Shelter Inlet is underlain by high grade metamorphic rocks of the Upper Paleozoic to Lower Mesozoic West Coast Complex. These metamorphic rocks are intruded by granodiorite of the Jurassic Island Plutonic Suite.
The High Boy occurrence is reported to consist of three parallel quartz-veins exposed for 15 metres along a bluff (Geological Survey of Canada, Memoir 204, page 25). The veins strike north and dip 58 degrees west. The upper most vein is 5 to 8 centimetres wide and shows ribboned, rusty quartz. The two lower veins are separated by 45 centimetres of chloritized granodiorite and have widths of 10 and 15 centimetres, respectively.
The principal mineral is pyrite. A sample is reported to have assayed $6.50 in gold (Geological Survey of Canada, Memoir 204, page 25), equivalent to 6.6 grams per tonne.