Upper Jurassic to Lower Cretaceous Bowser Lake Group sediments are intruded by the Early Tertiary Seven Sisters stock which forms the core of the Seven Sisters Peaks. The sediments are mainly siltstone and greywacke with minor conglomerate, greenstone and rhyo- lite. Near the stock, they are sharply crenulated and deformed. The stock is largely granodiorite with lesser granite and diorite. Quartz feldspar porphyry is gradational with the intrusive and forms dykes cutting the sediments. Aplitic dykes extend from the intrusive into the sediments.

Molybdenite, chalcopyrite and powellite occur in fractures and quartz veins within siltstone above its contact with granodiorite and within granodiorite and quartz diorite. A sample of a vein with chalcopyrite, in the sediments, assayed 0.54 per cent copper and 11.0 grams per tonne silver. A 2 centimetre quartz vein with molybdenite and minor powellite within quartz diorite assayed 0.15 per cent molybdenum (Assessment Report 8467). A talus sample of feldspathized granodiorite with a quartz vein mineralized with molybdenite, chalco- pyrite and powellite assayed 4.21 per cent molybdenum and 8.6 grams per tonne silver (Assessment Report 8467).