In the area north of Tatsamenie Lake, pre-Upper Triassic tuffs, phyllites, siltstones and limestones are underlain by Permian limestones of the Stikinia Terrane. These rocks are intruded by plutonic rocks associated with three separate igneous events. These consist of foliated diorite of Triassic Age, unfoliated diorite of Jurassic Age and feldspar porphyry basaltic dykes of the Sloko Group of Cretaceous to Tertiary Age.

The volcanics and sediments are pervasively silicified and pyritized. Chalcocite occurs in the rocks.