The Gun Metal Slate occurrence is located at a road borrow pit adjacent to the Williams Creek Main. Slate exposed there is part of the Leech River Formation. This is a package of turbiditic greywacke /argillite that has been deformed and metamorphosed to slate and schist. The Leech River Formation is bounded by the Leech River and San Juan River faults. Rock at the borrow pit varies from black through brown and some green. The slate's cleavage is not known but at the Tia occurrence (092B 150) it is fair, creating sheets 2 to 5 centimetres thick and 100 by 50 centimetres square.