The Tusulko River mineral occurrence is located within inter- mediate to felsic volcanic rocks. These rocks probably represent eroded remnants of mid to late Tertiary stratavolcanoes developed over Mesozoic rocks of both the Coast Plutonic Complex and the Intermontane Belt. The Tertiary volcanics have been tilted and faulted, exposing older, underlying rocks in places. Late Tertiary Miocene plateau basalts have obscured much of the earlier Tertiary volcanic stratigraphy. The Geological Survey of Canada has placed these earlier volcanic rocks in the Oligocene to Miocene Endako Group. The lithologies comprise andesite, dacite, tuff and breccia.

The mineral occurrence of the Tusulko River area is shown on GSC Map 1202A as consisting of copper, silver and gold. It occurs adjacent to a north-striking fault cutting the volcanic rocks but the relationship of the fault with the mineralization is not known. The constituent minerals of the showing have not been reported.