The Cotnoir - Fors is underlain by siltstone and wacke of the Middle Proterozoic (lower) Aldridge Formation.
A showing on the east side of Pitt Creek consists of a quartz-calcite vein hosting chalcopyrite, pyrrhotite and minor arsenopyrite and sphalerite. About 90 metres to the south, a quartz vein occurs hosting galena and sphalerite.