Feasibility Study and Technical Report - Pretivm

WEST ZONEThe West Zone gold-silver deposit (Figure 7.12 and Figure 7.13) is hosted by a northwesterlytrending band of intensely altered Lower Jurassic latitic to trachyandesiticvolcanic and subordinate sedimentary rocks, as much as 400 m to 500 m thick, whichpasses between two more competent bodies of hornblende plagioclase hornblendephyric flows (Figure 7.12). The stratified rocks dip moderately to steeply to the northeastand are intensely altered, particularly in the immediate area of the precious metalsmineralization. The West Zone appears to form the northern limb of an anticline thatlinks up with the VOK to the south (Figure 7.12), and the southern limb of a syncline thatextends further to the north.The West Zone deposit itself comprises at least 10 quartz veins and mineralized quartzstockwork ore shoots, the longest of which has a strike length of approximately 250 mand a maximum thickness of about around 6 m. Most mineralized shoots have verticalextents that are greater than their strike lengths. Veins and stockworks in this zonedisplay clear evidence of post-mineral ductile and brittle deformation. The West Zone isopen along strike to the southeast, and at depth to the northeast.In terms of hydrothermal alteration, the West Zone is marked by a central silicified zonethat passes outwards to a zone of sericite ± quartz ± carbonate and then an outer zoneof chlorite ± sericite ± carbonate. The combined thickness of the alteration zones acrossthe central part of the deposit is between 100 m and 150 m.Gold in West Zone occurs principally as electrum in quartz veins and is associated with,in decreasing order of abundance, pyrite, sphalerite, chalcopyrite, and galena. Besidesbeing found with gold in electrum, silver occurs in tetrahedrite, pyrargyrite, polybasiteand, rarely, stephanite and acanthite. Gangue mineralogy of the veins is dominated byquartz, with accessory adularia, albite, sericite, and minor carbonate and barite. Theincreased abundance of silver in West Zone may suggest that this zone was formed downtemperature gradient from the VOK (either spatially or temporally). The West Zone isopen to the southeast, northwest, and northeast (i.e. towards Gossan Hill).GOSSAN HILLThe mineralized zone known as Gossan Hill is a circular area, about 400 m in diameter,of intense quartz-sericite-pyrite alteration developed in Lower Jurassic volcanic rocks(Figure 7.7 and Figure 7.8). The visually impressive alteration zone at Gossan Hill is hostto at least 11 deformed quartz vein and quartz vein stockwork structures, most of whichtrend east-west and dip steeply to the north. Individual structures are up to 250 m longand 20 m thick.Precious metal mineralization at Gossan Hill occurs both as low-grade bulk tonnage andhigh-grade styles. The low-grade bulk tonnage style is associated with fine quartzstockworks and anhedral pyrite. Higher-grade gold mineralization at Gossan Hill differssomewhat from other zones on the Property in that it is associated with the larger quartzlenses, particularly where they contain local aggregates of pyrite, tetrahedrite, sphalerite,and galena. Electrum is observed in the bonanza grade intersections, while silver alsoPretium Resources Inc. 7-27 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC