The showing was discovered before 1919 by the Fyfe brothers; the sunk a shallow shaft on the beach. Harbledown Island lies at the eastern margin of the Insular belt near its contact with the Coast Crystalline Belt.

The northern part of the Island is underlain by Jurassic grano- diorite of the Coast Plutonic Complex which intrudes Upper Triassic Vancouver Group rocks comprised of Karmutsen Formation volcanics, and calcareous clastics of the Parson Bay Formation.

The occurrence is reported to be in graphitic schistose rock of the Parson Bay Formation.