The area is underlain by Upper Triassic Karmutsen Formation volcanic rocks of the Vancouver Group. These are interbedded with, and overlain to the northeast by a northwest trending belt of Quatsino Formation limestone (Vancouver Group) known historically as the "lime-belt". The Vancouver Group rocks are in fault and/or intrusive contact to the northeast with intrusive rocks of the Juro-Cretaceous Coast Plutonic Complex.

The Trilby skarn deposit occurs within a metamorphic zone of grey to green andesitic rock near its contact with granitic intrusive rocks and about 15 metres from a body of limestone. A narrow andesite dyke occurs in the orebody and roughly follows the strike of the ore. The deposit consists of pyrrhotite with associated chalcopyrite occurring in a gangue of quartz, garnetite, epidote and hornblende.

The strike of the orebody is nearly west. The dip varies from 30 degrees south to almost vertical. The orebody is exposed along strike by a series of open cuts for a distance of 90 metres. A 6 metre deep incline shaft sunk on the deposit exposes a 2.4 metre maximum ore thickness.

A grab sample from the dump at the mouth of the shaft assayed 3.43 grams per tonne gold, 89.14 grams per tonne silver and 6.2 per cent copper (Minister of Mines Annual Report 1916).