Quartz-Tourmaline Veins in the Northern Sierra Nevada Area

Summer 1991

Tourmaline-bearing quartz veins and replacement deposits, commonly copper- and gold-bearing, are found in unusual concentration in northwestern Nevada and adjacent northeastern California in Triassic and Jurassic arc rocks and in the Cretaceous plutons that intrude them. Mines and prospects that exploit the tourmaline-bearing deposits are found in a zone approximately 70 miles long and 50 miles wide. Many copper-bearing quartz- tourmaline veins contain appreciable gold ñ silver, but early miners were commonly discouraged by the difficult-to-treat sulfide ores encountered below the free-milling gold ore in the oxidized zone. Tourmaline-bearing aplite/pegmatite dikes, associated with Late Cretaceous plutons are also relatively common in the area, suggesting a genetic relationship between plutons and mineralization. A group of copper-bearing veins in the Genesee mining district near Taylorsville, California is probably also a related mineralization type. Tourmaline is known to occur in only a few of these mines, but there has been little recent work on them, and more widespread tourmaline may not have been recognized by early workers.

The quartz-tourmaline veins are usually mineralogically simple. In addition to black tourmaline (probably schorlite) and milky to clear quartz, the veins contain pyrite + bornite and/or chalcopyrite, ñ magnetite, and very rarely chalcocite, pyrrhotite, molybdenite, arseno-pyrite, tetrahedrite, sphalerite, and galena. Sulfide-mineral content may be 10% or more in major veins, and locally massive sulfide bodies occur, but minor prospects and occurrences often have very low sulfide-mineral contents. Epidote occurs in veins and is common as concentrations in the wall rock. Garnet is quite rare, occurring only in clearly skarn-related mineralized areas, often adjacent to plutons. There are sericitic alteration envelopes around some veins; chlorite is concentrated in the walls at others. The minor prospects and occurrences are often rather obscure, and few have been described in the literature, or when described, tourmaline was not recognized or reported.