The area is underlain by northwest trending and northeast dipping Upper Triassic Karmutsen Formation (Vancouver Group) massive and pillowed basalt flows and breccias, amygdaloidal and porphyritic basalt, and limestone.

The Stromberg showing occurs in a sequence of pillow basalt breccias and amygdaloidal and porphyritic basalt flows of the Karmutsen Formation with areas of massive limestone. Northeast trending shear zones cut the lithologies with diorite dykes often paralleling the shears and locally occurring in them.

A northwest trending mineralized zone, apparently stratigraphi- cally controlled, has been investigated by shallow shafts, numerous open cuts and trenches. Exposed in the zone are pyrite, bornite, minor chalcopyrite, sphalerite and trace galena mineralization in amygdules and fracture-fillings in basalt. Malachite is occasionally present as thin coatings on mineralized outcrops. Calcite, chlorite and epidote also occur as amygdule fillings. Minor bornite and chalcopyrite area also evident in shear zones in highly chloritized basalt. Quartz-calcite veins locally occur in the shear zones and host minor bornite mineralization.

Grab samples from old open cuts and shafts assayed up to 8.7 per cent copper and 34.28 grams per tonne silver (Minister of Mines Annual Report 1925).