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 THEMAGMATIC AND DEFORMATIONAL HISTORY OF THE JOHNNYMOUNTAIN AREA, NORTHWESTERN BRITISH COLUMBIABy David A. RhysB.Sc., The University of British Columbia, Vancouver, B.C., 1989A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFMASTER OF SCIENCEINTHE FACULTY OF GRADUATE STUDIES(Department of Geological Sciences)We accept this thesis as conforming to the requiredstandardTHE UNIVERSITY OF BRITISH COLUMBIAOCTOBER 1993© David Alan Rhys, 1993In presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.(Signature) Department of  Gledc ,y0.‘1^Ciepc.e S The University of British ColumbiaVancouver, CanadaDate ^Cc.4.oiNer- i 3 j 93DE-6 (2/88)ABSTRACTThe Snip mine consists of an auriferous southwest-dipping shear vein system in a north-dipping Triassicgreywacke-siltstone sequence altered with abundant veinlet and pervasive biotite. The deposit, termed theTwin zone, is the largest of numerous shear veins in the mine workings. It contains just under 30 tonnesof gold.The Twin zone is composed of four ore types that are mineralogical end members of two distinctivestyles of mineralisation. They are: (i) carbonate and (ii) chlorite-biotite ore consisting of laminatedschistose veins of calcite, chlorite, biotite and pyrite, which display textures indicative of an origin, atleast partially by, wall rock replacement; and (iii) dilatant quartz veins and (iv) dilatant pyrite-pyrrhotitesulphide veins. Alteration comprises pale calcite-K-feldspar-silica envelopes surrounding black biotiteenvelopes 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 adynamic tectonic environment characterised by semi-brittle deformation. Numerous kinematic features inthe 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 signaturessuggest an Early Jurassic age for the veins. Abundant shallow easterly-dipping quartz-calcite extensionveins formed during a later, probably Tertiary, event.The Red Bluff porphyry, an elongate K-feldspar megacrystic plagioclase porphyritic quartz diorite totonalite stock, intrudes the greywacke sequence 300-800 metres northeast of the Twin zone. Twosuccessive, intense hydrothermal events are centred on the porphyry and are associated with subeconomicAu 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-pyrite-quartz (phyllic) alteration characterised by pyrite veining. Intrusion, semi-brittle deformation, andii111alteration and mineralisation within the large hydrothermal system of the Red Bluff porphyry wereclosely related spatially and temporally. A genetic relationship is supported by: similarities in structuralfabrics and alteration histories in the Twin zone and the porphyry, alteration and metal zoning of veinsystems distributed concentrically around the porphyry, and apparently concordant Early Jurassic zirconU-Pb age from the porphyry with galena Pb-Pb signatures from the Twin zone and surrounding veinsystems. Two significant structurally-controlled Au deposits in the area, Inel and Stonehouse, havesimilar age, mineralogy, structure, alteration and spatial relationships to Early Jurassic intrusions. Theyrepresent contemporaneous, possibly genetically related, hydrothermal systems.Table of ContentsABSTRACTTABLE OF CONTENTS^ ivLIST OF TABLES viiLIST OF FIGURES^ viiiLIST OF PLATES ixACKNOWLEDGEMENTSCHAPTER 1: INTRODUCTION1.1.1 Introduction^ 11.1.2 Location and access 11.1.3 Previous studies 41.1.4 History^ 5Development of the Snip MineOther significant deposits in the Johnny Mountain areaCHAPTER 2: GEOLOGIC SETTING2.1.1 Regional Geology^ 92.1.2 Lithologies of the Johnny Mountain area^ 9Lower SequenceUpper sequenceIntrusive rocks2.1.3 Structure of the Johnny Mountain area^ 212.1.4 Metallogeny of the Stewart - Iskut River Area 23The Texas Creek plutonic suite and regional metallogenyMineralised structures in the Johnny Mountain areaGalena Pb-Pb isotopic data from veins on Johnny MountainBronson skarnCHAPTER 3: GEOLOGY OF THE SNIP MINE3.1 INTRODUCTION^ 373.2 MINE GEOLOGY 373.2.1 The greywacke sequence at Snip^ 37Alteration and metamorphism3.2.2 Dykes^ 54Plagioclase porphyritic dykeLamprophyresBiotite spotted unit3.2.3 Geochronology^ 60K-Ar datesU-Pb zircon dataGalena Pb-Pb isotopic dataiv3.2.4 Structural features^ 61Shear veinsFoliationQuartz stockwork (130 haulage level south)Calcite-chlorite-biotite-pyrite veinletsExtension veinsFaults3.3 THE TWIN ZONE SHEAR VEIN SYSTEM^ 843.3.1 Introduction^ 843.3.2 Composition of the Twin zone: Mineralogy and ore types^ 88Carbonate ore and chlorite-biotite oreSulphide oreQuartz oreBiotite and chlorite compositionGold occurrence in the Twin zone3.3.3 Alteration and vein paragenesis^ 1073.3.4 Structural style of the Twin zone and related veins^ 116Twin zone Footwall veinInternal structure of the Twin zone3.3.5 The 150 vein and other shear veins^ 140150 veinOther major veins3.3.6 Relationship of stratigraphy to the Twin zone^ 1473.4 ORE TYPE, MINERAL AND METAL DISTRIBUTION IN THE TWIN ZONE3.4.1 Introduction^ 1523.4.2 Ore type distribution in the Twin zone^ 1533.4.3 Mineral distribution in the Twin zone 1693.4.4 Gold distribution in the Twin zone 1723.5 DISCUSSION^ 1733.5.1 Structural history of the Snip mine^ 173Temporal relationships of structures at SnipRelative timing of deformation in the Twin zoneStructural history and relationships to structural events on Johnny Mountain3.5.2 Deformation processes within the Twin zone^ 179Deformation mechanismsFluid pressure cycling and ore type distributionStrain softening and the localisation of deformation to the Twin zoneShear sense indicators and effects of heterogeneous deformationMorphology, structural style and displacement on the Twin zoneCHAPTER 4: THE RED BLUFF GOLD-COPPER PORPHYRY SYSTEM4.1 INTRODUCTION^ 1994.2 THE RED BLUFF GOLD-COPPER PORPHYRY SYSTEM^ 1994.2.1 The Red Bluff porphyry^ 199Modal composition and texture4.2.2 Dykes within the Red Bluff porphyry 2014.2.3 Alteration related to the Red Bluff porphyryPotassic alterationSericite-pyrite-quartz alterationQuartz-hematite-sulphide veinsChlorite-calcite veinsQuartz-calcite-chlorite extension veins4.2.4 Structure of the Red Bluff porphyryFaults4.2.5 Metal distribution within and adjacent to the Red Bluff porphyryMetal distribution within the porphyryCu and Au grades in greywackes adjacent to the Red Bluff porphyryMolybdenite compositions4.3 DISCUSSIONEarly Jurassic intrusions and the origin of secondary biotite on Johnny MountainRelationship of the Red Bluff porphyry system to the Twin zone and other veins onJohnny MountainDepth of emplacement of the Red Bluff porphyry and implicationsDevelopment of the Red Bluff porphyry systemComparisons to other porphyry systemsCHAPTER 5: OTHER GOLD DEPOSITS IN THE JOHNNY MOUNTAIN AREA5.1.1 Introduction^ 2445.1.2 Inel^ 2445.1.3 Stonehouse 2525.1.4 Discussion 259Implications for explorationCHAPTER 6: SUMMARY AND CONCLUSIONS^ 265Geologic history of the Johnny Mountain areaREFERENCES CITED^ 269APPENDICESAppendix 1: List of sample locations, with northing, easting and elevation on the^276Snip grid systemvi205219226233viiList of TablesPageTable 2.1^Radiometric dates obtained in the Johnny Mountain area^ 21Table 2.2^Examples of gold deposits in the Stewart-Iskut River region associated with^25known and probable Early Jurassic (Texas Creek) IntrusionsTable 2.3^Showings and deposits, northern Johnny Mountain and Snippaker Ridge^29Table 2.4^Metal content and metal ratios of some mineralised structures, Johnny Mountain^30Table 2.5^Summary of zoning of mineralised structures on Johnny Mountain and^30Snippaker RidgeTable 2.6^Galena lead isotope analyses for the Johnny Mountain area, northwestern B.0^35Table 3.1^Stratigraphic units and associated alteration at the Snip mine^ 47Table 3.2^Dykes in the Snip mine^ 59Table 3.3^Common structures in the greywacke sequence at the Snip mine 62Table 3.4^Geochemical analyses obtained from ribboned stockwork veins^63Table 3.5^Geochemical analyses obtained from extension veins^ 75Table 3.6^Twin zone mineral species^ 89Table 3.7^Classification criteria and abundance of ore types in 456 intersections of the^90Twin zoneTable 3.8^Percentage abundance of common minerals in Twin zone ore types^90Table 3.9^Occurrence of gold in the Twin zone^ 106Table 3.10 Alteration and paragenesis, Twin zone and related shear veins, Snip mine^115Table 3.11 Intersection points of unit 3 with the Twin zone^ 149Table 3.12 Mineral distribution and associations in the Twin zone 171Table 3.13 Sequence of formation of structural features at the Snip mine^179Table 3.14 Deformation processes affecting common minerals in the Twin zone^185Table 4.1^Distribution and paragenesis of minerals in the Red Bluff porphyry 217Table 4.2^Veins in the Red Bluff porphyry^ 219Table 4.3^Red Bluff drill hole composite assays 227Table 4.4^Molybdenite compositions 232Table 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^ 267viiiList of FiguresPageFigure 1.1 Location of the Snip mine and the project area^ 2Figure 1.2 Geographic features of the Johnny Mountain area, with insets^ 3Figure 2.1 Geology of the Johnny Mountain area^ 10Figure 2.2 Geologic setting of the Snip mine, 1:5,000 scale^ (in pocket)Figure 2.3 Deposits on northern Johnny Mountain 32Figure 2.4 Lead-lead isotopic plots of galena from mineral deposits in the Stewart-Iskut^36River areaFigure 3.1 Schematic section from the Twin zone to the Red Bluff porphyry^38Figure 3.2 Cross-section through the Twin zone and stratigraphy on section (in pocket)4550 EastFigure 3.3 Equal area projections of bedding in the Snip mine workings^ 44Figure 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^45Figures 3.1 and 3.2Figure 3.6 Equal area projections of structural features in the Snip mine workings^66Figure 3.7 Cross-sections through the Twin zone and related veins^ 85Figure 3.8 Twin zone long section showing the locations of plans and sections and^86distribution of veinsFigure 3.9 Twin zone long sections showing drill hole pierce points and fault restoration^87Figure 3.10 Twin long section with contoured dip angle^ 118Figure 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 119Figure 3.17 Equal area projections of Twin zone structural features 120Figure 3.18 Equal area projections of 150 vein structure features^ 141Figure 3.19 Structure of the 150 vein, drawn from photographs 142Figure 3.20 Geologic map of the 130 vein, 430 level^ 146Figure 3.21 Intersection of the mixed greywacke-siltstone package (unit 3) with the Twin zone 150Figure 3.22 Calculation of the displacement of unit 3 on the Twin zone^ 151Figure 3.23 Contoured vertical long section plots of ore types in the Twin zone^154Figure 3.24 Hand contoured plots of true ore type thickness, central Twin zone 157Figure 3.25 Twin zone long section relating structural features to thickened areas of quartz^165and sulphide oreFigure 3.26 Contoured vertical long section plots of visually estimated mineral percentages^166in the Twin zoneFigure 3.27 Hypothetical morphology of the Twin zone during deformation^ 196Figure 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^214Figure 4.3 Equal area projections of structural features in the Red Bluff porphyry, 130 222haulage levelFigure 4.4 Au versus Cu scatter plots for selected Red Bluff drill holes^ 230Figure 5.1 Geology of the AK drift, Inel deposit^ 250Figure 5.2 Geology of the Discovery drift, Inel deposit 251List of PlatesPagePlate 2.1.^Aerial view of Johnny Mountain^ 12Plate 2.2.^Lithologies of the Johnny Mountain area 15Plate 2.3.^A: Red Bluff cliffs, Snip mine area 19B-D: K-feldspar megacrystic intrusive rocks, Johnny Mountain areaPlate 3.1.^Clastic units, Snip mine^ 40Plate 3.2.^Photomicrographs of clastic units, Snip mine^ 42Plate 3.3.^Greywacke alteration, Snip mine^ 49Plate 3.4.^Greywacke alteration, Snip mine 51Plate 3.5.^Biotite spotted unit and other dykes, Snip mine^ 56Plate 3.6.^Biotite Spotted Unit (BSU), Snip mine^ 58Plate 3.7.^Shear veins, Snip mine^ 71Plate 3.8.^Veins and veinlets, Snip mine 73Plate 3.9.^Extension veins, Snip mine 79Plate 3.10. Extension and shear veins and their structural associations and characteristics,^81Snip minePlate 3.11. Faults, Snip mine^ 83Plate 3.12. Carbonate ore, Twin zone, Snip mine^ 95Plate 3.13. Chlorite-biotite ore, Twin zone, Snip mine 97Plate 3.14. Sulphide ore, Twin zone, Snip mine 99Plate 3.15. Ore type relationships and character in various veins from the Snip mine^101Plate 3.16. Quartz ore, Twin zone, Snip mine^ 103Plate 3.17. Gold occurrence in the Twin zone, Snip mine^ 105Plate 3.18. Alteration in the Twin zone, Snip mine 110Plate 3.19. Alteration in the Twin zone, Snip mine 112Plate 3.20. Photomicrographs of chlorite-biotite relationships in the Twin zone and shear^114veins, Snip minePlate 3.21. Photomicrographs of deformation fabrics in the Twin zone and shear veins,^129Snip MinePlate 3.22. Deformation textures in the Twin zone, Snip mine^ 131Plate 3.23. Structural features of the Twin zone, Snip mine 133Plate 3.24. Mesoscopic folds in the Twin zone, Snip mine 135Plate 3.25. Shear bands and oblique foliations, Twin zone and 150 vein, Snip mine^137Plate 3.26. Twin zone, shear sense indicators in thin section, Snip mine^139Plate 3.27^Structure of shear veins at the Snip mine^ 144Plate 4.1.^Character and alteration of the Red Bluff porphyry^ 204Plate 4.2.^Alteration of the Red Bluff porphyry 211Plate 4.3.^Alteration of the Red Bluff porphyry^ 213Plate 4.4.^Photomicrographs of alteration, Red Bluff porphyry^ 216Plate 4.5.^Deformation of the Red Bluff porphyry, Snip 130 portal area^224Plate 5.1.^Inel deposit^ 247Plate 5.2^Stonehouse deposit 255ixACKNOWLEDGMENTSThis study would not have been possible without the generous assistance of Cominco Metals andCominco Explorations Ltd. The work and ideas presented benefited greatly from numerous invaluablediscussions with, and assistance from Cominco geologists Al Samis, Terry Hodson, Bruce Coates, EarlMasarsky, Ken Donner, Nick Callan, Ian Paterson and Jim McLeod. I thank Merlyn Royea and RayMerrifield of Cominco Metals for their hospitality, and permission to work and stay at the Bronsoncamp. Dale Craig of Cominco is also thanked for his help in logistical support. Special thanks go toBruce Coates and Terry Hodson for their play by play descriptions of new developments in mine geologyover the last year. Cominco Metals generously provided food, accommodation and logistical support forthe 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 liketo thank David Yeager of Skyline Gold Corp., Victor Jaramillo and Bob Gifford of Gulf InternationalMinerals, and Paul Metcalfe, Art Ettlinger and James Moors at The University of British Columbia forimportant discussions and the sharing of their ideas and information. Arne Toma expertly and artisticallydrafted 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 ofthe Iskut River Area", which is supported by thirteen mining companies, the Science Council of BritishColumbia and a Natural Science and Engineering Council CRD grant.xCHAPTER 1: INTRODUCTION1.1.1 IntroductionThe Snip mine, owned jointly by Cominco Ltd. (60 percent) and Prime Resources Group Inc. (40percent), commenced production in January, 1991. It is currently the largest gold producer in BritishColumbia. The deposit is a vein filled shear zone, named the Twin zone, that contAins a diversity of oretypes, all of which have high grade gold values. The mineralised zone is spatially associated with thetabular subeconomic Red Bluff Au-Cu porphyry deposit, 800 metres to the northeast. Numerousprecious and base metal showings, and the past producing Skyline Gold mine occur to the south, withinsix kilometres of Snip.Research was undertaken to document the geology of the Snip mine and its relationship to the geologichistory of the area, and to compare and contrast the various styles of mineralisation in the JohnnyMountain area. The study is based on two summers of fieldwork (1991 and 1992 seasons), during whichdetailed (1:500 scale) underground mapping, extensive core logging and sampling were completed atSnip. In addition, surface mapping of the area was carried out at 1:5,000 and 1:20,000 scale inconjunction with other workers (Peter Lewis and Paul Metcalfe). Thin section examination ofmineralogic relationships and structural features in oriented samples has corroborated the fieldinformation. The study was greatly augmented by geologic mapping, drilling and geochemicalinformation from Cominco Ltd. and Skyline Gold Corporation that was obtained during the course ofexploration and mining in the area.1.1.2 Location and AccessSnip mine is 85 kilometres east of Wrangell, Alaska, and 110 kilometres northwest of Stewart, BritishColumbia. The mine is on the south side of the Iskut River, two kilometres south of its confluence with2III Jurassic Intrusions^ km0^100^200^300Lower to Middle JurassicHazelton Group (volcanicrocks, 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 theSnip mine. Jurassic intrusions (including the Texas Creek plutonic suite), volcanics (HazeltonGroup) and Jurassic Bowser Lake group sediments are shown.3Figure 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.Bronson Creek (Figures 1.1 and 1.2). It occurs at the northwest end of Johnny Ridge. Mine workingsrange from 130 to 500 metres above sea level, and comprise nine levels. The mill site andaccommodation are within the Bronson Creek valley 1.5 kilometres northeast of the deposit and 120metres above sea level.The local terrain is extremely rugged, with many local peaks above 1900 metres in elevation. Glaciersare common, locally extending to low elevations (400-800 metres) in the valleys. The area is thicklyvegetated with a forest of mountain hemlock and Sitka spruce. Steeper slopes and gullies are commonlycovered 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 byhovercraft on the Iskut river from Wrangell, Alaska. DC-3, DC-4, Hercules and Bristol transport aircraftare also used. Central Mountain Air provided regular passenger service during the study from the airstripto several British Columbia destinations.1.1.3 Previous studiesNo systematic detailed geologic descriptions of the Snip mine or the Johnny Mountain area have beenundertaken, except for an unpublished review of the geology of northwestern Johnny Mountain byAtkinson et al., 1991. Regional mapping projects in the Iskut River region, including an overview of thegeology of the Snip mine area, are documented in Kerr (1948), Britton et al. (1990) and Metcalfe andMoors (1993). Published regional maps include Souther et al. (1979), Alldrick et al. (1990), Lefebureand Gunning (1989), and Fletcher and Hiebert (1990). Galena Pb-isotope data for showings and mineraldeposits in the Iskut River region are reported in Godwin et al. (1991). Exploration and briefdescriptions of Snip geology are documented in Nichols (1987, 1989). A series of short unpublishedcompany petrographic reports by McLeod (1987a-e, 1989a,b, 1991a,b, 1992) address specificmineralogic aspects of Snip geology. Read (1990) presents the results of a primarily stratigraphic study45of lithologies adjacent to the orebody. Preliminary descriptions of some of the findings of this project arepresented in Rhys and Godwin (1992), and Rhys and Lewis (1993).The Red Bluff porphyry deposit is described mainly in exploration reports. These include geologicoverviews 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 1965exploration by Cominco Ltd. is contained in Harris (1966). Macdonald et al. (1992) describe U-Pbzircon geochronometry of several plutons in the region, including the Red Bluff porphyry intrusion.1.1.4 HistoryThe 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 travelledthrough 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 islittle 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 inWrangell, Alaska. The initial claim group, the Iskoot claims (9 claims), covered the west side of Bronsoncreek 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 thepresent mine workings, was staked in 1909. Between 1908 and 1911, several short adits were started onvarious showings in both claim groups, and some trenching was done. One ton of selected material froma series of foliation parallel sulphide veinlets in schistose greenstone (Annual Report, B.C. Departmentof Mines, 1919, pp. N83-84) was shipped from one of the showings for a smelter test at Ladysmith in1909. 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 (Iskoot6claims: Annual Report, B.C. Department of Mines, 1919, pp. N83-84) in the vicinity of the currentBonanza showings on ground presently held by Skyline Gold Corporation. Only minor work was done bythe Iskut Mining Company on the Iskoot and Red Bluff claim groups between 1911 and 1929 (AnnualReport, B.C. Department of Mines, 1929, p. 114). Both claim groups were Crown granted during thistime. 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. Thesewere examined subsequently by Cominco geologists (Castle, 1929), but nothing of interest was foundand the claims were abandoned. No further exploration activity was carried out on Johnny Mountain until1949, when Kennco Exploration Company (Canada) Ltd. ran a brief prospecting program on BronsonCreek 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 aroundthese grants. Cominco personnel examined all of these the claim groups that year and in 1965 mapped thearea. Eight holes were drilled totalling 341 metres on optioned ground on the Red Bluff grants (AnnualReport, 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 atapproximately 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 thecontinuity of copper mineralisation, with limited success. The gold showing (future Snip orebody) wasexposed 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, sincefresher sulphide rich material returned lower assays (17 ppm). In addition, the vein was estimated tocontain between 2,000 and 3,000 tonnes--a figure too small to warrant further development (Nagy,1966).Development of the Snip MineCominco 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 goldshowing. A joint venture agreement was signed with Delaware Resources Corporation in 1986. Twelvedrillholes totalling 1494.2 metres and surface trenching located four gold bearing structures, the largestand most continuous of which was the Twin zone (Nichols, 1987). In 1987, an airstrip and a 40 mancamp were constructed beside Bronson Creek to provide access and accommodation. Seventy-three moresurface drill holes (13,857 metres) outlined the Twin zone on 50 metre centres. The Twin zone wasintersected 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 12.5metres to enable more confident ore reserve calculation and stope definition. By late 1990, a reserve of936,000 tonnes grading 28.6 ppm Au was delineated entirely within the Twin zone (A. Samis, personalcommunication, 1991). Delaware Resources, incorporated into Prime Resources Group Inc., had by thistime earned a 40% interest in the property by funding exploration between 1986 and 1990. Productionbegan 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 sulphideflotation concentrate. Production during 1991 was 123,000 tonnes grading 30.4 ppm Au (3.7 tonnes Autotal), and during 1992, 165,000 tonnes grading 31.7 ppm Au (5.2 tonnes Au total), for a total goldproduction up to 1 January 1993 of 8.97 tonnes (just over 288,000 ounces; T. Hodson, personalcommunication, 1993). New reserves have been added during 1991 and 1992 as a result of developmenton several veins in the foot wall of the Twin zone, primarily the 150 vein that contains new reserves ofapproximately 70,000 tonnes.7Other significant deposits in the Johnny Mountain areaThe Stonehouse deposit (Johnny Mountain mine), discovered originally by Hudsons Bay Mining andSmelting Company in 1954, preceded development of Snip mine. This deposit is 6 kilometres south ofSnip on Johnny Mountain (Figure 1.2). The Johnny Mountain mine produced 2.91 tonnes of gold, 4.56tonnes of silver and 973 tonnes of copper from 207,058 tonnes mined between August 1988 and itsclosing 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. andjoint 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 InternationalMinerals Limited; Figure 1.2), 11 kilometres southeast of Snip, and the Rock and Roll (Black Dogdeposit, 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 ofthe Red Bluff porphyry between 1988 and 1991 on behalf of the property owners, Solomon ResourcesLimited.8CHAPTER 2: GEOLOGIC SETTING2.1.1 Regional GeologyThe 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 sedimentaryarc 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 intrusionsthat 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 andcospatial with Hazelton Group volcanic strata. Tertiary elements of the Coast Plutonic Complex arerepresented 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 areaStrata in the Johnny Mountain area are defined here as a lower sequence and an upper sequence, probablycorrelative with the Triassic Stuhini and Jurassic Hazelton Groups, respectively. The sequences areseparated by a regional, flat lying to gently dipping unconformity, which is exposed at the break in slopeeast of the Skyline Gold Corporation Stonehouse camp (Figure 2.1; Plate 2.1). This unconformity ismapped, but not exposed, at the 1,800 metre level on Snippaker Ridge (Pegg and Travis, 1991; Metcalfeand Moors, 1993). All of the rocks have been affected by lower greenschist facies metamorphism withthe development of chlorite in clastic units and chlorite and epidote in volcanic units. A broad zone ofsecondary biotite development occurs at the northwest end of Johnny Mountain and along its southwestmargin, the significance of which is discussed in succeeding chapters.9TriassicDioriteJurassicK-feldspar megacrysticporphyryLOWER SEQUENCE(Triassic Stuhini Group) UPPER SEQUENCE(Jurassic Hcrzetton Group)Stratified RocksDiorite, plagioclaseporphyryLate steep4111%tit faultNo.^Si foliationS2 foliationBeddingFIGURE 2.1:Geology of the Johnny Mountain Area,Northwestern British Columbia. 0Greywacke, slltstone,mudstone and minorconglomerateAndesRic breccia tovolcanic conglomeratePlagioclase phyricandesiteIntrusive RocksGlacial IceU-Pb zirconIsotopic dateX Mineral depositDI fold axialsurface tracexDaclte - Andeslte flows,breccia, tuffRhyolite flows, weldedlapilli tuffBasalt flows, epiclasticrocksI ALower sequenceThe strata below the regional unconformity, here termed the lower sequence, consist of poly-deformedand moderately to weakly metamorphosed feldspathic turbiditic greywackes with subordinate interbeddedsiltstones, mudstones, volcanic conglomerate and rare dolostone and/or limestone. This sequenceunderlies most of northwestern Johnny Mountain and western Snippaker ridge, and it hosts the Snip mineand Inel deposit (Figure 2.1; Plate 2.1). The stratigraphy exposed in the Snip workings is describedfurther in Chapter 3.Lack of exposure over much of the area and complication by folding and faulting have hinderedconstruction of a stratigraphic column for the lower sequence on Johnny Mountain. Neither thestratigraphic top nor bottom is exposed, so the true thickness is unknown. The exposed section has aminimum true thickness of between 900 and 1200 metres, measured from the northeast end of the Snipworkings south to Sky Creek. Strata composed primarily of fine to medium grained feldspathic and lithicturbiditic greywacke comprise most of the sequence. Subordinate graded beds of siltstone and blackmudstone occur throughout the sequence, but are most common at the base of the exposed section alongSky Creek and along the northeastern part of Johnny Flats (along the northernmost anticlinal trace inFigure 2.1; Plate 2.1). The greywackes are massive to crudely bedded, with local graded beds up to 10metres in thickness. Individual graded beds may have sharp scoured basal contacts with siltstone ormudstone rip up clasts (Plate 2.2A). Fine grained porphyritic pebble to cobble sized mafic to felsicvolcanic clasts are common in coarser beds or at the base of thick graded beds. Interbedded monolithic topolylithic volcanic conglomerates, biotite rich plagioclase porphyritic tuff or flow units, and felsic crystaltuff are common in the highest exposed portion of the section on Johnny Mountain west of theStonehouse deposit. K-feldspar megacrystic and medium to fine grained equigranular intermediate tofelsic sills intrude the sequence in this area.1112Plate 2.1: Aerial view of Johnny Mountain, northwestern British Columbia. The photograph, lookingsoutheast, was taken approximately 1 kilometre northwest of the Snip camp. Important geologic and topographicfeatures referred to in the text are marked in the accompanying sketch. Volcanic rocks of the Jurassic upperpackage (Jr) occurs at the crest of the ridge, unconformably overlying folded Triassic clastic sediments (Tr). Aprominent anticline traces across Johnny flats (upper centre) and plunges gently towards Sky Creek (right). TheRed Bluff porphyry (+ +) intrudes the northeast edge of the mountain (left, bottom). The Twin zone runsthrough the lower centre of the picture, dipping to the southwest. It is intersected by a northwest-dipping faultnear the bottom of the photograph (squiggly lines). Sky Creek runs along a southwest-dipping fault. Photographcourtesy of Cominco. The photo was taken in 1986 before mine development.Several thin lenses of massive recrystallised limestone and dolostone, and crinoidal limestone occursporadically throughout the lower sequence on Johnny Mountain. A small northeast trending body ofrecrystallised limestone associated with a diopside-garnet skarn that occurs just north of the Snip minecamp (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 isparaconformably 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 ofSnippaker Peak has yielded Norian corals and ammonoids (Nadaraju and Smith, 1992), thus providing aminimum age of Upper Triassic for the lower sequence. The lower sequence is thus assigned to theTriassic Stuhini Group. No fossils have been found elsewhere in the sequence. Two samples, one ofcrinoidal limestone collected south of the Stonehouse deposit, and a second of calcareous mudstone froma drill hole on the northeast flank of Johnny Mountain (Skyline hole 975, 270.2-270.9 metres) failed toyield microfossils (R. G. Anderson and G. Nadaraju, personal communication, 1992).Plagioclase + hornblende + pyroxene phyric andesitic volcanics, including tuffs and flows, occur to thenortheast of Snip at low elevations on the south side of the Iskut River interbedded with greywacke (Peggand 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 contactrelations are described in Pegg and Travis (1991) or Britton et al. (1990), but if the contact isstratigraphic, then they indicate a vertical thickness for the clastic lower sequence on Snippaker Ridge of1.6 kilometres up to the Jurassic unconformity at the ridge top.Upper SequenceFlat 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 and13Plate 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 clastsfrom the lower sequence (Triassic) on eastern Johnny mountain. SkylineGold Corp., Bonanza drill hole DDH 975: 298.1 metres.B: Bronson stock west of Monsoon Lake. Biotite-rich dark grey medium tofine-grained equigranular diorite (left) containing a rounded xenolith ofplagioclase porphyritic diorite. Sample is DR-193.C: K-feldspar megacrystic plagioclase porphyritic mafic dyke intruding aschistose biotite-rich portion of the Bronson stock 400 metres northwest ofthe Snip camp. A laminated calcite > chlorite + epidote + pyrite shearvein with an epidote alteration envelope occurs along the margin of thedyke. Both dyke and shear vein cut foliation in the wallrocks.144.!• •4^rk^14! •^diki•16Snippaker Ridge unconformably overlying the greywacke sequence and the Norian greywacke (Metcalfeand Moors, 1993; Britton et al., 1990; Figure 2.1; Plate 2.1). Gold bearing veins of the Stonehousedeposit at the Johnny Mountain gold mine occur at the base of this sequence. These strata form threelithologically distinct units that are present on Johnny Mountain, and for the lowest unit, on SnippakerRidge (Atkinson et al., 1991; Metcalfe and Moors, 1993; Rhys and Lewis, in preparation). Lowest rocksof the upper sequence are andesitic to dacitic, medium to dark greenish grey ash to block tuff andtuffaceous sediments approximately 300 metres in thickness. Tuffaceous components are plagioclasephyric and poorly to moderately bedded. The age of the dacite-andesite and the basal unconformity isconstrained to Latest Triassic to Early Jurassic by: (i) Norian fauna in the underlying succession onSnippaker Ridge (Nadaraju and Smith, 1992), (ii) a U-Pb zircon age of 194 ± 3 Ma from a plagioclasephyric dyke that cuts tuffs in the lower part of the unit in the Stonehouse deposit (M.L. Bevier, personalcommunication, 1993; Table 2.1), and (iii) a U-Pb zircon age of 192.9 ± 1.3 Ma (preliminary minimumage only) obtained from massive plagioclase + hornblende phyric dacite 3.5 kilometres southeast ofSnippaker Peak (P. Metcalfe and J. Gabites, personal communication, 1993). Conformably succeedingthe andesitic to dacitic sequence on Johnny Mountain is a 350 metre thick dacitic to rhyolitic tuffaceousvolcanic 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 rocksyield an age of 192 ± 3 Ma (M.L. Bevier, personal communication, 1993; Table 2.1). Uppermost rocksof the sequence comprise dark green clinopyroxene + plagioclase-phyric basaltic flows. The lithologiccharacter, thickness and age of the upper sequence at Johnny Mountain compares closely to regionalHazelton Group successions of the Iskut River and Stewart areas, which currently are being reviewed(P.D. Lewis, personal communication, 1993).Intrusive rocksTriassic to Tertiary dykes and stocks, including the Red Bluff porphyry, intrude the Triassic and Jurassicrocks of Johnny Mountain. A heterogeneous medium grained equigranular plagioclase + clinopyroxene17± amphibole phyric diorite stock lies immediately north of Monsoon Lake, separated from thegreywacke sequence at the Snip mine by a strong northeast trending lineament and possible fault (Figures2.1 and 2.2). This unit, with deformed and biotite rich southern margins, was previously mapped asandesite (Lefebure and Gunning, 1989); however, the equigranular medium grained texture in relativelyundeformed areas suggests instead that it is intrusive. Brown biotite, pale green amphibole and accessorymagnetite commonly replace pyroxene grains; plagioclase is saussuritised. Biotite abundance decreasesnorthward. The unit contains common resistant weathering rounded xenoliths of a coarse plagioclase andclinopyroxene porphyritic andesite (Plate 2.2B). These comprise up to 30% of the outcrops in someareas, and commonly range from 4 to 30 centimetres in diameter; they are locally >1 metre across. A U-Pb 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 furthercomplication are the different names applied to the collective unit. It is proposed (Figure 2.1) here thatthe 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 (Figures2.1, 2.2; Plates 2.1, 2.3A). The porphyry is a K-feldspar megacrystic, plagioclase porphyritic quartzdiorite to tonalite body (Plate 2.3B) that is overprinted by a porphyry Au-Cu system. A sample obtainedfrom foliated porphyry in the Snip 130 portal returned a U-Pb zircon age of 195 ± 1 Ma (Macdonald etal., 1992; Table 2.1; sample site on Figures 2.1 and 2.2). The porphyry and its associated hydrothermalsystem is described in detail in Chapter 4.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 Bluffporphyry, a tabular steeply-dipping quartz + magnetite + sericite alteredK-feldspar megacrystic quartz diorite to tonalite intrusion that isapproximately 250 metres thick. The southwestern contact of the intrusionruns along the break in slope behind the top of the cliffs and continuesabove the lower cliffs to the far right. The northeast contact runs just belowthe cliff base. The prominent gully in the lower right corner is a steeply-dipping northwesterly-trending gouge-filled fault zone. Snip camp is just outof 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 andK-feldspar replacing plagioclase and matrix. K-feldspar megacrysts (tancolour) are intact. Disseminated and veinlet-controlled magnetite comprises5-10% of the samples. Quartz veins with magnetite (banding and selvage inthe sample) are common. Top sample is from Skyline DDH 964: 48.2metres; bottom is from Skyline DDH 944: 74.1 metres. Drill hole locationsare marked on Figure 2.2.C: Sample from the centre of a 15 metre wide dyke northeast of MonsoonLake. K-feldspar megacrysts containing grey quartz grains are in a matrix ofsericite-altered plagioclase. Sample is DR-186.D: Sample from a sill 1.5 kilometres west of the Stonehouse deposit. K-feldspar megacrysts are in a matrix of sericite altered plagioclase porphyry.Sample is DR-370.1820Orthoclase megacrystic dykes with moderate to steep southwesterly dips intrude the Bronson stock onekilometre north of the Snip camp (Figure 2.2; Plates 2.2C, 2.3C). These dykes are similarmineralogically and texturally to the Iskut River stock and Red Bluff porphyry. They range from 10centimetres up to 15 metres in thickness. The thickest have fine grained chilled margins with mediumgrained porphyritic cores. Phaneritic dykes consist of between 5 to 10% orthoclase phenocrysts in amatrix of medium grained plagioclase porphyry. Accessory apatite is common. Magnetite, occurringinterstitially and as thin stringers, is common in some dykes. The stringers are typically subparallel to themargins of the dyke. The dykes contain foliated xenoliths of the biotitic Bronson stock, indicating thatthey postdate foliation.Several small stocks, sills and dykes of unknown age and intermediate to mafic composition intrude thewestern side of Johnny Mountain. These include several northeast trending locally K-feldsparmegacrystic plagioclase porphyritic felsite sills, dykes and small stocks that occur between two and fivekilometres south of Snip (Figure 2.1; Plate 2.3d). North dipping plagioclase porphyritic, locally K-feldspar 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, asmall quartz-feldspar porphyritic felsite stock (Inel porphyry) intruding elastic rocks probably correlativewith the lower sequence on Johnny mountain returned a U-Pb zircon age of 190 ± 3 Ma (Macdonald etal., 1992).The relative ages (Table 2.1) of Jurassic volcanic rocks of the upper sequence (Snippaker Ridge daciteand Johnny Mountain rhyolite) and the Early Jurassic intrusions (Red Bluff porphyry, Inel stock andStonehouse feldspar porphyry dykes) suggest that the intrusions are subvolcanic. They are probablefeeders to the overlying volcanic units.21Table 2.1: Radiometric dates obtained in the Johnny Mountain area. Locations of dates are on Figures 2.1 and2.2.Material dated Location Age References(method)Clinopyroxene-plagioclasedioriteBronson stock, north of Snip Between 197 and 225 Ma(U-Pb zircon)Macdonald et al., 1992Foliated K-feldspar porphyriticintrusion (Red Bluff porphyry)Snip 130 level, near portal 195 + 1 Ma(U-Pb zircon)Macdonald et al., 1992Plagioclase porphyritic dyke Johnny Mountain mine 194 + 3 M.L. Bevier, personal(Stonehouse) (U-Pb zircon) communication, 1993Plagioclase + hornblende Snippaker Ridge, 3.5 km 192.9 + 1.3 Ma J. Gabites and P.phyric dacite southeast of Snippaker Peak (U-Pb zircon; preliminaryminimum age)Metcalfe, personalcommunication, 1993Flow banded rhyolite Johnny Ridge 192 + 3(U-Pb zircon)M.L. Bevier, personalcommunication, 1993Inel stock: Quartz-feldsparporphyry, aphanitic matrixInel camp site 190 + 3(U-Pb zircon)Macdonald et al., 1992Anomalous green biotite froma quartz vein in the Twin zoneSnip, 300 level west 51.9 + 1.8 Ma(K-Ar, biotite separate)R.L Armstrong, U.B.C.,personal communication,1991Biotite lamprophyre dyke Snip, 300 level east 32.0 + 1.1 Ma(K-Ar whole rock)R.L Armstrong, U.B.C.,personal communication,19912.1.3 Structure of the Johnny Mountain areaMegascopic folds are abundant in the Triassic succession on northwestern Johnny Mountain. The foldshave north-northwest trending subhorizontal axes, tight profiles and steep limb dips. Moderate southwestvergence is defined by northeasterly dipping axial surfaces and locally inverted southwest limbs. Twomajor fold pairs with wavelengths of 1-3 kilometres are defined by facing direction and bedding dipchanges. 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 fromnorthwesterly facing strata exposed west of Sky Creek and the Stonehouse deposit. Folds are truncated by22the flat lying largely unfolded angular unconformity at the base of the Jurassic sequence. Folding in theupper sequence is limited to broad warps of bedding attitude.A moderately to steeply northeast dipping penetrative flattening fabric (SI) forms a regionally persistentfoliation in the lower sequence. It is most strongly developed as a pervasive phyllitic flattening fabricdefined by the alignment of sericite and biotite west of Sky Creek and the Stonehouse deposit on thesouthwest 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 thesoutheast where it is most intensely developed it is subparallel to bedding. Here it locally contains astrong linear fabric defined by clast or phenocryst elongation. Elongation fabrics plunge moderately tothe 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 alater deformation resulting in a shallowly dipping to subhorizontal foliation (S2). It is best developed infine 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 spacedcleavage defined by preferred dimensional orientation of sericite. In regions of phyllitic to schistoserocks, such as on the southwest flank of Johnny Mountain, S2 forms a flat crenulation cleavage. Welldeveloped crenulation lineation here plunges shallowly to the northwest. Jurassic rocks above theunconformity contain a single foliation, which in most cases dips moderately to the northeast orsouthwest. This foliation is best exposed above the Stonehouse deposit where it is subparallel to S2 in thelower sequence.Abundant shallow dipping extension veins cut the SI and S2 fabrics on Johnny Mountain. Moderate tosteep northwest dipping and southwest dipping fault sets cut all other lithologies and structures in thearea.23North and west of Monsoon Lake in the southern portion of the Bronson stock (Figure 2.1), the earliestformed foliation (phyllitic) dips moderately southeast to south. It is pervasive, is defined by biotitealignment and is well developed in the southern portion of this unit. The foliation rotates to variablesouthwest and northeast dipping bedding subparallel orientations west of the stock in metasedimentaryrocks of the lower sequence. Elongate biotite-magnetite blebs and a parallel striation on the foliationsurfaces define a lineation in the Bronson stock that is subhorizontal to gently plunging west-southwest oreast-northeast. The significance of the foliations in this area is uncertain. Crenulation of the southwestdipping foliation in metapelites west of the Bronson stock by flat lying S2, however, indicates that thesouthwest dipping fabrics predate the S2 forming event. The changes in orientation imply folding of thefoliation 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 runsthrough Monsoon Lake.2.1.4 Metallogeny of the Stewart -Iskut River regionThe Texas Creek Plutonic suite and regional metallogenyThe age, mineralogy and texture of the Red Bluff porphyry suggest that it belongs to themetallogenetically 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 196to 185 Ma (Anderson and Bevier, 1990; Macdonald et al., 1992, and in preparation). The two largestexposed, the Texas Creek pluton (west of Stewart) and the Lehto batholith (20 kilometres east-southeastof Snip), are predominantly calc-alkaline medium grained biotite-hornblende granodiorite to quartzmonzonite 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 tomonzonite or andesite, which are texturally and mineralogically similar to the Red Bluff porphyry(Grove, 1971; Britton et al., 1990). Prismatic hornblende and common, widespread alteration of maficminerals 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 eitherequigranular hornblende granodiorite to monzodiorite (e.g. Summit Lake stock, and Inel stock) or K-feldspar 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 associatedwith 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 haveproduced greater than 25 tonnes of gold. Deposits in the area that have Pb-Pb isotopic data consistentwith 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 etal., 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 auriferoussulphide-quartz-carbonate veins (Twin zone, Scottie Gold, Stonehouse, Marc zone, Inel and SalmonRiver 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).24Snip (Twin zone)^936,000 tonnes(Rhys and Godwin, grading 28.6 ppm1993; Macdonald^Au (R, 1990)et al., 1992)Johnny Mountain(Stonehouse)(Yeager andMetcalfe, 1990;Bevier, pers.comm., 1993)Inel(Rhys and Lewis,1993; Macdonaldet al; 1992)207,058 tonnesgrading 14.1 ppmAu, 22.0 ppmAg, and 0.47%Cu (P, 1988-1990)AK zone, 57,600tonnes grading11.7 ppm Au (R,1991)Scottie Gold(Alldrick, 1991)Red Mountain(Marc zone)(Vogt et al., 1992;Schroeter et al,1992)Salmon Riverveins; Alaska Star(AUdtick, 1991)197,522 tonnesgrading 16.5 ppmAu, 16 ppm Ag(P, 1981-1985)N/A (approx. 1million ounces)N/A25Table 2.2: Examples of gold deposits in the Stewart-Iskut River region associated with known and probableEarly Jurassic (Texas Creek) intrusions.Phyllonitic southwest dippingshear vein system, calcite-quartz-sulphides-chlorite-biotiteSteep north dipping quartz-sulphide veins obliquely cutandesitic dykes; strong K-feldspar alterationAK zone: southwest dippingpyritic breccia adjacent to a K-feldspar phyric andesite dykeDiscovery zone: phylloniticsulphide, calcite, chlorite veinsand shear veins, southwest andnortheast dippingCrescent shaped epithermalquartz-sulphide veinstockworks and breccia zonesenveloping steep dippingnortheast and southwesttrending porphyry dykesRed Bluff porphyry:strongly altered K-feldspar-megacrysticplagioclase porphyriticquartz diorite to tonaliteSteep north dippingplagioclase phyricandesite dykesInel stock: quartzmonzodiorite, 500 mwest; K-feldsparmegacrystic andesiteand diorite dykes areassociated with bothzonesPremier porphyry: K-feldspar megacrystic,plagioclase porphyriticandesite dykes formingelliptical plugs andpipesDeposit name and Production (P) or^Descriptionreferences^Reserves (R) 1Host rocks^Associated intrusionSilbak Premier(Brown , 1987)4.3 million tonnesgrading 14.3 ppmAu and 304 ppmAg (13, 1919-1992)TriassicfeldspathicgreywackesequenceEarly Jurassicdacitic toandesiticvolcanicsTriassicfeldspathicgreywackeand siltstoneHazeltongroupandesitic anddaciticvolcanicsIntrusionage (Ma)2195 + 1(U-Pbzircon)194 + 3(U-Pbzircon)190 + 3Inel stock(U-Pbzircon)194.8 ± 2(U-Pbzircon)192.8 ± 2(U-Pbzircon)Between200 and160(K-Ar)195 + 2(U-Pbzircon)UndatedSummit Lake stock:coarse grainedhornblendegranodiorite; <500 mwest of veinsGoldslide intrusion:Hornblende-plagioclaseporphyritic granodioriteto dioriteTexas Creek pluton:border phase; K-feldspar megacrystichornblende granodioriteLehto batholith: K-feldspar megacrysticand equigranular quartzdiorite phasesNortheast dipping pyrrhotite -quartz-calcite veins andstockworks in shear zonesDensely disseminated tomassive and stringer pyritelenses along the brecciatedsouth dipping contact with theGoldslide intrusionPyrrhotite veins within theperiphery of, and marginal to,the Texas Creek intrusionVeins pods and irregularmasses of calcite, pyroxene,garnet, amphibole, epidote,quartz and chlorite skarn,commonly with magnetite,pyrite, chalcopyrite andsphaleritePotassic and sericite-pyritealteration zones withauriferous quartz-magnetiteveins; adjacent to a large east-southeast striking shear zoneHazeltongroupandesiticvolcanicsGoldslideintrusion andHazeltonandesiticvolcanicsTexas Creekpluton,border phase;HazeltonvolcanicsVariable;mainlycalcareousTriassicvolcanicsediments?EarlyJurassicintermediateto maficvolcanicsSnippaker Creek^N/Askarns (Websterand Ray, 1991)Khyber pass^N/A(H. Marsden, pers.comm., 1993)Northwest trending K-^Undatedfeldspar megacrysticdiorite dykes26K-feldspar megacrystic^Undateddiorite dykes; adjacentto the Strip Mountaindiorite to monzonitestockIntermediate to maficpm- syn- and post-mineral dykes,including late syn-mineral K-feldsparmegacrystic varieties195 ± 1.5(U-Pbzircon; K-feldsparmegacrysticdyke)Bald Bluff stock: K-^185 + 3feldspar megacrystic^(U -Pbhornblende phyric zircon)?andesiteTable 2.2 (continued)Sericite Ridge^N/A(H. Marsden, pers.comm., 1993)Kerr^127.5 million(Bridge and^tonnes at 0.62%Godwin, 1992)^Cu and 0.27 ppmAu (R, 1992)Sulphurets(Roach andMacdonald, 1992:Macdonald, 1993);West zone:750,000 tonnes at15.4 ppm Au and644 ppm Ag (R,1992)Hank^245,000 tonnes(Kaip and^grading 4 ppm AuMcPherson, 1993; (R, 1992)J. Gabites, pers.comm. 1993)Zoned potassic and sericite-pyrite alteration zones withauriferous quartz-magnetiteand pyrite vein stockworksQuartz, Fe-oxide, sulphideand gypsum vein stockworksin quartz-sericite-pyrite andpropylitic alteration zonesWest zone: steep-dippingnorthwest trending Au-Agquartz-sulphide shear veinsSnowfield zone: porphyrystyle pyritic propyliticalteration zonesEpithermal phyllic and argillicalteration zones withauriferous quartz-carbonatestockworks surround a weaklyaltered K-feldspar megacrysticstock?EarlyJurassicsedimentsandvolcaniclasticrocksDykes,intermediatevolcanics andsedimentsHazeltongroupintermediatevolcanics andsedimentsTriassicvolcanics andsedimentsoverlain byJurassicclastics1P=production; R= reserves; N/A=not announced2Early Jurassic galena Pb-Pb isotopic signatures have been obtained from all of the deposits except for Red Mountain (Marczone), the Snippaker Creek skarns, and Salmon River valley veins, which have not been analysed. K-feldspar from alteration atHank returned an Early Jurassic Pb-Pb signature (A. Pickering, personal communication, 1993).Mineralised structures in the Johnny Mountain areaMineralised veins, shear veins and shear zones in the Bronson Creek area are abundant in a northwesterlytrending belt from five kilometres northwest of Snip on the north side of the Iskut River, to Inel andKhyber pass, 13 kilometres to the southeast. Geologic descriptions, mineralogy, associated alteration andmetal contents for many of the deposits located on northwestern Johnny Mountain are summarised onTable 2.3; locations are shown on Figure 2.3. The structures include isolated veins and sets of tabulardilatant sulphide-quartz veins (e.g. the Stonehouse deposit, Silver Dollar showing), layered calcite-sulphide-chlorite-biotite shear veins (e.g. Snip, Sky Creek veins), and pervasive sulphide disseminationsand veins in phyllonitic shear zones (e.g. SMC, C-3, Evermore and Blue Grouse). The veins lacktextures typical of epithermal systems, such as vuggy crustiform banded or comb quartz. With the27exception 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 andnorth to northeast dipping. Southwest dipping orientations predominate, usually cutting beddingobliquely to orthogonally. Northerly and northeasterly dipping orientations generally are controlled bypre-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 arecommonly parallel to bedding. Similarly, veins of the Stonehouse deposit obliquely cut or are subparallelto north dipping plagioclase porphyritic dykes. The most continuous set of structures occurs along thenortheast side of Johnny Mountain, and includes the Twin zone, and to the southeast, the CE contact andBonanza zones (Figure 2.3). These define a set of southwest dipping veins that is continuous over a 6kilometre strike length. Mineralised structures are abundant within 1-2 kilometres west of the Red Bluffporphyry in the Snip mine workings (see Chapter 3).Mineralised structures on Johnny Mountain and Snippaker ridge display zoning of both alterationmineralogy and metal abundance. West and southwest of the Red Bluff porphyry, relatively Au-Cuenriched structures with potassic alteration envelopes occur over an area of approximately 8 squarekilometres (Figure 2.3; Table 2.5). These include the Twin zone, abundant shear veins throughout theSnip workings, Monsoon north shear veins, Sky Creek veins, Road showing, shear veins in the Bronsonskarn, Mike, O.S.C. and Boundary. They consist of laminated calcite-biotite-chlorite-quartz or massivepyrite ± pyrrhotite ± magnetite with or without envelopes of biotite and/or K-feldspar. The veins arerelatively 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 assemblagesoccupy an area of greater than 35 square kilometres east and southeast of the porphyry, and south of the28previously described region (Figure 2.3). The structures include: (i) sericitic shear zones with pervasivesulphide 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 Siparallel 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 theypredate the mineralising event.Veins of the Stonehouse deposit define a second region containing Au-Cu enriched veins with potassicalteration assemblages (Figure 2.3; Tables 2.4, 2.5). Mineralised boulders of vein material similar to theStonehouse veins occurring in till at the toe of the Johnny Mountain (McFadden zone till) indicate thatveins with similar metal contents and mineral assemblages lie to the south under the glacier.29Table 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^ Veinj or shear zone^Alterationdeposit name' mineralogy2^ mineralogy2Twin zone^Southwest dipping shear vein system with quartz-sulphide CA, QZ, CL, BI, PY, PO^Potassic: BI,veins^ KSPBonanzab^Southwest dipping sulphide rich shear veins and shear^PY, CA, QZ, PO, SP, CL, SER, CL (BI, SER)zones^ BI, GL, CPYCEa^Southwest and northeast dipping shear zone and veins;^QZ, PY, SP, SER^QZ, SERalso broad zones of pervasively disseminated sulphideswithout associated structuresSMC - 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, Fe-subordinate pyrite-calcite-chlorite-biotite veins and carbonate;veinlets with biotite + magnetite envelopesMikes^Subvertical north striking pyrite vein^ PY, CL, GL, CPYSky 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 veinletsBlue 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 dolostoneRoad Showing^Subvertical vein, strikes 130 degrees^ QZ, CA, PY, CL, BI^KSP, CAChopin^Variable, but predominantly southwest dipping sericitic^SER, QZ, CA, PY, SP^SER, PY, claysshowingse^shear zones with quartz-calcite lenses; sulphidesdisseminatedCottonwooda^Southwest dipping quartz sulphide veins and stringers^QZ, PY, SP, GL, ASPY^CLBronson 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^ TRMonsoon Lake^Southwest dipping shear veins^ CA, CL, BI, QZ, PY, CPY^BInorth11 OzaCopper QueenaoPaStairway CreekaSouthwest dipping sulphide vein^ PY^ QZ, SERNorth dipping shear zones QZ, SER, CL, PO, PY, SP^QZ, SER, CLSouthwest and northeast dipping veins and altered shear^PY, CPY, SP, GL, QZ, SER^QZ, SERzonesSubvertical to northeast dipping shear zone hosted^QZ, PY^ QZ, SERsulphide vein striking 120 degreesTable 23 (continued)Ladder Creeka^North dipping shear zone hosted breccia vein^QZ, PYEvermore^Northeast dipping to vertical shear zone^PY, SP, GL, QZ, SERBlackcata^Shallow northeast dipping sulphide vein^PO, SP, GL, CPYWindsock (Zinc^Steep north dipping veins and pervasive pyrite^PY, PO, SPtrench)a^disseminations in greywacke30SER, QZSER, QZ, PY,Fe-carbonateSER, PY, QZTwo Barrela^Pervasive sulphide disseminations and veins in greywacke PY, SPVertical sulphide veins and pervasive disseminationsstriking 110Steep north dipping quartz-sulphide dilatant veinsPO, PY, SP, GLQZ, PY, CL, CA, CPY^KSP, BI, CLTwo BitaStonehousedSubvertical northwest striking sulphide veinSubvertical north striking breccia veinAbundant southwest dipping sulphide veinsModerate northeast dipping shear zone with pervasivesulphide disseminationPY, QZ, SP, GL^KSPQZ, PY, CPY KSPPO, SP, CA^SER, PYQZ, KSP,SER, CL, CA, PY, PO, KSP, SER, CA,SP, CPY, Fe-carbonate^QZ, Fe-carbonateBoundarya0.S.C.aCE ContactaC-3SilvertipaBernieC-1Moderate northeast dipping sulphide vein^PO, QZ, SP, GLLensoidal northeast dipping quartz extension veins that^QZ, PY, SP, GL, SER, BIobliquely cut regional foliation, disseminated sulphidesalso occurNortheast dipping quartz >calcite veins containing^QZ, CA, PY, GLdisseminated sulphidesSER, 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.31Table 2.4: Metal content and metal ratios of some mineralised structures, Johnny Mountain, northwesternB.C. Showings and deposits are located in Figure 2.3. Calculated from unpublished exploration data to 1993.Showing ordeposit nameNi Au ppm Ag ppm Cu ppm Pb ppm Zn ppm (Au x 100)/Cu Zn/Cu Ag/Au (Ag x 10)/CuTwin zone 836 ddh 61.5 23.1 1028 605 2719 5.98 2.64 0.38 0.23Bonanza 17 ddh 0.4 26.1 600 7900 38500 0.06 64.2 65.25 0.43SMC 60 ddh 3.7 22.5 1319 3893 33650 0.28 25.51 6.08 0.17Cottonwood 12 ddh 0.84 25.5 324 1947 5890 0.25 18.18 30.36 0.79Stonehouse2 productiondata14.04 22.03 4700 N/A N/A 0.29 N/A 1.6 0.47CE Contact 18 ddh, tr 0.65 36.7 575 2710 57538 0.11 100.1 56.5 0.631N=number of analyses; abbreviations refer to data source for analyses: ddh=diamond drilling, tr=trenching.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^Zn/Cu Ag/Aualteration^mineralogymineralogy2 D. Yeager, personal communication, 1993. N/A = not available.North, west andsouthwest of the RedBluff porphyry, overa 8 km2 areaEast, south andsoutheast of the RedBluff, and south andwest of the zonedescribed aboveTwin zone, minor shear veinsthroughout the Snip workings,Monsoon North veins, Roadshowing, Sky Creek veins,Bronson Skarn shear veins 1SMC - Tillerman, C-3,Evermore, Bonanza, CEveins; Blue Grouse, SilverDollar, Cottonwood, Blackcat,Windsock, Silvertip, ChopinshowingsBiotite-K-feldspar +-chloriteSericite-quartz-Fe-carbonate-pyrite +chloriteLaminated calcite + biotite-chlorite-quartz or massivepyrite + quartz + pyrrhotiteveins and shear veins<5^<2Massive pyrite+sphalerite +^> 15^> 5quartz + calcite + chloriteveins, and pervasive pyrite +sphalerite dissemination insericitic shear zones•IA/ems of the Stonehouse deposit would also fit into this category based on alteration and metal ratios (see text).0 2-\,^X^I^/1^- -^/--/‘ / I^I 1, • BRONSON SKARN_ ^/ •^'MONSOON NORTH I- 4\ \ \ \ \ \\ \ \ \ \ \\^\ \ \ \SKYLINE\ \ \^\ \ \_SIOtIEHCUSE COLDN^1 `1^NBURNIE PROSP CT \1.3 KM^LTSERICITE-PYRITE ALTERATION, RUSTY WEATHERINGZONE CONTAINING Au-Cu MINERALIZEDSTRUCTURES WITH BIOTITE ±K-FELDSPAR±CHLORITE ALTERATIONZONE CONTAINING Zn-Pb MINERALIZED STRUCTURESWITH SERICITE ± CHLORITE ALTERATIONSHOWING OR DEPOSIT NAMEMINERALIZED VEIN, SHEAR VEIN OR SHEAR ZONEFAULTROADCREEKRED BLUFF PORPHYRYBRONSON STOCKLOWER SEQUENCE (TRIASSIC)UPPER SEQUENCE (EARLY JURASSIC)Kilometres//^/\ C-1LEGEND• CE%.•••• %.■•••32Figure 2.3: Showings and deposits in the northwestern Johnny Mountain area, northwestern BritishColumbia. See Figure 1.2 for location.Galena Pb-Pb isotope data from veins on Johnny MountainPb-isotope ratios from mineral deposits and showings in the Stewart-Iskut River area plot in twodistinctive clusters (Figure 2.4; Alldrick et al., 1987; Godwin et al., 1991). The clusters define twodistinct, short lived but regionally extensive metallogenic events, defined as Tertiary and Early Jurassicby Alldrick (1991) based on stratigraphic information, and K-Ar and U-Pb zircon dates of relatedalteration and intrusions.Samples from 15 different showings and deposits on northwestern Johnny Mountain and three depositswithin 10 kilometres southeast of Johnny Mountain (Inel, Khyber Pass and Sericite Ridge) have beenanalysed (Table 2.6; Godwin et al., 1991; A. Pickering, personal communication, 1992). Theseconsistently plot in either the Jurassic or the Tertiary clusters.Early Jurassic data were obtained from southwest and northeast dipping sulphide rich shear zonehosted veins and shear veins on Johnny Mountain associated with potassic alteration, as described inTable 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 veinswithin broad alteration zones defining the Inel, Khyber Pass and Sericite Ridge deposits returned similarratios (Table 2.6).Samples which plot in the Tertiary Pb-isotopic cluster from Johnny Mountain come fromsoutheast and northeast dipping lensoidal blocky to fibrous quartz-calcite ± chlorite extension veins withdisseminated galena, sphalerite and pyrite (Table 2.6). The veins have no associated alteration. They arediscontinuous (the largest at C-1 are 5-10 metres long), and they cut foliation associated with shear zonesand veins with Jurassic Pb-Pb signatures. Samples were from the Bernie and C-1 showings, andextension veins within the Knob Hill stock and Stonehouse mine workings (Johnny Mountain). All arefrom the southwestern area of Figure 2.3. One sample from a vein at Khyber Pass also returned aTertiary Pb-Pb signature, but no information is recorded about the setting of the vein or its characteristicsin The University of British Columbia LEADTABLE database.3334Extension veins with Tertiary Pb-Pb signatures cut veins of the Stonehouse veins, with Early Jurassicgalena Pb-Pb isotope signatures, corroborating the potential age relationship. The lack of spread betweenthe two clusters, close spatial relationship of some deposits with contrasting Pb signatures--as atStonehouse (above) and Big Missouri in the Stewart camp (Alldrick, 1991)--and different structural andmineralogic characteristics of each type suggest that only two discrete mineralising events occurred in thearea.Bronson SkarnA small pyroxene-garnet skarn (80 by 60 metre exposure) occurs at the southwestern end of the pod ofrecrystallised limestone north of the Snip camp adjacent to its contact with foliated biotitic Bronson stock(Figure 2.