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 rhyolite. 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 sediment. On the northeast side of the Seven Sisters Peaks, an aplitic dyke, cutting diorite carries molybdenite and assays 0.28 per cent molybdenum and 0.08 per cent tungsten (Assessment Report 8467). A nearby siltstone sample assayed 0.014 per cent copper (Assessment Report 8387). A hornblende rich, later phase, of the stock carries molybdenite, with values of 0.0003 per cent molybdenum and 0.10 per cent tungsten (Assessment Report 8467).