Feasibility Study and Technical Report - Pretivm

VALLEY OF THE KINGSHigh-grade gold mineralization in VOK, the current focus of the Project, occurs in a seriesof west-northwest trending sub-vertical corridors of structurally reoriented veinstockworks and subordinate vein breccias, hosted in a folded sequence of fine grainedvolcanic siltstone and sandstone, variably silicified polylithic volcanic conglomerate, andfragmental latite volcanic rocks (Figure 7.9, Figure 7.10, and Figure 7.11). Relativelymassive latite flows are present to the immediate north and south of this mineralizationhost rock sequence.Gold is typically present as gold-rich electrum within deformed quartz, and quartzcarbonate(±adularia?) vein stockworks, veins, and subordinate vein breccias, withgrades ranging up to 41,582 ppm Au and 27,725 ppm Ag over 0.5 m. The gold occursboth as inclusions in euhedral pyrite, as well as interstitially in textural equilibrium withstrained quartz (exhibiting primary recrystallization textures), carbonate, severalgenerations of pyrite, and, to a lesser extent, vein-hosted sericite. Gold has also beenfound in the central parts of deformed quartz veins, as dendritic lattice works pervasivethroughout deformed quartz, and quartz-carbonate veins, as well as in the matrix ofhydrothermal breccias. The various textural associations of gold suggest a multi-stageparagenesis for gold mineralization.The relatively common association of gold and pyrite suggests a link in their precipitation.The presence of pyrite in a porphyry-epithermal environment indicates elevated levels ofhydrogen sulphide in the magmatic-hydrothermal fluids, which suggests gold solubilityand mobility as bisulphide complexes (Gammon and Williams-Jones 1997).Destabilization of the bisulphide complex during pyrite precipitation, brought on bychanges to one or more physicochemical parameters (e.g. change in pH, oxidation state,fluid mixing, depressurization, cooling, sulphur activity), would result in gold precipitation.Gold is also present in veins and silica-flooded host rocks that do not contain pyrite. Thisindicates that gold precipitation is not solely linked to pyrite, and that other factors havealso played a role in controlling gold mineralization during the genesis of the VOK deposit.Early pyrite precipitation during initial porphyry development is ubiquitous in the hostrocks to the VOK mineralization. This would have created a favourable environment forgold remobilization, enrichment, and transportation as bisulphide compounds above thetelescoping porphyry system, as the hydrothermal fluids would effectively be unbufferedby the already altered host rocks (Gammon and Williams-Jones 1997). An increase in theresidency time of the cooling hydrothermal fluid in previously mineralized rocks(mineralized during the earlier porphyry phase) beneath siliceous caprocks, where thegold is transported as bisulphides is considered a key factor in the generation of theelevated grades in the VOK deposit.While quartz veining and stockworks are common throughout the zone, the majority ofsignificant gold intersections are confined to corridors within a 100 m to 125 m widezone on the southern limb of the syncline. The orientation of these corridors is subparallelto the fold axis, with some of the stockworks being spatially associated withintensely silicified zones developed in and at the contacts of the polylithic conglomerate,as well as in the overlying fragmental volcanic rocks. Asymmetrical alteration is presenton either side of the intensely silicified conglomerate zones, with (the underlying rocksPretium Resources Inc. 7-20 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC