The Cap showing is located near Quantam River, approximately 6 kilometres from Quantam Bay on Ramsay Arm.

The area is underlain by intrusive rock of the Jurassic to Cretaceous Coast Plutonic Complex. Samples from 10 kilometres west on Bute Inlet give an age of 97 to 99 million years by the potassium-argon method from biotite and hornblende (Geological Survey of Canada Open File 480).

The showing is described as "disseminated chalcopyrite, pyrite, and pyrrhotite which occur mainly within a breccia pipe. Host rocks are all plutonic, chiefly quartz monzonite and quartz diorite" (Geology, Exploration and Mining 1970, page 229).

In 2007, Archangel Resources took rock samples from the area. In 2010, AZ Copper completed a program of rock and soil sampling.