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
Carbonate-hosted lead-zinc ore deposits brines (10-30 wt.% NaCl equivalent) with pH's of 4.5-5 (buffered by host carbonates). This hydrothermal fluid may or may not carry the required sulfur to form sulfide minerals. Mobile hydrocarbons may have played a role in delivering reduced sulfur to certain MVT systems, while methane and other organic matter can potentially reduce sulfate carried by an acidic fluid. The ore fluid is suspected to be derived from clastic red bed sequences (potential metal source) that contain evaporites (potential sulfur source). Two potential transportation mechanisms for the metal-bearing ore fluid have been proposed. The first involves compaction of sediments in basins