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
Iron ore foundry iron should have less than 0.15% sulfur. In the rest of the world a high sulfur cast iron can be used for making castings, but will make poor wrought iron. There are a number of remedies for sulfur contamination. The first, and the one most used in historic and prehistoric operations, is avoidance. Coal was not used in Europe (unlike China) as a fuel for smelting because it contains sulfur and therefore causes hot short iron. If an ore resulted in hot short metal, ironmasters looked for another ore. When mineral coal was first used in European blast furnaces