The Maid of Erin underground past producer is located at the headwaters of the Klehini River.

Skarn mineralization occurs in Devonian-Upper Triassic sediments which have been intruded by Oligocene quartz diorite stocks and gabbro and feldspar porphyry dykes and sills. The sediment package, which is locally hornfelsed, dips northeast at low to moderate angles, and contains quartzite, argillite, and carbonate units. Irregular skarn lenses with disseminated to massive sulphides and magnetite occur near the top of a marble unit. Mineralization is mainly associated with yellowish green andradite and monticellite skarn. Monticellite-carbonate, zoisite-andradite, diopside and wollastonite-calcite skarns are also mineralized. The principal sulphides are bornite, chalcocite, chalcopyrite, sphalerite and wittichenite.

Intermittent production from 1911 to 1956, totalled 3,285 tonnes mined, resulting in 1,486,599 grams per tonne silver, 342 grams per tonne gold and 243,631 kilograms copper.