The area is underlain mainly by diorite with discontinuous bands of Paleozoic to Mesozoic sediments and minor volcanics. A major fault, striking 060 degrees, cuts off the north striking sills and sediments with granodiorite occurring northwest of the fault. To the east, are pyroxene porphyry tuffs, with lenses of cherty sedi- ment and graphitic shale.

A sphalerite-galena quartz vein, striking 145 degrees and dip- ping 70 degrees northeast, occurs in pyroxene porphyry tuffs on the east shore of Clam Bay. A sample assayed 0.43 per cent lead and 13 grams per tonne silver. On the west shore of the bay, a grab sample of black graphitic shale assayed 0.05 per cent zinc, 0.01 per cent copper and 1.8 grams per tonne silver (Assessment Report 12777).