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
Sulphur Bank Mine tin ore. Oxland believed the cinnabar ore at Sulphur Bank had been formed from hot springs. His thesis stated that hot springs brought metals in a dissolved state from igneous rock deep in the earth through a thick block of metamorphised ancient seabed to form cinnabar ore near the surface of the mine. Oxland also believed the cinnabar deposit was continually forming. Becker came to agree with the Oxland thesis. There were a number of mysteries about the Sulphur Bank that Becker attempted to solve. Among them was how sulfur had been delivered to the surface of the mine and