Feasibility Study and Technical Report - Pretivm

7.2 LOCAL GEOLOGY - SULPHURETS MINING CAMPThe Sulphurets Mining Camp, which includes the Snowfield and Brucejack Properties, islocated on the eastern limb of the broad McTagg anticlinorium, a major north-trendingmid-Cretaceous structural culmination in the western SFB (Figure 7.3). Sedimentary andvolcanic rocks of the Upper Triassic Stuhini Group form the core of the anticlinorium, andare successively replaced outwards towards the west, north, and east of the core byprogressively younger rocks of the Lower to Middle Jurassic volcanic and lessersedimentary rocks of the Hazelton Group followed by sedimentary rocks of the BowserLake Group.Details of the local geology of the Sulphurets Mining Camp in northwestern BC presentedin this section are partly drawn from existing literature, including Kirkham (1963), Grove(1986), Britton and Alldrick (1988), Alldrick and Britton (1988, 1991), Anderson (1989),Anderson and Thorkelson (1990), Kirkham (1991, 1992), Henderson et al. (1992),Roach and MacDonald (1992), Margolis (1993), Davies et al. (1994), Kirkham andMargolis (1995), Childe (1996), Macdonald et al. (1996), Lewis et al. (2001), Evenchicket al. (2007), Armstrong et al. (2011), Gagnon et al. (2012), and the Seabridge Gold Inc.(Seabridge Gold) website (accessed September 2012), and from work conducted byPretivm’s geologists.7.2.1 STRATIGRAPHIC SETTING AND MAJOR MINERAL DEPOSITSThe Stuhini Group, which generally underlies the western and northern parts of theSulphurets Mining Camp (Figure 7.4), is characterized by fine-grained and well-stratifiedsedimentary rocks and subordinate mafic volcanic arc-related rocks. The sedimentarypackage includes dark grey turbiditic siltstone, minor interbedded micritic limestone, andthick sequences of immature conglomerate and sedimentary breccia. Mafic volcanicrocks in this unit include alkalic pyroxene- and hornblende-phyric massive and pillowedbasaltic flows, flow breccia, and tuff.The central and eastern parts of the Sulphurets Mining Camp are largely underlain bysubaqueous to locally sub-aerial, arc-related volcanic and subordinate sedimentary rocksof the lower Hazelton Group, which unconformably overlie the Stuhini Group. Thelowermost unit of the lower Hazelton Group, the Lower Jurassic Jack Formation, ischaracterized by polylithic (granitoid and volcanic) pebble to boulder conglomerate andlimy fossiliferous sandstone and siltstone. The Jack Formation appears to beconformably overlain by the volcanic rocks of the lower Hazelton Group, which generallyconsist of thick massive plagioclase (± hornblende, K-feldspar, and pyroxene)-phyricandesitic and dacitic flows, breccias, and related predominantly pyroclastic fragmentalrocks, with subordinate mafic and felsic rocks and minor siltstone and mudstone layersof the Unuk River Formation. These rocks are overlain by well-bedded green, maroon,and grey andesitic to dacitic pyroclastic and epiclastic rocks, mafic flows, and minorcarbonaceous mudstone, chert and limestone of the Betty Creek Formation, which are inturn disconformably overlain by the Mount Dilworth Formation. The Mount DilworthFormation is characterized by dacitic and rhyolitic tuff, welded ash-flow tuff, volcanicPretium Resources Inc. 7-5 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC