Phyllites, slates, quartzites, conglomerates and limestone of the Horsethief Creek Group (Proterozoic) are folded into the Purcell Anticlinorium. This major structure includes the smaller Ruth syncline which plunges 5 degrees southeasterly. Argentiferous galena, sphalerite, pyrite, arsenopyrite, minor chalcopyrite, tetrahedrite, boulangerite, scheelite and carbonates are associated with south-dipping quartz veins cutting the southwest limb of the syncline.