The Big Creek polymetallic vein showing, 4.5 kilometres north- west of Elbow Mountain, is within andesitic tuff and breccia and minor epiclastic rocks of the informally named Upper Cretaceous Powell Creek Formation. These rocks are crosscut by a stock of Late Cretaceous to Early Tertiary hornblende feldspar porphyry and feldspar porphyry. A zone of pervasive quartz-sericite-pyrite and carbonate-sericite-quartz-pyrite alteration exposed over 700 by 200 metres contains veins, stockwork and disseminations of pyrite, sphalerite, arsenopyrite, and chalcopyrite. These polymetallic veins do not exceed one centimetre in thickness.