The main Marble Cove showing is located on a limestone knoll at about 470 metres northeast of Marble Cove on the west coast of Tzartus Island (locally known as Copper Island) in Barclay Sound. Previous work was conducted in 1917 and consisted of a 0.8 kilometre trail from the shore to the main showing, a 30.4 metre adit at the base of the limestone knoll and some trenching.

Tzartus Island is underlain by Lower Jurassic Bonanza Group volcanics and Upper Triassic Quatsino Formation limestone (Vancouver Group). These are intruded by granitic rocks of the Early to Middle Jurassic Island Plutonic Suite. Geological Survey of Canada Open File 1272 indicates an east trending regional fault just north of the showing.

The main showing is a 9 by 18 metre lens of massive, grading to disseminated, chalcopyrite and pyrite in a calcsilicate gangue grading into crystalline limestone. The showing occurs a short distance from a limestone/igneous contact.

Five other showings outcrop within 385 metres southwest of the main showing. Two consist of pyrrhotite-filled fractures within gossanous shear zones in Bonanaza volcanics. Lenses of chalcopyrite in a garnetite outcrop occur at a limestone/igneous contact 322 metres from the main showing. Two showings comprise disseminated chalcopyrite associated with pyrrhotite and magnetite in a hornblende-epidote-garnet skarn within Quatsino limestone.

A grab sample from the dump next to the adit on the main showing assayed 2.3 per cent copper, 3.43 grams per tonne silver and trace gold (Minister of Mines Annual Report 1917, page 245).