The Mountain Boss deposit is notable for high values of gold and silver in quartz veins and zones of silicification, and has had a long history of exploration. It is located 2.5 kilometres northeast of Perkins Peak, and 21 kilometres southwest of the community of Kleena Kleene.
The deposit lies within Lower Cretaceous sedimentary and volcanic rocks of the Gambier overlap assemblage, 12 kilometres southwest of the Tchaikazan fault, and about 5 kilometres northeast and southeast of the margin of the Jurassic to Tertiary Coast Plutonic Complex (Geological Survey of Canada Open File 1163, Map 1713A).
The deposit is centred on the Mountain Boss adit; the Commodore adit is situated about 100 metres to the west. Rocks in the area consist of silicified black carbonaceous argillite, dark brown argillaceous sandstone or greywacke, and cherty conglomerate. The beds are gently folded but generally strike between 060 and 070 degrees, and dip southeast between 30 and 60 degrees. Faulting is generally minor, although locally there is strong fracturing. Andesitic flows and breccias conformably overlie the sedimentary rocks, and outcrop near Perkins Peak and southwards.
The silicification covers an area of about 2100 by up to 275 metres, which includes several gossans. It has been attributed to a small quartz diorite stock which occurs about 1 kilometre southeast of the deposit. Numerous small, altered felsic to intermediate dykes and sills which intrude the sedimentary rocks may be related to the stock; a quartz diorite dyke forms the footwall of the mineralization at the Commodore adit (the hanging wall is black argillite).
Sulphide mineralization is proportional to the degree of silicification in the sedimentary rocks and quartz dioritic intrusions. The main silicified, mineralized zone in the vicinity of the two adits is partly obscured by talus but is at least 260 metres long; at the Commodore adit the zone averages 15.5 metres in width. It is marked by a strong geophysical anomaly (Assessment Report 6397). The zone is characterized by large mineralized quartz veins, and 3 to 6-metre thick, strongly silicified zones (apparently referred to as quartzite in some reports). The veins and silicified zones are generally subvertical and strike north. Calcite veining is also widespread.
Sulphides occur as small lenses and aggregates disseminated throughout the rocks, as well as in concordant and discordant veins, lenses and quartz-filled fractures. Arsenopyrite predominates over pyrite; chalcopyrite occurs locally. Massive arsenopyrite occurs in lenses up to 33 centimetres thick. Gold and silver are associated with the arsenopyrite and pyrite in quartz veinlets.
There is a long history of work in the area, going back to the early century. At least 8 opencuts and 2 adits exist on the property. One mineralized section assayed 32.4 grams per tonne gold and 10.3 grams per tonne silver over 24 metres (Assessment Report 2540). A report by J. Mandy (Property File, 1948) describes an inferred tonnage of 30,000 tonnes in a single ore shoot; twenty-seven channel and chip samples from the Commodore adit were collected by Mandy, which gave a weighted uncut average for all assays of 14.0 grams per tonne gold and 5.5 grams per tonne silver across a width of 15.5 metres. A selected grab sample assayed 25.4 grams per tonne gold and 34 grams per tonne silver (Minister of Mines Annual Report 1938).
Numerous diamond drill holes have been completed (Assessment Reports 5301, 5773, 6960). Most penetrated silicified argillite or intrusives, with variable amounts of quartz veining and mineralization, and rarely calcite stringers and skarn. One core sample assayed 8.23 grams per tonne gold over 1.5 metres (Assessment Report 6960).