Metal contents of recent thermal waters, mineral precipitates and hydrothermal alteration in active geothermal fields, Kamchatka

Abstract

All the Kamchatkan recent hydrothermal systems are restricted to two volcanic zones, Central Kamchatka of Late Miocene-Pliocene age and East Kamchatka, where several active volcanoes are located. Solutions from active hydrothermal systems commonly contain elements, including As, Sb, Hg, Li, Rb, Cs, B, Cu, Pb, Zn, Ag, Au,Sr and Ba, with the first seven predominating. Higher abundances of ore elements occur in active hydrothermal systems with solutions of sodium chloride composition. Those are the Kireunskaya, Dvukhyurtochnaya and Apapelskaya systems in the Central Kamchatka volcanic zone and the Uzon hydrothermal system in the East Kamchatka volcanic zone. The hydrothermal systems are restricted to structures having very long histories of evolution and which are characterized by contrasting types of magmatism. At present chemical precipitates and altered rocks with higher abundances of As, Sb and trace amounts of Au, Ag, Cu, Ph and Zn are forming in the discharge zones of these hydrothermal systems. Large zones of alterations (alunitic quartzites * and argillites) with high abundances of As, Sb, Hg, Cu, Pb, Ga and Zr occur in the Central Kamchatka volcanic zone. Here zones of mineralization (cinnabar, realgar, stibnite, orpiment, pyrite, chalcopyrite, sphalerite, galena) occur also; native gold, native silver and gudmundite occur rarely. In the recent Uzon caldera hydrothermal system, As-Sb-Hg mineralization with bitumen and oils is now forming. The ore deposit is zoned, with the most abundant ore minerals being realgar, uzonite, alacranite, stibnite and pyrite. Cinnabar, orpiment, marcasite and native mercury occur occasionally, and single grains of native gold, native silver and native copper are present. At present a total of 7000 t As, 350 t Sb and 200 t Hg have been deposited in the mineralization zone at geochemical boundaries. The general geological and geochemical data suggest that at depth the As-Sb-Hg mineralization may change to gold-silver mineralization.