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Russian Geology and Geophysics

2009 year, number 8

The Asachinskoe epithermal Au-Ag deposit in southern Kamchatka: physicochemical conditions of formation

A.A. Borovikov, A.S. Lapukhov, A.S. Borisenko, Yu.V. Seryotkin
Sobolev Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: fluid inclusions; Au-Ag deposits; ore formation
Pages: 685-694

Abstract

The Asachinskoe epithermal Au-Ag deposit (southern Kamchatka) is referred to as low-sulfidation in quartz-adularia-sericite in Corbett's classification. Research into fluid inclusions of its minerals gave an insight into the PT -conditions of formation and gas composition of ore-forming fluids as well as the vertical variations in these parameters to a depth of more than 200 m within a 2 km long horizontal site of the deposit ore zone. It is shown that mineral assemblages formed at 320 to <100 °C. Ore-forming hydrothermal solutions were poor in salts (3-9.2 wt.% NaCl equiv.), with NaCl being the main component. Mineral assemblages with high contents of Au crystallized at 250-175 °C. Ore-free quartz-carbonate veins formed at 80-120 °C. High-temperature (300-320 °C) veins also lack ores. Rich gold ores were deposited in the environments where ore-bearing fluids boiled, mixing with meteoric waters.