Follow-up in 1974 led to discovery of a hillside secondary iron oxide gossan containing highly anomalous lead, zinc and silver.

Core drilling to test the unoxidized bedrock under the gossan was initiated in 1975 and penetrated a 82 feet (25 m) thick lens of massive sulfide mineralisation.

An extensive exploration drilling program began after the discovery hole and positive results led to full-scale development beginning in 1987 and production of metal concentrates in 1989.

Concentrates are trucked 8 miles (13 km) from the mine/mill complex to a port on Hawk Inlet; from there they are shipped worldwide for smelting and refining.

The deposit is hosted in metamorphosed, multiply deformed, and hydrothermally-altered mainly marine Triassic sediments and mafic volcanic rocks within the exotic Alexander terrane.

Mineralization occurs as discontinuous vein or blanket-like bodies of laminated or replacement-textured massive sulfides; roughly along a structural lithology contact in the sediments.