New Almaden hydrothermal deposition of cinnabar from deep within the earth is found in a gangue of silica-carbonate rock formed locally by hydrothermal alteration of serpentine. The Guadalupe mine produced about 10% as much mercury as the New Almaden. There are several smaller mines in the mining district, but their ore production was not significant. The only significant quicksilver ore is cinnabar; other sulfides are present in small quantities. Mining, other than a single placer deposit of cinnabar, was underground. There is a high probability of undiscovered high-grade ore which could be found and exploited using modern techniques. Mining operations resulted in
Browns polymetallic ore deposit "sulfide" resources. The oxide resources consist of supergene or weathered sulfide ore where the ore mineralogy is dominated by metal oxides, hydroxides, clays and carbonates after the original sulfide mineralogy. The Browns deposit is currently being developed as a major base metals mine by Compass Resources NL, an Australian public company, in joint venture with Hunan Nonferrous Metals Corporation, a Chinese government company. The mine is due to be complete in August 2008, after suffering cost escalation and construction delays, and will produce 15,000 tonnes of copper, 4,000 tonnes of cobalt and 4,000 tonnes of nickel per annum, with a