Feasibility Study and Technical Report - Pretivm

7.3.4 GEOCHRONOLOGYUranium-lead zircon and rhenium-osmium molybdenite age dates have been obtainedfrom suitable geologically-constrained surface and drill core samples collected fromacross the Property (Figure 7.16). Zircon age dating was conducted at the Pacific Centrefor Isotopic and Geochemical Research (PCIGR) analytical facility, Department of Earth,Ocean, and Atmospheric Sciences (EOAS), University of British Columbia. Molybdeniteage dates were determined at the Radiogenic Isotope Facility (RIF), Department of Earthand Atmospheric Sciences, University of Alberta, having been contracted through ALS inNorth Vancouver.Magmatic zircons constrain the volcano-sedimentary rock sequence underlying theProperty to between c.196 Ma and c.182 Ma, consistent with previous stratigraphicinterpretations that placed these rocks in the Lower Jurassic Lower Hazelton Group.Detrital zircons hosted in immature volcaniclastic conglomeratic rocks display a range ofTriassic and Jurassic ages (from c.222 Ma to c.183 Ma), which are interpreted asindicating uplift and erosion of an earlier island arc assemblage (Stuhini Group) duringthe formation of the Lower Jurassic Hazelton Group. This is consistent with the presenceof a regional-scale angular unconformity between rocks of the Stuhini and HazeltonGroups, as well as the volcano-sedimentary growth basin interpretation for the LowerHazelton Group rocks on the Property. Both magmatic and detrital zircons display adecrease in age towards the east across the Property, consistent with the regionalgeological way up on this (the eastern) side of the McTagg Anticlinorium.Rhenium-osmium ages obtained from two vein-hosted molybdenite samples yielded agedates of 191.5 ±0.8 Ma and 190.2 ±0.8 Ma. These samples were collected fromdrillhole SU-151 in the Bridge Zone, which is directly south of VOK, and represent theoldest mineralization age reported from the Property. Rhenium-osmium age datescollected from Pretivm’s Snowfield porphyry gold-copper deposit indicate an age of 191.1±0.8 Ma for porphyry mineralization, which is statistically indistinguishable from theBrucejack molybdenite age dates. This indicates that the hydrothermal systemresponsible for the molybdenum mineralization in the porphyritic flows in the Bridge Zonewas contemporaneous to the porphyry system developed in the upper (i.e. Snowfield)parts of the Mitchell stock. This provides further evidence for the suggested link betweenat least the onset of magmatic-hydrothermal mineralization on the Property and asubjacent porphyritic intrusive. The similarity in molybdenum/rhenium ratios in rocksfrom the Bridge Zone to those in the Snowfield Deposit further supports this contention.Uranium-lead zircon age date of 182.7 ±1.0 Ma obtained for a deformed post-mineralmafic dyke provides a minimum age for the mineralization, with the youngest altered andmineralized flows dated at c.185 Ma. These data indicate that the mineralizing systemswere relatively long-lived, spanning approximately 8 Ma, and coeval with island arcvolcanism. Sillitoe (2010) notes that porphyry deposit clusters, like those in the vicinityof the Property, may remain active for 10 Ma or longer. The Brucejack geochronologicaldata are consistent with field observations that the volcanic basin formation andmineralization were pre-tectonic with respect to the pervasive Cretaceous deformation,Pretium Resources Inc. 7-36 1291990200-REP-R0012-02Feasibility Study and Technical Report on the BrucejackProject, Stewart, BC