The Larcom Island showing is located on the north end of Larcom Island in the Hastings Arm of Observatory Inlet. Silica was reported to have been shipped from here to the copper smelter at Anyox (103P 021) for flux.

The region is underlain by a roof pendant, consisting of volcanic and sedimentary rocks, within the Eocene Coast Plutonic Complex. These pendant rocks have been correlated with Middle-Upper Jurassic Hazelton Group rocks and overlying upper Middle to Upper Jurassic Bowser Lake Group sedimentary rocks (Geological Survey of Canada Open File 3453). The Hazelton rocks consist of variably chloritized pillow and massive basalt with minor mafic tuffs. The overlying Bowser Lake sediments consist of siltstone and sandstone with minor chert and limestone. These rocks have been regionally metamorphosed to greenschist grade and have been subjected to a north-northeast trending phase and a later east-northeast trending phase of folding.

The Larcom Island occurrence consists of a pyritic, silicified and shattered dike cutting argillite. The dike, exposed in a 9.0 metre long trench on the beach, contains veinlets and lenses of white and blue quartz. The quartz itself contains some pyrite, sphalerite and galena. A sample assayed trace gold and 37.7 grams per tonne silver (Minister of Mines Annual Report 1947).

Seven thousand tonnes were reported to have been removed from this property and shipped to the Anyox copper smelter for silica flux (Minister of Mines Annual Report 1947).