400 4412.5 4425 4437.5 4450 4462.5 4475 4500 4550  Intersection of unit 3 with the Twin zone (elevation in metres) 1 Footwall of the zone Hanging wall of the zone Top of unit 3  Bottom of unit 3  280 275 294 310 or more 315 325 330 328 335 360-370  220 — --250 260 260 258 274 300-320  'No information is represented by "—"  —  Top of unit 3 -260 260-280 faulted -270-290 — 282 320 295-325  Bottom of unit 3  — 190  — — — — —  225 240 —  150  0  450 CD  Easting (metres) Figure 3.21: Intersection of the mixed greywacke-siltstone sedimentary package (unit 3) with the central Twin zone, plotted on vertical long section (looking toward 030 azimuth). Intersection points are derived from Table 3.8. Dots = intersection of unit 3 with the footwall of the Twin zone, crosses = intersection of unit 3 with the hanging wall of the Twin zone. The shaded outline of the area of the intersection is shown for both the footwall (horizontal hatching) and the hanging wall (stippling). The projection of the stretching lineation on foliation surfaces onto the long section is shown, and has a 48 degree rake to the west in a vertical plane (see Figure 3.22). The base and eroded top of the Twin zone are shown as continuous lines, and faults are squiggly lines.  151  Al.—..Plane that is perpendicular to the long section which contains the lineation  a—Lineation projected to the vertical long section (300;48)  2l0  Figure 3.22: Calculation of the displacement of unit 3 on the Twin zone.  A: Contoured stereonet of the lineation on foliation surfaces within the Twin zone. The peak is at 250/35. See text for details. This is the contoured version of Figure 3.17B (n=92). B: Calculation of the rake of the average Twin zone lineation projected from the Twin zone to the vertical long section. See text for details. C: Calculation of displacement of unit 3 on the Twin zone. The block diagram shows the Twin zone, vertical long section, average lineation on the Twin zone (58 degrees westerly rake on the Twin zone, from B above), and projection of the lineation to the long section (48 degrees rake to the west, from B above). The apparent net displacement of unit 3 was measured parallel to lineation on Figure 3.21, and ranges from 60 to 90 metres both for the top and bottom of the unit. The true strike slip, true net slip and true dip slip vectors were then calculated trigonometrically as follows: True strike slip = cos48(apparent net slip) = cos48(60 to 90 metres) = 40 to 60 metres. True net slip = (true strike slip)/cos58 = (40.1 to .60.2 metres)/cos58 = 76 to 114 metres. True dip slip = tan58(true strike slip) = tan58(40.1 to 60.2 metres) = 64 to 96 metres.  152  3.4 ORE TYPE AND MINERAL DISTRIBUTION WITHIN THE TWIN ZONE  3.4.1. Introduction  Distribution of ore types and minerals in the Twin zone was evaluated using 365 intersections extracted from the large database of 456 intersections. Holes in the database with missing data (e.g. with missing core or analytical data, or holes that did not intersect or cross the entire Twin zone) and widely spaced holes drilled to the east and west of the central orebody were excluded from the data set. The extracted holes used in this study (365 holes) were drilled between 4300 to 4700 metres east and 200 to 500 metres elevation on the Cominco Snip grid. These holes were drilled mainly in one cohesive fault bounded block, which forms the bulk of the Snip ore (Figure 3.9). Offset portions on both sides of this central block have been restored to their probable original position prior to faulting in Figure 3.9b. Restoration is based on the fault slickensides, offset of the base of the Twin zone and relative position of the BSU dyke to the zone, as outlined in section 3.24. Restored sections have been used in most of the spatial plots, with the positions of the faults marked for reference (Figures 3.23 to 3.26). The plotted points are the central pierce point of the Twin zone intersection.  The spatial distribution plots assume no displacement of ore across the BSU dyke, following observations made during stope mapping. Thus, in intersections where the vein was intersected on both sides of the dyke, the two sections of the vein have been treated as one, and the effect of the dyke has been ignored. The Footwall vein has been included in ore type, mineralogical and metal distribution plots because of its intimate relationship with the zone (Figure 3.7). The 150 vein and other veins are not included in this study, since they are not directly connected to the Twin zone.  Mineral and ore type zoning in the Twin zone has been evaluated using both computer generated and hand contoured vertical long section plots (Figures 3.23, 3.24, 3.26). These are based on weighted visually estimated mineral percentages and measured ore type thickness in 365 intersections of the Twin  153  zone. The computer program PRES, recently developed at The University of British Columbia (Bentzen and Sinclair, in preparation) was used to generate the computer plots. They have been contoured using the mean, and 0.75 and 1.5 standard deviations above and below the mean.  Many of the plots presented form the basis of a preliminary investigation of ore type, mineral and metal distribution within the Twin zone by the author (Rhys, 1993). Metal distribution, with the exception of gold, is not described here. Further investigation of metal distribution is underway (Rhys, Sinclair and Godwin, in preparation).  3.4.2. Ore type distribution in the Twin zone  Points plotted on the vertical long section for ore type thickness represent cumulate true thicknesses of each ore type in individual drill intersections. Abrupt changes in a particular ore type thickness may indicate the presence of different lenses (veins) of that ore type within the Twin zone. In any one locality, several veins of a single ore type may be present across its width. Thus, where several layers of a particular ore type were intersected in a drill hole, their thicknesses have been added to create one point for plotting.  Hand contoured plots of the distribution of ore types for the central Twin zone block exclude the offset Twin zone across the faults (Figure 3.24). The four plots are shown because they allow a detailed view of variations in the thickness of the ore types and are not subject to the smoothing effects of the computer generated plots. However, computer contoured plots of each ore type in the central block are included for comparison (Figures 3.23B, 3.23E, 3.23H, 3.23K). In these latter plots, intersections with 0 values (i.e., not containing the particular ore type) are excluded so that variations within the thickness of each ore type is clearer (Figures 3.23B, 3.23E, 3.23H, 3.23K).  5.00 5.00  Carbonate ore thickness (m)  Carbonate ore thickness (m)  Mean = 0.73  Excluding intersections nut containing this ore type  Standard deviation = 0.69 N=365 4.00  Mean 0.81 Standard deviation = 0.65 N = 278  4.00  3.00  3.00  2.00  2.00  Chlorite-biotite ore thickness (m)  Chlorite-biotite ore thickness (m)  Standard deviation = 0.32 4 00  (Chlorite-biotite ore)/(Twin thickness)  Excluding Intersections not containing this ore type  Nte.an^0.25  Mean = 0.15 Standard deviation = 0.18 N=365  Mean = 0.41  N=365  Standard deviation = 0.33 N = 203  080  3.00  Mean = 0.44 Standard deviation = 0.30 N=365  6  Cr../ / • g)  ows  2.00  4 .30  4.40  4.50  4.60  4.40^  4.50^  4.60  Figure 3.23, A-P: Contoured vertical long section graphs of ore type and zone thickness, Twin zone, Snip mine, northwestern British Columbia. View is looking north-northeast (030). Axes are Easting (metres x1000 = X axis) and Elevation (metres x100 = Y axis). All units are in metres, except plots C, F, I and L, which are ratios. The mean is the thick contour line. Stippled areas lie between the mean and +0.75 standard deviations; black areas from 0.75 to 1.5 standard deviations above the mean, and hatched areas >1.5 standard deviations above the mean. Contours below the mean are: (i) a thin continuous line at -0.75, and (ii) a short dashed line at -1.5 standard deviations below the mean. The structural base and erosional top of the Twin zone arc shown as dashed lines. Faults bounding the central block are shown for reference; where shown, blocks east and west of the faults have been moved to restore fault displacement (see Figure 3.9).  5.00  Sulphide ore thickness (m) Excluding Intersections not containing this ore type  Mean = 0.41 Standard deviation = 0.51 N=365 4.00  Mean = 0.24  Mean = 0.57 Standard deviation = 0.53 N = 226  4.00  3.00  Standard deviation = 0.27 N=365  3.00  O  2.00  2.00 4.40  4.50  4.60  5.00  Quartz ore thickness (m) Mean 0.33 Standard deviation — 0.46 N = 365  Excluding Intersections not containing this ore type  Mean 0.54 Standard deviation = 0.50 N .2. 216  Mean = 0.18 Standard deviation = 0.20 4.00  3.00  2.00  Figure 3.23 (continued)  N=365  5 . 00  4.00  Carbonate + Chlorite-Biotite ore thickness (m) Excluding intersections not containing these ore types  Sulphide + quartz ore thickness (m Excluding Intersections not containing these ore types  Mean = 1.03  Standard deviation = 0.75 N = 280  Standard deviation = 0.8 N 298  MI^ 0 0  3.00  no 0 R o o o o  a,.  Mean = 0.88^• b  =  nr.  o 90 o  10 " )  M  2.00 4.40  4.50  4.60  6 00  S.00  Twin zone vein thickness (m)  4.00  Mean = 1.73 Standard deviation = 1.26 N=365  Mean = 3.51 4.00  3.00  3.00  2.00  2.00  4.30^4.40  4.50^4.60  Standard deviation = 2.96 N=365  4.30  Figure 3.23 (continued)  4.40  4.50  4.60  157  Figure 3.24, A-E^g pages): Hand contoured plots of true ore type thickness,central Twin zone, Snip mine, northwestern British Columbia.The plots are vertical long sections of the central Twin zone, looking toward 030 azimuth (north-northeast). Bounding faults are shown, as are the upper erosional surface (dashed line) and structural base (solid line) of the zone. A: Drill hole pierce points in the central zone. Section lines are marked for each intersection. The points are the central pierce point tig each intersection. Drill hole points below the base of the Twin zone which did not intersect it are shows, as they provide control on its distribution. B-E: Contoured plots of ore type true thickness. Contours are in centimetres. Lines are drawn at 0, 15, 40, 65, 90, 130, 180 and 2.i0 centimetres. Colours are as follows: 0-15 cm=light blue; 15-40 cm=dark blue; 40-65 cm=green; 65-90 cm= yellow; 90-130 cm=orange; 130-180 cm=purple; 180-250 cm=red. The plots are: B = Carbonate ore, C = Chlorite-biotite ore, D =- Sulphide ore, and E = Quartz ore.  ^  co  • •  Figure 3.24A: Drill hole pierce points, central Twin zone 450 •  ^• •  • •  •  400  • • •  •  250  •  •  •  •  • • • • • • • • • • • •^• • •^• • •  • • • • •  • • • • •  ---'  •  •^  • • • ,^ • ••^•• • •^ • •^•• •^ • •^  •  •  •  •  •  •  • •  • • • • • • • • • •^ • • • • • •^ • • • • • • • • • • • • •^ •^• • • • • • • • • •^ • •• • • • •• • • • • • • • • • • • • • • •  •  •  • • • • • •  • • • •^• • • • • • • • • •• •^ •^• • • • • .• • • • • • • • •^ • • • • • •^ • •^ • • ••^ • • • • • •^• • • • • • ••^ •^• • •^• •^ • • •^•^ • • ••• • • •^ • • • • • •^ • • • • • •^•^ • •^ • • • •^•^• •^ • • : • • • •^ •  ^  •  •^ • • • •^•^• • •^• •^•  •• • •• • • • • •  ....."---  300  • • •  •• •  •^•  •  350  •  •  •  •• • • • •• • •  •  •  •  •  Easting (metres)  Figure 3.24B: Carbonate ore, true thickness (cm)  450  400  350  300  250  Figure 3.24C: Chlorite - biotite ore, true thickness (cm)  450  400  Easting (metres)  Figure 3.241): Sulphide ore, true thickness (cm)  4=6^ 01  4:6  Figure 3.24E: Quartz ore, true thickness (cm)  450  400  350  300  250  163  The plots indicate that the ore types have variable but distinctive distributions. Carbonate and chloritebiotite ore are similarly distributed (Figures 3.23A, 3.23B, 3.23D, 3.23E, 3.24B, 3.24C). They are markedly thickened in a restricted zone in the lower western parts of the orebody. Proportionately, carbonate ore comprises most of the vein material in the lower western parts of the zone (Figure 3.23C). Sulphide ore forms a narrow shoot in the centre of the orebody, and is thickened in the upper levels of the mine (Figures 3.23A, 3.23B, 3.24 D). The narrow sulphide ore shoot in the centre of the orebody has three distinct trends that plunge more shallowly to the west than the overall trend of the shoot itself (Figure 3.24D). Proportionately, sulphide ore is most abundant in the eastern portions of the zone where it can comprise the entire Twin vein (Figure 3.231). Quartz ore defines an irregular, overall west plunging elongate trend in the central western parts of the zone, but is thickened mainly in a shallow dipping narrow zone in the upper portions of the zone (Figure 3.24E).  Plots of the combined thickness of related ore types are shown in Figure 3.23M and N. Both the linear sulphide ore shoot and the shallow dipping trend of the quartz ore are reflected in the plot of quartz + sulphide ore, which reflects the overall distribution of dilatant veins in the Twin zone. This close association of quartz and sulphide ore types is apparent in Figure 3.25. Here, thickened areas of quartz and sulphide ore lie adjacent to one another. The quartz veins defining these peaks are probably lateral extensions of the adjacent sulphide veins and vice-versa, as is suggested by the intimate relationship of quartz with sulphide veins in stope maps. The combined plot of carbonate and chlorite-biotite ore is nearly identical to that of carbonate ore (Figures 3.23A and M).  Stope mapping verifies the presence and location of the ore type trends described above. For example, the sulphide ore trend can be traced through the stope maps (refer to Figure 15). Beginning at its base at 260 metres elevation in 2647 stope (Figure 3.15, section 4462.5 East), the sulphide veins gradually move east and upward in the zone through 3049 (sections 4500 and 4512.5) and 3451 stopes (Figure 3.14). The lower portions of this shoot comprise many spatially related sulphide veins that commonly splay into the hanging wall of the zone. The base of the thickest portion of the narrow subhorizontal trend of quartz  164  ore (Figure 3.24E) is exposed in 4055/4061 stope undercut (Figure 3.11). Quartz here occurs both in the main portion of the Twin zone and in the Twin zone Footwall vein. At the west end of the map it is associated with thick veins of carbonate and chlorite-biotite ore, which define the central portion of the thick trend in Figure 3.24A.  The plot of the total thickness of vein material (all four ore types together, Figure 3.230) reflects the distribution of the ore types and their relative abundance. Mean vein thickness is approximately 1.7 metres. Veins are thickest (Figures 3.23M and N): (i) in the upper parts of the zone, (ii) in a linear trend defined by quartz and sulphide ore, and (iii) in a thickened area in the western parts of the zone straddling the fault that is defined by quartz and carbonate ore together. Dilution is also greatest where the veins are thicker. This is shown in Figure 3.23P, which contains approximately 100% dilution of vein material by internal greywacke and BSU dyke with respect to Figure 3.230. Together greywacke, BSU and veins define a mean Twin zone thickness of 3.5 metres. Significant greywacke dilution occurs where the veins bifurcate into the hanging wall and footwall of the Twin zone (e.g. the Twin zone Footwall vein).  There is no direct relationship between dip angle and thickness of quartz ore, of sulphide ore or of quartz + sulphide ore (Figures 3.23G, 3.23H, 3.23J, 3.23K; compare to Figure 3.10). However, carbonate and chlorite-biotite ore are thickest in areas of shallowest dip (Figure 3.23M). The line of inflection between the shallow and steep dips of the Twin zone plunges shallowly west, shallower than the thickness of sulphide ore and quartz ore trends.  Several of the distribution patterns described above correspond with both internal and external structural features associated with the Twin zone: (1) The thickened carbonate and chlorite-biotite ore distribution in the upper part of the mine (Figure 3.23M) corresponds with the distribution of the Twin zone Footwall vein (Figure 3.8).  165  Easting (metres)  Figure 3.25: Vertical long section (looking toward 030 azimuth) showing important structural features and thickened areas of quartz and sulphide ore, Twin zone, Snip mine, northwestern British Columbia. The base and eroded top of the Twin zone are shown as continuous lines, and faults are squiggly lines. Areas containing >65 centimetres of quartz ore are stippled, while areas containing >65 centimetres of sulphide ore have a horizontal dashed pattern. The structural base of the Footwall vein is a solid line. The arrow is the slip direction (Figure 3.22) projected to long section. The intersection trace of the top and bottom of unit 3 with the Twin zone (Figure 3.21) are shown for both the footwall (-- ^--) and hanging wall (-- x x --) of the zone.  Mean = 17.9 Standard deviation = 15.9 N =365  Mean = 38.0 Standard deviation = 18.11 N =365  Mean = 7.4 Standard deviation  Mean^18.1 Standard deviation^16.9  N =365  N =365  Mean = 11.3 Standard deviation = 8.1 N =365  Mean = 1.9 Standard deviation = 5.5 N=365  9.30  9.90  9.  50  Figure 3.26, A Q: Contoured vertical long section of visually cstimetcd mineral percentages and gold concentration (ppm), Twin zone, Snip -  mine, northwestern British Columbia. View is looking north-northeast (030). Axes are easting (metres x1000 = X axis) and elevation (metres x100 = Y axis). All units are %, except plot 3.26Q, which is in ppm. The mean is the thick contour line. Stippled areas lie between the mean and +0.75 standard deviations; black areas from 0.75 to 1.5 standard deviations above the mean, and hatched areas > 1.5 standard deviations above the mean. Contours below the mean are: (i) a thin continuous line at -0.75, and (ii) a short dashed line at -1.5 standard deviations below the mean. The structural base and erosional top of the Twin zone are shown as dashed lines. Faults bounding the central block are shown for  reference; where shown, blocks east and west of the faults have been moved to restore fault displacement (see Figure 3.9).  9.60  ^ ^ ^ ^  167  \ \ CO^ \ O C^C pp^..^ C 0 \ \ Cp00 a Dacca.^a^\  no^.1' VP  ,  \a a^a aaaaa0 a \ a oa tha a a la a a aro oa ci a ampocloacaocia :p a 0:4s \7__,  ...^...^.^• .° 0.001 \a^ 11-11. ^'dpo a 0 .10 . • 13 .^a^ ‘ . c anon a'  1 CC ' emCI gd, a a al' a 0 a a 0 ., \ l'a0 O al:a :: :12:g a Ctla 0 \a'-ra a )  a ...■  ^DO  e  ap o \  \ a % a : :tI MI: 0 :TA acs 0 an a a be. Dia^Diaa^C a a CO  a  ^o  ^6  F  o  II^  .?2 i^  as  i:j  D.-^\ ^■  \^CCOO 00001\  6^\  V < i ...,  Ceara o : oacc a0 a aa^a^a a^a■ a a^00 1:1^p 0 COO p .0 0 0ril 0 as 0  a /  Da ealoa  a^  a^a Oa a Ca^a a ..-1 a ca  ^ao • a a cmai ' a  plIla MCP  ^a ,  Capin Duca a"  ^\^DOC a p  . \ - ..,!..;t: B . a ams7a.‘  II^  \^On 0 ,. BO , 00  a  oW ‘13^a II pa 0 .2^ '^ 0 a 01 ^ 1^Dm.  , 0^ 5Z v,z  \^coe.^\\  \ 0 0  0 0  a m 0\ O  Ca a  malt p  a  \  ass• Mara a V^\ a a \ Ocala a Vaal/^a a^\ Aa a^a 01:100•a  11\  ‘.5. 0.11 °. 93: °.:170°. aa aa% a \ s\ DO riaaa acaNg.00a \Da^ \a1:0^0000 pap CC  a  a  Oa^cr..^ Cla^a D.— • „ \ ▪ 00 a Ditc0‘ a 0 a a a- 72 DODD^p a as  \a  o ^6  c Obrt al:age  ^.^0  a  0 p^C '• .  8 ,,^mew  \^0^a C^\  ^2  ;,"  ^0  V  .t4 ,  \ S \ CZ % a rap% o 0 a \ \  ^\^Pao  ^II ^G  a aa 0 . 2 o _a  a  0  9° a " \ 74^ ^am ams ^\ aaoa • N a\  6 ".^ \ a a a II I' .43 ^ \ aa ° OI 17^ aDaa 0 Z^  I^DO a a 1  c^a^7.  5.00  4 00  5.00  Pink carbonate thickness  Pink carbonate/Twin thickness  Mean = 0.05 Standard deviation = 0.14 N =365  Mean = 0.022 Standard deviation = 0.058 N=365  4.00  4dig  5P  °  0  Bleach alteration (%)  no  o 13  r •73  Mean = 4.1 Standard deviation = 6.4 641 .  4_00  N=365  /  3.00  3.00  3.00 6  M  2 00  .:1141  2.00  1^,  4.30  4.40^4.50^4.60  4.30^4.40  Itiotite/(chlorite+ biotite)  Mean = 0.38 Standard deviation^0.27 N=365  Mean = 55.9 Standard deviation = 49.8 N=365  4. 50  Figure 3.26 (continued)  4.60  169  (2) The structural base of the Footwall vein coincides with the distribution of the linear quartz trend (Figures 3.24D, 3.25). (3) The three westerly plunging trends in the sulphide ore are parallel to the displacement direction on the zone, and are equivalent in length to the magnitude of displacement of unit 3 defined in section 3.36 (Figure 3.25). (4) The lowest and thickest trend in the sulphide ore shoot is bound in the upper west by the top of unit 3 with the Twin zone in the hanging wall of the zone. The lower eastern portion of this trend is bounded by the bottom of unit 3 in the footwall of the Twin zone. In addition, the top of unit 3 in the footwall of the zone is parallel to the base of the central trend in the sulphide ore shoot (Figure 3.25).  3.4.3. Mineral distribution in the Twin zone  Mineral distribution plots in Figure 3.26 are summarised in Table 3.12. The distributions of quartz, calcite and pyrite, not surprisingly, reflect the distribution of the ore types that they define (Figures 3.26A, 3.26B, 3.26E). Chlorite and biotite have antithetic distributions (Figures 3.26C, 3.26D). Chlorite is most abundant in the upper western parts of the zone, corresponding with the distribution of calcite and carbonate ore. Biotite, most abundant in the east and lower parts of the zone, corresponds with the distribution of sulphide ore (proportionate thickness) and pyrite. The biotite/(chlorite +biotite) ratio (Figure 3.26P) is almost exactly opposite to that of the chlorite distribution.  Pyrite, chalcopyrite, pyrrhotite and magnetite all correspond to the abundance of sulphide ore, as expected (Figures 3.26E, 3.26F, 3.26G, 3.26H). Pyrrhotite is most abundant in the lower portions of the sulphide ore and magnetite is most abundant in the upper eastern parts of the zone. Sphalerite and arsenopyrite have significantly different distributions to the rest of the sulphide minerals and to the sulphide ore (Figures 3.261, 3.26L). The data for molybdenite and galena are too sparse and standard deviations too great to compare with other sulphide distributions (Figures 3.26J, 3.26K). Galena,  170  however, is common in the Twin zone Footwall vein. This is reflected by the largest galena peak in the upper parts of the zone.  The thickness of pink carbonate was also recorded during core logging. Thickest development of pink carbonate occurs in the western and upper parts of the zone (Figures 3.26M, 3.26N). The amount of strongly altered wallrock internal to the vein has also been plotted (Figure 3.260) as a percentage of the vein width. It closely resembles the abundance of calcite (Figure 3.26B). The alteration of this included wallrock is variable, but consists primarily of strongly quartz-Fe-carbonate-pyrite ± sericite ± Kfeldspar altered and bleached greywacke that is associated with carbonate ore. This style of alteration is significantly different from the biotite ± waxy K-feldspar or calcite envelopes typical of alteration associated with shear veins at Snip, but is instead typical of alteration associated with pervasively disseminated and veinlet base metal sulphides at the SMC and C-3 showings to the south (Figure 2.3). It may represent a late syn-mineralising alteration that is superimposed on biotite-K-feldspar alteration, as is the case at the SMC showing (Rhys, unpublished report for International Skyline Gold Corp., in preparation).  The transition from biotite rich veins on the lower and eastern portions of the Twin zone (Figures 3.26D, 3.26P) to chlorite rich veins associated with pink calcite (Figures 3.26C, 3.26N) in the upper and western portions of the zone mimics the progressive alteration sequence outlined in section 3.42. The trends are oblique to the intersection of bedding with the zone shown in Figure 3.21, and thus, may not reflect chemical changes related to changing wallrock lithologies. Biotite to the east occurs in thin portions of the Twin zone mainly as schistose selvages to other veins, commonly sulphide, as is reflected by the common distribution of pyrite and biotite in these areas (Figures 3.26E, 3.26D). At the western end of the orebody, chlorite-biotite and carbonate ore types are thicker (Figures 3.24B, 3.24C), and chlorite and calcite are more abundant than in the lower east (Figure 3.26B, 3.26C). In addition, pink carbonate, which is transitional in the alteration of biotite to chlorite rich veins, and bleached altered wallrock are most abundant in the upper and western portions of the zone (Figures 3.26N, 3.260).  171  Table 3.12: Nimeral distribution and associations in the Twin zone, Snip mine, northwestern British Columbia.  Relationships, defined from core logging and petrography, are illustrated in Figures 3.23, 3.24 and 3.26. Mineral or ^ Ore type association mineral^Distribution pattern in the Twin assemblage^zone (Figure 3.26) Quartz^Wide trend down the west central^Quartz ore portion of the zone ^ Carbonate ore Calcite^Abundant in the lower west portions of the zone, and in a trend the upper west adjacent to the surface trace  Associated minerals Calcite, pyrite, chlorite Quartz, chlorite, biotite, pyrite  Biotite  Abundant in the eastern parts of the zone  Sulphide and chlorite-biotite ore on the east side of the Twin zone  Pyrite, pyrrhotite, chalcopyrite, magnetite, chlorite  Chlorite  Abundant in the western parts of the zone  Carbonate ore, and western parts of chlorite-biotite ore  Calcite, quartz, biotite  Pyrite  Abundant in the eastern parts of the zone  Sulphide ore (directly proportional to ratios of sulphide to Twin relative thickness)  Pyrrhotite, chalcopyrite, magnetite, biotite, arsenopyrite  Pyrrhotite  Abundant in the lower central portion of the zone  Sulphide ore, central portion  Pyrite, biotite, chalcopyrite, magnetite  Arsenopyrite  Irregular, but it occurs mainly in the centre of the zone  Most common in sulphide ore, but distributed through all ore types  Pyrite, quartz  Sphalerite  Abundant in the central portions of the zone  Sulphide, carbonate and quartz ore  Calcite, quartz, pyrite  Galena  Abundant in the Twin zone footwall vein and erratically through the rest of the zone; has a skewed distribution  Sulphide, quartz  Pyrite, quartz, chlorite  Molybdenite  Abundant in the central western Twin zone adjacent to sphalerite; however, data is strongly skewed  Chlorite-biotite and carbonate  Chlorite, calcite, pink carbonate  Chalcopyrite  Abundant in the eastern parts of the zone  Sulphide ore (directly proportional to sulphide/Twin relative thickness)  Pyrite, biotite, magnetite, pyrrhotite  Magnetite  Abundant in the upper eastern parts of the zone  Sulphide ore; less abundantly in chlorite-biotite ore  Pyrite, chalcopyrite, biotite, pyrrhotite  Sericite  N/A  Carbonate ore  Calcite, chlorite  Carbonate and chlorite-biotite ore  Calcite, chlorite, biotite  Carbonate and chlorite-biotite ore;  Fe-carbonate, quartz, pyrite, muscovite, minor K-feldspar.  Actinolite^N/A ^  Abundant in the lower western Bleached silica-Fe-^parts of the zone carbonatesericite-claysalteration Pink carbonate  Major thickness abundance trends^Carbonate and chlorite-biotite along the western edge of the zone^(biotite is altered to chlorite)  Calcite with fine-grained biotite; associated with chlorite and molybdenite  172  The distributions thus suggest an increase in the amount of alteration to the west, and an alteration from early biotite in the lower eastern to later chlorite-calcite in the upper western portions of the zone.  There is good continuity of the mineral distribution patterns across the faults in many of the plots in Figures 3.26. This suggests that the correction for fault offset in the diagrams is accurate, and that the correction reflects the approximate true offset on the faults.  3.4.4. Gold distribution in the Twin zone  A contoured plot of the distribution of gold values is provided in Figure 3.26Q for comparison to the distribution of ore types and minerals. Like the previous diagrams, this plot is contoured at the mean (55.9 ppm) and 0.75 and 1.5 standard deviations above the mean. The contoured values represent weighted averages of gold grades over the entire width of the vein intersection. In many cases, these values include variable amounts of dilution by greywacke inseparably contained in the assay intervals. The BSU dyke was consistently separated from the assay intervals during exploration, and is thus not a diluting factor in Figure 3.26Q. The resulting plot indicates that the highest gold values (above 55.9 ppm) coincide with the thickest areas of quartz and sulphide ores combined (Figure 3.23N), and with the relative thickness of pink carbonate above 270 metres elevation (Figure 3.26N).  The transition from biotite to chlorite rich vein material, as recorded by pink carbonate, is commonly associated with high gold grades. Above the 300 level in the central Twin zone block, pink carbonate is associated with coarse free gold, and grades are often > 200 ppm Au. Below this, and west of the central block, however, gold grades are not as high as the mean value of the Twin zone and are often far below it (Figure 3.26Q), even though pink carbonate is abundant (Figure 3.26N). Biotite forms only a small volume percent of the vein in this area (Figure 3.26D).  173  3.5 DISCUSSION  3.5.1 Structural History of the Snip mine  Temporal relationships of structures at Snip  Crosscutting relationships and kinematics of structural features described in the previous sections and reviewed in Table 3.3 indicate that several periods of deformation and veining affect the greywacke sequence at Snip. The earliest veining event in the mine is the stockwork of ribboned quartz veins in the 130 haulage level, based on crosscutting relationships with shear veins and extension veins. Shear veins are the next oldest feature, and are in turn cut by extension veins. All of these features are cut by northwest dipping gouge filled faults that have oblique right lateral displacements.  The consistency of mineralogy, identical progression of the same alteration facies from vein to wallrock, and the continuity of structural thickness from the biotite-pyrite veinlets to shear veins suggest that these structures were formed during the same hydrothermal event. Similarly, the occurrence of biotite within and as envelopes to all scales of these veins and veinlets, and the continuum from veinlet controlled to disseminated biotite in the greywacke sequence suggests that a common hydrothermal system was also responsible for the widespread development of biotite. Calcite-biotite-chlorite-pyrite veinlets frequently are associated intimately with both shear veins and the biotite-pyrite veinlets. The similar mineralogy of these veinlets to shear veins and biotite-pyrite veinlets, common occurrence in the alteration envelopes of these other structures, and common oblique joining with biotite-pyrite veinlets suggest that they also are related to the same system. Flat foliations throughout the mine are subparallel to the flat oblique foliations developed adjacent to and within the shear veins, so their development may have been synchronous with the shear veins. However, these flat foliations may represent the local development of the flat S2 fabric that occurs to the south and west on Johnny Mountain. If so, the flat foliation probably  174  postdates the Snip shear veins, since mineralised shear zones and shear veins on western and central Johnny Mountain that have Jurassic galena Pb-Pb isotopic signatures are folded and crenulated about S2.  The two successive northeast and southeast dipping extension vein sets cut shear veins and the Twin zone and their associated fabrics, including oblique internal foliations and folds (e.g. Plates 3.10A, 3.10C). In addition, the occurrence of extension veins in sigmoidal arrays with reverse shear sense is inconsistent with kinematic indicators within the Twin zone. These structures must therefore be related to different deformational events. However, the extension veins are displaced in a normally directed shear sense on many shear veins which they cut indicating a late period of movement on the shear veins. The significance of this late event is discussed in the following section.  Relative timing of deformation in the Twin zone  The consistency of all of the kinematic indicators within the Twin zone and the compatible sense of offset of the sedimentary unit suggest only one major period of displacement on the Twin zone. However, the deformation and offset of extension veins by shear veins calls into question the timing of deformation within the Twin zone and raises the possibility that the structures observed in the zone formed after the extension veins. However, the extension veins cut veins, folds and oblique fabrics in the Twin zone, indicating that the structures must have formed before the extension veining event (Plates 3.15B, 3.23B).  The BSU dyke provides several important related constraints on the timing of deformation within the Twin zone: (1) Penetrative foliation and lineation within the dyke are compatible with internal structures of the surrounding Twin zone (Plate 3.5C; Figure 3.6), indicating that the dyke is affected by the same period of deformation. (2) The dyke intrudes all of the ore types and is unmineralised, indicating that it is younger than the mineralising event. Since there is no measurable offset of ore types across the dyke (e.g. Figures  175  3.13, 3.15), and it is affected by deformation, it must have intruded late in the 75-114 metres movement history. (3) Biotite-pyrite-calcite alteration affects the dyke, and foliation parallel to discordant laminated calcite + pyrite + biotite + chlorite veinlets occur within it (Plates 3.6A, 3.6B). The implication is that the dyke was intruded before the termination of biotite-calcite alteration and veining, which is pervasive through the greywacke sequence. (4) Southeast dipping blocky quartz-calcite extension veins cut foliation within the dyke indicating that the dyke intrusion occurred prior to the formation of the extension veins (Figure 3.6).  These observations indicate that the dyke was intruded late in the deformation history of the Twin zone, after ore type formation and mineralisation, but during the waning stages of the hydrothermal system. Also, displacement on the Twin zone and shear veins during the event that offset the extension veins must have only minor offset since there is no offset along the dyke, which predates the extension veins. The displacement of the extension veins must thus define a late reactivation of the shear veins that is minor and temporally unrelated to the main period of offset on the Twin zone.  Several additional observations provide information concerning the relative timing of ore type formation, deformation and alteration: (1) The presence of both deformed and undeformed auriferous quartz and sulphide veins in single exposures (e.g. Plate 3.13D), and by deformed veins crosscutting obliquely across foliation (e.g. Plate 3.12C) suggest formation of these veins at different stages of the deformational history of the Twin zone. (2) Stacked repetitive sets of quartz and sulphide veins at single localities indicate multiple periods of quartz and sulphide veining. (3) Biotite envelopes on deformed veins and biotitic shear veins indicate that biotite alteration must have been continuous from the time of formation of the veins, through deformation, and after intrusion of the dyke (see (3) in two paragraphs above).  176  (4) The plunge direction and length of trends in the central shoot of sulphide ore is parallel to, and the equivalent length of, the displacement of unit 3 (Figure 3.25). (5) Sulphide-quartz veins (quartz and sulphide ore types) are cut and offset by laminated calcite-chlorite shear veins (e.g. 150 vein, 385 Sill drift; Figure 3.13). However, sulphide-quartz veins also commonly dilate or obliquely cut the foliation in laminated calcite-chlorite-biotite shear veins (carbonate and chlorite-biotite ore types), indicating multiple age relationships between these two styles of veining. (6) Orientations of the veins and their character are consistent with the internal and external kinematic indicators associated with the Twin zone that indicate a steep principal shortening direction. A steep shortening direction should be associated with steep dilatant veins, intermediate dipping veins with a large shear component and non-dilatant shallow dipping structures. These predictions are consistent with the observed veins: the steeply dipping 150 vein is primarily a dilatant quartz-sulphide vein, the moderately dipping Twin zone is primarily a shear vein system, and shallow dipping auriferous veins do not exist at Snip.  These observations suggest that deformation, ore type formation and alteration were synchronous and part of a protracted process. Early veins are highly deformed but younger veins are less deformed. Multiple phases of veining span the period of deformation. The morphology of the veins is consistent with the kinematic indicators indicating that the structures that host the veins were formed by the same deformational event. The relative timing of the two distinctive styles of mineralisation, quartz-sulphide ores and carbonate-chlorite-biotite ores, indicates that the formation of both of these occurred throughout the mineralising event.  The plagioclase porphyritic dyke, encountered in drillholes within the footwall of the Twin zone, like the BSU dyke is biotite-sericite-pyrite-calcite-K-feldspar altered, suggesting that it predates the termination of or is synchronous with the biotite forming hydrothermal system.  177  Snip structural history and relationships to structural events on Johnny Mountain  Locally developed flat foliation cuts and crenulates northeast dipping foliation in the Snip workings. These two foliations have similar orientations and relationships as are observed between the S1 and S2 foliations to the south on Johnny Mountain. Thus, the northeast dipping foliation is here assigned to the Si event and is earlier than the Snip shear veins, and the flat foliation is assigned to the S2 event. The flat foliation is therefore younger than the shear veins, as previously discussed. However, shallow dipping foliations are also developed adjacent to and within the Twin zone and other shear veins at Snip, raising the possibility that these fabrics and the kinematic indicators that they are consistent with formed during S2. However, the observations presented in the preceding section argue against substantial posthydrothermal deformation in the Twin zone. In addition, mineralised Jurassic shear zones (e.g. SMC showing) on the west side of Johnny Mountain contain kinematic indicators consistent with Twin zone internal structures, such as shear bands and rotated porphyroclasts, that are folded by S2. It is probable, however, that some of the asymmetric folds and crenulations with horizontal to gently northwest plunging axes that fold foliation in the Twin zone formed during the S2 event due to vertical flattening. Since the S2 foliation postdates mineralised veins with Early Jurassic galena Pb-Pb isotopic signatures, it may represent the local manifestation of Cretaceous deformation observed extensively in the eastern Iskut River area (P. Lewis, personal communication, 1993) and the Skeena fold belt (Evenchick, 1991).  Quartz-calcite-chlorite extension veins cut flat foliation and shear veins at the Snip mine (e.g. Plate 3.8B). Tertiary galena Pb-Pb isotopic signatures from similar veins on Johnny Mountain suggest a similar relative age for the extension veining event at Snip. Late stage movement on the shear veins offsets, and may locally boudinage, the extension veins.  The preceding information suggests the following structural history for the Snip mine, summarised in Table 3.13: (1) Deposition of the turbiditic sedimentary sequence at Snip in a volcanic setting during the Triassic.  178  (2) Folding of the sequence about northwesterly trending upright folds and Si foliation. (3) Formation of the ribboned quartz stockwork. (4) Formation of primarily southwesterly dipping shear veins. Normally directed simple shear, mineralisation, calcite veinlets and biotite alteration occur synchronously with progressive shear vein formation over a single, probably protracted event involving multiple pulses of mineralising fluids. The BSU dyke was intruded late during this event, following mineralisation and ore formation. Galena Pb-Pb isotopic signatures support an Early Jurassic mineralising event. (5) Formation of flat S2 resulted in folding and crenulation of mineralised structures with Jurassic galena Pb-Pb isotopic signatures. (6) Early northeast dipping extension veins are succeeded by a better developed southeast dipping extension vein set. These events were probably early Tertiary and related to the Tertiary Coast Intrusions (55-45 Ma), as suggested by galena Pb-Pb isotopic signatures obtained from similar veins on Johnny Mountain and in the Stewart area (Godwin et al., 1991; Alldrick et al., 1993). (7) Limited late movement on the shear veins reactivated the previous slip direction and offset extension veins. (8) Gouge filled faults offset all previous structures with oblique right lateral displacement. A hydrothermal system was active synchronously with the faults. (9) Lamprophyre dykes intruded the faults and adjacent wallrocks at 32.0 ± 1 Ma (see section 3.23).  179  Table 3.13: Schematic representation of the sequence of formation of structural features and their timing with respect to alteration and deformation, Snip mine, northwestern British Columbia. Based relationships described in sections 3.2 and 3.3 and discussion in section 3.5.1 (this section).  Late Triassic to Early Jurassic) ?Cretaceous ^  I  - --  ^Tertiary  Deformation/alteration Biotite alteration Si and regional folding S2 event (flat foliation)  — ?^?  Structures Ribboned stockwork Shear veins (Twin zone) Calcite veinlets Extension veins Gouge filled faults  — -  Dykes Plagioclase porphyritic dyke Biotite Spotted Unit Biotite lamprophyre dykes  ?  ? —  3.5.2 Deformation processes within the Twin zone  The schistose foliation and abundant internal fabrics suggest that the Twin zone and shear veins are zones of localised high strain. The following section discusses the deformation mechanisms and the reasons for strain localisation with respect to the mineralogy and ore types.  Deformation mechanisms  Marked difference in the grain size, development of fabrics, and degree of strain of individual veins even in a single thin section indicate that deformation in the Twin zone and shear veins was heterogeneous. In addition, broad variations in fabric texture, style, and degree of development suggest that multiple deformation mechanisms were active. A number of microscopic textures described in section 3.34 can be attributed to at least three deformation mechanisms (Table 3.14; based on reviews by: Knipe, 1988; Kerrich and Allison, 1979; Cox, 1987; and Schmidt, 1982):  180  (1) Diffusive mass transfer: Mechanisms in this category accommodate strain with the redistribution of material during deformation by diffusion processes. Redistribution processes (Kerrich and Allison, 1979) include Coble creep (diffusion via solid grain boundaries), Nabarro-Herring creep (use of the internal crystal structure as a diffusion mechanism) and pressure solution (diffusion path via a grain boundary fluid phase). Diffusional mass transport of material is from points of high normal stress to points of low normal stress, permitting shape change of the grains. The process involves three stages (Knipe, 1988): (i) source mechanisms, associated with how a material enters a diffusion path, including controls that influence activation of diffusion as well as those that dictate corrosion and reaction processes; (ii) diffusion mechanisms, involved in the transport of material along a range of mass transport paths (including Coble creep, Nabarro-Herring creep and pressure solution); and (iii) sink processes, where material is precipitated or deposited in sites of crystal growth. Because hydrothermal fluids were circulating through the Twin zone during deformation, it is likely that pressure solution was the dominant, if not exclusive, diffusion mechanism.  Transported material may be added to the original grain as overgrowths, in which case mass is conserved, or may be totally removed and redeposited (i.e. long range diffusion) into areas of low normal stress or into configurations energetically most stable under the stress field associated with deformation (e.g. on more favorably oriented grains, within dilatant fractures in other minerals, or in pressure shadows; Kerrich and Allison, 1979). A mobile fluid phase carrying abundant dissolved components can provide a mechanism for long range mass transfer.  Evidence for diffusive mass transfer in the Twin zone and shear veins is abundant. Discrete, spaced foliation surfaces, some with phyllosilicates, that truncate adjoining calcite (Plate 3.21A), phyllosilicate (Plate 3.21B) and quartz grain boundaries are typical pressure solution effects. These surfaces may result in well developed shape fabrics in calcite, especially where chlorite or biotite laminae are present (Plate 3.21A). Tabular and elongate pyrite and pyrrhotite crystals in phyllosilicate  181  rich veins may also result from diffusive mass transfer (Plates 3.13A, 3.24C; McClay and Ellis, 1984). Sink (depositional) sites include calcite, quartz, chlorite and biotite pressure shadows adjacent to rigid grains, such as pyrite, arsenopyrite, or in some cases, quartz (Plates 3.22C, 3.26A, 3.26C), or voids between fractured and extended grains of these harder minerals (Plates 3.22B, 3.24C). The observation, above, that calcite veins with phyllosilicate impurities have the best developed pressure solution fabrics implies that pressure solution is enhanced in impure calcite veins. This feature has been noted by other workers in similarly deformed rocks (e.g. Kerrich and Allison, 1979). Relatively rapid dissolution and removal of calcite in phyllosilicate rich areas would thus result in concentration of the phyllosilicates in localised areas. This may explain the existence of compositional layers that are common in carbonate and chlorite-biotite ore types. Precipitation of materials from the hydrothermal fluid into these layers and resulting grain growth would further assist the development of compositional layering. Crenulation fabrics are commonly developed in intrafolially folded chlorite or biotite compositional layers, and are defined by the folded foliation surface together with overprinting pressure solution surfaces that are parallel or oblique to the shear vein walls. Elsewhere, similar intrafolial folds are not affected by pressure solution. This suggests that pressure solution was an active deformation mechanism while folding occurred in the Twin zone. The crenulated texture in Plate 3.21B is typical of that produced by pressure solution of a folded chlorite compositional layer.  (2) Dislocation glide: Dislocation glide involves the accumulation of strain by the intracrystalline movement of dislocations (linear lattice defects; Knipe, 1988). At low temperatures, deformation by the motion of dislocations through the crystal lattice is dominated by dislocation glide where dislocation motion is confined to slip planes in the crystal structure (Knipe, 1988). Gliding dislocations may become pinned by impurities, inclusions, dislocation tangles and grain boundaries, thus increasing the stored strain energy and requiring continuous increases in applied stress to produce a constant strain rate (Kerrich and Allison, 1979). At higher temperatures ( > 0.5 melting temperature) dislocations may cross slip or climb past obstacles from one slip plane to another (dislocation climb), and may annihilate one  182  another, thus reducing dislocation density and strain energy (Kerrich and Allison, 1979). The high temperature flow of a material where these recovery processes can counteract the hardening process is termed dislocation creep. The process results in a characteristic set of microstructures, all of which are present in the Twin zone and are best developed in quartz and calcite. These include (Knipe, 1988): (i) well defined subgrain structure within grains, where low angle grain boundaries, generated by the reorganisation of dislocations, separate areas of the crystal with slightly different (<5 degrees) lattice orientations (Plate 3.21D), (ii) undulose extinction, deformation bands, deformation twins and deformation lamellae (Plate 3.26) formed by distortions in the crystal lattice, (iii) ribbon grains, often separated by subgrains or new strain free small grains (Plates 3.21C, 3.22A), (iv) serrated interlocking grain boundaries, and (v) patches or bands of approximately equigranular fine grained aggregates of quartz and calcite resulting from recrystallisation of coarser grained polycrystalline aggregates, often spatially associated with ribbon grains or polygonised porphyroclasts. Dislocation creep thus results in grain size reduction by recrystallisation of larger grains to form less strained smaller grains. This process is termed dynamic recrystallisation (White, 1977; Knipe, 1988). Elongation of the grains produced, including ribbon grains, commonly defines a fabric that is oblique, and shallower dipping than the vein walls of the Twin zone (Plate 3.21C).  Textures produced by dynamic recrystallisation through dislocation creep are distinctive from those produced by annealing or cataclastic processes. Annealing forms equant, polygonal unstrained grains, while cataclastic deformation, although associated with grain size reduction, is not associated with ribbon grains or crystal fabrics. Cataclastic deformation does not produce fine grained aggregates of approximately equant grains as does dynamic recrystallisation (see below).  In Twin zone sulphide veins, sulphides such as pyrrhotite, sphalerite, chalcopyrite and galena commonly exhibit shape fabrics that are parallel to or shallower dipping than vein walls. In addition, cusp and piercement structures on pyrrhotite rich veins (Figure 3.19B) and the anhedral mantling character of these sulphides suggest that they deformed plastically. These features may result from  183  diffusive mass transport processes or by dislocation creep; both are common deformation mechanisms for these minerals (Cox, 1987). However, the poor polish on most samples and opaque nature of most of these minerals prevented identification of any textures characteristic of either style of deformation. No attempt was made to highlight sulphide textures by etching.  (3) Frictional sliding, fracture processes and cataclastic flow These are brittle processes involving the creation of new surfaces, loss of cohesion by fracturing, and frictional sliding along grain boundaries and surfaces (Knipe, 1988). They result when the tensile and shear failure strengths of materials are exceeded. Within the Twin zone, pyrite, arsenopyrite and quartz most commonly exhibit fracturing, often while the surrounding matrix exhibits evidence for microscopically cohesive crystal plastic processes (diffusional mass transport and dislocation glide; Plate 3.22B). In these situations, fracturing may occur due to a number of processes that were probably active during deformation. These include (summarised from Knipe, 1988): (i) crystal plastic processes, whereby fracturing occurs when dislocations or high twin densities develop, or impurities restrict further deformation by crystal plasticity and induce tensile cracks, (ii) elastic strain accumulation at crack tips, promoting crack propagation, (iii) hydraulic fracturing resulting from fluid pressure exceeding the tensile strength of a mineral, and (iv) diffusion processes leading to the development of voids at grain boundaries or triple points by the concentration of impurities, point defects or vacancies. Resulting voids between fractures may be filled with fibrous quartz, calcite, chlorite or biotite deposited from the hydrothermal fluid. Alternatively, materials may flow by crystal plastic processes into some fractures and may be concentrated in them as residues due to diffusive mass transfer. If the minerals were impurities in the fractured grain, they may occur in fractures generated by fracture nucleation around them. Thus, the presence of minerals or native metals on fractures may have no relevance to the original paragenetic history.  Pervasive microfracturing and the subsequent loss of cohesion facilitates cataclastic flow involving relative movement of grain fragments by sliding and rolling processes. Unlike the products of  184  dynamic recrystallisation where ribbon grains and shape fabrics are common, cataclasites formed purely by brittle processes have little or no fabric, variable grain size, and angular unstrained grains. No cataclasites were identified in the Twin zone, except where unconsolidated gouge is developed along foliation parallel bleached faults, commonly adjacent to the BSU dyke. These developed after the foliation forming event in the Twin zone and are typical of the faults associated with Tertiary lamprophyres. However, some pyrite-arsenopyrite veins do exhibit cataclastic textures with fractured and broken grains, although the common presence of strained interstitial quartz and calcite suggests the interplay of cataclasis with crystal plastic and diffusive mass transfer mechanisms in the gangue matrix. In these cases, brittle fracturing of pyrite and arsenopyrite in the quartz-calcite matrix may result from rigid body rotation of these minerals, with resultant abrasion of adjacent grains and fracturing. Rounded pyrite and arsenopyrite grains in sulphide veins probably attained their shapes through this milling process.  Other consequences of cohesion loss include the development of shear bands, dilatant veins and slip along foliation parallel decollements. These processes occur when the cohesion of friction or tensile strength of the material is overcome. Materials bounding these planar fractures behave in a rigid or semi-rigid manner. Development of these features is discussed in the following sections.  The descriptions of the deformation textures and probable related deformation mechanisms above and in Table 3.14 indicate the variable response of different minerals and mineral aggregates to deformation in the Twin zone. The textures indicate abundant evidence for inhomogeneous plastic flow during deformation. Deformational processes are extremely complex, involving the interaction of a variety of defects (microcracks, voids, dislocation and mechanical twins) within individual crystals, interaction of mineral species, grain size, orientation, impurities in the surrounding matrix, and the mineralogy of the matrix in addition to conditions of temperature, pressure and fluid presence. The relative strength an individual grain, and thus the ease with which it deforms with respect to a particular deformation mechanism is dependant on all of these factors, and may thus be entirely different from the response of a  185 Table 3.14: Deformation processes affecting common minerals in the Twin zone as determined from deformation textures. See text for discussion. Deformation process  ^  Minerals most affected  ^  Evidence  Diffusive mass transfer (Pressure solution; Coble creep; Nabarro-Herring creep)  Calcite and quartz; probably pyrrhotite, chalcopyrite, galena and sphalerite; chlorite, biotite and pyrite may also be affected  Relatively unstrained grains with preferred orientations and truncated boundaries, compositional layering, interpenetration of adjoining grains, pressure shadows, isolated tabular grains of normally equant minerals  Dislocation creep; dislocation glide, dynamic re-crystallisation  Quartz, calcite; probably pyrrhotite, chalcopyrite, galena and sphalerite  Undulose extinction, deformation lamellae, ribbon grains, subgrains, grain size reduction, serrated grain boundaries, deformation twinning  Cataclasis^ Pyrite, arsenopyrite, magnetite, (fracture processes)^quartz  Fracturing of grains, rounded grains,  similar grain in a different area under the same physical conditions. For example, where minerals of  different strengths occur together, deformation is partitioned into the most easily deformed mineral. Thus, the common presence of euhedral pyrite grains and clear unstrained quartz eyes in pyrrhotite rich veins (Plates 3.14A, 3.14C) implies strong deformation partitioning into the pyrrhotite matrix. However, where quartz forms a matrix to pyrite, the quartz may instead be highly strained. These variations in texture allow determination of the relative ease of deformation of minerals in the Twin zone by crystal plastic processes (i.e. the relative strength of the minerals; cf. Cox, 1987). In order of decreasing relative strength, these are pyrite, arsenopyrite and magnetite, greater than quartz, greater than calcite, sphalerite, pyrrhotite, chalcopyrite and galena. The strongest minerals (pyrite, arsenopyrite and magnetite), especially when in a matrix of weaker minerals, commonly exhibit brittle fracturing and resist crystal plastic processes, while weaker minerals exhibit textures suggestive of plastic deformation. Quartz exhibits both styles of deformation. Biotite and chlorite are difficult to fit into this scheme because of their platy habit and common confinement to compositional layers. The different responses of minerals to the deformation mechanisms will thus determine their textures and obscure original paragenetic relationships.  186  Textures indicate that ductile deformation in the Twin zone was accommodated by crystal plastic processes (diffusive mass transfer and dislocation glide) associated with limited cataclastic flow in pyritearsenopyrite veins. The preservation of small grains, including subgrains and strain free grains produced by dynamic recrystallisation, indicates that no significant recrystallisation has occurred since deformation, although annealing textures locally affect some veins. The high strains that accumulated could only have occurred before intrusion of the BSU dyke, since there is no significant offset along it. The deformation mechanisms are compatible with the probable high temperature of fluids suggested by the biotite alteration envelopes.  Fluid pressure cycling and ore type distribution  The presence of both deformed and undeformed quartz veins, and multiple discrete quartz and/or sulphide veins suggest that several generations of dilatant syntectonic quartz and sulphide veins formed during deformation in the Twin zone. Dilatant veins form in shear zones when the effective normal stress acting on the zone is exceeded by fluid pressure (Phillips, 1972). The fluid pressure may then initiate hydraulic fracturing, creating a fluid filled space in which a dilatant vein may form. To fracture, the fluid pressure must also exceed the tensile strength of the rock, which is weakest along foliation anisotropies or earlier dilatant veins. Thus veins produced by this process are commonly parallel to foliation or other dilatant veins. The presence of multiple dilatant veins in the Twin zone suggests a corresponding number of high fluid pressure events. Possible reasons for fluid pressure cycling and thus multiple dilational events in auriferous shear zones are discussed by Sibson et al. (1988), Sibson (1990) and Cox et al. (1986, 1990). These authors suggest that the shear zones act as valves to fluid circulation. Their model involves five stages: (i) fluid pressure build up due to restriction of fluid flow in the shear zone, (ii) seismogenic brittle failure due to the high fluid pressure exceeding the effective normal stress on the shear zone, (iii) post failure discharge, where fluid pressures are reduced by flow through the shear zone or permeability barriers adjacent to the shear zone, (iv) hydrothermal deposition of minerals that seals the  187  fractures, and (v) fluid pressures build up and repetition of the process. This type of fluid pressure cycling thus requires the existence of a hydrostatic pressure gradient and directed fluid flow along the shear zone (Cox et al., 1986). Development of such gradients requires the existence of low permeability barriers to fluid migration, such as impermeable sedimentary units, that allow fluid pressure buildup (Sibson, 1990; Cox et al., 1986, 1990).  Thus, to discuss the potential for a similar scenario to have occurred during the formation of the Twin zone, assessment of the direction of fluid flow and potential flow barriers is important. Fluids must have: (i) entered the Twin zone by diffusion through the greywacke sequence, from an external source probably at depth or (ii) flowed along or down the Twin zone using the zone as a fluid channel. Two independent observations suggest the latter: (1) Gold grade distribution in Snip veins, as previously described, is such that the Twin zone and related shear veins in its footwall are the only currently economically mineable veins in the workings (grades averaging >40 ppm Au). Veins between the Twin zone and the Red Bluff porphyry exposed along the Snip 130 haulage level, although abundant, have grades averaging less than 2 ppm Au; veins en echelon below the termination of the zone have slightly higher, but also low grades (<5 ppm typically). Thus, if fluids entered the Twin zone by diffusion through the greywackes other veins outside the immediate vicinity of the Twin zone should have comparable gold grades; this is not observed. (2) Greywacke adjacent to the shear veins is completely replaced by biotite, calcite, K-feldspar and/or quartz, and textural evidence suggests that chlorite-biotite and carbonate ore types formed at least partially by wallrock replacement. This indicates that the hydrothermal fluids that formed the Snip veins were not in equilibrium with the wallrocks. If the fluids had diffused through the greywacke sequence before reaching the Twin zone, then upon reaching the Twin zone it is unlikely that they would replace the wallrocks as they would be saturated with dissolved components of the greywacke through which they had passed.  188  Further evidence for fluid flow along or down the Twin zone is provided in Chapter 4. Thus, if fluid flowed down the Twin zone then fluid pressure in the zone would have been controlled by the rate of flow through the zone and the rate of diffusion from the zone into the abundant biotite-pyrite veinlets and pore spaces in the surrounding greywackes. Any decrease in permeability of the greywackes through mineral precipitation (primarily biotite, pyrite and calcite) in the veinlets and pore spaces would thus have increased fluid pressures within the Twin zone. Progressive fluid pressure build up would eventually result sequentially in (i) dilation of the zone, (ii) fracturing or reopening of biotite-pyrite veinlets as the tensile strength of the greywackes are exceeded, and (iii) a resultant drop in fluid pressure and resumed diffusive flow from the Twin zone into the greywackes. Further mineral precipitation in fluid channelways in the greywackes would result in decrease in permeability and a rise in fluid pressure, thus repeating the sequence.  The hypothesised fluid pressure gradient between the veins and wallrock during periods of permeability restriction may have resulted in formation of the calcite veinlets that commonly occur in the carbonatealtered vein envelopes (Plate 3.3). This style of brittle fracturing may have caused fracturing of the veinlet walls due to fluid overpressuring within the veinlets. Similarly, calcite veinlets that are locally parallel to flat foliation in the greywacke sequence and adjacent to shear veins may have formed by failure along the foliation surfaces due to fluid overpressuring. High fluid pressures and resulting nonplanar brittle fracturing and dilatancy may explain the irregular morphology of many dilatant sulphide veins that occur in the hanging wall of the Twin zone below 340 level (Figure 3.15).  Alternatively, dilatancy may develop in shear zones by the overriding of asperities (irregularities) in the morphology of the shear zone during shear zone movement (e.g. Guha et al., 1983). Asperities may form by due to minor changes in the orientation of the shear zone upon intersection with a lithologic unit. The resulting dilatant vein will be prolate and parallel to the intersection of the unit and the shear zone and/or parallel to the slip direction of the zone, as is reflected in the long section plot of sulphide ore distribution (Figures 3.23H, 3.24D). Trends in the upper portions of the Twin zone, for example the  189  thick quartz trend and the distribution pattern of the Twin zone Footwall vein (Figures 3.8, 3.24E, 3.25), are parallel to the intersection of bedding with the zone and may be controlled by an unrecognised sedimentary unit.  Dilatancy localised at the intersection of the Twin zone and sedimentary units, however, probably reflects the interplay of several factors, including shear zone boundary irregularities within these units, the relative permeability of the units and the dip angle of the zone. Highest fluid pressure would occur in portions of the zone bounded by the least permeable lithologies, assuming fluid flow was through the zone. As described above, different rheologic properties of the lithologies may have produced perturbations in the morphology of the zone, contributing to dilation. In addition, the normal sense of motion on the zone would preferentially allow dilation in areas of steepest dip. Thus the complex interplay of these factors during deformation may be responsible for the distribution patterns of sulphide and quartz (dilatant) ore types. Similarly, thickened portions of carbonate and chlorite-biotite ore, like that developed in the upper portions of the zone associated with the Twin zone Footwall vein, may have developed in the most chemically reactive sedimentary units.  Strain softening and the localisation of deformation to the Twin zone  Deformation is commonly localised into areas that are easily deformed. A mineral grain that will accommodate strain easily by a given deformation mechanism is considered soft, while a grain that will resist deformation is hard. Thus during deformation, areas that are relatively soft will accommodate more strain than those that are hard and consequently localise deformation. The process(es) whereby a mineral or localised areas become soft is termed strain softening. Strain softening processes thus promote the localisation of strain into a shear zone and restrict the area of deformation. Several factors that contribute to strain softening (reviewed by White et al., 1980) were probably active during the formation of the Twin zone. These include:  190  (1) Hydrothermal fluids Fluids have profound effects on both crystal plastic and brittle forms of deformation in shear zones. Fluids affect the deformation in two ways (Evans et al., 1990; Rutter, 1972): (i) mechanical effects that occur when effective pressure is reduced during infiltration of hydrothermal fluid into a ductile deforming shear zone reduces the effective normal stress acting on the shear zone allowing transient tensile failure and brittle fracture propagation; (ii) chemical processes that affect both diffusional mass transport and dislocation migration processes in the crystal lattice. Fluids enhance ductile deformation by encouraging the accumulation of higher strains by: (i) increasing the rate of strain by diffusion processes, and (ii) providing new, strain free (i.e. soft) grains that may accommodate strain. Mobile hydrothermal fluids may facilitate and enhance both dissolution and precipitation by diffusive mass transfer processes by providing constant exposure to new, potentially unsaturated fluids, and thus new material for deposition in sink sites. This process also enhances diffusion within grains through a fluid layer at stressed grain surfaces, or through a mobile grain boundary fluid permitting long range mass transfer (White et al., 1980). A second important chemical effect is hydrolytic weakening, which usually effects quartz and calcite. Hydrolytic weakening involves the intracrystalline transport of water in communication with advancing dislocation kinks and jogs. Water related defects gain access to grain interiors and dislocation cores by fluid infiltration along open microcracks followed by diffusion along mobile dislocations (e.g. inclusion trails within the ribbon grain in Plate 3.22A) or by incorporation directly into the crystal during its formation (Kronenberg et al., 1990). Other processes such as grain boundary sliding are also facilitated by fluids (White and Knipe, 1978). The mechanical effects of fluid infiltration at high fluid pressures result in brittle failure, cataclasis and dilatant vein formation. These mechanical effects are further discussed in the following sections.  (2) Reaction softening (reaction enhanced ductility) Metamorphic reactions such as hydrothermal alteration aid in strain softening by producing new strain free grains, new soft minerals and small grains that are likely to promote grain boundary sliding and diffusive mass transport (White et al., 1980). During hydrothermal alteration, hard phases such as  191  feldspars that are abundant in the feldspathic greywacke wallrocks of the Twin zone are converted to soft assemblages such as calcite, biotite, quartz and sericite. Stresses induced by volume changes and by increased diffusion rates during mineral phase changes and related chemical reactions results in an additional weakening effect known as transformational plasticity (White and Knipe, 1978). Together these processes cause reaction softening and result in reaction enhanced ductility due to the interaction of fluids and wallrock.  (3) Effects produced by activity of deformation mechanisms These effects occur through the progressive activity of different deformation mechanisms. They include: (i) geometric (fabric) softening, where the alignment of crystallographic axes due to dislocation creep or where grain reorientation (e.g. micas in foliation laminae) causes strain softening related to the preferred orientation of slip systems in the crystal lattice (White et al., 1980), (ii) continual recrystallisation (e.g. dynamic recrystallisation) provides newly formed strain free grains that can accommodate strain, and (iii) change in deformation mechanism. The latter process commonly occurs when the grain size of quartz and calcite is reduced due to mechanisms such as dynamic recrystallisation, facilitating processes such as diffusive mass transfer or grain boundary sliding, which accommodate strain more efficiently at fine grain sizes (White et al., 1980). When these mechanisms occur, deformation is commonly localised to the most deformed areas of the zone.  4. Fluid temperature The migration of hydrothermal fluids through the Twin zone may have created elevated temperatures in the zone. Biotite envelopes around many of the veins indicate potassic alteration was the predominant alteration style during hydrothermal alteration. Fluid inclusion studies suggest that temperatures >400° Celcius are typical fluid temperatures of veins with potassic alteration assemblages (Roedder, 1984). High fluid temperatures would thus have promoted strain softening in the twin zone by facilitating both crystal plastic processes. Elevated temperatures promote the ease of glide in crystals. As temperature is raised, dislocation densities become more homogeneous, tangles  192  occur less frequently and microcracking is less pervasive (Knipe, 1988). In addition to fluid temperatures, shear heating, the increase in temperature that can accompany deformation, may also raise temperatures (White et al., 1980). However, the effects of shear heating are controversial, and may be minimal.  5. Formation of new veins Newly formed dilatant veins would be unstrained and able to accommodate progressive strain.  These processes acting singularly, or in combination, may have lead to strain softening, and thus localised deformation within the Twin zone and shear veins. Fluid related effects, in particular, increase and facilitate crystal plastic processes, accelerate deformation and expansion of the shear zone through reaction enhanced ductility, and provide elevated temperatures that accelerate and enhance deformation processes.  Shear sense indicators and effects of heterogeneous progressive deformation  The pronounced anisotropic nature of the Twin zone caused by the layering of ore types, compositional layering within ore types, irregularities in the surface of the zone, relative timing of veins, incorporated blocks of greywacke, and changes in the orientations of individual veins are all important factors governing the local style and intensity of deformation in the Twin zone. These heterogeneities result in a varied deformational response that is recorded by the abundant asymmetric structures within the Twin zone. Those common to both the Twin zone and other shear veins at Snip include oblique foliation, down dip verging folds, probable sheath folds, synthetic shear bands, asymmetric augen and rotated porphyroclasts. These structures are indicative of non-coaxial (rotational) deformation in the zone with a normally directed shear sense parallel to the lineation developed on foliation surfaces. All of these structures represent responses to deformation partitioning at different scales and times during progressive deformation.  193  Folds may form where the translatory movement of the different layers is facilitated in certain segments and inhibited in others due to the lensoidal morphology of the ore types, oblique foliations, discontinuous nature of laminae in laminated carbonate and chlorite-biotite veins, and in shear bands. This will give rise to zones of layer parallel shortening where the foliation can be folded or boudinaged (Ghosh and Sengupta, 1987). Similarly, a variation in the strength properties of layers translating past each other, or a change in orientation or thickness of the zone may cause a perturbation in the flow field and generate a local spin or body rotation (Lister and Williams, 1983). If the spin is sympathetic to the bulk shear sense, then the perturbation will amplify and eventually propagate over a larger area, leading to the development of a fold packet. Indeed, folds are developed most abundantly in the Twin zone where individual quartz veins occur in a carbonate or chlorite-biotite ore matrix (Plates 3.24A, 3.24C), characterised by well developed calcite-chlorite-biotite compositional layering, and by perturbations (asperities) along the margins of the Twin zone (Plate 3.12D). The preferential development of sheath folds in chlorite and biotite rich portions of the Twin zone implies strong strain partitioning into these rheologically weak materials. The preservation of internal structural features, such as bladed chloritequartz intergrowth, in strongly boudinaged and folded quartz veins contained within carbonate ore, further illustrates this strain partitioning (Figure 3.16A).  Shear bands form as a result of semi-brittle failure oblique to the shear foliation (Platt and Vissers, 1980). In the Twin zone, shear bands range from discrete slip surfaces (Figure 3.16D) to miniature ductile shear zones where no fracturing has occurred (Plates 3.25A, 3.25B). These structures translate slip across, and commonly are restricted to, individual compositional layers or veins (Plate 3.25A). Like boudins, they may form due to a difference in ductility between the layer and its matrix or by extension on the strong planar anisotropy of the foliation. Since they are asymptotic, with both ends terminating in shear zone parallel (shear foliation parallel) slip surfaces, continuing slip on the shear band results in rotation of the adjacent block of foliation to maintain cohesion. Continuing displacement moves the rotated foliation block beyond the asymptotic shear band surfaces and along the shear vein parallel slip  194  surfaces that the shear bands join. This results in lensoidal blocks with oblique shallowly dipping to subhorizontal foliation that are bounded by shear vein parallel slip surfaces, which often display no remaining evidence of the original shear band (Plates 3.23A, 3.27D). Shear bands commonly cut foliated veins and compositional layers within the Twin zone and thus may represent one of the last forms of deformation. They are kinematically consistent with all of the other shear sense indicators and thus are interpreted to be late features in the deformational and mineralising event that formed the Twin zone. Shear bands are commonly late in a sequence of generally decreasing ductility that characterises many shear zones (Passchier, 1984). Ductility decrease in the Twin zone may have been caused by a decrease in the fluid flow rate and temperature late in the mineralising event. These decreases may have inhibited crystal plastic processes and facilitated slip on foliation surfaces and shear bands.  The variability of the orientation of fabrics, produced by both coaxial and noncoaxial strain accumulation, further illustrates the heterogeneous nature of deformation within the Twin zone. Although shear bands can rotate lensoidal foliated blocks to produce oblique subhorizontal foliation, oblique subhorizontal flattening foliations that formed by coaxial strain accumulation are also common in the Twin zone. Areas where strain has accumulated by crystal plastic processes commonly have oblique foliation. These include quartz or calcite lenses and pods that are separated by fine grained shear foliation parallel quartz-calcite bands of a finer grained quartz-calcite. Similarly, the shape fabrics attributed to diffusive mass transport processes that are commonly defined by spaced dissolution surfaces also form oblique shallow dipping fabrics in the absence of shear bands. Shear vein parallel fabrics of this type are also common, however. Shallowly dipping oblique foliations adjacent to shear veins formed by coaxial strain accumulation.  Other shear sense indicators that form by heterogeneous deformation include rotated pressure shadows around pyrite and polycrystalline quartz porphyroclasts (Plate 3.26). The porphyroclasts are able to spin, because of their size and low aspect ratios, relative to their surroundings. This process may take place by means of sliding in and through the micaceous minerals and calcite in the surrounding matrix (Lister and  195  Williams, 1983). Crystal plastic deformation of these grains is therefore avoided and deformation, which would have otherwise taken place, is converted to spin or brittle fracturing.  Morphology, structural style and displacement on the Twin zone  The morphology of the Twin zone and related veins in its footwall, and the truncation of the zone at surface suggest that it represents the erosional remnant of a larger shear vein system. The distribution pattern of the veins (Figure 3.7B) is typical of the horsetail pattern of veins commonly developed at shear zone or shear vein terminations, or where shear zones change their orientation (e.g. Sibson, 1990; Figure 3.27). Horsetail structure develops due to the interaction of extensional veins and shear zones or shear veins, and results in the accommodation of displacement by dilation on the side of the shear zone or shear vein where the host rocks are extended by movement away from the shear zone termination or inflection point (Figure 3.27). Similar dilation may occur at the other end of the shear zone on its opposite side, which in the case of the Twin zone is eroded (Figure 3.27). Steepening and ultimate termination of the Twin zone upon intersection with unit 3, the mixed siltstone and mudstone package, is probably a mechanical response to the change in lithologic character. The resultant change in orientation may have allowed the development of extensional veins, such as the 150 vein, in the footwall.  The interaction of shear veins and extension veins may also explain the development of the cross veins developed between the Twin zone and Twin zone Footwall vein in 3852 and 4055 stopes (Figures 3.11, 3.12, 3.13). The veins commonly dip more steeply that the surrounding shear veins and have 30 to 50 degree greater strikes, similar to the 150 vein. These veins are thus consistent with formation primarily as extension veins (Figure 3.27). Locally, horsetail type geometries may form consisting of both southwesterly and westerly dipping veins that are developed at vein terminations or flexures (Figure 3.12, 150 vein). Northwest dipping veins, especially common on 340 level (Figure 3.14) are not dilatant, and may represent bedding plane activation. Their slip direction is parallel to that on the southwest  196  Figure 3.27: Hypothetical cross-section through the Twin zone, looking northwest. The diagram shows the possible relationship during formation of the zone between shear along shallow to moderately dipping sections (i.e., the upper portions of the zone and possible shallow dipping linking structures with deeper shear veins developed at depth) and extension on steep-dipping portions of the structure (e.g. in 2647 stope at the base of the zone) splays, and related veins (e.g. the 150 vein and the 130 vein). Extension occurs where the zone changes its orientation and becomes steeper dipping, resulting in a horsetail structure. The possible morphology of eroded portions of the zone is also shown.  197  dipping shear veins and this is incompatible with their potential formation as a conjugate orientation to the southwesterly dipping structures.  Although the Twin zone terminates below its intersection with unit 3, displacement continues beyond the termination of the zone. Veins in the footwall of the Twin zone (150 vein, 130 vein, Twin zone Footwall vein) accommodate only an insignificant portion of the offset when their cumulate dilation is considered (Figure 3.7B). Displacement could not have been taken up on the dyke, because there is negligible offset of ore types across it. Thus, displacement may have been accommodated by tight flexural folding of the greywackes and/or on a shallowly dipping non-dilatant narrow slip surface that extends from the base of the Twin zone to other shear veins below. A narrow, shallowly dipping slip surface would be difficult to distinguish from the many narrow shear veins intersected in drill core, and thus, would be easy to miss. The S-shaped fold defined by the shallowing of bedding 50-100 metres from the Twin zone is compatible with the predominantly normal displacement on the zone and suggests that bedding flexure accommodated some of the displacement. Alternatively, this fold may reflect the cumulate slip on the numerous minor shear veins adjacent to the Twin zone.  The unusual shallow westerly plunging synclinal fold at the base of the Twin zone Footwall vein (Figures 3.11, 3.12; Plate 3.27C) is difficult to explain kinematically with respect to other structures in the Twin zone. However, this structure is not only associated with folded veins. For example, a planar northwest dipping laminated calcite-chlorite shear vein is developed adjacent to the folded quartz-sulphide vein in 3852 stope, lift 5 (Figure 3.12), and joins the Footwall and Twin veins without being folded itself. At lower levels in 3852 stope (Figure 3.13), no fold structure is developed. Instead, a northwest dipping sulphide vein joins the gap between the Twin zone and Footwall vein. In the 4061 stope undercut, where the folded structure is best developed, the folded quartz vein has a planar northwest dipping orientation until its intersection with the trace of the Footwall and 150 veins, where it curves into parallelism with these latter veins. Northwest dipping orientations of shear veins are common elsewhere in the mine (Figure 3.6) and often occur bridging Twin zone veins that are separated by blocks of greywacke (e.g.  198  Figure 3.14, centre). Thus instead of indicating folding, the curved structure connecting the Twin and Footwall veins may instead represent an arcuate dilation plane that curves between southwesterly and northwesterly dipping orientations of the associated veins.  Although clearly younger than the shear veins, extension veins are commonly localised adjacent to and may terminate against them (e.g. Plate 3.27A). The shear veins may have acted as fluid conduits during the extension veining event. Thus fluid flux may have enabled attainment of high fluid pressures within, or in wallrocks adjacent to, the shear veins, thus allowing preferential brittle failure and extension vein formation adjacent to the shear vein margins.  199  CHAPTER 4: THE RED BLUFF GOLD-COPPER PORPHYRY SYSTEM  4.1 INTRODUCTION  The Red Bluff porphyry is a tabular intrusion overprinted by a gold-copper porphyry system. The intrusion is parallel to the strike of the Twin zone, located 400 metres to the southwest (Plate 2.1). This chapter documents the geology of the Red Bluff porphyry and its related hydrothermal system. It discusses probable relationships to mineralised shear zone hosted veins and shear veins developed in the Snip mine and the surrounding area. Information presented is based on drill core logging, petrography, and surface and underground mapping.  4.2 THE RED BLUFF GOLD-COPPER PORPHYRY SYSTEM  4.2.1 The Red Bluff Porphyry  The Red Bluff porphyry, 2 kilometres long and 250 metres wide, trends northwest and follows the northeast edge of Johnny Ridge (Figures 2.1, 2.2; Plates 2.1, 2.3A). The northwest end terminates at Monsoon Lake, where it may be cut off by a fault. The southeastern exposures end in a recent landslide. The porphyry occurs northeast of, and is parallel to, the strike of the Twin zone. Distance to the Twin zone varies with elevation (Figure 2.2; Plate 2.1). The southwest contact is 850 metres horizontally from the base of the Twin zone at 180 metres elevation. Higher, at 600 metres elevation, the horizontal distance narrows to 400 metres.  Contact relationships with country rock are poorly defined because of the steepness of the slope and lack of outcrop. Where intersected by drilling and mine development, contacts are faulted or intrusive. The southwest contact varies from moderately southwest dipping at the north end of the intrusion in the Snip  200  workings, to subvertical 1 kilometre to the southeast. The northeast contact is also steep, probably subvertical.  Marginal features of the Red Bluff porphyry include chilled margins characterised by fine grained aphyric felsite exposed near the contacts at the base of the Red Bluff cliffs (Kerr, 1948; Metcalfe, 1988) and screens of potassically altered greywacke commonly up to 10 metres wide. Several Cominco Ltd. drill holes located in the western portion of the porphyry were collared in large screens of altered greywacke that are at least 40 metres wide (Parsons, 1966).  Modal composition and texture  The Red Bluff porphyry is a strongly altered holocrystalline medium grained K-feldspar porphyritic intrusion. It is tan to greenish grey, depending on the type of alteration, and weathers to a pale yellow or rusty colour. The entire accessible volume of the stock, both at surface and in drill core, is pervasively altered.  Modal quartz (<1 to 4% as phenocrysts and 15-35% of the groundmass) and relatively low K-feldspar (usually <10% as both phenocrysts and within the groundmass) content of the porphyry indicate a composition between quartz diorite and tonalite. Local areas relatively enriched in K-feldspar phenocrysts (20%) have monzodiorite compositions.  Tabular pink K-feldspar phenocrysts ranging from 2 to 20 millimetres in length usually comprise from < 1 to 5 percent of the mode, and rarely up to 15 percent (Plates 2.3B, 4.1A, 4.2A). Isolated megacrysts up to 7 centimetres long occur in the 130 level at Snip. The phenocrysts are often euhedral; serrated margins with adjoining altered plagioclase grains are also common. Crystals are sometimes perthitic.  201  The matrix to the K-feldspar megacrysts consists of medium grained porphyry containing phenocrysts of plagioclase and subordinate altered ferromagnesium minerals and quartz (Plate 4.1B). Plagioclase forms 35 to 55% of the rock as 1-3 millimetre laths. It is usually completely altered to aggregates of sericite ± quartz ± K-feldspar. Polysynthetic twin extinction angles from remnant cores and rarer unaltered grains in thin section indicate a composition of about An30 . Mafic phenocrysts, probably originally hornblende from grain shapes, are commonly altered to magnetite, hematite, pyrite, biotite and chlorite. They comprise up to 4% of the mode. Equant, clear to smoky subrounded quartz phenocrysts, 0.2-1.5 millimetres in diameter, comprise <1 to 4%. In areas of moderate to intense alteration these are difficult to distinguish because they blend into the alteration assemblage. Accessory minerals include apatite, zircon and sphene. Apatite occurs in some samples as disseminated rounded to sub-prismatic grains, usually 0.03-0 1 millimetres in length. Grains up to 0.5 millimetres long were observed in one sample from the north end of the intrusion in the Snip workings, where the apatite comprised approximately 0.5% of the rock volume. Apatite is unaffected by the sericitic alteration which preferentially replaces plagioclase. Sparse disseminated subhedral clear zircons, usually less than 0.03 millimetres in length, were observed in some samples, in one case within apatite grains. Sphene occurs rarely.  The fine grained matrix to the K-feldspar, plagioclase and quartz phenocrysts forms between 35 and 60% of the rock volume. Unaltered matrix, observed only in two samples (Plate 4.1B), consists of a fine grained aplitic intergrowth of 0.1-0.2 millimetre equigranular anhedral quartz (15-35 %), plagioclase (40 to 70%) and K-feldspar (5 to 15%). Usually, however, the matrix is altered to pink K-feldspar + quartz + sericite (see section 4.2.3).  4.2.2 Dykes within the Red Bluff porphyry  Fine grained, aphanitic, dark grey mafic dykes, commonly 0.5 to 3 metres wide, occur throughout the porphyry. These have variable orientations, but commonly have northerly strikes and steep dips. Some are porphyritic, with 2-5% 0.5-2 millimetre plagioclase and/or 5-10% chloritised mafic phenocrysts.  202  They are usually pervasively altered to sericite + chlorite + calcite ± biotite. Dyke margins may be strongly foliated, with a weaker phyllitic foliation developed in dyke cores (Metcalfe, 1988). Where foliation is developed, it is parallel to the dyke margins. Foliation parallel 0.1 to 1 centimetre wide calcite + chlorite ± quartz ± Fe-carbonate veinlets are developed in foliated dykes. Subrounded calcite blebs (1-5 millimetres wide), probable amygdales, occur in some dykes, and form up to 5% of the dyke volume (Metcalfe, 1988). Pervasive calcite-chlorite alteration of the dyke groundmass is common. The dykes cut quartz-magnetite-hematite veins of the potassic alteration assemblage (see section 4.2.3 below), but their relationship to other alteration types was not ascertained.  At least three of these unmineralised but altered dykes intrude the porphyry in the Snip 130 portal area and in adjacent surface exposures (Figure 4.1). They range in thickness from 0.3 to 2 metres. The matrix consists of a fine grained intergrowth of plagioclase and sericite. Mafic phenocrysts altered to biotite, pyrite, calcite and/or magnetite, form spots 0.5 to 2 millimetres in length that comprise 10 to 15% of the dyke (Plate 3.6B). Alignment of the long axes of the spots parallels the southwest plunging lineation on the foliation in the porphyry. Biotite occurs as veinlets and as disseminations with sericite and abundant calcite through the fine grained matrix. It is olive green in thin section. The dykes are mineralogically and texturally similar to the BSU dyke within the Twin zone (Plate 3.6).  Biotite lamprophyre dykes, undeformed and unaltered, intrude northeast trending faults in the Red Bluff cliff area (Metcalfe, 1988), as they do to the west in the southern Snip workings. Their confinement to within and immediately adjacent to fault zones, lack of foliation or alteration, and euhedral biotite and subhedral pyroxene phenocrysts distinguish them from earlier foliated and altered mafic dykes within the porphyry. They are probably Tertiary in age.  203  Plate 4.1. Character and alteration of the Red Bluff porphyry, northwestern British Columbia. Drill hole locations are shown on Figure 2.2. A: K-feldspar megacrysts in a green-grey matrix of sericite-magnetite altered plagioclase porphyry. Note the banded quartz + magnetite vein that crosses the lower core which is cut by a later quartz vein. Sample is from Skyline DDH 954: 57.5 metres. The scale is in centimetres. Photo taken by A. Ettlinger. B: Photomicrograph (crossed nichols) of the plagioclase porphyry matrix to the Kfeldspar megacrysts. Plagioclase phenocrysts (An30) in a crowded equigranular matrix of fine-grained plagioclase, quartz and K-feldspar. The dark aggregate at bottom left (above and right of plate number) consists of secondary K-feldspar (brown), quartz (grey subrounded grains) and magnetite (opaque). The thin section is slightly thick so some quartz and feldspar grains appear yellow or orange. Sample is from Skyline DDH 959:79.0 metres. The field of view is 5 millimetres. C: Photomicrograph (plane polarised light) of intergrown magnetite + hematite (mag/hem), K-feldspar (pale brown patches = ksp) and biotite (dark olive-brown = bio) in a sericite-quartz altered matrix. This is typical of much of the pervasive potassic alteration that forms broad overlapping envelopes to quartz-magnetite veins. Sample is from Skyline DDH 964: 43.4 metres. The field of view is 1.3 millimetres. D: Photomicrograph (crossed nichols) of magnetite (black), biotite (red-brown birefringence) and sericite (felted matrix) that form an envelope to a quartzmagnetite vein (at lower right). Sample is from Skyline DDH 964: 66 metres. The field of view is 1.3 millimetres  p  I  205  4.2.3 Alteration related to the Red Bluff porphyry  The porphyry and adjacent country rocks are affected by several styles of alteration and related veining spatially associated with the intrusion. Two successive phases of alteration are most intensely developed within the intrusion. They are: (i) early potassic alteration (quartz-magnetite-sericite-K-feldspar-biotitehematite) characterised by quartz-magnetite-hematite veins, and (ii) late phyllic alteration (sericite-pyritequartz-albite) characterised by pyrite veins and veinlets. The alteration phases are cut by three minor phases of veining: (i) quartz-hematite-sulphide veins, (ii) chlorite-calcite veins, and (iii) quartz-calcite extension veins.  Potassic alteration  in the Red Bluff porphyry is characterised by a quartz-magnetite-sericite-K-feldspar-  biotite-hematite-pyrite-chalcopyrite assemblage. It is the most intense and widespread alteration within the Red Bluff porphyry and affects the entire intrusion, comprising more than 80% of the alteration. Sericite, K-feldspar, magnetite, hematite and biotite form envelopes around quartz-magnetite-hematite veins. Locally, in intensely sheeted or stockworked areas, the envelopes merge to pervasive alteration. Secondary biotite developed pervasively, as veinlets and as envelopes to shear veins in the greywacke sequence within the Snip workings may be related to this alteration assemblage.  Quartz-magnetite-hematite veins usually range from 0.5 to 3 centimetres in thickness, and form sheeted to stockwork zones (Plates 4.2, 4.3A) that are confined to the Red Bluff porphyry. Magnetite with lesser intergrown or intergranular specular hematite constitutes from 0.5 to 25 % of the vein volume, often as multiple 0.1 to 1 millimetre wide bands (Plates 4.2A, 4.2C, 4.3A ). Magnetite and hematite commonly occur together in individual grains with undulating irregular boundaries separating the two phases. Paragenetic relationships are unclear and often contradictory. Magnetite to hematite ratios are usually greater than 3:1, but in some sections, equal proportions of both minerals are present. Vein quartz is white and translucent. It consists of equant 0.05-0.2 millimetre grains. Magnetite-hematite and olive green biotite often occur as thin envelopes at the borders of ribboned quartz-magnetite-hematite veins  206  (Plate 4.1D). Multiple generations of obliquely crosscutting quartz-magnetite-hematite veins are common (Plate 4.3A). Younger veins contain progressively less magnetite and hematite, from 5-25% in the oldest veins to 0.5-5% in the youngest. The veins locally form dense stockworks, forming between 60 and 90% of intersections over lengths of up to 15 metres (Plate 4.2C), indicating significant dilation. Three phase fluid inclusions, with salt daughter grains volumetrically greater than the vapor phase, were observed in quartz from quartz-magnetite-hematite veins from the 130 haulageway at Snip (K. Dunne, personal communication, 1993).  Sericite, quartz, K-feldspar, biotite and carbonates are common alteration minerals in moderately to strongly potassic altered areas of the intrusion. K-feldspar phenocrysts are unaltered to partially replaced by quartz, secondary K-feldspar, and possibly later, carbonate (Plate 4.4B). Plagioclase is usually completely replaced by a pale green fine grained felted sericite with minor quartz and K-feldspar (Plate 4.4B). Pink K-feldspar often replaces 25 to 50% of the fine grained quartz-plagioclase matrix to the plagioclase and K-feldspar phenocrysts (Plate 4.2A). In thin section, it is typically pale brown from abundant dusty opaque inclusions (Plates 4.1C). It often forms anhedral intergrowths with quartz. Grains are typically equant and fine grained, ranging from 0.1 to 0.02 millimetres in diameter. Secondary Kfeldspar is distinguishable from the primary fine grained igneous matrix by coarser grain size (Figure 4.1B), polygonal grain shapes, abundance in the envelopes of quartz-magnetite-hematite veins (Plate 4.2A), and intergrowth with aggregates of magnetite-hematite and biotite (Plate 4.1C). Pink K-feldspar forms discrete veinlets with accessory quartz and calcite within a relatively weakly altered porphyry in drill hole 959 of Skyline Gold Corp., drilled at the southeast end of the intrusion (A. Ettlinger, personal communication, 1991; see Figure 2.2 for location). Disseminated to veinlet controlled magnetite with subordinate hematite, constituting between 3 and 10% of the rock volume, occur as individual grains and aggregates that are often intergrown with secondary K-feldspar and olive green biotite after mafic minerals (Plate 4.1C). Where pervasive potassic alteration is strongest, intrusive textures are obliterated resulting in a dark grey fine grained mixture of quartz + sericite + magnetite + hematite + K-feldspar  207  (Plates 4.2B, 4.3A). Disseminated calcite and rhombohedral Fe- or Mg-carbonate grains 0.01-0.1 millimetres in diameter commonly form up to 1% of the rock in potassically altered areas.  Pyrite and subordinate chalcopyrite, ranging from trace to 4%, are disseminated throughout the potassic alteration assemblage. Pyrite to chalcopyrite ratios are usually >8:1. In areas only affected by potassic alteration, pyrite and chalcopyrite grains are rimmed and/or partly replaced by hematite and magnetite. This is also common in quartz-magnetite-hematite veins (Plates 4.4C, 4.4D). The sulphides usually form less than 15% of the metallic mineral assemblage in these areas, but their replacement by magnetite and hematite suggest that the abundance could have been greater originally. Disseminated and veinlet controlled pyrite associated with later sulphide rich sericitic alteration replaces magnetite and hematite, often obscuring the relationship between sulphides and oxides in the potassic assemblage (Plate 4.3B).  Veinlet controlled and disseminated brown biotite occurs broadly and abundantly throughout the greywacke sequence of northern Johnny Mountain. It is not just confined to the immediate vicinity of the Red Bluff porphyry in the Snip workings (Figure 4.2). Biotite abundance is greatest in the greywackes between the Red Bluff porphyry and Sky Creek, the southernmost kilometre of the Bronson stock, the northwestern end of Snippaker Ridge within 1 kilometre of the Red Bluff porphyry (J. Moors, personal communication, 1992), and in greywacke and volcanic conglomerate units along the west side of Johnny Mountain. Within the greywacke, 50 to 100 metres from the southwestern contact of the Red Bluff porphyry, and in greywacke screens, biotite occurs with magnetite, chlorite and sulphides. Biotite is absent in greywacke and interbedded siltstone west of Monsoon Lake and on most of Snippaker Ridge (R. Pegg, personal communication, 1993), except near the Stonehouse veins. Southeast of the Red Bluff porphyry along the northeast side of Johnny Mountain, biotite is sparsely present to absent. Possible origins of this broad zone of biotite development are outlined section 4.3.  Phyllic alteration in the Red Bluff porphyry is characterised by texturally destructive sericite-pyrite-  quartz ± albite assemblage (Plate 4.4A). It is commonly developed as envelopes around abundant pyrite  208  veins and veinlets. This alteration overprints the potassic assemblages (Plates 4.3B, 4.3C; see below), and comprises approximately 10-20% of the overall alteration assemblage. Although sericite from the potassic alteration event occurs throughout the Red Bluff porphyry, it is more abundant in the phyllic assemblage. Phyllic alteration is distinguishable from the earlier potassic alteration by: (i) the higher pervasive abundance of disseminated sericite and pyrite, (ii) association with veins and veinlets of pyrite, (iii) replacement of both primary and secondary K-feldspar by sericite, quartz and albite, and (iv) alteration of magnetite and hematite in the potassic assemblage to pyrite (Plate 4.3B). Phyllic alteration is restricted to the porphyry, greywackes adjacent to the southeast end of the porphyry, and an elongate alteration zone along Sky Creek (Figure 2.3). It is present throughout the entire Red Bluff porphyry, although development is erratic and large areas of potassic alteration are unaffected.  Strong sericite + quartz + pyrite + albite alteration envelopes around pyrite veins and veinlet stockworks bleach the porphyry groundmass to a pale greenish yellow (Plate 4.3C). In zones of intense sericitic alteration secondary magnetite and hematite are completely altered to pyrite and relict textures of the potassic alteration are preserved. Specifically, where quartz-magnetite-hematite veins are altered, the ribbon like texture of the magnetite-hematite is preserved by the later pyrite (Plate 4.3B). Albite, quartz, sericite, and more rarely, pink calcite often completely replace K-feldspar phenocrysts and secondary Kfeldspar in strongly phyllic altered zones, altering the K-feldspar chalk white, yellow or pink. Molybdenite is common on foliation parallel stylolitic surfaces in sericite schist associated with sericitepyrite alteration at the northwest end of the porphyry in the Snip 130 portal. It is associated with areas of pink calcite replacing K-feldspar. Chlorite occurs rarely as disseminated clots and grains in sericite-pyrite alteration assemblages.  Sheeted and stockworks of pyrite veinlets associated with the phyllic alteration assemblage occur with variable intensity throughout the Red Bluff porphyry. Chalcopyrite and molybdenite are common vein constituents, and bornite occurs occasionally (A. Ettlinger, personal communication, 1991). Pyrite and subordinate quartz + calcite + sericite ± chlorite veins more than 5 centimetres in thickness are  209  abundant in the west central portion of the porphyry near its north contact in Skyline drillholes 954, 955, 963 and 964 (Figure 2.2). In other areas, thick veins are rare, and 1 to 5 millimetre wide pyrite veinlets predominate.  The phyllic alteration zone occurs in both the porphyry and surrounding sediments. In the phyllitically foliated elastic rocks along the south margins of the porphyry, pyrite veins and stringers are parallel to foliation (Metcalfe, 1988). Strong sericite-pyrite alteration is also developed in the sedimentary sequence for approximately 1.2 kilometres beyond the southeastern end of the porphyry (Kerr, 1948; Figure 2.3). The zone, which reaches a maximum of 600 metres in thickness (Metcalfe, 1988), contains both disseminated and vein controlled pyrite + sericite ± sphalerite. Sericite-pyrite-quartz alteration is nearly absent in greywacke adjacent to the northwest end of the intrusion in the Snip workings. A second conspicuous zone of sericite-pyrite alteration affects thickly bedded greywacke in the hanging wall of a southwesterly dipping, gouge filled fault zone along Sky Creek (Figure 2.3). The exposed alteration zone is more than a kilometre long, and it affects up to 50 metres of stratigraphy. Disseminated pyrite commonly exceeds 3% of rock volume and is associated with locally abundant pyrite + chalcopyrite veinlets.  210  Plate 4.2. Alteration of the Red Bluff porphyry, northwestern British Columbia. The coin is 2.4 centimetres in diameter. A: Quartz vein with patches of magnetite (black) is oblique to foliation (parallel to the bar at the top of the photo) in deformed K-feldspar megacrystic porphyry. Plagioclase phenocrysts and the fine-grained matrix are altered to sericite + Kfeldspar. Disseminated magnetite comprises approximately 4% of this sample. Note the centimetre-wide tan coloured K-feldspar envelope on the quartz-magnetite vein and the thin foliation parallel veinlet that branches off the larger vein in the lower left hand corner. Sample is AJM-ISK90-306, from the 130 portal at Snip. The sample location is shown on Figure 4.1. Sample was collected by James Macdonald. B: Sheeted quartz-magnetite-hematite veins with well developed magnetite + hematite laminae. The veins occur parallel to foliation in a strongly altered phyllitic matrix of dark grey sericite + magnetite + quartz + hematite + biotite. Sample is DR-10, from the 130 portal at Snip. Sample location is shown on Figure 4.1 C: Intense quartz-magnetite-hematite veining. Multiple crosscutting veins with abundant magnetite-hematite laminae comprise the entire volume of both samples. Younger veins have progressively less Fe-oxides. Both samples were collected from the base of the Red Bluff cliffs. Left sample is DR-208 and right is DR-205. Sample locations are shown on Figure 2.2 D: Quartz veins with magnetite-hematite laminae in a fine-grained strongly altered matrix of sericite + magnetite + quartz + biotite. Note the irregular vermicular veinlets of quartz in the matrix. Sample is AJM-ISK90-144, from the 130 portal at Snip. The sample location is shown on Figure 4.1. Sample was collected by James Macdonald.  212  Plate 4.3. Alteration of the Red Bluff porphyry, northwestern British Columbia.  The coin is 2.4 centimetres in diameter. Drill hole locations are shown on Figure 2.2. A: Multiple generations of quartz-magnetite-hematite veins in a matrix of sericitemagnetite-quartz-biotite altered porphyry. Younger veins have progressively less Feoxides. Note the offset on the early, central vein. Sample is AJM-ISK90-144, from the 140 portal at Snip (the same sample is shown in Plate 4.2D). Sample location is shown on Figure 4.1. Sample was collected by James Macdonald.  B: Sericite-pyrite alteration. Top is from Skyline DDH 964: 65.3 metres. The dark area at the right consists mainly of magnetite > hematite laminae and altered rock fragments in a quartz vein. To the left, beside the coin, magnetite laminae are altered to pyrite. Bottom is from Skyline DDH 964: 16.9 metres. It is strongly sericite > pyrite altered porphyry with quartz veins that contain pyrite, probably after magnetite. C: Sericite-pyrite alteration, on left ends of cores, and potassic alteration at right ends of the core. Note that the pyrite replaces magnetite laminae within the quartz vein in the upper core. Top is from Skyline DDH 964: 17 metres. Bottom is from DDH 964: 66 metres. D: Pyrite and orange carbonate veinlets cut quartz-magnetite veins. Veinlet-controlled pyrite is the most widespread manifestation of phyllic alteration within the Red Bluff porphyry. Sample is from Skyline DDH 959: 22.5 metres. Photo by A. Ettlinger.  214  -^40'N.:.  SC AWN ---  SNIPWAKER SHOWINGS  SOLOMON RESOURCES SKYLINE GOLD CORP.  •  OLD PIT CE CONTACT  •  • COTTONWOOD  • CE  TWO BR  .r`  • BONANZA  BLUE GROUSE SILVER DOLLAR  J  r  _r  --•• SILVER TIP  STAIRWAY CREEK  • ZINC TRENCH^ WINDSOCK^  N  UDDER CREEK \ \  \ TWO BARREL  \^  \^\^\ \ \  KNOB HILL °  1,4  ^N ^L  \  ,\ 21=4E \ \ \ X \ \ \ \ \  STOtIEHRUSE,GOlp DEPOSIT N^ •'‘ N^N  \  \  \  \  NNNNNN \  \  \  \  \  \  '  ..••  LEGEND .1.^  •  W.25  ..\\\\\\\\ BURNIE PROSPCT^N N 1.3 KM • L.,  RED BLUFF PORPHYRY BRONSON STOCK LOWER SEQUENCE (TRIASSIC) UPPER SEQUENCE (EARLY JURASSIC) GREATER THAN 1% SECONDARY BMTITE, DISSEMINATED AND VEINLETS  •CE  SHOWING OR DEPOSIT NAME MINERALIZED VEIN, SHEAR VEIN OR SHEAR ZONE FAULT ROAD  0^ 1^ 2  Kilometres  CREEK  Figure 4.2: Northwestern Johnny Mountain in northwestern British Columbia showing the general distribution of secondary disseminated and veinlet biotite with respect to showings and deposits.  215  Plate 4.4. Photomicrographs of alteration, Red Bluff porphyry, northwestern British Columbia. Drill hole and sample locations are shown on Figures 2.2 and 4.1. A: Photomicrograph (crossed nichols) of sericite-pyrite-quartz alteration. The field of view is composed entirely of sericite (high birefringence = ser), quartz (qz), pyrite (py) and albite (alb). Sample is from Skyline DDH 964: 66 metres. The field of view is 1.3 millimetres. Thin section is from the left hand side of the sample in Plate 4.3C, bottom. B: Photomicrograph (crossed nichols) of potassically altered Red Bluff porphyry. Plagioclase is completely altered to fine grained sericite. The matrix to the plagioclase is altered to an intergrowth of quartz and K-feldspar. The large Kfeldspar phenocryst at the bottom right is relatively unaltered, except where it is cut by calcite veinlets. Sample is AIM-ISK90-127. Field of view is 5 millimetres. Sample was collected by James Macdonald. C: Photomicrograph (reflected light) of pyrite (py) in a quartz-magnetite-hematite vein. Note the magnetite (mag) rims and replacement of pyrite. Sample is DR-127. The field of view is 1.3 millimetres. D: Photomicrograph (reflected light) of pyrite (py) rimmed by hematite (hem). Aggregates of hematite + magnetite (mag) occur to the right (grey). Sample is DR208. Sample location is shown on Figure 2.2. Field of view is 0.63 millimetres.  217  Table 4.1: Distribution and paragenesis of minerals in primary igneous rocks, potassic alteration and phyllic alteration in the Red Bluff porphyry, northwestern British Columbia. Mineral^Igneous mineralogy K-feldspar  ^  ^Potassic alteration'^  Plagioclase^Phenocrysts 1-3 mm, 3555%; 40-70% of the fine grained matrix Quartz  ^  Phenocrysts 0.2-1.5mm, <1-4%; 15-35% of the fine grained matrix  Sericite  Biotite  ^  Chlorite  Phyllic alteration  ^ Altered to sericite, quartz Megacrysts 2-20 mm, ^Replaces the fine grained porphyry ^ ^ matrix with equant pink to tan and albite <1-5%; 5-15% of the fine grained groundmass grains; common in envelopes to qzmag-hem veins  Not observed  Altered to sericite > quartz + Kfeldspar  Igneous plagioclase altered to sericite + albite; albite replaces K-feldspar  Abundant in qz-mag-hem veins; with sericite it replaces igneous plagioclase and the fine grained matrix  In pyrite veins and as disseminations with pyrite, sericite and albite that often replaces K-feldspar  Replaces igneous plagioclase, and as envelopes to qz-mag-hem veins  Replaces igneous plagioclase, and both igneous and secondary Kfeldspar  In envelopes of qz-mag-hem veins, and with aggregates of mag and hem; replaces mafic phenocrysts  Occasionally observed: may be remnant of potassic alteration  ^  Rare disseminations and traces in pyrite veins ^  Epidote^  Rare disseminated acicular grains  Carbonates  Disseminated fine grained rhombs of calcite and Fe- or Mg-carbonate  Calcite occurs in pyrite veins and locally replaces igneous K-feldspar with albite and quartz  Magnetite^Not observed and hematite  Phases are intergrown; occur disseminated and in veinlets; as laminae and disseminations in qzmag-hem veins; alter mafic phenocrysts  Altered to pyrite  Pyrite  Disseminated with mag and hem; often rimmed or partially replaced by mag and hem  Abundant as veins and veinlets; also commonly disseminated; replaces mag and hem  Chalcopyrite —  Disseminated with mag and hem; often rimmed or partially replaced by mag and hem  Disseminated in pyrite veins  'Mineral abbreviations: qz = quartz; mag = magnetite; hem = hematite  Rarely in some pyrite veins  218  Quartz-hematite-sulphide veins in the Red Bluff porphyry cut the potassic alteration without associated visible alteration. The veins are composed of milky quartz with hematite + magnetite + chalcopyrite + pyrite ± molybdenite. They occur in several drillholes throughout the porphyry, but are volumetrically insignificant (overall <1% of the alteration assemblage). Vugs are usually 0.2 to 1 centimetres in diameter and comprise up to 3% of the vein volume. The vugs, lined with clear to milky euhedral quartz crystals, commonly contain specularite and sulphides. In drill core the veins are commonly 5 to 20 centimetres wide, but are locally more than 60 centimetres. Talus blocks containing vuggy quartzhematite and bladed specularite veins and veinlets that cut well banded quartz-magnetite veins are common at the base of the Red Bluff. Vuggy quartz-hematite veins were not observed in areas of sericitic alteration, so their relationship to that stage of alteration is not clear. The development of iron oxides suggests that these veins may have formed late in the potassic alteration event.  Chlorite-calcite ± pyrite veins in the Red Bluff porphyry are late and cut both pot'ssic and phyllic alteration assemblages throughout the porphyry. The veins comprise less than 1% of the overall alteration assemblage, usually as closely spaced veinlets <2 centimetres in diameter. Near the south contacts in the east-central portion of the porphyry, these veins contain, or are associated with, pink carbonate veinlets, possibly rhodochrosite (they do not react strongly with acid; Metcalfe, 1988). These veins may be synchronous with the development of fine grained euhedral disseminated carbonates and rare chlorite in the potassic and phyllic alteration assemblages.  Quartz-calcite-chlorite extension veins are sparsely developed in the Red Bluff porphyry. They are lenticular and 0.2 to 2 metres long. They contain quartz + calcite ± chlorite fill and form en echelon arrays that cut all other vein types. The veins dip moderately to steeply southeast in the Snip 130 portal (Figures 4.1, 4.3D). Magnetite is commonly altered to hematite along narrow envelopes where these veins cut potassic alteration. These veins are similar to and probably coeval with the Tertiary extension veins that occur throughout the Snip greywacke sequence.  219  Table 4.2: Veins, from oldest to youngest based on crosscutting relationships in the Red Bluff porphyry, northwestern British Columbia. Vein  ^  Characteristics  ^  Associated alteration  ^  Abundance  Quartz-magnetite-^Quartz with laminae and hematite^disseminations of magnetite and hematite; minor pyrite and chalcopyrite  Potassic assemblages; Kfeldspar, sericite, biotite, magnetite and hematite envelopes  Abundant throughout the Porphyry  Magnetite-hematite 0.5-4 mm wide veinlets of veinlets^magnetite with subordinate specular hematite  Associated with pervasive disseminations of magnetite and hematite in pervasive potassic assemblages  Locally abundant in potassic assemblages  Vuggy quartz  White quartz with disseminated hematite, magnetite, pyrite, chalcopyrite and molybdenite; metallic minerals also often in vugs  Cut, but occur with, potassic assemblages; no alteration envelopes  Throughout the porphyry, but volumetrically insignificant  Pyrite  Pyrite > quartz + calcite + sericite + chlorite + chalcopyrite veins and veinlets  Envelopes of intense sericite + quartz + pyrite + albite (phyllic) alteration, and pervasive phyllic assemblages; cut potassic assemblages  Common throughout the Porphyry, especially in the northwest  Chlorite-calcite  ^ ^ Calcite + chlorite + pyrite None ^ veinlets  ^  Throughout the porphyry, but <1% of the alteration assemblage  Extension  Lenticular quartz > calcite + chlorite; commonly southeasterly dipping  None, except locally where magnetite alters to hematite in thin ( <1 cm) envelopes; cut all veins and alteration listed above  Common throughout all rocks in the Johnny Mountain area  Faults  Contain massive milky quartz > calcite veins with coarse disseminated pyrite and subordinate chalcopyrite; veins are usually in a matrix of rusty clay gouge  Rusty bleached envelopes on faults with clays + quartz + sericite  Localised to within faults where thick ( >50 cm) northeasterly trending rusty gouge filled faults intersect the Porphyry  4.2.4 Structure of the Red Bluff porphyry  A detailed structural study is precluded because of the difficulty of access to most of the porphyry, except in the 130 haulageway at the Snip mine and in adjacent surface exposures. Limited surface mapping and  220  drilling indicates the existence of two orthogonal foliations with similar strike in the intrusion: moderate to steep southwest dipping and northeast dipping. The two foliations were not observed together, so their relative relationship is unknown. Foliation is usually phyllitic and defined by the alignment of phyllosilicates. It is inhomogeneously developed and large portions of the porphyry are unfoliated. Foliation is commonly localised within narrow zones sometimes associated with and parallel to the mafic dykes, or forms broad zones >50 metres in width with weakly developed to locally strongly phyllitic fabrics. The porphyry is most strongly foliated in the Snip 130 portal, where it has a strong south to southwest dipping schistose to phyllitic fabric (Figures 4.1, 4.3A). Here, the K-feldspar phenocrysts are often augen shaped and are flattened. A weak elongation or alignment of the phenocrysts parallels the lineation developed on foliation surfaces.  Foliation is usually spaced, defined by coalescing flattened bands and patches of sericite after plagioclase. Striations developed on the foliation surfaces define a lineation that plunges shallowly to moderately southwest (Figure 4.3C). A component of normally directed simple shear on the southwest dipping foliation, parallel to the lineation in the 130 portal at Snip is supported by: locally developed synthetic and antithetic shear bands, oblique shallowly dipping foliation (Plate 4.5A), S-shaped asymmetrically folded and flattened K-feldspar phenocrysts and rare asymmetric down dip to westerly vergent folded intrafolial quartz-magnetite-hematite veins (Plate 4.5D).  Veins related to both potassic and phyllic alteration are commonly sheeted and foliation parallel (Figure 4.3B; Plates 4.2B, 4.5D). In the Snip 130 portal where host rocks have a phyllitic to schistose foliation, these veins are neither boudinaged nor folded, with the exception of the rare minor folds described above. They preserve polyphase salt bearing fluid inclusions. Thus, these veins are relatively undeformed. Mesoscopically undeformed subordinate moderate to steeply dipping quartz-magnetitehematite veins crosscut obliquely both foliation and sheeted southwest dipping foliation parallel quartzmagnetite hematite veins. Sheeted pyrite veinlets and stringers with shallow to moderate southwest dips cut both southwest dipping and steeply dipping quartz-magnetite-hematite veins, indicating that the  221  angular relationships between the quartz-magnetite-hematite veins were developed prior to the formation of the pyrite veinlets. These crosscutting relationships argue against reorientation of the sheeted veins into parallelism with the foliation due to deformation, and indicate that the present vein geometries have not changed since vein formation. Other vein types display similar structural control. Foliation parallel magnetite stringers and bands often occur in strongly foliated potassic altered zones. Quartz-magnetitehematite and vuggy quartz-hematite-sulphide veins are also commonly foliation parallel, or sheeted with southwest and northeast dips in unfoliated sections of the porphyry (see discussion).  Pyrite veins associated with the phyllic alteration have two predominant orientations that parallel the southwest dipping and subordinate northeast dipping foliations. Moderate to steep southwest dips are most common and are parallel to a schistose internal foliation defined by chlorite, sericite and biotite. These veins are also parallel to the Twin zone. In the 130 portal, pyrite veinlets are parallel to foliation and subparallel to the sheeted quartz-magnetite vein sets that they overprint (Figure 4.3B).  A strongly foliated, fine grained, white to tan weathering, 15 metre wide mylonite zone is exposed west of the Snip 130 portal (Figure 4.1). Foliation is parallel to that developed in the rest of the porphyry, and is moderately south to southwest dipping. In thin section, the zone consists of 2 to 6% subrounded to angular K-feldspar porphyroclasts, 0.2-1.5 millimetres in diameter, in a fine grained sericite-K-feldsparquartz rich matrix. Thin elongate pods of sericite 0.5 to 5 millimetres long are common. Foliation is pervasive, and is defined by the alignment of matrix sericite and discontinuous thin mineral trails and pods of nearly pure sericite and disaggregated K-feldspar. Rotated and asymmetric alkali feldspar porphyroclasts indicate an oblique, normally to dextrally directed sense of simple shear on the foliation (Plate 4.5B, 4.5C). This is compatible with kinematic indicators observed elsewhere in the porphyry, and is parallel to a slickenside lineation developed on the fabric. The deformation zone widens to the east in the 130 haulageway.  222  Figure 4.3 A D: Equal area projections (lower hemisphere) of structural features in the Red Bluff -  porphyry, Snip mine workings and adjacent surface exposures, northwestern British Columbia. A: Foliation in the Red Bluff porphyry. B: Quartz-magnetite-hematite veins (+) and pyrite veinlets (o). C: Slickenside and elongation lineation on foliation surfaces. D: Lenticular quartz-calcite extension veins.  223  Plate 4.5. Deformation of the Red Bluff porphyry, Snip 130 portal area, northwestern British Columbia. Sample and photograph locations are shown on Figure 4.1. The coin is 2.4 centimetres in diameter and the hammer is 32.5 centimetres long. The shear sense is shown with arrows. The views are approximately in the XZ plane of the finite strain ellipsoid (i.e. the views are parallel to lineation and perpendicular to foliation). A: Strongly foliated K-feldspar megacrystic porphyry. Note the oblique synthetic shear bands that cut the foliation and give an apparent right-lateral shear sense. The view in the oriented sample is to the southeast, corresponding with a normallydirected shear sense. Sample is DR-3. B and C: Rotated K-feldspar porphyroclasts in a fine-grained sericite + quartz + Kfeldspar matrix. Note the rotation of the foliation around the porphyroclasts and the weakly developed sericite (high birefringence) and K-feldspar pressure shadows and tails that give an apparent left-lateral shear sense. Sample is DR-164, from the mylonite zone exposed on the surface road near the Snip 130 portal. D: Sheeted foliation parallel quartz veins with magnetite ± pyrite laminae in a matrix of foliated K-feldspar megacrystic porphyry. Note the asymmetric fold in the largest vein that gives a normally-directed shear sense. A late thin milky quartz veinlet cuts the other veins and foliation. It is only narrow (<1 centimetre), but the rock has broken along it, giving it a misleading apparent thickness. The view is looking southeast.  225  Kink banding of the south dipping foliation defines a subhorizontal fabric, which is sometimes present in the most highly deformed portions of the porphyry, within and adjacent to the 130 portal at the Snip mine. The kink band fabric was observed in the mylonite zone described above, and in strongly foliated porphyry near the southern contact in the 130 haulageway. In both cases, the kink banded material has a significantly finer grain size than the adjacent porphyry. The flat fabric may be equivalent to the S2 fabric that is developed elsewhere on Johnny Mountain.  Faults  Gouge filled faults cut the porphyry and all of the previously described structural features. The largest of these dip subvertically to steeply northwest, defining pronounced gullies that cut the Red Bluff cliffs at the northwest end of the intrusion (Plate 2.3A). Minor faults are more variable in orientation, such as those with steep southwest and southeast dips that are common in the Snip 130 portal. Like those in the adjacent Snip mine workings, the faults are filled with rusty clay gouge, which sometimes contain late quartz-calcite veins with accessory pyrite. Bleached argillically altered envelopes up to 2 metres wide surround the faults. Slickensides plunging shallowly northwest and drag folded foliation indicate a predominantly dextral sense of motion on one of these faults cutting the Red Bluff cliffs ("Big fault", Metcalfe, 1988). One vertical 030 degree striking fault zone, which has up to 2.5 metres of gouge, cuts through the centre of the porphyry where exposed in the 130 haulage drift (Figure 4.1). It contains several 0.3-1.5 metre wide milky quartz veins with pyrite and chalcopyrite clots and patches. This fault zone also cuts the western end of the Twin zone (see Figure 3.14). The contact between the porphyry and the greywacke sequence in the Snip 130 haulage level is defined by a series of thin southwest dipping, foliation parallel, clayey gouge filled faults with bleached envelopes.  226  4.2.5 Metal distribution within and adjacent to the Red Bluff porphyry  Geochemical analyses from drillholes completed by Skyline Gold Corp. (17 holes) and sampling and drilling (2 holes) by Cominco Metals in the area of the 130 portal at Snip allow a broad view of metal distribution within and adjacent to the Red Bluff porphyry. The locations of the 16 drillholes completed within the Red Bluff porphyry by Skyline Gold Corp. and the two by Cominco Metals near the Snip 130 portal are shown on Figure 2.2. Composited chemical analyses are shown in Table 4.3. Over a total length of 1775 metres drilled entirely within the intrusion, the holes averaged 0.49 ppm Au, 2.6 ppm Ag and 1024 ppm Cu. Mo and Zn concentrations are generally low, usually <40 and <100 ppm, respectively, except at the southeast end of the porphyry where Mo grades are an order of magnitude higher.  Drilling and sampling, conducted in four broad areas about 500 metres apart, span the porphyry from west to east (Figure 2.2; Table 4.3). Highest Au, Ag and Cu average values were obtained from the 10 holes drilled by Skyline in the east central portion of the intrusion (holes: 944 to 949, 955, 957, 961 and 962). Five hundred metres to the northwest (Skyline holes: 954, 956, 958, 963 and 964), and at the west end of the porphyry (Cominco holes: S-48 and S-111), all three of these elements have lower values (Table 4.3). Holes 959 and 960, drilled at the southeast end of the porphyry, are significantly enriched in Mo (averaging 260 ppm) with respect to the rest of the porphyry (usually <35 ppm). No analyses were performed for Mo in the Cominco holes at the northwest end of the porphyry, but the common molybdenite observed in the Snip 130 portal suggests that Mo grades here may be significant.  The variable intensity of alteration types in all of the drillholes makes comparison of their metal contents difficult. However, areas only affected by potassic alteration have Cu, Au and Ag values similar to the drill hole averages shown on Table 4.3. Where pervasive phyllic alteration is developed, Au, Ag and Cu values are similar to those in adjacent areas that are only affected by potassic alteration. These  227  Table 4.3: Drill hole composite assays from intersections in the Red Bluff porphyry, northwestern British Columbia. Holes are located in Figure 2.2. Cominco drilling adjacent to the 130 portal at Snip Hole #^From (n) To (m) Length(m) Au (ppm) Ag (ppm) Cu (ppm) Mo (ppm) Zn (ppm)  Northwest^S-48^4.60^39.30^34.7^0.30^2.4^946^N/A^N/A  porphyry^S-111^0.00^114.30^114.3^0.31^1.5^485^N/A^N/A  Total^149.0^031^1.7^592  Skyline Gold Corp., 1988 drilling Hole #^From (m) To (m) Length(m) Au (ppm) Ag (ppm) Cu (ppm) Mo (ppm) Zn (ppm)  954^2.1^100.0^97.9^1.04^3.9^291^19^71 West^955^2.7^91.1^88.4^0.62^1.8^482^20^80 central^956^3.1^88.1^85.0^0.29^1.1^641^26^68 porphyry^958^3.7^127.1^123.4^0.49^1.0^93^21^55  963^3.1^115.5^112.4^0.34^3.2^459^14^72 964^6.1^109.4^103.3^0.35^2.2^495^18^60 Total^610.4^0.52^2.2^392^19^71  944^70.2^206.3^136.1^0.60^5.2^2862^36^77 946^1.5^121.6^120.1^0.84^3.4^2083^24^93 947^3.4^78.9^75.5^0.76^4.5^1044^51^73 East^948^3.0^66.8^63.8^0.57^6.5^1705^79^436 central^949^1.5^123.4^121.9^0.67^3.5^834^46^80 porphyry ^957^4.6^118.6^114.0^031^1.4^961^27^88 961^3.1^133.2^130.1^0.30^1.1^1066^26^96 962^3.1^117.3^114.2^0.39^2.1^1695^19^97 Total^875.7^0.54^3.2^1565^35^112  Southeast^959^2.1^108.8^106.7^0.18^0.9^702^287^106 porphyry^960^183^52.0^33.2^0.43^2.0^1367^172^151  Total^139.9^0.24^1.2^860^260^117  Weighted average overall grades within the^Length(m) Au (ppm) Ag (ppm) Cu (ppm)^Mo^Zn Red Bluff porphyry^  (PM11)*^(PM)*  1775^0.49^2.6^1024^48^97  Drilling in the greywacke sequence adjacent to the porphyry  over l626ni excluding Canine° drilling in die northwest porphyry  Hole #^From (m) To (m) Length(m) Au (ppm) Ag (ppm) Cu (ppm) Mo (ppm) Zn (ppm) CE^911^10.2^250.6^240.4^0.54^8.4^436^N/A^3212 zone^918^83.0^296.0^213.0^0.32^3.9^270^N/A^3570 919^16.4^318.8^302.4^0.51^7.9^466^N/A^3365  Total^755.8^0.47^6.9^401^N/A^3374 Southwest^944^6.4^70.2^63.8^0.63^2.0^1760^52^126  porphyry ^945^4.3^48.0^43.7^0.78^5.3^2395^50^322 Total^1075^0.69^33^2018^51^206  Metal ratios Au/Ag^Cu/Au^Cu/Ag^Zn/Au^Zn/Cu^Au/Mo^Ag/Zn^Mo/Zn  Northwest porphyry^0.18^1909^348^N/A^N/A^N/A^N/A^N/A West central porphyry^0.23^754^178^137^0.18^0.027^0.031^0.27 East central porphyry^0.17^2898^489^207^0.07^0.015^0.029^0.31  Southeast porphyry^0.20^3583^717^488^0.14^0.0009^0.010^2.22 CE zone^ 0.07^853^58^7179^5.26^N/A^0.002^N/A  228  Table 4.3 (continued) 1965 Cominco drilling in and adjacent to the Red Bluff porphyry (data from Parsons, 1966) Hole /I 65-1 65-2 65-3 65-4 65-5 65-7 65-8  To (m) Length (m) Unit 60.4 Greywacke/siltstone 60.4 53.1 34.2* Greywacke/siltstone Greywacke/siltstone 43.0 43.0 67.1 18.0* Altered porphyry Greywacke/siltstone 23.4 23.4 Altered porphyry 25.0 1.6 37.1 Greywacke/siltstone 37.1 47.0 9.9 Altered porphyry Greywacke/siltstone 8.4 8.4 Altered porphyry 32.9 24.4 49.1 Greywacke/siltstone 49.1 0.0 *Some core was lost in shipping; **Over 25 metres only; - = no data From (m) 0.0 0.0 0.0 43.0 0.0 23.4 0.0 37.1 0.0 8.4  %Cu 0.29 0.28 0.25 <0.1 0.21 0.07 0.15 0.06 0.30 0.09 0.03  %Mo 0.01** -  0.04  observations suggest that base and precious metals were introduced during the potassic alteration event, and that they have not been modified significantly by the overprinting phyllic alteration. Chip samples taken at 3 metre intervals in quartz-magnetite-hematite veined and potassic altered porphyry in the 130 haulageway at Snip over a distance of 76 metres (43 samples) averaged 0.37 ppm Au (Cominco Metals, unpublished data). Over a 78 metre long section of foliated porphyry affected by pervasive sericite ± pyrite ± K-feldspar ± magnetite alteration (containing both pervasive phyllic and potassic alteration) without quartz-magnetite-hematite veins, however, gold grades in 53 samples averaged only 0.07 ppm. This implies that the quartz-magnetite-hematite veins associated with potassic alteration introduced Au. Plots of Au versus Cu indicate locally linear correlations between these elements in areas affected by potassic alteration that have little phyllitic overprint (Figure 4.4). For example, linear relationships are well developed in Figure 4.4A (which comprises the data from adjacent Skyline drill holes 944, 961 and 962 that were drilled within the central southwest portion of the porphyry) and in Figure 4.4B (containing the data from Skyline hole 956, drilled in the west central portion of the porphyry). These figures contain data from holes that intersected strong potassically altered and quartz-magnetite veined porphyry with only sparse pyrite veinlets representing the phyllic overprint (<2% of the alteration assemblage). Skyline holes 963 and 964, containing 5-15% pyrite veins and veinlets that cut potassic veins and alteration, display a weak linear correlation between Au and Cu (Figure 4.4C). These holes were drilled near hole 956 (Figure 2.2).  229  Screens of greywacke are often metal enriched when compared to the surrounding porphyry. Cominco holes 65-3, 65-4, 65-5 and 65-7 were collared in greywacke screens (locations are on Figure 2.2). Each shows higher Cu values within the altered greywacke screens (0.15-0.3%) than within the altered porphyry (<0.05-0.09%; Table 4.3).  Several 0.5-2 metres wide pyrite veins and schistose shear zones with predominantly southwest dips within the porphyry returned erratic, often high, gold values (Metcalfe, 1988). However, they appear to be discontinuous and are seldom traceable for more than 50 metres in strike length. These structures are not usually precious metal or Cu enriched with respect to the surrounding altered intrusive.  Cu and Au grades in greywackes adjacent to the Red Bluff pcnphyty  Grades in the greywackes at Snip typically range from 50-220 ppm Cu, trace to 40 ppb Au, and trace to 1 ppm Ag. At the northwest end of the porphyry, concentrations of these elements in drillholes within the greywacke sequence less than 200 metres from the southwest porphyry contact show no enrichment when compared to holes drilled up to 1 kilometre southwest of the porphyry. In greywackes within the Snip 130 haulageway, 26 samples taken within 40 metres of the porphyry contact averaged <10 ppb Au. However, gold and copper are more abundant: (i) within 5-50 metres of shear zones, where gold values commonly range up to greater than 200 ppb, and (ii) in irregular intersections, up to 50 metres long, marked by abundant fracture controlled and disseminated sulphides (mainly pyrite).  Drilling indicates that metal values are enriched within at least 50 metres of the porphyry in greywacke adjacent to the central southern contact of the porphyry. 1965 Cominco drill holes 65-1 and 65-2, which have a cumulative length of 95 metres, average 0.29% Cu (Parsons, 1966). Skyline holes 944 and 945,  •^  1.50  O  n  1.25  O  Ci  1.00 ▪  a  0  a a Co 13a  0  CIO a 0 ana Imam on3^a^n n CO3 0 0  0 0^0  a  0 .75  0^0 0  a s  ^  o  Masa 0 13133 a 13^0  0.50  a 020113® 0  Or 0  =313 IIIIKEZMna 1331:03 0 031100030,113 ammal co 13 ^  Camzi  0.25  Cu (ppm x 10 3)  2.00^4.00  ^  6.00^6.00  Cu (ppm x 10 3) ^  1.00  ^  2.00  ^  3.00  ^  9.00  ^  1.00  ^  2.00  Figure 4.4: Au versus Cu scatter plots of analyses from selected Skyline drill holes drilled within in the Red Bluff porphyry, northwestern British Columbia. Drill hole locations are shown on Figure 2.2. A: Data from Skyline Gold Corp. holes 944, 961 and 962, drilled adjacent to each other in the central southwest portion of the porphyry. Note the close correlation between Au and Cu. The plot contains 252 analyses entirely within potassically altered porphyry containing abundant quartz-magnetite-hematite veins. Overprinting by phyllic alteration in the form of pyrite veinlets is minimal, and comprises <2% of the alteration assemblage. 22 analyses with missing data, data below detection limit or data with anomalously high values are excluded. 47 analyses in hole 944 are excluded because they were drilled outside the porphyry in altered greywacke. However, these also show a linear correlation between Au and Cu. B: Data from Skyline hole 956, drilled in the western portion of the Red Bluff porphyry. Note the correlation between Au and Cu. The plot contains 62 analyses. No data are excluded. The hole intersected potassically altered and quartz-magnetite-hematite veined porphyry with minimal phyllic overprinting. C: Data (149 analyses) from Skyline holes 963 and 964, drilled in the western portion of the Red Bluff porphyry near hole 956. The data show a weak correlation between Au and Cu. The holes intersected potassically altered porphyry with abundant quartz-magnetite-hematite veins that are overprinted by abundant pyrite veins, veinlets and associated phyllic envelopes (15-25% of the alteration assemblage). 29 analyses with missing data, data below detection limit or data with anomalously high values are excluded.  ^  3.00  ^  4.00  231  drilled 250 metres to the southeast, returned 0.2% Cu and 0.69 ppm Au over a cumulative length of 108 metres (Table 4.3). Analyses for Mo over 25 metres in hole 65-2 averaged 130 ppm. Cominco hole 65-8, however, drilled in greywacke and siltstone approximately 150 metres from the northeast porphyry contact (Figure 2.2), averaged only 0.03% Cu but contained 0.04% Mo. All of these holes were drilled within altered greywacke containing abundant quartz veins and disseminated to veinlet controlled magnetite, pyrite and chalcopyrite.  The pervasive phyllic alteration zone that extends southeast of the Red Bluff porphyry is anomalously enriched in Au, Ag and especially Zn. Skyline holes 911, 918 and 919 drilled in this area averaged 0.47 ppm Au, 6.9 ppm Ag and 3374 ppm Zn (Table 4.3; Figure 2.2: CE zone holes). Disseminated and veinlet controlled pyrite and subordinate sphalerite occur throughout this area. Outside this zone to the west and southeast, these metal values are substantially reduced, typically below 200 ppm for Zn, Cu and Pb, and less than 0.01 ppm Au in holes drilled at the Bonanza showings, except within or adjacent to mineralised structures (Atkinson, 1990). No metal contents are known for the Sky Creek pervasive sericite-pyrite quartz alteration zone, although chalcopyrite is observed on fractures.  Molybdenite compositions  Molybdenite taken from the Twin zone (2 samples of chloritic vein), Red Bluff porphyry in the 130 haulageway at Snip (2 samples) and from the Bronson skarn was analysed by Rodney Churchill and Derek Wilton at Memorial University using laser-mass spectrometer-inductively coupled plasma emission (LAMS-ICP) multi-element analysis (Table 4.4). The data are acquired by laser decrepitation and vaporisation of individual molybdenite grains. The vaporised material is passed to a mass spectrometer and relative elemental quantities are measured in counts per second. As the technique is currently under development, the data (Table 4.4) is considered qualitative.  232 Table 4.4: LAMS-ICP analyses of molybdenite from the Red Bluff porphyry, Bronson Skarn and Twin zone, northwestern British Columbia. Cu*  Pb**  Zn  Au  AR  Cu/Zn  Cu/Pb  Cu/Au  Zn/Au  Ag/Au  D1-172 (K-feldspar Porphyry)  5400.0  15452.5  70.56  8.83  3350.1  76.5  0.35  611.6  8.0  379.4  DR-138 (qr. magnetite veins)  4423.5  13059.0  176.48  2.94  1785.4  25.0  0.34  1504.6  60.0  607.2  DR-116  564.7  1289900.0  168.61  330.39  52373.7  3.4  0.0004  1.65  0.5  158.5  DR-72  5923.5  372625.0  1906.00  1191.21  37222.0  3.1  0.015  4.97  1.6  31.2  194.1  17860.0  152.95  0.00  291.2  1.3  0.01  N/A  N/A  N/A  Red Bluff Porphyry  Twin zone  Bronaon Skarn DR-247  *All elements are measured in counts per second **Total lead (206 + 207 + 208)  The data show a similar base metal ratio zoning to that described above and in section 2.1.4. There is a decrease in Cu/Zn, Cu/Pb, Cu/Au, Zn/Au and Ag/Au from the Red Bluff porphyry to the Twin zone. Cu/Pb and Cu/Zn are lowest (other ratios are not applicable) in the Bronson skarn.  233  4.3 DISCUSSION  Intrusion and subsequent crystallisation of the Red Bluff porphyry was followed by the development of two major successive hypogene fluid systems centred on the intrusion: early extensive potassic and later phyllic alteration. Both styles of alteration are associated with intense veining, from early quartzmagnetite-hematite veins of the potassic event to pyrite veins and veinlets of the phyllic alteration. Pyrite and chalcopyrite were deposited during both alteration events, but these sulphides are subordinate to magnetite and hematite in the potassic assemblage. During the potassic event there is a progressive decrease in the Fe-oxide content of quartz-magnetite-hematite veins is observed through time (replacement of some sulphides by Fe-oxides notwithstanding), probably terminating in the formation of late vuggy Fe-oxide poor quartz veins. Fe-oxides are altered to pyrite in the subsequent phyllic alteration assemblage. Cu and Au values are similar in areas affected by each style of alteration suggesting that potassic alteration introduced the bulk of these metals and that overprinting phyllic alteration neither remobilised nor introduced metals. Chlorite-calcite ± pyrite veins and veinlets cut phyllic and potassic assemblages and represent a late weakly developed propylitic overprint on the system.  Deformation within the Red Bluff porphyry is inhomogeneous and semi-brittle. The porphyry is most strongly deformed in the Snip 130 portal, where structures indicate a component of normally directed simple shear parallel to a westerly plunging elongation lineation on the southwest dipping phyllitic to schistose foliation. Southwest dipping foliation predominates elsewhere in the porphyry, but it is inhomogenously developed, and like that developed in the 130 portal, is probably confined to shear zones of variable size. Northeast dipping spaced phyllitic foliation is less well developed and was observed at the southeast end of the porphyry on surface. The significance of this foliation is not understood, but its erratic development suggests that it too may be in shear zones.  Quartz-magnetite-hematite veins, magnetite-hematite veinlets and pyrite veins are commonly sheeted, southwest dipping, and parallel to foliation. Angular relationships of sheeted, foliation parallel quartz-  234  magnetite-hematite veins with subordinate oblique veins, and consistent acute angular relationships between quartz-magnetite-hematite and pyrite veins argue against post vein structural reorientation of the quartz-hematite-magnetite veins into parallelism with the foliation. This suggests that the quartzmagnetite-hematite veins are either synchronous with or younger than the foliation. Deformation of some sheeted quartz-magnetite-hematite veins (asymmetric folds and boudinage) together with the preceding argument argues the former. Similarly, sheeted foliation parallel southwest and more rarely, northeast dipping pyrite veins and veinlets, occurring even in the absence of foliation, suggest formation during or after deformation. Sericite schists in the Snip 130 portal with disseminated and veinlet pyrite suggest that phyllic alteration was also affected by deformation. Thus, these relationships imply that the potassic and possibly phyllic alteration events were synchronous with foliation forming deformation in the Red Bluff porphyry. Deformation may have been continuous, spanning both alteration events, or punctuated occurring during each alteration event if they were temporally separated. Semi-brittle deformation may have been accentuated or facilitated by the hydrothermal fluids (see section 3.5.2). Steeply southeast dipping extension veins postdate the foliation forming deformational event.  The biotite spotted and andesitic dykes associated with the Red Bluff porphyry are chlorite-biotitesericite-carbonate pyrite altered and foliated, indicating that they predate the termination of the hydrothermal system and deformation. Their abundance within the intrusion suggests that they may be related to late magmatic activity comagmatic with the Red Bluff porphyry. They may thus represent a late stage of emplacement of less differentiated and fluid depleted magma late during the potassic alteration event.  Early Jurassic intrusions and the origin of secondary biotite on Johnny Mountain  The broad arcuate zone of pervasive and veinlet controlled biotite ± pyrite development that surrounds the Red Bluff porphyry and extends along the southwest side of Johnny Mountain covers at least 15 square kilometres. The biotite predates propylitic and phyllic alteration associated with the Red Bluff  235  porphyry and Sky Creek, since it is overprinted by the latter. The restriction of biotite to Johnny Mountain, especially its west side and adjacent to the Red Bluff porphyry, argues against a regional metamorphic origin. Also, the abundant biotite developed in areas distal to the Red Bluff porphyry along the west side of Johnny Mountain argues against a hydrothermal origin directly related to the Red Bluff hydrothermal system alone. If the biotite is a contact metamorphic effect, then a large intrusion may underlie much of western Johnny Mountain. Further features that could be explained by a large buried intrusion comagmatic with the Red Bluff porphyry includes: (i) sills and dykes of similar age (Stonehouse intermediate dykes) and K-feldspar megacrystic sills which are texturally and mineralogically identical to the Red Bluff porphyry (Plate 2.3D) and that lie within or just east of the biotite zone six kilometres south of the Red Bluff porphyry (Figure 2.1), and (ii) the phyllic alteration zone on Sky Creek that could be explained if a second intrusion comagmatic with the Red Bluff porphyry underlies it. All of these intrusions may represent dykes or cupolas derived from an hypothetical buried pluton that also may be the source of hydrothermal fluids.  The abundant biotite, common veinlet control, especially in the Snip workings, and common association with pyrite argues against isochemical crystallisation of the biotite and pyrite from the affected units and instead suggests the addition of potassium and sulphur, probably by hydrothermal fluid circulation. Heberlein and Godwin (1984) demonstrated potassium addition in a similar broad zone of biotite development that was associated with the Berg porphyry Cu-Mo deposit.  Relationship of the Red Bluff porphyry system to the Twin zone and other veins on Johnny Mountain  Geologic relationships and characteristics of the Red Bluff porphyry and the Twin zone discussed in this and the preceding chapter suggest several common important temporal and genetic relationships These include:  236  (1) A close spatial association of the Red Bluff porphyry and the Twin zone. Elongation of the porphyry is parallel to the Twin zone.  (2) Both have potassic alteration. If Twin zone mineralisation were younger than the Red Bluff porphyry hydrothermal system, then the porphyry related sericitic alteration should be overprinted by the biotite (potassic) alteration that is pervasive through the greywacke sequence adjacent to the porphyry at Snip and related to the shear vein hydrothermal system, and it is not. Conversely, if the Twin zone predates the porphyry, then there are two extensive unrelated potassic alteration events in the same area: the first is associated with Twin zone formation and the second with the porphyry (see also point 5 below).  (3) The vein systems on northern Johnny Mountain have metal and alteration zoning consistent with a porphyry system. Distal veins are base metal rich with sericitic to propylitic alteration assemblages; proximal gold rich veins have potassic assemblages (refer to Chapter 2). Similarities in structural style and orientation of the structures suggest they all formed during the same event. Metal ratios from LAMS-ICP analysis of molybdenites in the Bronson skarn, Twin zone and Red Bluff porphyry veins are consistent with the zoning of veins on Johnny Mountain, and indicate a relative increase in Zn and Pb with respect to Cu away from the porphyry.  (4) Both have kinematically consistent veins. Sheeted southwesterly dipping veins in the porphyry suggest that the potassic and phyllic alteration in the porphyry were syntectonic. A normally directed shear sense is indicated on both the Twin zone and Red Bluff foliations.  (5) Offset caused by normally directed simple shear on the Twin zone was accomplished synchronously with ore type formation and mineralisation, before intrusion of the BSU dyke and before termination of the biotite forming hydrothermal system in the Twin zone (Chapter 3). Thus, if the Twin zone predates the intrusion of the Red Bluff porphyry, then deformation of the Red Bluff porphyry must  237  postdate the Twin zone. There is no evidence in the Twin zone for a second period of deformation as intense as that observed in the Red Bluff porphyry in the Snip 130 portal.  (6) Pb-isotopic data from the Twin zone and other Johnny Mountain veins is consistent with the Early Jurassic U-Pb zircon age of the Red Bluff porphyry (195 ± 1 Ma; Table 2.1).  (7) Deformed and biotite-sericite-calcite-pyrite altered biotite spotted dykes occur both in the porphyry and the Twin zone cutting quartz-magnetite-hematite veins and Twin zone veins, respectively. This suggests that they intruded both areas late during potassic alteration and mineralisation.  (8) The Red Bluff porphyry is an Au rich porphyry system that could have contributed gold and other components to the Twin zone.  Taken together, these observations suggest that: (i) mineralised structures on northwestern Johnny Mountain with Early Jurassic galena Pb isotopic signatures formed during one magmatically driven hydrothermal event that was synchronous with deformation, (ii) metals were not mobilised into the structures by later fluid circulation during a subsequent phase of hydrothermal activity or deformation, (iii) hydrothermal activity and mineralisation in the Red Bluff porphyry and the Twin zone were synchronous, and thus the Red Bluff porphyry is a potential fluid source for the Twin zone, (iv) movement and localised deformation was synchronous with deformation in the Red Bluff porphyry, and (v) the abundant secondary biotite developed throughout the greywacke sequence in the Snip workings and the biotite envelopes on shear veins is contemporaneous with the potassic alteration event in the porphyry.  If the Red Bluff porphyry was the fluid source for the Twin zone, then fluids must have migrated: (i) through the greywacke sequence from the Red Bluff porphyry or its probable batholithic parent, or (ii) directly through the Twin zone, presumably from its projected (now eroded) intersection with the  238  porphyry. Evidence discussed in Chapter 3 suggests that fluid flow was along the Twin zone, and that fluids did not enter the zone by infiltration through the greywackes. Thus, fluids from the Red Bluff porphyry may have entered the Twin zone structure directly. Temperature and fluid pressure gradients, increasing toward the porphyry, could have driven fluid flow along the Twin zone. Fluctuating fluid flow rate and corresponding fluid pressure fluctuation from the porphyry into the Twin zone may thus have been another important mechanism in the formation of multiple dilatant quartz and sulphide veins in the Twin zone (see section 3.5.2).  Mineralised structures on northwestern Johnny Mountain may have formed initially by fluid overpressuring and resultant brittle failure subsequent to release of a hydrous magmatic fluid from the Red Bluff porphyry or its batholithic parent. Once formed, these structures may have acted as fluid channelways, distributing hot hydrothermal fluids throughout northwestern Johnny Mountain, and localising deformation. Thus, the temperature and presence of the fluids probably facilitated semi-brittle deformation in these structures. Lateral and vertical fluid migration through these structures across thermal gradients, and mixing with cooler pore fluids would have generated a decreasing temperature and fluid pressure gradient from the porphyry outward. This would be marked by corresponding changes in alteration style, metal content and dilatancy, as described in section 2.1.4. Thus, a second cupola comagmatic with the Red Bluff porphyry underneath the Sky Creek alteration zone, as suggested in the preceding discussion, may explain why the distribution of veins with potassic alteration is skewed to the southwest of the Red Bluff porphyry.  Depth of emplacement of the Red Bluff porphyry and implications  The ages of the Red Bluff porphyry and volcanics of the upper sequence on Johnny Mountain and Snippaker Ridge suggest a relatively shallow depth of emplacement of the intrusion. Dykes in the Stonehouse deposit, dated at 194 ± 3 Ma are indeterminate in age from the Red Bluff porphyry (195 ± 1 Ma; Table 2.1). This indicates that the dacitic to andesitic volcanics at the base of the upper sequence  239  volcanics must have been deposited before or during crystallisation of the Red Bluff porphyry. A minimum age of this lowest unit of the upper sequence from dacite on Snippaker Ridge (192.9 ± 1.3 Ma) and a date from the overlying rhyolite on Johnny Ridge (192 ± 3 Ma) are both slightly younger than, but have overlapping ranges of analytical error with the Red Bluff porphyry and Stonehouse dyke dates (Table 2.1). The dates indicate rapid accumulation of volcanics close to the time of emplacement of the Red Bluff porphyry.  Thus, to determine the approximate depth of emplacement, the shallow dipping Jurassic unconformity surface, which is at 1200 metres on Johnny Mountain and 1900 metres on Snippaker Ridge, can be projected to the present top of the Red Bluff porphyry, at 600 metres elevation. Assuming no movement on faults between the present position of the porphyry and the unconformity and no dip on the unconformity, this results in a range of 600-1300 metres for the vertical distance from the unconformity to the porphyry. With a 10 to 20 degree southerly dip on the unconformity, as suggested by Alldrick et al. (1990), the projected vertical distance increases to between 1100 and 2300 metres. If the unconformity was the paleosurface at the time of the Red Bluff intrusion, then the emplacement depth was probably between 0.6 and 2.5 kilometres. If the dacitic and rhyolitic units of the upper sequence had been deposited by that time (cumulate thickness = 650 metres), then the maximum depth would be still deeper, but probably no greater than 3 kilometres.  The Twin zone must thus have formed at an approximate depth of between 1 and 3 kilometres, if its hydrothermal system was active soon after crystallisation of the porphyry, as the preceding evidence suggests. For fluid pressure cycling and initial fluid induced failure and formation of the shear veins to have occurred at these relatively shallow depths, boundaries to surface fluid release must have existed to generate the necessary high fluid pressures for multiple dilatant veins and initial fluid induced brittle failure. These may have included impermeable mudstone or siltstone units in the folded lower sequence above the present level of Johnny Mountain, or the flat lying Jurassic unconformity and units above it.  240  The high temperature of the mineralising fluids and other strain softening mechanisms discussed in section 3.5.2 may have allowed semi-brittle deformation to proceed at these shallow depths.  Development of the Red Bluff porphyry system  The following sequence of events during the Early Jurassic formation of the Red Bluff porphyry system are thus suggested by the observations described above: (1) Early pervasive and veinlet biotite forms over an arcuate area of >15 square kilometres on northern Johnny Mountain, possibly due to the intrusion of a large buried batholithic parent to the Red Bluff porphyry. (2) Intrusion and crystallisation of the Red Bluff porphyry with release of a fluid phase was followed by brittle failure and development of fluid channeling structures, and development of a large zoned hydrothermal system. Zonation is developed by lateral fluid migration, cooling and probable fluid mixing and reaction. Alteration zones are as follows (refer to Figure 2.3): (i) inner potassic, confined to the Red Bluff porphyry, characterised by the development of abundant quartz-magnetite-hematite veins, (ii) outer potassic alteration characterised by biotite ± K-feldspar associated with shear veins (e.g. Twin zone) and veinlet and pervasive biotite development, and (iii) distal sericite-pyrite alteration associated with veins, shear zones and shear veins. Deformation and formation of inhomogenously developed southwest dipping and subordinate north-northeast dipping shear zones was probably synchronous with this phase of hydrothermal activity, both within and external to the porphyry. The shear zones focussed hydrothermal fluids outside the porphyry. (3) Sericite-pyrite alteration overprinted potassic assemblages within and southeast of the porphyry, and at Sky Creek (see Figure 2.3). Continuing deformation and inhomogenous foliation formation may have occurred within the porphyry during phyllic alteration. There is no evidence for extensive post potassic movement on the Twin zone, so the deformation may have been localised to the porphyry that was the focus of the hydrothermal fluids. These events were probably temporally overlapping.  241  Comparisons to other porphyry systems  The style and progression of alteration in the Red Bluff porphyry system is typical of many porphyry systems. Successive events commonly become increasingly restricted in area and occur closer to parent plutons (Titley, 1982). At Bell copper in west-central British Columbia for example, intense phyllic alteration restricted to the western part of the orebody is superimposed on an extensive earlier potassic assemblage dominated by biotite (Carson et al., 1976). Within the overprinting phyllic alteration at Bell copper and in many Phillipine porphyry copper systems (Sillitoe and Gappe, 1984), like the Red Bluff porphyry, the pyrite is veinlet controlled, while quartz and sericite are envelope and pervasive in habit. Potassic alteration characterised by hydrothermal K-feldspar and biotite is the principal alteration directly associated with ore in most porphyry deposits (Titley, 1982). Veinlet and disseminated magnetite with subordinate hematite are also common components of potassic alteration in Au rich porphyry systems (Sillitoe, 1979; Godwin, 1976) such as the Red Bluff porphyry. Major quantities of quartz were introduced with potassic alteration at several deposits, parts of which comprise > 25 % quartz (Sillitoe and Gappe, 1984).  Porphyry deposits are commonly surrounded by a large biotite aureole that can occur over areas many kilometres in diameter, like the large arcuate biotite zone of biotite development on Johnny Mountain. Development of pervasive biotite alteration is mainly of pre-mineralisation age and is one of the earliest recognised alteration events in a large number of porphyry systems (Titley, 1982; Heberlein and Godwin, 1984). It is commonly overprinted by later syn-mineralisation hydrothermal biotite veinlets (Titley, 1982).  Mineralised structures are broadly zoned in a 40 kilometres square area around the Red Bluff porphyry. This is not unusual. Where continuous vein systems are developed around intrusions, as opposed to typical porphyry stockworks, zoning is often developed over extensive areas. For example, northwest  242  trending veins are concentrically zoned around the Mineral Park porphyry Cu-Mo deposit (Arizona) from inner Cu-Mo enriched zones to outer Zn-Pb veins and peripheral precious metal veins over the 120 square kilometre elliptical Mineral Park (Wallapai) mining district (Wilkinson et al., 1982). The large size of the zoned area is in contrast to the less than 1 square kilometre exposed area of the mineralising intrusion directly associated with the porphyry deposit, which is even smaller than the Red Bluff. Similar vein zoning occurs at Butte, where large veins (up to 3 km long and > 10 m wide) with sericitic and argillic envelopes are concentrically zoned from inner Cu to peripheral Zn-Mn zones over an approximately 30 kilometre square area (Meyer et al., 1968). Within the Cu zone, an intense zone of structurally early quartz-molybdenite veinlets with potassic alteration envelopes is developed, displaying a zonation of alteration. Other districts with well developed intrusion related vein metal zoning include the Cornwall tin district (reviewed in Guilbert and Park, 1986), where several granite intrusions are surrounded by overlapping metal zones, and the Keno Hill Ag-Pb-Zn mining district, zoned laterally up to 25 kilometres from the Mayo Lake granite to granodiorite pluton (Lynch, 1989). In all of the districts described above, like the Bronson Creek area, veins are generally subparallel or have two common orientations, strike parallel to the elongation of the mining district and perpendicular or at a high angle to the metal zone boundaries. Metal zoning is dictated predominantly by distance from the pluton, not by host rock type, although vein development may be lithologically controlled (e.g. veins are developed preferentially in quartzite at Keno Hill). Single veins and vein systems are often zoned laterally and/or vertically as they cross the boundaries of different metal zones in each district (e.g. the Anaconda vein at Butte; Meyer et al., 1968), as they are on the northeast side of Johnny Mountain from the Twin zone to the Bonanza veins. The large size of the zoned systems may be related to the permeability caused by structures, that allow fluids to migrate further than in those systems without continuous peripheral veins.  Coeval semi-brittle deformation and porphyry hydrothermal alteration and mineralisation, as suggested above for the Red Bluff porphyry, is also documented at the Gibraltar porphyry Cu-Mo deposit in central British Columbia (Drummond et al., 1976). Here, four stages of vein development that span the hydrothermal history of the porphyry system are imposed on, and modified by, progressive deformation  243  within the host intrusion. Deformation is inhomogenous and confined to phyllitic and schistose shear zones of variable thickness and abundance.  244  CHAPTER 5: OTHER GOLD DEPOSITS IN THE JOHNNY MOUNTAIN AREA  5.1 Introduction  The Johnny mountain area contains numerous mineralised structures in a belt from north of Snip on the north side of the Iskut River, to Khyber pass, which is south of Inel. Many of those in the northern Johnny Mountain area have been previously discussed in Chapters 2 and 4 and are probably related to the Red Bluff porphyry hydrothermal system. However, other deposits to the north and south appear too distant to be related to the Red Bluff system. Thus, to further evaluate the relationships between Early Jurassic intrusions, deformation and mineralisation in the area, two of the most significant deposits, Inel and Stonehouse, were examined.  5.2 Inel  The Inel property lies 11 kilometres southeast of the Snip mine at the south end of the Bronson Creek valley (Figure 1.2). Inel, originally staked by R.G. Gifford in 1969, was subsequently acquired by Skyline Explorations Limited. In 1987 the property was optioned and later acquired by Inel Resources Ltd. (now Gulf International Minerals Limited). Between 1987 and 1990 two adits were driven (AK and Discovery levels). During August 1992 geologic mapping was conducted on both levels of the Inel workings by the author and P.D. Lewis (Figures 5.1, 5.2). The work, reported in Rhys and Lewis (1993), is summarised here.  The Inel property is underlain by a mixed volcanic and sedimentary succession that is laterally equivalent to Upper Triassic strata exposed at Snippaker Peak, and to the lower sequence on Johnny Mountain (Lefebure and Gunning, 1989; Metcalfe and Moors, 1993). Rocks exposed in the AK and Discovery drifts are predominantly moderate to shallowly easterly dipping upright interbedded greywacke, and laminated to thinly bedded graded siltstone and mudstone. Subordinate interbeds of matrix (mudstone)  245  supported tonalite and mudstone cobble conglomerate and breccia up to 5 metres thick occur in the AK drift. The Discovery drift is dominated by massive to medium bedded poorly sorted feldspathic greywacke containing scattered siltstone interbeds. Bedding in the Discovery drift is upright and has shallow to moderate northeasterly and southeasterly dips that define two broad, west trending upright folds.  Rocks previously described as heterolithic intrusive breccias are exposed in the west end of the AK drift (Gulf, unpublished mapping). These rocks (cobble conglomerate on Figure 5.1) have concordant contact relationships to mudstones underground, and a matrix composition similar to that in conglomeratic rocks observed elsewhere in the drift. Rounded massive to medium grained tonalite to diorite clasts and angular mudstone to siltstone clasts occur in a medium to coarse grained lithic greywacke matrix. The sedimentary clasts display variable degrees of pyrite alteration, and often have 1 to 4 millimetre bleached haloes. Surface exposures of this unit show that it forms a tabular body discordant to bedding in enclosing strata, thus indicating an intrusive origin (V. Jaramillo, personal communication, 1992; P. Lewis, personal communication, 1993).  Exploration drilling from the AK drift intersected a southwesterly dipping K-feldspar porphyritic dyke 7 to 15 metres wide, about 50 metres northeast of the drift. An altered, 5 to 12 metres thick, mineralised discordant heterolithic breccia in its immediate footwall is known as the AK zone. It strongly resembles the intrusive breccia described above. The AK zone consists of tonalite, diorite and siltstone/mudstone clasts in a sandy to silty matrix. Drill core samples often have a porous to pyritised matrix. Areas of highest pyrite content carry subeconomic copper, lead and zinc values associated with significant gold content. This unit and the discordant intrusive breccia dyke described above may have an origin similar to the pebble dykes described in some copper porphyry systems (e.g., El Salvador: Gustafson and Hunt, 1975). The spatially associated K-feldspar porphyritic dyke probably intruded synchronously with both mineralisation and alteration on the AK and Discovery levels.  246  Plate 5.1.^Inel deposit, northwestern British Columbia. Sample and photograph locations are marked on Figure 5.2. The coin is 2.4 centimetres in diameter and the hammer is 32.5 centimetres long.  A: Discovery drift north, looking west. Southwest dipping pyrite vein with chlorite and calcite compositional layers. Note the shallow dipping calcite veinlets in the footwall of the vein to the right of the hammer These parallel a locally developed spaced phyllitic foliation. B: Discovery drift north. Sample is of a northeast-dipping compositionally layered calcite > chlorite + quartz + pyrite shear vein approximately 50 metres southeast of Plate 3.32B. Oblique foliation in the chlorite + pyrite layer (top, parallel to white bar) and an asymmetrically folded quartz vein indicate a right lateral shear sense corresponding with a sense of normally directed shear in the oriented sample. The view is to the northwest. The sample is cut parallel to lineation and perpendicular to foliation (i.e., it is observed in the XZ plane of the finite strain ellipsoid). The coin is 2.4 centimetres in diameter. Sample is 92-IN-9. C: Inel, Discovery drift south. Laminated K-feldspar altered siltstone containing a discontinuous pyrite veinlet with a biotite envelope. D: K-feldspar megacrystic, plagioclase porphyritic dyke that dips south in the south end of the Discovery drift. Plagioclase is saussuritised. Mafic minerals (dark green) are altered to sericite + chlorite + pyrite. Sample was collected by A. J. Macdonald in 1991.  248  Two intrusive bodies are exposed at the southern end of the Discovery workings (Figure 5.2, inset map). A steeply southwest dipping K-feldspar porphyritic dyke, 6 metres wide, is exposed at the far southern end. This dyke contains 5 to 10 per cent, 0.3 to 3 centimetre K-feldspar crystals in a chloritic, medium grained plagioclase rich matrix (Plate 5.1D). It is texturally and compositionally similar to the dyke associated with the AK zone mineralisation, of which it may be an offset extension. Five metres north of this dyke, a parallel medium grained massive, plagioclase porphyritic dyke, 10 metres wide, intrudes the greywackes. The fine grained matrix of the dyke is moderately to strongly K-feldspar altered. In addition, medium grained plagioclase porphyritic diorite dykes intrude the north-central portion and the southeastern portion of the mapped workings.  Mesoscopic structural features on the Discovery level area include sheeted shear veins, sulphide veins, faults, foliation and extension veins (Figure 5.2); many have biotite alteration envelopes 0.2 to 1.5 centimetres wide (Plate 5.1C). Shear veins are most common and generally have moderate southwest, northeast and southeast dips. Two main varieties of vein infillings occur: (i) calcite-chlorite veins, with subordinate quartz, biotite, pyrite and sphalerite, and (ii) massive pyrite-calcite-quartz veins with lesser chlorite and biotite. Calcite-chlorite veins are the most abundant, and range up to 40 centimetres in thickness. These commonly have a laminated fill of alternating chlorite and calcite rich layers (Plate 5.1B). Massive pyrite veins are mostly thicker (up to 2.0 m; Plate 5.1A), strike 090° to 110° with moderate northeast and southwest dips, and are locally cut by calcite-chlorite veins, which usually strike 120° to 140°. Calcite-chlorite veins often contain a subhorizontal internal foliation oblique to vein walls. Slickenside lineations on chlorite foliation surfaces, asymmetric down dip verging folds, offset markers, asymmetric pressure shadows and oblique shallowly dipping foliation in the veins mostly record normally directed dip slip movement. Offset markers are rare; one southwest dipping, 15 centimetres wide, vein containing pyrite + calcite + biotite + chlorite at the southeast corner of the mapped area offsets one of the K-feldspar altered dioritic dykes by 1.5 metres in an apparent normal sense. The northeast and southwest dipping orientations of shear veins on the Discovery level may represent a conjugate array. The normal sense of motion for both sets is consistent with this interpretation. Minor, southeast dipping  249  shear veins are parallel to bedding, suggesting theologically controlled failure and movement along bedding surfaces during formation of the conjugate vein sets. Crosscutting relationships show the massive pyrite veins predate the calcite-chlorite veins. The veins are most abundant within massive greywacke or in pods of siltstone adjacent to the greywacke.  In the AK drift (Figure 5.1) several steep southwest striking pyrite + calcite + sphalerite ± biotite ± chlorite veins, up to 40 centimetres wide, are associated with wide zones of K-feldspar alteration. Some of these steep veins are folded about flat lying axial surfaces. Veins here are considerably less abundant than in the Discovery drift. Late folding of AK sphalerite-pyrite veins about subhorizontal axial surfaces is kinematically consistent with, and may be linked to, formation of the shear veins on Discovery level.  Blocky quartz-calcite filled extension veins occur rarely in all rock units on both the Discovery and AK levels. The veins have various orientations; a well developed moderately southeast dipping set occurs at the central east end of the mapped area. Some extension veins cut shear vein fabrics, but are also offset along them.  Rusty gouge filled faults cut all other structures on both levels and form northwest and northeast striking sets. Faults of both sets dip moderately to steeply to both sides and rarely have down dip slickensides. Sense and amount of displacement, and relative chronology of fault sets could not be determined from the mapped exposures.  Two styles of alteration are developed in both mine levels: broad bedding parallel to discordant zones of predominantly pervasive K-feldspar alteration associated with sulphide-chlorite-calcite stockwork veins (Figures 5.1, 5.2); and biotite-K-feldspar-chlorite-silica envelopes developed around shear veins and veinlets (Plate 5.1C). Both styles occur together, but the broad, stockworked alteration zones may slightly predate the shear veins in some places, as demonstrated by their local offset by shear veins. The broad alteration zones may represent a channeling of fluids along permeable rock units that were  pe 11.41er-^  compiled from mopping by Gulf Internotionol  Ad  Or  "  -  ^J  thinly bedded to laminated graded slitstone, sandstone, and mudstone cobble conglomerate, tonalite to diorite and mudstane dasts, coarse lithic 'racks matrix cobble conglomerate, toilette to diorite and modstane daft.; silty matrix fine to medium—grained massive plagioclase—phyla diorite  k stockwork weinlets  moo of potoesic alt ration bedding  METRES  101101100  extension vein  shear vein (showing 00 and tOckensIde orientation) fault, commonly with rusty gouge (showing dip and elichensIde orientation)  Figure 5.1 (from Rhys and Lewis, 1993)  Geology of the AK drift, Inel deposit, northwestern British Columbia  25 1  thinly-bedded to laminated graded sitstone. sandstone. and mudstone medium-bedded to massive mediumgrained greywocke and mil.' sitstone andesite cobble breccia  fine to medium-grained massive plagioclase porhyry. .windy altered  direction  Oleo, vein (showing dip and sackenside orientation)  Po—isotope ^  UG-87^fault. commonly with rusty goug e !alt +44'^ (shooing dp and Slickenslde orientation)  sample IP 46.95m ::k^ow of potosolc altarat:on  Figure 5.2 (from Rhys and Lewis, 1993)  Geology of the Discovery drift Inel deposit, northwestern British Columbia  252  superseded by flow along the shear veins once they developed. The spatial association of the K-feldspar porphyry dyke with alteration and mineralisation (Figure 5.2, south end) implies that it may be a potential source of fluid and/or heat for at least part of the hydrothermal system. Dioritic dykes in the Discovery workings are offset by shear veins and are pervasively K-feldspar altered, indicating that they predate the mineralising event.  Samples of galena collected from a 1 metre quartz-sulphide vein at 46.95 metres in Discovery drill hole U-87 (Figure 5.2) and a sphalerite-galena veinlet from the east end of the AK drift returned Early Jurassic Pb-Pb isotopic signatures (A. Pickering, personal communication, 1992 and A.J. Macdonald, personal communication, 1992, respectively).  5.2 Stonehouse deposit  The Stonehouse deposit lies 6 kilometres south of Snip near the base of the Jurassic upper sequence on Johnny Mountain (Figure 1.2). The deposit consists of a set of parallel, tabular, moderately to steeply northwest dipping 0.2 - 2.5 metre wide quartz-pyrite veins that are displaced by northwest trending gouge filled and flat lying quartz vein filled faults. At least two major veins were mined by Skyline Gold Corp. (now International Skyline Gold Corp.) between 1988 and 1990, including the 16 vein and its possible fault offsets (the Zephrin zone and Discovery vein), and the Pickaxe vein (see section 1.1.4 for exploration history and mining statistics). Most of the production (approximately 80%) came from the 16 vein. The mine has been recently reopened by International Skyline Gold Corp. (September, 1993), with production concentrated in the Zephrin zone and in remaining pillars and blocks of the 16 vein. The information presented here is based on consulting work conducted by the author during August and September, 1993 for International Skyline Gold Corp.  253  Flat lying intermediate volcanic sediments including massive andesitic tuff, volcanic conglomerate, lapilli tuff and greywacke comprise the predominant rock types in the mine workings. Volcanic clasts occur in all of these lithologies and are highly variable in composition, abundance, size and angularity. Common clast types include (i) fine-grained dark grey biotitic aphanitic fragments, commonly with aphyric biotite spots, (ii) variably altered ± plagioclase ± biotite-chlorite-pyrite altered mafic minerals porphyry, and (iii) cream to pale grey fine grained felsite. Clast sizes are typically from less than 0.5 to 2 centimetres in diameter. Local heterolithic volcanic boulder conglomerates contain large rounded 0.2-2.5 metre fine grained dark grey biotitic clasts that in turn may contain internal volcanic clasts. Clasts are commonly epidote + calcite + pyrite altered. Crystal and lapilli tuffs have been locally identified (Yeager and Metcalfe, 1990). Due to the massive and lithologically gradational nature of the rock units and the abundance of faults, no stratigraphic sequence has been defined for the mine sequence.  The volcanic rocks are intruded by a series of approximately northeasterly trending, steeply dipping plagioclase porphyry dykes that are up to 20 metres in thickness. The dykes are generally tabular, but contacts are commonly irregular and non-planar. The porphyry comprises 25-75% 0.5-3 millimetre plagioclase phenocrysts in a fine grained groundmass. Both matrix and phenocrysts are commonly sericite and/or K-feldspar altered. The dykes contain rare, but locally abundant (0.5-2%), subhedral tabular pink K-feldspar megacrysts that are 0.2 to 0.8 centimetres long. Vertical, northeasterly striking flow banding is developed rarely. A U-Pb zircon date of 194 + 3 Ma was obtained from a plagioclase porphyry unit near the 11 level portal (M.L. Bevier, personal communication, 1993).  Steeply dipping intrusive breccia units cut the feldspar porphyry in two locations on 12 level. These range from <0.3 to 2.5 metres in thickness and are parallel to the feldspar porphyry dykes. They contain 10-50% pale grey variably altered feldspar porphyry fragments in a fine grained dark grey matrix. Contacts range from sharp and intrusive, cutting flow banding in the feldspar porphyry, to gradational.  254  Plate 5.2^Stonehouse deposit, northwestern British Columbia. The coin is 2.4 centimetres in diameter and the hammer is 32.5 centimetres long. A: Plagioclase porphyritic dyke. Anhedral to subhedral white plagioclase phenocrysts occur in a sericte altered grey fine grained matrix. From 12 level east. B: Steep north-dipping quartz-pyrite veins in the footwall of the Pickaxe vein, 12 level southwest. The veins have quartz rims and pyrite cores. Note the shallow north dipping cleavage in the wall rock (bottom right). Photo is taken looking east. C: Zephrin zone, looking north. Note tha intense K-feldspar alteration associated with moderate northeast and northwest dipping quartz-pyrite-chlorite veins and veinlets. D: Quartz + pyrite > chlorite vein in plagioclase porphyry. The vein has a bleached K-feldspar alteration envelope. Note the comb textured quartz indicative of open space filling, and a paragenetic sequence in the vein from early quartz (selvage) to later (central) pyrite + chlorite. Sample is from muck, 11 level. E: Shallow southeast-dipping quartz calcite veins with clay gouge on the vein selvages cut an en echelon set of moderate southeast dipping extension veins. These shallow dipping veins often cut and offset ore bearing quartz-sulphide veins. Picture is from 12 level, looking east.  256  Auriferous quartz-pyrite veins and related K-feldspar alteration envelopes are superimposed on all of the lithologies. The veins are subparallel to but slightly steeper than the north dipping plagioclase porphyry units (Yeager and Metcalfe, 1990). The most productive vein, the 16, was stoped continuously over 200 metres laterally. The veins commonly have pyrite cores and grey to white quartz rims (Plates 5.2B, 5.2D). Pyrrhotite, chalcopyrite, sphalerite and subordinate galena, occur with the pyrite; chlorite, sericite and calcite are often significant vein components. In some smaller veins, quartz selvages exhibit drusy textures indicative of open space filling (Plate 5.2D). In addition, vein infillings lack the foliated, sheeted character common in the Snip and Inel shear veins, and are thus probably largely extensional in origin. Galena PbPb isotope ratios plot in the Early Jurassic cluster (Godwin et al., 1990). Wallrock breccias are common in some quartz veins. In these, 0.5 to 10 centimetre wide wallrock fragments are commonly sericite-Kfeldspar-chlorite-pyrite + carbonate altered. Veins commonly bifurcate and splay, resulting in two or more parallel veins over widths of 1 to 5 metres.  Massive grey K-feldspar + sericite forms wide vein envelopes commonly equal to or several times the width of the vein (Figure 5.2D). Some of the larger veins have K-feldspar-sericite envelopes that are up to 10 metres thick. Numerous quartz-sulphide veins and veinlets are common in these wide envelopes and are either parallel to, or shallower dipping than, the larger veins. The K-feldspar-sericite alteration grades outward to biotite and chlorite + disseminated pyrite in some areas (Yeager and Metcalfe, 1990).  Gold occurs within quartz-pyrite veins and/or in zones of K-feldspar alteration that contain quartz-pyrite + chlorite veinlets (Plate 5.2C). Gold grades are commonly related to pyrite grain size. Coarse 2-5 millimetre grains typically are associated with low gold grades (< 3 ppm); however, fine grained, often subrounded, pyrite is associated with higher grade (> 15 ppm; Metcalfe, personal communication, 1992). Gold occurs both as electrum and the native metal. Highest gold grades and visible gold/electrum are often associated with chalcopyrite, galena and/or sphalerite (Yeager, personal communication, 1993). Veins are commonly highest grade where they splay to form footwall and hangingwall veins. Gold grades often decline rapidly greater than 5 metres from splays. Where well developed and linear, ore shoots are  257  5 - 20 metres wide, typically grade more than 20 ppm gold, and plunge moderately to the east or are steeply  dipping. Gold grade commonly correlates spatially and positively with vein thickness.  Other structures in the mine include foliation, quartz faults, extension veins and gouge filled faults (Table 5.1). A shallow northeast dipping spaced slaty to phyllitic foliation (Plate 5.2B) that is probably related to S2 occurs throughout the mine workings. Foliation is inhomogenously developed, and it is developed most strongly in the volcanics. It is defined by the platy alignment of sericite, biotite and chlorite and by flattened clasts. The foliation locally crenulates and folds auriferous quartz-sulphide veins.  Shallow dipping 3-30 centimetres wide quartz veins ('quartz faults') offset the auriferous quartz-sulphide veins. They have a vertical spacing of 3 to 10 metres. Quartz faults commonly dilate foliation, but elsewhere obliquely cut it. Offset direction is consistently upper plate to the west-southwest, parallel to the strike of the quartz-sulphide veins. Kinematic indicators include (i) a northeast-southwest slickenside lineation on chloritic foliation surfaces, (ii) spectacular linear boudins that plunge shallowly to the northwest or southeast and are perpendicular to the slickensides, (iii) oblique moderate south dipping quartz-chlorite extension veins that are commonly developed adjacent to the quartz faults (Plate 5.2E), (iv) northeast dipping stylolitic pressure solution surfaces locally developed within the quartz veins that are oblique to vein walls, and (v) offset markers such as ore shoots and ore vein bifurcations. Magnitude of offset is variable; 1-5 metres is common on narrow (1-5 centimetre) quartz veins that lack gouge, but thicker veins (5-40 centimetres) with marginal clay gouge may have more than 30 metres of offset. The shallow dipping quartz veins are associated with at least two sets of quartz-calcite extension veins, which may be parallel to (i.e., shallow east to southeast dipping) and oblique to (moderate south to southwest dipping) the quartz veins. The oblique south to southwest dipping extension veins commonly form en echelon arrays adjacent to or centred on the shallow quartz veins, giving a compatible sense of shear to the observed offsets (Plate 5.2E). Galena obtained from a shallow northeast dipping extension vein returned a Tertiary galena Pb-Pb isotopic signature (Godwin et al., 1990).  258  A series of shallow north to northwest dipping slip surfaces coated with 1 to 10 millimetres of white to red (hematitic) indurated gouge locally offsets veins. These structures are best developed in the Zephrin zone, which is a rotated fault bounded block that occurs at the west end of the 16 vein. Hematitic slip surfaces offset quartz faults and auriferous quartz-sulphide veins consistently with the upper plate to the west. Displacements are typically 0.3 to 1.5 metres.  A series of moderate to steep northeast and southwest dipping gouge filled faults cut the mine sequence and all of the veins, separating the mine package into a series of 50-100 metre wide tabular to triangular shaped blocks. These have a normal sense of displacement with predominantly dip slip displacement indicated by slickensides. The faults commonly have bleached rusty to tan coloured alteration envelopes. Steeply dipping clay gouge + Fe-carbonate + chlorite filled fractures with tan coloured 1-3 centimetres wide envelopes are commonly spatially associated with the faults. These are locally filled with white quartz >> pyrite + chalcopyrite veins. Fresh dark grey basaltic dykes, commonly plagioclase and pyroxene phyric, intrude the southwest dipping #6 fault zone in the central mine workings. Local rusty bleached fracture surfaces and sparse gouge filled fractures within the dykes suggest that they intruded late during fault movement and associated hydrothermal alteration. These dykes may have affinities to the biotite lamprophyres at Snip which have similar tectonic setting, mineralogy and temporal relationships with adjacent structures.  A set of northwest dipping grey clay gouge filled faults that are parallel to the auriferous quartz-sulphide veins cut and displace the northeast and southwest dipping gouge filled faults. Unlike these faults, however, the northwest dipping structures lack alteration and associated veining. Displacement magnitude or direction was not determined.  259 Table 5.1: Common structures, listed from oldest to youngest, in the Johnny Mountain mine (Stonehouse deposit), northwestern British Columbia. Structure Vein fill  ^  Orientations  ^Associated fabrics^Dimensions/ ^Alteration^Displaceabundance ^ ment  Quartzsulphide veins  Quartz-pyrite + chlorite + sericite + calcite + ?biotite  Steep northwest dipping  Locally vein parallel foliation defined by platy minerals  0.2-2.5 metres wide veins spaced separated by wide intervals of wallrock containing common pyrite-quartz veinlets.  Envelopes of None K-feldspar + sericite + quartz, up to 10 m wide on larger veins  Foliation (S2)  None, except where dilated by quartz faults (see below)  Shallow to moderate northeastdipping  Slaty to phyllitic spaced foliation defined by chlorite, sericite and biotite  Developed in all lithologies except late basalt dykes; crenulates and folds quartz-pyrite veins  None  Quartz faults  Massive quartz ± chlorite ± pyrite + calcite, commonly with marginal clay gouge; locally laminated quartzchlorite.  Shallow east and southeast dipping  Phyllitic cleavage locally developed by chlorite and foliated wallrock within and adjacent to veins  3-60 cm wide, commonly 4-10cm; vertical spacing of 310 metres.  Hematitic slip surfaces*  None; narrow slip surfaces coated in thin layers of indurated cream gouge + red hematite  Shallow north to northwest dipping  None  Faults, southwest and northeast dipping  Filled with grey to rusty clay gouge; locally contain quartz > sulphide veins, or Fecarbonate chlorite veinlets  Moderate to steep northeast and southwest dipping  None  ^  Locally spaced at 1-4^None metres in the Zephrin zone  ^ Clay gouge-filled ^ Rusty to tan zones 0.5 cm to >1 bleached m wide commonly ^envelopes up spaced at 2-10 metres to 2 m wide  ^  Upper plate offset to the westsouthwest  None usually; locally chlorite  Normal sense; upper plate offset to the west  Normal displacement, mainly dip slip  ^ ^ ^ ^ Narrow <0.5-4 cm^None Faults,^Pale grey clay ^Northwest None Not known ^ ^ faults spaced at 2-15 northwest and crushed rock dipping, m dipping^gouge^parallel to ^ sulphide-quartz veins *Hematitic slip surfaces were measured only in the Zephrin zone; their orientation and displacement direction in other fault blocks may be different.  5.4 Discussion  The geology of the Inel and Stonehouse deposits contain notable similarities to the Snip mine Structures at both Inel and Snip are dominated by shear veins with layered calcite, chlorite and biotite fill hosted by probable Triassic sedimentary rocks (Rhys and Lewis, 1993). Kinematic indicators in both locations  260  indicate a large component of normal simple shear associated with vein formation. In contrast, the Stonehouse veins consist of a set of parallel, tabular, extensional quartz-sulphide veins cutting Jurassic volcanic and volcaniclastic strata. However, extensional type sulphide-quartz veins are present at both Snip and Inel. At Snip the steeply dipping 150 vein system, and at Inel the sulphide veins on the Discovery level are similar to the Stonehouse veins. At both of these latter deposits, the dilational sulphide-quartz veins are cut by laminated calcite-chlorite-biotite-pyrite shear veins.  Shallow to moderate dipping extension veins cut shear veins and quartz-sulphide veins at all three deposits. At both Snip and Inel, these veins are often offset along the shear veins by a late phase of movement.  Porphyritic intrusions are cospatial with alteration and mineralisation at Snip, Stonehouse and Inel. The plagioclase porphyry dykes at Stonehouse are subparallel to and are cut by the Stonehouse veins. Altered K-feldspar megacrystic and dioritic dykes occur within the mine sequence at Inel, spatially associated with the Inel stock. The close relationships between the Red Bluff porphyry and the Twin zone at Snip has been discussed extensively in preceding sections. Isotopic data are consistent with intrusion broadly coeval with mineralisation. U-Pb zircon analyses for the Red Bluff porphyry (195 ± 1 Ma, Macdonald et al., 1992), the Inel stock (190 ± 3 Ma, Macdonald et al., 1992), and the Stonehouse two feldspar porphyry dykes (194 ± 3 Ma, M.L. Bevier, personal communication, 1992) are consistent with Early Jurassic galena Pb-Pb isotopic signatures from all three deposits.  Potassic alteration is widespread at Snip, Stonehouse, and Inel. Biotite envelopes are common around veins at Snip and Inel. Wide zones of K-feldspar alteration containing sulphide-calcite-chlorite vein stockworks occur at both Stonehouse and Inel, and abundant secondary biotite associated with biotitepyrite veinlets is developed throughout the greywacke sequence at Snip.  261  Associated intrusions have similar orientations to associated dilatant veins in all three deposits suggesting that their morphology was controlled by the same structural conditions active during emplacement of the veins. The steeply dipping, northwesterly trending Red Bluff porphyry is parallel to the steep lower end of the Twin zone. Dykes at Stonehouse are subparallel to the veins. The southerly dipping K-feldspar megacrystic dykes at Inel are parallel to many of the veins.  Rheologic control is important in the localisation of veins. The Stonehouse veins are subparallel, to and localised within and immediately adjacent to, the plagioclase porphyry. Shear veins at Inel are most abundant in, or adjacent to, contacts with massive greywacke; veins usually form discontinuous stockwork zones in siltstone and mudstone units. Vein localisation to the greywacke extends beyond the workings, and some company reports describe the greywacke unit as the Inel Horizon, because of it localises mineralised veins (Gifford, 1991). At Snip, the largest veins are developed in the massive greywacke sequence, and veins are smaller and discontinuous southwest of the Twin zone where mixed siltstone-greywacke-volcanic conglomerate units are encountered. Localisation of mineralised structures in massive units probably results from both high permeability, and thus enhanced fluid flow, and the ability of these rock types to fracture in a brittle manner.  The shallowly dipping to flat lying Early Jurassic unconformity in the Johnny Mountain area indicates that the deposits are in their approximate original orientations. Thus, veins at all three deposits are consistent with a steeply dipping maximum shortening direction (Z-axis of the finite strain ellipsoid) suggesting formation in an extensional environment.  The depth of formation of the Twin zone, assuming that it is genetically related to the Red Bluff porphyry hydrothermal system, as the evidence suggests, is bracketed to approximately 1 to 3 kilometres based on its position with respect to the Jurassic unconformity and dates of the overlying volcanic rocks (section 4.3). The same relationships suggest a depth of formation for the Inel veins of between 0.8 and 1.5 kilometres and a depth of less than one kilometre for the Stonehouse deposit. All of these depths  262  hinge on the relative timing of mineralisation and intrusion, and the rate of build up of the Jurassic volcanic package, but they probably represent fair estimates. The deposits may thus represent different mechanical responses to the same deformational event at different paleodepths and confining pressures. Dilatant shear zones (shear veins) at the Snip and Inel deposits occur in Triassic rocks while steep extensional vein arrays at the Stonehouse deposit occur in Early Jurassic rocks. These depths are permissible for the deformational style within the shear veins at Snip and Inel with high temperature fluids in the veins facilitating deformation.  North and east of Snip, showings with similar characteristics to the Snip, Inel and Stonehouse deposits are common. Auriferous northeast and southwest dipping quartz-carbonate and sulphide veins, many of which contain magnetite, arsenopyrite and chalcopyrite, occur on the Waratah claim group 3-5 kilometres east of Snip and north of Snippaker Ridge on the south side of the Iskut River (Pegg, 1991; Figure 1.2). Some of these veins occur adjacent to, or are spatially associated with, southwest dipping K-feldspar megacrystic porphyry dykes (D. Caulfield, personal communication, 1993). Showings surround the Kfeldspar megacrystic porphyry stock on the north side of the Iskut River, 3-4 kilometres north of Snip. Here, as on Johnny Mountain, mineralised southwest dipping schistose biotite-sericite shear veins are copper-gold or lead-zinc rich (Jeffrey, 1967). Showings between Stonehouse and Inel are Zn-Pb sulphide veins with southwest to northeast dipping orientations. Other structures on northern Johnny Mountain are discussed in Chapter 2.  In conclusion, the relationships between Early Jurassic intrusion, deformation, alteration and mineralisation observed at Snip also occur at a camp scale. The mineralised structures and intrusions define an Early Jurassic intrusion related deformational and hydrothermal event in an extensional subvolcanic environment. Deformation is heterogeneous and partitioned into the mineralised structures. The close timing, textural and mineralogical similarities of the Early Jurassic intrusions in the Johnny Mountain area suggests a large buried batholithic parent. Deformation and hydrothermal alteration were probably facilitated by the release of large amounts of exsolved fluids, resulting in increases in fluid  263  pressure and temperature that initially caused brittle failure and subsequently promoted semi-brittle deformation.  The exsolved fluids associated with mineralisation and deformation in the Johnny Mountain area may have been released by: (i) the hypothetical parent intrusion, and subsequently channeled up dykes and cupolas such as the Red Bluff porphyry, or (ii) crystallisation of these smaller intrusions. The former, or a combination of both, is favoured since it is unlikely that the small dykes and stocks associated with the various deposits (e.g. dykes at Inel) could alone have generated the large volume of hydrothermal fluids necessary to cause the extensive alteration, veining and mineralisation.  The Early Jurassic intrusions and mineral deposits in the Johnny Mountain area may thus overly a buried western northwest to southeast trending arm of the Lehto batholith, which is exposed 10 kilometres east of Johnny Mountain. Extensive zones of hydrothermal alteration developed southeast of Inel at Khyber Pass, Pyramid Hill, Sericite Ridge and Pins Ridge, several of which are associated with K-feldspar megacrystic dykes, extend the trend to the west side of the Lehto batholith in the Pins Ridge and Sericite Ridge area. These altered zones are developed in the Early Jurassic volcanics, and they may represent the tops of similar systems to those exposed in the Triassic sequence at Snip and Red Bluff, and Inel.  Implications for exploration  The veins at Snip, Inel and Stonehouse have several common characteristics useful in auriferous vein exploration in the Johnny Mountain area: (1) The presence of Early Jurassic plagioclase porphyritic + K-feldspar megacrystic intermediate to mafic intrusions; these often strike parallel to the veins. (2) An association with massive host rocks such as greywacke, or in the case of Stonehouse, plagioclase diorite and massive volcanic sediments. (3) Widespread biotite-K-feldspar + chlorite alteration.  264  (4) Veins with Zn/Cu ratios < 5 are commonly auriferous (with > 3 ppm Au; see below). (5) Early Jurassic galena Pb-Pb isotopic signatures. (6) Dilatant quartz-sulphide and/or laminated calcite-chlorite-biotite-pyrite shear veins. (7) Structures exhibiting evidence for semi-brittle deformation. (8) Structures with moderate to steep southwest, northeast or northwest dipping orientations.  Characteristics of structures not usually associated with economic auriferous mineralisation in the Johnny mountain area include: (1) Veins or shear zones with sericite-pyrite alteration. (2) Shear zones lacking discrete veins (non-dilatant). (3) Veins with Zn/Cu ratios > 15 that typically have low (< 3 ppm) gold values. (4) Brittle gouge filled faults and associated vuggy calcite-quartz-pyrite veins. (5) Shallowly dipping quartz-calcite extension veins. (6) Tertiary galena Pb-Pb isotopic signatures.  265  CHAPTER 6: SUMMARY AND CONCLUSIONS  The Twin zone and other shear veins and shear zones in the Johnny Mountain area record an Early Jurassic mineralising and extensional event (Table 6.1). Deformation is inhomogenous, semi-brittle (Snip, Inel) to brittle (Stonehouse) and localised primarily to the shear veins. Mineralised structures are superimposed on Late Triassic to Early Jurassic folds and associated penetrative cleavage (Si), and are developed in both Triassic elastic rocks and unconformably overlying Early Jurassic volcanics. The structures and Si are folded and crenulated by a regionally developed flat foliation (S2) that may be related to Cretaceous deformation in the Iskut River area and Skeena fold belt (e.g. Evenchick, 1991). Extension veins with Tertiary galena Pb-Pb isotopic signatures cut and locally offset mineralised structures and cut S2 fabrics. Northeast trending brittle faults that are associated with Tertiary biotite lamprophyre dykes are the youngest structural features in the area (Table 6.1). The faults have oblique right lateral displacements.  Initial formation of shear veins at the Snip mine, including the Twin zone, may have occurred with the development and propagation of southwest dipping fractures formed by high fluid pressure induced brittle failure. Bedding anisotropies in the greywacke sequence may have allowed some of these structures to form with a bedding parallel north to northwest dipping orientation. Once formed, these zones allowed channeling of hydrothermal fluids that facilitated crystal plastic deformation through wallrock alteration, hydrolytic weakening and elevated temperature, and thereby localised deformation. Fluids progressively altered and replaced wallrock with biotite, calcite and chlorite forming carbonate and chlorite-biotite ore types. Periodic fluctuations in fluid pressures, possibly due to the inhibition of fluid diffusion from the zone by mineral precipitation in wallrock fractures and pore spaces, allowed dilation of the zone and the development of multiple dilatant quartz and sulphide veins. Semi-brittle deformation in the zone occurred throughout vein formation and was both coaxial and non-coaxial, the latter associated with a normally directed sense of simple shear. Continuing deformation within the shear veins may have allowed some of them to join, especially those developed in en echelon arrays, and form  266  larger structures such as the Twin zone. Larger zones could accommodate more strain and focus a larger volume of hydrothermal fluid than the smaller ones, allowing a sympathetic increase in the volume of the zone. Sphalerite and arsenopyrite rich sulphide veins formed late. Deformation changed to a more brittle style late during the deformation period, probably due to temperature decrease, decrease. in fluid flow or change in strain rate, resulting in slip along shear bands and foliation surfaces. The BSU dyke was intruded late during the period of deformation and after formation of mineralised veins.  The Red Bluff porphyry is overprinted by: (i) early potassic alteration characterised by intense quartzmagnetite-hematite veining and pervasive K-feldspar-sericite-biotite-magnetite and (ii) later phyllic alteration characterised by pyrite veins associated with sericite-pyrite-quartz + albite alteration. The abundant secondary biotite developed throughout the greywackes in the Snip mine workings, and the biotite + K-feldspar + calcite + sericite + quartz envelopes on the Twin zone and shear veins are consistent with formation during the potassic alteration event within the Red Bluff porphyry. Lack of overprinting of the porphyry phyllic alteration by biotite indicates that the biotitic alteration in the greywackes must predate the phyllic event. In addition, deformation of the porphyry with a normally directed shear sense, and evidence for syntectonic veining of veins associated with both potassic and phyllic alteration suggest that porphyry potassic alteration, deformation and formation of the shear veins in the greywacke sequence were synchronous. These implications are supported by Early Jurassic galena Pb-Pb isotopic signatures for the Twin zone that are concordant with the Early Jurassic U-Pb zircon age of the Red Bluff porphyry. Metal and alteration zoning of mineralised structures with Early Jurassic galena Pb-isotope signatures to the south of the Snip mine on northwestern Johnny Mountain suggests that these may also be related to the Red Bluff porphyry hydrothermal system. Constraints imposed by the age of the porphyry and relative position of the flat lying Early Jurassic unconformity to the south indicate that the porphyry was intruded in a subvolcanic environment between one and three kilometres depth. Semibrittle deformation in this environment may have been facilitated by the presence and high temperature of intrusion related hydrothermal fluids, as described above.  267  Table 6.1: Geologic history of the Johnny Mountain area, northwestern British Columbia. Summary is from discussions in Chapters 2, 3, 4 and 5. Approximate age  Geologic event  Late Tertiary - Recent  Glaciation and erosion  Mid-Tertiary (32 Ma)  Intrusion of biotite lamprophyres into and adjacent to fault zones  Mid-Tertiary  Brittle faulting and associated argillic alteration  Tertiary  Reactivation of Early Jurassic shear veins.  Early Tertiary (? 55-45 Ma)  Formation of quartz-calcite extension veins by fluid overpressuring during a compressional event. Probably synchronous with the Early Tertiary thermal peak of the Coast Plutonic Complex.  ?Cretaceous  S2 (flat) foliation forms and mineralised Jurassic structures are locally folded and crenulated  Early Jurassic (196-190 Ma)  Intrusion, deformation and development of structurally hosted gold deposits. A broadly overlapping sequence of events probably occurred as follows: (1) Intrusion of a batholithic stock under Johnny Mountain and development of secondary biotite, (2) Intrusion of subvolcanic feldspar porphyritic dykes and stocks, including the Red Bluff porphyry, and extrusion of volcanics of the upper sequence, (3) Formation of hydrothermal systems spatially associated with the dykes and stocks, (4) Fluid induced brittle failure and fluid channeling into structures. Semi-brittle deformation and vein formation follows in an extensional tectonic environment. Veins display systematic metal and alteration variations compatible with distance to the intrusions.  Upper Triassic - Early Jurassic  Erosion of the lower sequence and folds.  Upper Triassic - Early Jurassic  Folding of the Triassic sequence about upright west to northwesterly trending fold axes and development of an axial planar foliation (S1).  Upper Triassic  Intrusion of the Bronson stock diorite.  Upper Triassic  Deposition of the lower sequence. Early turbiditic elastics are succeeded by deposition of younger mixed elastics and volcanic sediments.  Auriferous veins at the Inel and Stonehouse deposits: (i) are spatially related to Early Jurassic intrusions, (ii) have Early Jurassic galena Pb-isotope signatures, (iii) are associated with extensive potassic alteration, and (iv) are kinematically compatible with structures at Snip. This suggests that they represent coeval, and potentially cogenetic, deformational and intrusion related hydrothermal systems. All of these deposits, other showings, alteration zones and early Jurassic stocks are contained within a 30-40  268  kilometre long northwesterly trending belt, which at its southeast end, joins the Early Jurassic Lehto batholith. The belt may represent the trace of a buried branch of the Lehto batholith that is the magmatic parent to the intrusions and related hydrothermal systems.  269 REFERENCES Alldrick, D.J. (1985): Stratigraphy and Petrology of the Stewart Mining Camp (104B/1); in Geological Fieldwork 1984, B. C. Ministry of Energy, Mines, and Petroleum Resources, Paper 1985-1, pages 316341. Alldrick, D.J. (1991): Geology and Ore Deposits of the Stewart Mining Camp; Unpublished PhD thesis, The University of British Columbia, 417 pages. Alldrick, D.J., Britton, J.M., MacLean, M.E., Hancock, K.D., Fletcher, B.A., and Hiebert, S.N. (1990): Geology and Mineral Deposits of the Snippaker Map Area (104B/6E,7W,10W,11E); B.C. Ministry of Energy, Mines, and Petroleum Resources, Open File 1990-16. Alldrick, D.J., Gabites, J.E., and Godwin, C.I. (1987): Lead Isotope Data from the Stewart Mining Camp (104B/1); in Geological Fieldwork 1986, B.C. Ministry of Energy, Mines, and Petroleum Resources, Paper 1987-1, pages 93-102. Alldrick, D.J., Godwin, C.I., and Sinclair, A.J. (1993): An Exploration Application for Lead Isotope Ratios, Stewart Mining Camp, Northwestern British Columbia; Exploration and Mining Geology, Volume 2, pages 121-129. Anderson, R.G. (1989): A Stratigraphic, Plutonic, and Structural Framework for the Iskut River Map Area, Northwestern British Columbia; in Current Research, Part E. Geological Survey of Canada, Paper 89-1E, pages 145-154. Anderson, R.G., and Bevier, M.L. (1990): A Note on Mesozoic and Tertiary K-Ar Geochronometry of Plutonic Suites, Iskut River Map Area, Northwestern British Columbia; in Current Research, Part E, Geological Survey of Canada, Paper 90-1E, pages 141-147. Anderson, R.G. (1993): A Mesozoic Statigraphic and Plutonic Framework for Northwestern Stikinia (Iskut River Area), Northwestern British Columbia, Canada; in Dunne, G., and McDougall, K. Editors, Mesozoic Paleogeography of the Western United States, Volume II, Society of Economic Paleontologists and Mineralogists, Pacific Section. Atkinson, J.R. (1990): Report on Diamond Drilling Placer Dome/Skyline Joint Venture, Bronson Project; unpublished company report, Skyline Gold Corp. Atkinson, J., Metcalfe, P., and Moore, M. (1991): Summary Report 1990 Program, Skyline Gold Corp./Placer Dome Inc. Joint Venture, Bronson Project; unpublished company report, Skyline Gold Corp.. Bridge, D.J. and Godwin, C.I. (1992): Preliminary Geology of the Kerr Copper - Gold Deposit, Northwestern British Columbia; in Geological Fieldwork 1991, Newell, J.M. and Grant, B., Editors, B. C. Ministry of Energy, Mines, and Petroleum Resources, Paper 1992-1, pages 513-516. Britton, J.M., Fletcher, B.A., and Alldrick, D.J. (1990): Snippaker Map Area (104B/6E, 7W, 10W, 11E); in Geological Fieldwork 1989, B. C. Ministry of Energy, Mines and Petroleum Resources, Paper 1990-1, pages 115-125. Brown, D.A. (1987): Geological Setting of the Volcanic-Hosted Silbak Premier Mine, Northwestern British Columbia; Unpublished M.Sc. thesis, the University of British Columbia, 216 pages. Buddington, A.F. (1929): Geology of Hyder and Vicinity, Southeastern Alaska; United States Geological Survey, Bulletin 807.  270  Carson, D.J.T, Jambor, J.L., Ogryzlo, P.L. and Richards, T.A. (1976): Bell Copper: Geology, Geochemistry and Genesis of a Supergene-Enriched, Biotized Porphyry Copper Deposit with a Superimposed Phyllic Zone; in A. Sutherland-Brown (ed.) Porphyry Deposits of the Canadian Cordillera, Canadian Institute of Mining and Metallurgy, Special Volume 15, pages 245-263. Cobbold, P.R., and Quinquis, H. (1980): Development of Sheath Folds in Shear Regimes; Structural Geology, Volume 2, pages 119-126. Cox, S.F. (1987): Flow Mechanisms in Sulphide Minerals; Ore Geology Reviews, Volume 2, pages 133171. Cox, S.F., Etheridge, M.A., and Wall, V.J. (1986): The Role of Fluids in Syntectonic Mass Transport and the Localization of Metamorphic Vein-Type Ore Deposits; Ore Geology Reviews, Volume 2, pages 65-86. Cox, S.F., Etheridge, M.A., and Wall, V.J. (1990): Fluid Pressure Regimes and Fluid Dynamics During Deformation of Low-Grade Metamorphic Terranes: Implications for the Genesis of Mesothermal Gold Deposits; In Robert, F., Sheahan, P.A., and Green, S.B. (eds.), Greenstone Gold and Crustal Evolution, Geological Association of Canada, NUNA Conference Volume, pages 46-53. Deer, W.A., Howie, R.A. and Zussman, J. (1966): An Introduction to the Rock-Forming Minerals; John Wiley and Sons Inc., New York, 528 pages. Drummond, A.D., Sutherland Brown, A., Young, R.J. and Tennant, S.J. (1976): Gibraltar: Regional Metamorphism, Hydrothermal Alteration and Structural Development; in A. Sutherland-Brown (ed.) Porphyry Deposits of the Canadian Cordillera, Canadian Institute of Mining and Metallurgy, Special Volume 15, pages 195-205. Evans, B., Fredrich, J.T., and Wong, T.F. (1990): The Brittle-Ductile Transition in Rocks: Recent Experimental and Theoretical Progress; In Duba, A.G., Durham, W.B., Handin, J.W., and Wang, H.F. (eds.), The Brittle-Ductile Transition in Rocks, American Geophysical Union, Geophysical Monograph 56, pages 1-20. Evenchick, C.A. (1991): Structural Relationships of the Skeena Fold Belt West of the Bowser Basin, Northwestern British Columbia; Canadian Journal of Earth Sciences, Volume 28, pages 973-983. Fletcher, B.A. and Hiebert, S.N. (1990): Geology of the Johnny Mountain area (104B/11); B.C. Ministry of Energy, Mines, and Petroleum Resources, Open File 1990-19. Gifford, R.G. (1991): Report on the Inel Property, British Columbia, Canada; Gulf International Minerals Limited, unpublished company report. Ghosh, S.K. and Sengupta, S. (1987): Progressive Development of Structures in a Ductile Shear Zone; Journal of Strucural Geology, Volume 9, pages 277-287. Godwin, C.I. (1976): Casino; in A. Sutherland-Brown (ed.) Porphyry Deposits of the Canadian Cordillera, Canadian Institute of Mining and Metallurgy, Special Volume 15, pages 344-358. Godwin, C.I., Gabites, J.E. and Andrew, A. (1988): LEADTABLE: A Galena Lead Isotope Data Base for the Canadian Cordillera, With a Guide to its Use by Explorationists; B. C. Ministry of Energy, Mines, and Petroleum Resources, Paper 1988-4, 188 pages.  271  Godwin, C.I., Pickering, A.D.R., and Gabites, J.E. (1991): Interpretation of Galena Lead Isotopes from the Stewart-Iskut Area (1030, P; 104A, B, G); in Geological Fieldwork 1990, B.C. Ministry of Energy, Mines, and Petroleum Resources, Paper 1991-1, pages 235-243. Grove, E.H. (1971): Geology and Mineral Deposits of the Stewart Area, British Columbia; British Columbia Department of Mines and Petroleum Resources, Bulletin 58, 219 pages. Guha, J., Archambault, G., and Leroy, J. (1983): A Correlation Between the Evolution of Mineralizing Fluids and the Geomechanical Development of a Shear Zone as Illustrated by the Henderson 2 Mine, Quebec; Economic Geology, Volume 78, pages 1605-1618. Guilbert, J.M., and Park, C.F., Jr. (1986): The Geology of Ore Deposits; W.H. Freeman and Company, New York, 985 pages. Gustafson, L.B., and Hunt, J.P. (1975): The Porphyry Copper Deposit at El Salvador, Chile; Economic Geology, Volume 70, pages 857-912. Harris, J.F. (1966): The Nature and Origin of Rocks and Disseminated Copper Ores from Bronson Creek, B.C.; unpublished company report, Cominco Ltd., 4 pages. Heberlein, D.R. and Godwin, C.I. (1984): Hypogene alterationat the Berg Porphyry CopperMolybdenum Property, North-Central British Columbia; Economic Geology, Volume 79, pages 902-918. Jeffrey, W.G. (1967): Ray, Joann; B. C. Ministry of Energy, Mines and Petroleum Resources, 1966 Annual Report, pages 34-37. Kaip, A.W. and McPherson, M.D. (1993): Preliminary Geology of the Hank Property, Northwestern British Columbia (104G/1,2); in Geological Fieldwork 1992, Newell, J.M. and Grant, B., Editors, B.C. Ministry of Energy, Mines, and Petroleum Resources, Paper 1993-1, pages 349-357. Kerr, F.A. (1948): Lower Stikine and Western Iskut River Map Areas, British Columbia; Geological  Survey of Canada, Memoir 246, 94 pages.  Kerrich, R., and Allison, I. (1978): Flow Mechanisms in Rocks; Geoscience Canada, Volume 5, pages 109-118. Knipe, R.J. (1989): Deformation Mechanisms - Recognition from Natural Tectonites; Journal of Structural Geology, Volume 11, pages 127-146. Kronenberg, A.K., Segall, P., and Wolf, G.H. (1990): Hydrolitic Weakening and Penetrative Deformation Within a Natural Shear Zone; In Duba, A.G., Durham, W.B., Handin, J.W., and Wang, H.F. (eds.), The Brittle-Ductile Transition in Rocks, American Geophysical Union, Geophysical Monograph 56, pages 21-36. Lefebure, D.V. and Gunning, M.H. (1989): Geology of the Bronson Creek Area (104B/10W, 11E);  B. C. Ministry of Energy, Mines, and Petroleum Resources, Open File 1989-28.  Lister, G.S., and Williams, P.F. (1979): Fabric Development in Shear Zones: Theoretical Controls and Observed Phenomena; Journal of Structural Geology, Volume 1, pages 283-297. Lister, G.S., and Williams, P.F. (1983): The Partitioning of Deformation in Flowing Rock Masses; Tectonophysics, Volume 92, pages 1-33.  272 Lynch, J.V.G. (1989): Large-Scale Hydrothermal Zoning Reflected in the Tetrahedrite-Friebergite Solid Solution, Keno Hill Ag-Pb-Zn District, Yukon; Canadian Mineralogist, Volume 27, pages 383-400. Macdonald„ A.J. (1993): Lithostratigraphy and Geochronometry, Brucejack Lake, Northwestern British Columbia (104B/8E); in Geological Fieldwork 1992, Newell, J.M. and Grant, B., Editors, B.C. Ministry of Energy, Mines, and Petroleum Resources, Paper 1992-1, pages 315-323. Macdonald, A.J., van der Heyden, P., Alldrick, D.J., and Lefebure, D. (1992): Geochronometry of the Iskut River Area-an Update; in Geological Fieldwork 1991, Newell, J.M. and Grant, B., Editors, B.C. Ministry of Energy, Mines, and Petroleum Resources, Paper 1992-1, pages 495-501. McClay, K.R., and Ellis, P.G. (1984): Deformation of Pyrite; Economic Geology, Volume 79, pages 400-403. McLeod, J.A. (1987a): Petrography and Ore Microscopy of Selected 1986 Snip Drill Core; unpublished company report, Cominco Ltd., 26 pages. McLeod, J.A. (1987b): Mineral Identification, Snip (Job V87-370/371R); unpublished company report, Cominco Ltd., 3 pages. McLeod, J.A. (1987c): Snip Mineral Identification (Job V87-370/401/403); unpublished company report, Cominco Ltd., 5 pages. McLeod, J.A. (1987d): Snip Petrographic Study (Job V87-547R); unpublished company report, Cominco Ltd., 5 pages. McLeod, J.A. (1987e): Snip Mineral Identification (Job V87-274R); unpublished company report, Cominco Ltd., 1 page. McLeod, J.A. (1989a): Snip Thin Sections (Job V89-074R); unpublished company report, Cominco Ltd., 3 pages. McLeod, J.A. (1989b): Ore Microscopy of Concentration Products for G.W. Hawthorn, Snip Project; unpublished company report, Cominco Ltd., 13 pages. McLeod, J.A. (1991a): Snip Microscopy (Job V90-541R); unpublished company report, Cominco Ltd., 11 pages. McLeod, J.A. (1991b): Snip Process Samples - Ore Microscopy (Job V91-695R); unpublished company report, Cominco Ltd., 9 pages. McLeod, J.A. (1992): Mica/Chlorite Identification, Snip Mine (Job V92-186R); unpublished company report, Cominco Ltd., 2 pages. McLeod, J.A. and Armstrong, R.L. (1989): Snip Thin Sections/K-Argon Samples (Job V89-006R); unpublished company report, Cominco Ltd., 5 pages. Maiden, K.J., Chimimba, L.R., and Smalley, T.J. (1986): Cuspate Ore-Wall Rock Interfaces, Piercement Structures, and the Localization of some Sulphide Ores in Deformed Sulphide Deposits; Economic Geology, Volume 81, pages 1464-1472. Mawer, A.B. (1965): Report on Geological Survey of Bron Groups of Mineral Claims in Bronson Creek - Iskut River Area - Liard M.D. (N.T.S. 104B/11); unpublished company report, Cominco Ltd., 4 pages.  273  Metcalfe, P. (1988): Red Bluff Project (Exploration), Geological Termination Report; unpublished company report, Skyline Explorations Ltd., 23 pages. Metcalfe, P., and Moors, J.G. (1993): Refinement and Local Correlation of the Upper Snippaker Ridge Section, Iskut River Area, B.C. (104B/10W and 11E); in Geological Fieldwork 1992, Grant, B. and Newell, J.M., Editors, B.C. Ministry of Energy, Mines and Petroleum Resources, Paper 1993 1, pages 335-339. -  Meyer, C., Shea, E.P. and Goddard, C.C., Jr. (1968): Ore Deposits at Butte, Montana; in Ridge, J.D. (Ed.), Ore Deposits in the United States, 1933-1967; The American Institute of Mining, Metallurgical and Petroleum Engineers, New York, pages 1373-1416. Nadaraju, G.T. and Smith, P.L. (1992): Jurassic Biochronology of the Iskut River Map Area, British Columbia: A Progress Report; in Current Research, Part A, Geological Survey of Canada, Paper 92-1A. pages 333-335. Nagy, L.J. (1966): Exploration Report (1966), Bronson Creek; unpublished company report, Cominco Ltd., 7 pages. Nichols, R.F. (1987): Snip Property, 1986 Year End Report; unpublished company report, Cominco Ltd., 10 pages. Nichols, R.F. (1989): Snip Property, Final Project Report; unpublished company report, Cominco Ltd., 22 pages. Parsons, G. (1966a): Exploration Report (1965), Bronson Creek - Stikine River Area (N.T.S. 104B/11); unpublished company report, Cominco Ltd., 10 pages. Parsons, G. (1966b): Geological Report on Bronson Creek Nos. 1-3 Claim Groups, Liard M.D. 56 degrees, 131 degrees NE, N.T.S. 104B/11; unpublished company report, Cominco Ltd., 7 pages. Parsons, G. (1966c): 1965 Summary of Exploration - Copper Soo (Iskut River Area), Liard M.D. (N.T.S. 104B/11); unpublished company report, Cominco Ltd., 4 pages. Passchier, C.W. (1984): The Generation of Ductile and Brittle Shear Bands in a Low-Angle Mylonite Zone; Journal of Structural Geology, pages 273 281. -  Pedley, S.J. (1950): The Bronson Creek Orthoclase Porphyry Sill and its relation to the Geology of the Johnny Mountain Area; unpublished B.Sc. thesis, The University of British Columbia. Pegg, R. and Travis, A. (1991): Geological, Geochemical and Geophysical Report of the 1990 Exploration Program on the Snippaker Mountain Property; unpublished company report for Soloman Resources Limited. Phillips, W.J. (1972): Hydraulic Fracturing and Mineralization; Journal of the Geological Society of London, Volume 128, pages 337-359. Platt, J.P., and Vissers, R.L.M. (1980): Extensional Structures in Anisotropic Rocks; Journal of Structural Geology, Volume 2, pages 397-410.  Read. P.B. (1990): Snip mine: Stratigraphy and Structural Geology of Part of the Footwall; unpublished company report for Cominco Metals, 17 pages.  274 Rhys, D.A. (1993): Mineral and Metal Zoning in the Twin Zone, Snip Mine; unpublished report, The University of British Columbia, 37 pages. Rhys, D.A., and Godwin, C.I. (1992): Preliminary Structural Interpretation of the Snip Mine; in Geological Fieldwork 1991, Newell, J.M. and Grant, B., Editors, B. C. Ministry of Energy, Mines, and Petroleum Resources, Paper 1992-1, pages 549-554. Rhys, D.A., and Lewis, P.D. (1993): Geology of the Inel Deposit, Iskut River Area, Northwestern British Columbia (104B/11); in Geological Fieldwork 1992, Newell, J.M. and Grant, B., Editors, B. C. Ministry of Energy, Mines, and Petroleum Resources, Paper 1993-1, pages. Roach, S. and Macdonald, A.J. (1992): Silver-Gold Vein Mineralization, West Zone, Brucejack Lake, Northwestern British Columbia (104B18E); in Geological Fieldwork 1991, Newell, J.M. and Grant, B., Editors, B.C. Ministry of Energy, Mines, and Petroleum Resources, Paper 1992-1, pages 503-511. Roedder, E. (1984): Fluid Inclusions; Mineralogical Society of America, Reviews in Economic Geology, Volume 12, 646 pages. Rutter, E.H. (1972): The Influence of Interstitial Water on the Rheological Behaviour of Calcite Rocks; Tectonophysics, Volume 14, pages 13-33. Schmid, S.M. (1982): Microfabric Studies as Indicators of Deformation Mechanisms and Flow Laws Operative in Mountain Building; In Hsu, K.J. (ed.), Mountain Building Processes, Academic Press, London, pages 95-110. Schroeter, T., Lane, B. and Bray, A. (1992): Geologic Setting and Mineralization of the Red Mountain Mesothermal Gold Deposit; in Exploration in British Columbia 1991, Newell, J.M. and Grant, B., Editors, B. C. Ministry of Energy, Mines, and Petroleum Resources, pages 117-125. Setterfield, T.N., Mussett, A.E., and Oglethorpe, R.D.J. (1992): Magmatism and Associated Hydrothermal Activity During the Evolution of the Tavua Caldera: 40Ar-39Ar Dating of the Volcanic, Intrusive and Hydrothermal Events; Economic Geology, Volume 87, pages 1130-1140. Sibson, R.H. (1990): Faulting and Fluid Flow; in Nesbitt, B.E. (ed.), Short Course on Crustal Fluids, Mineralogical Association of Canada, Handbook Volume 18, pages 93-132. Sibson, R.H., Robert, F., Poulsen, K.H. (1988): High-Angle Reverse Faults, Fluid-Pressure Cycling, and Mesothermal Gold-Quartz Deposits; Geology, Volume 16, pages 551-555. Sillitoe, R.H. (1979): Some thoughts on Gold-Rich Porphyry Copper Deposits; Mineralium Deposita, Volume 14, pages 161-174. Sillitoe, R.H., and Gappe, I.M. Jr. (1984): Phillipine Porphyry Copper Deposits: Geologic Setting and Characteristics; CCOP Technical Publication 14, 89 pages. Smith, J.G. (1977): Geology of the Ketchikan D-1 and Bradfield Canal A-1 Quadrangles, Southeastern Alaska; United States Geological Survey, Bulletin 1245, 49 pages. Souther, J.G., Brew, D.A., and Okulitch, A.V. (1979): Iskut River, British Columbia-Alaska (Sheet 104, 114); Geological Survey of Canada, Map 1418A. Titley, S.R. (1982): The Style and Progress of Mineralization and Alteration in Porphyry Copper Systems; in Titley, S.R. (Ed.), Advances in Geology of Porphyry Copper Deposits, Southwestern North America; The University of Arizona Press, Tucson, pages 93-116.  275  Vogt, A.H., Bray, A.D. and Bull, K. (1992): Geologic Setting and Mineralization of the Lac Minerals Red Mountain Deposit; Lac Minerals, unpublished company information circular, 3 pages. Webster, I.C.L. and Ray, G.E. (1991): Skams in the Iskut River -Scud River Region, Northwestern British Columbia; in Geological Fieldwork 1991, B.C. Ministry of Energy, Mines, and Petroleum Resources, Paper 1992-1, pages 245-254. White, S.H. (1977): Geological Significance of Recovery and Recrystallization Processes in Quartz; Tectonophysics, Volume 39, pages 143-170. White, S.H., and Knipe, R.J. (1978): Transformation- and Reaction-Enhanced Ductility in Rocks;  Journal of the Geological Society of London, Volume 135, pages 513-516. White, S.H., Burrows, S.E., Carreras, J., Shaw, N.D. and Humphreys, F.J. (1980): On Mylonites in Ductile Shear Zones; Journal of Structural Geology, Volume 2, pages 175-187. Wilkinson, W.H., Jr., Vega, L.A., and Titley, S.R. (1982): Geology and Ore Deposits at Mineral Park; in Titley, S.R. (Ed.), Advances in Geology of Porphyry Copper Deposits, Southwestern North America; The University of Arizona Press, Tucson, pages 523-541. Yeager, D.A. and Metcalfe, P. (1990): Geology of the Stonehouse Gold Deposit, Iskut River Area; Geological Association of Canada, Annual Meeting, Program with Abstracts, Volume 15, page 143.  276  Appendix 1 Sample and photograph location coordinates on the Snip mine grid for plates 3.1 - 3.27 and 4.1 - 4.5. (Refer to Figure 3.5 for an outline of the grid system) Coordinates of rock samples: Plate 3.1A 3.2A 3.2B 3.2C 3.2D 3.2D 3.4B 3.5A 3.5B 3.5C 3.6B 3.7D 3.8A 3.8C 3.9C 3.11C 3.11D 3.12C 3.13A 3.14C 3.14D 3.15D 3.16A 3.17D 3.17F 3.18A 3.18B 3.18C 3.19A 3.20A 3.20B 3.20C 3.21A 3.21B 3.21C 3.21D 3.22A 3.22B  Sample DR-280 DR-16 DR-248 DR-141 DR-280 AJM-290 DR-324 DR-264 DR-245 DR-217 DR-97 DR-22 DR-278 DR-121 DR-2 DR-127 DR-110 DR-328 DR-129 DR-91 DR-215 DR-220 DR-279 DR-116 DR-84 DR-352 DR-352 DR-126 DR-129 DR-65 DR-22 DR-77 DR-22 DR-38 DR-147 DR-38 DR-69B DR-69A  Location 130 haulage 130 haulage 130 haulage Ramp, 300 level 130 haulage 130 haulage 150 Footwall vein 300 level 4055 stope 300 level 130 haulage 130 haulage 3852 stope 340 level east 130 haulage 340 level east 340 level east 3852 stope 3451 stope 400L-150 vein 3852 stope 300 level 3852 stope 3242 stope 4061 stope 3852 stope 3852 stope 3242 stope 3451 stope 4055 stope 130 haulage 4055 stope 130 haulage 2242 stope 4061 stope 2242 stope 4055 stope 4055 stope  Elevation 156 145 144 290 156 145 390 315 408 304 130 148 396 336 157 336 350 395 341 401 383 305 396 336 413 395 395 336 341 408 148 409 148 242 411 242 408 408  Easting 4491 4576 4579 4584 4491 2630 4513 4975 4543 4438 4486 4553 4534 4425 4493 4431 4596 4527 4508 4573 4562 4510 4528 4445 4617 4528 4528 4441 4508 4437 4553 4532 4553 4405 4620 4405 4531 4531  Northing 2417 2658 2642 2021 2417 4565 2128 2017 2087 1991 2900 2574 2131 2059 2405 2055 2088 2125 2016 2154 2057 1993 2124 2051 2090 2133 2133 2056 2016 2087 2574 2087 2574 1965 2083 1965 2089 2089  277  3.22C 3.22D 3.23B 3.23C 3.23D 3.24A 3.25A 3.25B 3.25C 3.26A 3.26B 3.26C 3.26D 4.2B 4.5A 4.5B 4.5C  DR-129 DR-116 DR-152 DR-129 DR-129 DR-162 DR-328 DR-129 DR-223 DR-69 DR-69 DR-152 DR-152 DR-10 DR-3 DR-164 DR-164  341 336 264 341 341 304 327 341 408 408 408 264 264 131 136 133 133  3451 stope 3242 stope 260 level 3451 stope 3451 stope 300 level 3049 stope 3451 stope 4061 stope 4055 stope 4055 stope 260 level 260 level 130 haulage 130 haulage 130 haulage 130 haulage  4508 4445 4384 4508 4508 4475 4516 4508 4625 4531 4531 4384 4384 4664 4629 4462 4462  2016 2051 1984 2016 2016 1986 1993 2016 2087 2089 2089 1984 1984 2882 2786 2877 2877  Coordinates of underground photographs (location refers to coordinates of the centre of the photograph): Plate  Location  3.6C 3.7A 3.7B 3.7C 3.8B 3.9A 3.9B 3.10A 3.10B 3.10C 3.10D 3.11 A 3.12D 3.13D 3.15A 3.15B 3.15C 3.16B 3.23A 3.24B 3.24C 3.27A 3.27B 3.27C 3.27D 4.5D  3860 stope 180 level 130 haulage 385-150 vein 130 haulage 4055 stope 130 haulage 410 level ramp 4055 stope 4055 stope 130 haulage 180 level 4061 stope 4061 stope 385L-150 vein 3242 stope 3852 stope 4055 stope 3852 stope 3451 stope 3451 stope 430L-130 vein 385L-150 vein 3852 stope 4055 stope 130 haulage  Elevation 395 191 145 390 173 411 157 418 413 415 146 193 410 410 385 339 395 408 395 341 341 430 385 398 408 135  Easting  Northing  4575 4477 4569 4548 4376 4564 4493 4674 4575 4578 4563 4343 4591 4592 4573 4426 4538 4528 4531 4549 4501 4644 4613 4543 4536 4639  2113 1849 2637 2120 2104N 2102 2405 2180 2111 2114 2603 1702 2082 2087 2096 2065 2134 2087 2127 2005 2018 2223 2096 2135 2090 2811  278  Drill core samples: Plate 3.1B 3.1C 3.1D 3.1D 3.3A 3.3A 3.3B 3.3B 3.3C 3.3D 3.4A 3.4C 3.4C 3.4C 3.6A 3.6A 3.6D 3.11B 3.11B 3.12A 3.12A 3.12B 3.12B 3.12B 3.12B 3.13B 3.13B 3.13C 3.13C 3.13C 3.14A 3.14A 3.14B 3.14B 3.14B 3.16C 3.16D 3.16D 3.16D 3.16D 3.17B 3.17C 3.19B 3.19B 3.19C 3.19C  Drill hole UG-686 UG-33 UG-4 UG-32 UG-641 UG-652 UG-315 UG-33 UG-655 UG-659 UG-10 UG-656 UG-656 UG-656 UG-462 UG-369 UG-188 UG-639 UG-652 UG-238 UG-33 UG-150 UG-89 UG-195 S-58 UG-470 UG-408 UG-370 UG-451 UG-398 UG-257 UG-420 UG-459 UG-538 UG-417 UG-527 UG-173 UG-318 S-63 UG-377 S-8 S-45 UG-271 UG-399 UG-185 UG-418  Metres 49 74.7 96.95 112 45.5 116.2 11.9 17.6 21.2 24.4 13.4 107.9 109.4 107 28.9 49.9 63.5 8.9 47.4 63.9 126.5 71.6 60.6 45.7 37.6 46.9 35.7 50.2 4.54 32.2 33.2 72.4 59.2 37.2 67.7 38.8 34.3 10.8 58.9 49.55 5.6 61.9 44.6 34.6 35.9 53  Elevation  Easting  Northing  185 229 238 214 428 78 382 283 184 171 287 170 170 170 413 432 296 415 145 288 178 273 233 338 475 415 443 437 428 428 277 347 478 398 433 387 332 393 420 420 620 309 272 435 263 443  4500 4553 4501 4550 4713 4300 4513 4553 4300 4350 4550 4300 4300 4300 4512 4548 4488 4713 4300 4364 4553 4346 4499 4538 4602 4633 4648 4548 4609 4624 4586 4676 4610 4613 4677 4563 4489 4513 4550 4570 4800 4398 4537 4624 4489 4676  1650 1880 1945 1943 2118 1718 2079 1875 1722 1713 1870 1809 1810 1808 2095 2108 1964 2155 1709 1985 1885 1976 1930 2003 2148 2096 2128 2116 2177 2120 1963 2000 2155 2065 2082 2053 2007 2085 2098 2098 2253 2015 1956 2127 1967 2102  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0052894/manifest

Comment

Related Items