Summary:
Brucejack is a deformed, porphyry-related transitional to intermediate sulphidation epithermal high-grade gold-silver deposit. Gold is hosted in quartz-calcite vein stockworks, sheeted veins and veinlets and can also be associated with arsenian pyrite.
The Brucejack Deposit has many characteristics in common with intermediate sulphidation epithermal systems. Intermediate sulphidation epithermal systems occur in calc-alkaline andesite-dacite arcs and can be spatially associated with porphyry systems and individual volcanic centers (Sillitoe and Hedenquist 2003).
The Brucejack Project area is largely underlain by volcano-sedimentary rocks of the Lower Jurassic Hazelton Group. These rocks unconformably overlie volcanic arc sedimentary rocks of the Upper Triassic Stuhini Group along the western-most part of the Brucejack Project area. The rocks are variably altered and deformed, with zones of intense quartz-sericite-pyrite (phyllic) alteration being associated with increased deformation due to preferential strain partitioning in sericite-rich zones. A north-south trending, broadly arcuate, concave-westward 0.5 to 1.5 km wide band of variably phyllic-altered rocks and associated quartz stockwork extends over 5 km across the Brucejack Property area. The band straddles the Brucejack Fault across the Brucejack project area, shifting from the west side of the fault in the north of the Brucejack Project area to the fault’s east side further south. The phyllic alteration typically contains between two and 20% pyrite, affects rocks from the bottom to the top of the lithological sequence, and, depending on the alteration intensity, can preclude protolith recognition. More than 40 mineralization showings, associated with the alteration band, have been identified on the Brucejack Project area, highlighting the exceptional exploration potential of the area (McPherson 1994; Board et al. submitted).
Ten mineralized zones are currently recognized on the Brucejack Project area, extending from the Hanging Glacier Zone in the north to the Bridge Zone in the south. Although five of these zones have been explored in some detail (West Zone, Valley of the Kings Zone, Bridge Zone, Gossan Hill Zone, and Shore Zone), mining is focused on just the two zones for which there are current Mineral Resources and Reserves: the Valley of the Kings Zone and the West Zone.
Visible gold and silver mineralization in the Brucejack Deposit occurs as electrum and is predominately hosted in quartz-carbonate to carbonate vein and vein breccia structural corridors within broader stockwork zones (McPherson 1994; Kirkham and Margolis 1995; Tombe et al. 2018; Board et al. submitted). Additionally, lowgrade (less than 5 g/t) gold mineralization occurs sub-microscopically in vein- and wall rock-hosted arsenian pyrite (invisible gold) throughout the Valley of the Kings Zone and possibly within the West Zone as well. Electrum-bearing quartz-carbonate veins and stockwork overprint and are co-spatial with earlier porphyry-related phyllic alteration in the Brucejack Deposit.
The Valley of the Kings Zone is currently defined over 1,200 m in east-west extent, 700 m in north-south extent, and 650 m in depth. Deep drilling has indicated that the alteration, mineralization, and veining in this zone extend to a depth of at least 1,100 m. Mineralization in the Valley of the Kings Zone is open to the east, west, and at depth. Deep exploration drilling conducted under the Flow Dome Zone in 2018 was successful in confirming the presence of Valley of the Kings Zone-style mineralization from the eastern edge of the Valley of the Kings Zone to beneath the Flow Dome Zone, which lies approximately 1,000 m further east. The West Zone is currently defined over 590 m along its northwest strike, 560 m across strike, and down to 650 m in depth, is open to the northwest, southeast, and at depth to the northeast. The Valley of the Kings Zone contains higher gold and lower silver grades than the West Zone.
Precious metal mineralization is ubiquitous throughout the vein systems, however, its continuity is not correlated to any specific geologic continuity; although mineralized structural corridors can be continuous on the meters- to tens-of-meters scale, the within-vein gold and silver distribution is highly erratic. Nevertheless, the distribution and grade of precious metal mineralization within the mineralized structural corridors within the broader stockwork system is of significant economic interest.