Geologic descriptionThis mineralization, at a roadside outcrop, has been known since at least the 1980s, when industry was searching for volcanogenic massive-sulfide deposits and staked claims throughout the area. The outcrop consists of about 200 feet of chlorite-quartz schist and sericite-quartz schist, possibly derived from a felsic volcanic protolith. The rocks are part of the Wales Group of Late Proterozoic and Cambrian age (Eberlein and others, 1983; Brew, 1996). Locally, the rocks contain chalcopyrite, sphalerite, and up to 20 percent pyrite; there is minor copper staining. Grab samples of the sulfide-rich layers contained up to 1 part per million (ppm) silver, 2,000 ppm copper, and 500 ppm zinc (D.J. Grybeck, unpublished analyses, 1991). A selected sample collected by Maas and others (1995) contained 2.5 percent copper, 1.0 percent zinc, 790 parts per billion gold, and 11.6 ppm silver. They conclude that while the mineralization at this outcrop is limited in extent, it suggests the potential for volcanogenic massive sulfide deposits nearby in Wales Group rocks. |
