Quicksilver and antimony deposits of the Stayton district, California

Abstract

The Stayton district, which lies 13 miles northeast of Hoilister, Calif., includes parts of San Benito, Santa Clara, and Merced Counties. The district has yielded about 1,700 flasks I/ of quicksilver, mostly between 1870 and 1880, and a .few tons of antimony ore. The rocks of the district include Jurassic (?) (Franciscan formation) and Cretaceous (?) sedimentary rocks, serpentinlzed ultrabasic rocks intruded into the Franciscan rocks, Miocene (?) basaltic and andesitic extrusive rocks, and several intrusive bodies of Miocene (?) andeslte and rhyolite. The basaltic extrusive rocks were arched into a northward-trending asymmetrical anticline, then planed by erosion and capped by the andesitic rock. All the rocks are cut by northward-trending faults along which there have been several periods of movement. Veins containing stibnlte occur mainly in the basaltic rocks along faults in the central part of the' district. They are estimated to contain several tens of thousands of tons of potential ore averaging about 1^ percent of antimony. Cinnabar, the only commercially important quicksilver mineral, has three different modes of occurrence: (1) Veins and coatings in fractures in broken antimony veins, (2) coatings on otherwise unmineralized fractures in basalt, and (3) veins and replacement deposits in silica-carbonate rock derived from serpentine. . The possible reserves of the five largest mines amount to slightly more than 1,000 flasks of quicksilver. The largest mine, the Stayton, is probably capable of producing nearly 100 flasks per year for a few years. Additional prospecting along broken antimony veins immediately below the contact, between the two volcanic units might uncover additional deposits of mediumgrade quicksilver ore.