THE BRUCEJACK HIGH GRADE AU-AG DEPOSIT, NORTHWESTERN BRITISH COLUMBIA, CANADA

The Brucejack high grade Au-Ag deposit, part of the Sulphurets Au-Ag-Cu Camp, is located 65 km north of Stewart, BC. The camp contains a well-mineralized gossanous trend, associated with the Early Jurassic Mitchell Intrusions, which runs for at least 25 km from Brucejack in the south to Treaty Creek in the north. Deformed Lower Jurassic island arc rocks of the Stikine Terrane, exposed in the core of the Cretaceous McTagg anticlinorium, host mineralization at Brucejack.

The Brucejack deposit is interpreted as being a deformed porphyry-related transitional to intermediate sulfidation Au-Ag epithermal deposit. High grade Au-Ag mineralization occurs as coarse aggregates of electrum and silver sulfosalts in steeply dipping E-W to NW-trending quartz-carbonate vein stockwork and breccia zones within a broader halo of sericite alteration and low grade stockwork mineralization. High grade gold deposition probably resulted from a com­plex series of interactions between various physicochemical parameters.

Progressive island arc development during the Late Triassic-Early Jurassic was associated with active tectonism and multiple stages of magmatism, lasting until c.180 Ma. Porphyry-style Cu-Au(-Mo) mineralization in the Sulphurets Camp is associated with calc-alkaline magmatic bodies formed between 195-191 Ma. Pervasive sericitic alteration and associated low grade stockwork mineralization at Brucejack was formed at c.191 Ma. High grade Au-Ag epithermal mineralization developed in response to N-S extension at c.183 Ma in association with a deep-seated porphyry system, and may overprint an initial phase of folding. Porphyry-driven hydrothermal systems were likely controlled, in part, by the developing volcano-sedimentary basin structural framework. Mineralized zones were affected by folding, tilting, thrusting, and shearing during Cretaceous compressional deformation.

Detailed surface and underground exploration of the Brucejack Au-Ag vein stockwork, focusing on the West Zone, was conducted during the 1980s and 1990s. The high grade Valley of the Kings Zone, discovered in 2009, has been the focus of detailed exploration by Pretium Resources Inc. since acquiring the project in late 2010. The Brucejack deposit is currently estimated to contain mineral reserves of 7.5 Moz. Au and 31 Moz. Ag.