The Keystone-3 showing is located 6 kilometres north-northwest of Vernon, between Swan and Okanagan Lakes.
In this area, west of the Okanagan Valley fault zone, volcanic and sedimentary rocks of the Devonian to Triassic Harper Ranch Group are unconformably overlain by Upper Triassic to Lower Jurassic Nicola Group sedimentary and volcanic rocks. These units are intruded by Middle Jurassic granitic rocks. Patches of Eocene Penticton Group volcanic rocks overlie the older rocks.
A quartz vein within argillaceous rocks of the Nicola Group hosts lead mineralization. The vein is up to 0.9 metre thick and carries minor pyrite and galena. The vein strikes 035 degrees and dips 30 degrees east.
By 1931, an open cut and a short inclined shaft had been completed.