The western half of Quadra Island is underlain primarily by andesitic volcanic rocks of the Upper Triassic Karmutsen Formation which are overlain and bounded on the east by a northwest trending belt of Upper Triassic Quatsino Formation limestone, both of the Vancouver Group.

Heriot Island is underlain by amygdaloidal andesitic flows of the Upper Triassic Karmutsen Formation. The occurrence is comprised of native copper grains in amygdaloidal andesite, the amygdules of which are otherwise filled with calcite, quartz and epidote.