The T.B. occurrence area is mainly underlain by Lower Jurassic Bonanza Group basaltic to andesitic pyroclastics and flows with some interbedded volcano-sedimentary rocks. A small wedge of Upper Triassic Karmutsen Formation (Vancouver Group) basalt occurs to the north and appears to be in fault contact with the Bonanza Group.

The pyroclastic rocks are multicoloured tuff breccias with interbedded amygdaloidal and massive flows. There are some interbedded siliceous rocks of rhyolitic composition. The volcano-sedimentary rocks generally dip moderately south to east and consist of thin-bedded tuffaceous shale, siltstone, greywacke and minor amounts of bedded siliceous sedimentary rocks. The Bonanza sequence is intruded by dykes and small stocks ranging in composition from diabase to quartz diorite. Some recrystallization, chloritization and epidotization has taken place near these intrusions.

Elongate alteration zones related to shears and hosted in the volcanic rocks contain quartz, sericite and pyrite. These zones commonly contain relatively unaltered dykes.

The siliceous, sericitic and pyritic alteration zones are not consistently well mineralized. Some contain pods and stringers of chalcopyrite and lesser amounts of bornite. Minor magnetite is evident in drill core.