EVOLUTION OF SULPHOSALTS IN THE MALETOYVAYAM EPITHERMAL AU-AG DEPOSIT, KAMCHATKA
N.D. Tolstykh1, M.O. Shapovalova1, V.M. Chubarov2
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences,
Novosibirsk, Russia
2Institute of Volcanology and Seismology, Far Eastern Branch of the Russian Academy of Sciences,
Petropavlovsk-Kamchatsky, Russia
Keywords: epithermal deposits, evolution of ore-forming system, enargite, luzonite, famatinite, goldfieldite, fluid acidity, oxidation potential, Kamchatka
Abstract
Sulfosalts of the tetrahedrite and enargite groups from the epithermal Maletoyvayam Au-Ag deposit were studied by optical and scanning electron microscopy. It was revealed that they crystallized from acid magmatic volcanogenic hydrothermal fluids under conditions of elevated oxygen potential. Early sulfosalts of the pre-gold ore stage of the Maletoyvayam deposit, argentotetrahedrite-(Zn,Fe) and tetrahedrite-(Zn,Fe), associated with pyrite, arsenopyrite and galena, evolved with their enrichment in Te, Se and Cu. An increase in the activity of these elements, which is a consequence of an increase in the oxidation potential of the environment, led to the crystallization of subsequent stibio-, arsenogoldfieldite and enargite group minerals, the excess of Cu in which increased with the evolution of the ore-forming system. Au-bearing minerals are paragenetically related to sulfosalts of the final stage of this evolution. The crystallization trend of sulfosalts (As → Sb → Te) from the Maletoyvayam deposit is also characteristic of other acid-sulfate type deposits, which also include Ozernovskoe and Prasolovskoe, in contrast to the opposite trend (Te → Sb → As), characteristic of sulfosalts from epithermal deposits of the adularia-sericite type of epithermal Au-Ag deposits.
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