Underlying rocks include conglomerate, sandstone, greywacke, argillite, arkose and interbedded tuffs of the Jurassic to Cretaceous Bowser Lake Group. To the northeast, the sediments are intruded by a stock which forms the core of the Seven Sisters Mountain. This intrusion resulted in the folding and faulting of the strata and the emplacement of quartz veins and mineralized zones.

Sphalerite and galena mineralization, and quartz and calcite gangue occur as replacement zones along sheared bedding planes in the sediments. The mineralized zone, striking north-south and dipping 30 degrees east, is traced for 500 metres and is up to 1 metre wide. A 60 centimetre sample assayed 257 grams per tonne silver, 3 per cent lead, 18 per cent zinc and trace gold (Minister of Mines Annual Report 1927). A 45 centimetre sample taken at the shaft collar assayed 492 grams per tonne silver, 0.16 per cent copper, 3.60 per cent lead, 24.80 per cent zinc and 0.17 grams per tonne gold (Property File: Lorimer, 1972). A sample of a massive pyrrhotite and pyrite vein, 800 metres to the north, assayed 14.1 grams per tonne silver, 0.32 per cent copper and trace gold (Geological Survey of Canada Memoir 212).