The Open Bay Epithermal occurrence is located 400 metres north of Open Bay on the eastern shore of Quadra Island. The geology of the area consists of a northwest trending belt of Upper Triassic Quatsino Formation limestone with interbedded andesitic volcanics and possibly sediments. To the west of the belt and stratigraphically below, lies the main body of the andesitic volcanics, the Upper Triassic Karmutsen Formation. To the east the belt is in contact (partly intrusive, partly faulted) with quartz diorite of the Juro-Cretaceous Coast Plutonic Complex.

The epithermal zone occurs in strongly brecciated limestone. The zone contains cinnibar, stibnite and several per cent sulphides (pyrite, marcasite and pyrrhotite). Some areas are massive, fine- grained and black with disseminated stibnite and cinnibar on fracture plane surfaces. Other areas are light coloured and very porous with disseminated cinnibar. Seven 3-metre samples across the zone averaged 1.21 per cent arsenic, 0.13 per cent antimony and 0.0016 per cent mercury (Assessment Report 16143). Some of the arsenic could be contained in the yellow to greenish-yellow goethite(?) occurring on some outcrops.