The area is underlain by rocks of the Lower-Middle Jurassic Unuk River Formation, Hazelton Group. These rocks consist of sandstone, wackes and shale overlain by lapilli tuff of andesitic composition. The Brucejack fault and associated splay faults cut the country rock in a north to northwest direction. North of Brucejack Lake the fault system is bounded on the east by rocks of the Betty Creek Formation, Hazelton Group. A variety of Jurassic hornblende syenites and alkali feldspar syenites occur in the area.

The Gossan Hill zone consists of an epithermal-type quartz vein stockwork occurring within silicified and sericitized lapilli tuffs. The zone was originally defined as being 150 metres north of the West zone (104B 193) but by the 2012 was defined as a circular area, about 400 metres in diameter centred about 500 metres west of Brucejack Lake. Recent (2012) diagrams by Pretium Resources show its outline as encompassing the area from Sulphurets Creek north to, and now including the plotted location of MINFILE occurrence Big Sleep (104B 386). Assessment Report 32074 states that the "visually impressive alteration zone at Gossan Hill is host to at least eleven quartz vein and quartz vein stockwork structures, most of which trend east-west and dip steeply to the north. Individual structures are up to 250 metres long and 20 metres thick."

These zones include the Marie Gold, PM-1 to PM-6, Tommyknocker and Silver Streak. Veins host pyrite, sphalerite, electrum and galena. Pyrite also occurs as fine disseminations and fracture fillings. One diamond-drill hole intersected a 1.2 metre section that assayed 374.75 grams per tonne gold and 408.00 grams per tonne silver (George Cross News Letter No.192, 1985).

The Marie Gold zone was mapped in detail in 1993. It is exposed for approximately 80 metres strike length and consists of a number of east trending, en echelon quartz vein lenses hosted within sericite-pyrite +/- quartz altered volcanic rocks. Mineralization within the quartz lenses consists of pyrite, tetrahedrite, polybasite, sphalerite, galena and rare electrum. Four grab samples collected from the zone yielded between 14.9 and 111.7 grams per tonne gold and 920 and 1693 grams per tonne silver (Assessment Report 24610).

The 1994 exploration program on the Bruceside Project consisted of detailed mapping and sampling in the vicinity of the Gossan Hill Zone, and 735 1.6 metres of diamond drilling, primarily on the West, R8, Shore and Gossan Hill Zones. One of the Gossan Hill drill holes, S94-449 (462.3m), is being filed for assessment purposes. Drillhole S94-447 was designed to test the Gossan Hill Zones (PM-I, PM-2, PM-5) and the Tommyknocker Zone at considerably deeper depths below previous drilling in the vicinity (Assessment Report 23609).

Drilling beneath the Gossan Hill area failed to intersect material that would indicate the presence of a large, low grade gold deposit within the quartz-sericite-pyrite alteration zone. While drilling in this area did prove the PM structures are continuous to depths of up to 200 metres below surface, these structures showed no appreciable increase in precious metal content (Assessment Report 24610).

The Tommyknocker zone remains open along strike to the west and downdip and contains complicated vein geometry that will need to be examined in considerable detail before additional drilling or underground exploration can take place. Drill results (1994) indicate the zone decreases in width towards the west, and dips subvertically at depth. The zone is poorly constrained, typically consisting of a weak stockwork as opposed to a well-defined vein.

Pre 2011, historical work undertaken at Gossan Hill has included rock-chip sampling, hand trenching and limited diamond drilling, with a few +400 metres deep drillholes concentrated in the central part of the mineralized area (Assessment Report 32074). Precious metal mineralization at the Gossan Hill Zone occurs in two styles. As is the case elsewhere on the Brucejack property, a bulk tonnage style of mineralization is associated with anhedral pyrite and a fine quartz stockwork. Higher-grade gold mineralization at Gossan Hill differs somewhat from other zones on the property in that it is associated with the larger quartz lenses, particularly where they contain local aggregates of pyrite, tetrahedrite, sphalerite, and galena. Electrum is observed in the bonanza grade intersections, while silver also occurs in tetrahedrite, pyragyrite, and polybasite.

Drilling in 2011 was focused on defining structural controls to mineralization within the larger lower grade halo. The program was very successful, with numerous holes intersecting very high-grade gold mineralization; including 372.3 grams per tonne gold across 7.1 m in hole SU-136, 16.4 grams per tonne gold Across 7.9 metre in hole SU-147, 168.4 grams per tonne gold over 1.5 m in hole SU-201, and 44.2 grams per tonne gold over 14.0 metre in hole SU-207 (Technical Report for Pretium Resources Inc, January 12, 2012).

Refer to West (104B 193) for details of related mineralization and work history.