The Santa Maria Island showings are located at the southern tip of the island.

The island and adjacent shore are underlain by sedimentary rocks of the Upper Triassic Quatsino Formation (Vancouver Group) and volcanic rocks of the Lower Jurassic Bonanza Group. These have been intruded by granitic rocks of the Early to Middle Jurassic Island Plutonic Suite.

At the south end of Santa Maria Island, just at the high water mark, a shaft was sunk on a small exposure of magnetite containing sulphides. Iron ore was extracted, from a skarn developed at the contact of limestone and granodiorite, from here many years ago (Minister of Mines Annual Report 1896, Bulletin 1, page 4).

More recently documented mineralization consists of massive to disseminated pyrite with pyrrhotite, chalcopyrite, and tetrahedrite. The mineralization occurs in a series of 3 or 4 subparallel, 1 to 4 metre bands which trend 47 to 58 degrees and dip 45 to 32 degrees south. The bands are hosted in Bonanza volcanics or fine grained diorite. A chip sample (#18902) across 0.8 metres of massive sulphide from this area assayed 0.51 per cent copper (Assessment Report 18773).