The Fox Pass area is underlain by flat-lying Upper Proterozoic Swannell Formation (Ingenika Group) amphibolite, quartzite, gneiss and limestone, intruded by Tertiary granites and quartz monzonites.

Pyrrhotite, pyrite, chalcopyrite, scheelite and molybdenite are contained in some of the bands of garnet gneiss and interlayered limestone, and in crosscutting quartz-carbonate veins.