Sulphur Bank Cinnabar-Deposits.
The quicksilver-mines at Sulphur Bank, in California, furnish important evidence in relation to the genesis of oredeposits by solfataric action. At this place the basements rocks are slates and sandstones overlain by a fresh-water
formation, which in turn is capped by a flow of basalt. The sandstones and slates are broken and fissured in such a way as to form a breccia. The interspaces are filled partly with a still soft or already indurated siliceous paste, containing finely disseminated metallic sulphides, and partly with cinnabar, for the most part in coherent crusts.* In the same mine the basalt is reduced to a porous mass, and traversed by irregular fissures filled with sulphur and cinnabar.† Hot mineral water and gases carrying H2S force their way through the interstices of the deposit in the fissured sandstones and slates.
The silica-deposits are found in all stages of consolidation, from a gelatinous mass to chalcedony, and alternate with layers of metallic sulphides, consisting of cinnabar and pyrites.
Unfortunately, no information is obtainable as to the nature of the fresh-water formation lying between the Cretaceous sandstone and basalt.
According to Becker, the hot water is rich in chlorides, borax, and sodium-carbonate. The gases liberated from the water consisted of 893 parts of CO2, 2 parts of H2S, 79 parts of marsh-gas (CH4), and 25 parts of nitrogen, in 1,000 parts.
According to Dr. Melville the marcasite associated with the cinnabar contains traces of gold and copper; and in the efflorescence from the mine-workings Becker detected traces of cobalt and nickel.
In the upper zone only sulphur was found; lower down sulphur and cinnabar, and in depth cinnabar and pyrites occurring upon or within deposits of silica.
[Footnote] * J. Le Conte, “On Mineral Veins now in Progress at Steamboat Springs compared with the same at Sulphur Bank,” Am. Jour. of Science, vol. xxv, p. 404.
[Footnote] † Prof. F. Posepny, “The Genesis of Ore-deposits,” Trans. Amer. Inst. Min. Eng., vol. xxiii, p. 197.