Feasibility Study and Technical Report - Pretivm

eccia, flow-layered lava domes, and subordinate interbedded limy fossiliferoussandstone.The upper Hazelton Group, which is limited to the northern and extreme eastern parts ofthe Sulphurets Mining Camp, is characterized by distinctive black carbonaceous pyriticmudstone, light and dark banded tuffaceous siltstone, and local amygdaloidal basalt ofthe Salmon River Formation. These rocks display unconformable relationships to therocks of the lower Hazelton Group. Recent re-examination of stratigraphic sectionsthrough the Hazelton Group (Gagnon et al. 2012) has suggested that the term "SalmonRiver Formation" be replaced by "Iskut River Formation". These rocks clearly delineatethe outline of the anticlinorium in the broader Sulphurets area (Figure 7.3).Rocks of the Middle to Upper Jurassic Bowser Lake Group, which are generallycharacterized by clastic basin-fill sediments including submarine fan, prodelta slope,shelf, and fan delta sedimentary assemblages, are limited to the extreme north andnortheast of the Sulphurets Mining Camp (see Figure 7.4). These rocks displayconformable to disconformable relationships to the underlying Hazelton Group rocks.Plutonic rocks are located in the western and northern parts of the Sulphurets MiningCamp, and occur as dykes, sills, and plugs, which generally intrude Stuhini Group rocks.These rocks, the so-called "Mitchell intrusions" of Kirkham and Margolis (1995), includediorite, monzodiorite, monzonite porphyry, syenite porphyry, quartz syenite porphyry,porphyritic aplitic low-silica granite, sodic albite-hornblende porphyry, and K-feldsparmegacrystic porphyry. Monzonitic, syenitic, and granitic intrusions display a close spatialand temporal relationship to the porphyry-style copper ± gold ± molybdenummineralization in the KSM deposits.A number of internally consistent uranium-lead zircon dates from pre-, syn- and postmineralintrusive phases of the Mitchell intrusions at the KSM deposits suggest thatporphyry-style mineralization was emplaced between 192 and 195 Ma. This EarlyJurassic age is consistent with a number of galena lead dates for mineralization fromthese deposits, as well as for mineralization from the Snowfield Deposit and from theWest Zone on the Property. All of these dates plot in the “Jurassic cluster” of galena leaddates defined by Alldrick, Gabites, and Godwin (1987) and Alldrick et al. (1990) for theso-called “Stewart Mining Camp.” Other regionally close mineral deposits that havesimilar age dates include Silbak-Premier and Big Missouri.7.2.2 ALTERATION AND MINERALIZATIONLarge, coalescing hydrothermal alteration haloes are developed around the intrusivecomplexes. Potassic K-feldspar alteration associated with copper and goldmineralization is widespread in the Mitchell Intrusions and adjacent Stuhini Group rocks.Propylitic and chlorite-sericite alteration is also developed around the KSM intrusions andthe Snowfield Deposit, often overprinting earlier potassic alteration at KSM. Quartzsericite-pyritealteration is widely developed in the Stuhini Group and lower HazeltonGroup rocks further to the east of the intrusions in the Sulphurets Mining Camp (Figure7.4), and also occurs as a pervasive overprint to earlier alteration in the intrusive rocks.Pretium Resources Inc. 7-6 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC