Mercury as an Indicator of Temperature and Geochemical Barriers in Hypergenesis Zone of Geothermal Deposits (Kamchatka)

Abstract

The distribution of mercury in all types of solid deposits presented in the hypogene zone of the South Kamchatka geothermal fields is demonstrated: in rocks, in hydrothermally-altered rocks, in soils and soil-pyroclastic cover, in bottom sediments, in hydrothermal clays, in siliceous sinter deposits and in iron sulfides (Rychagov et al., 2009). Mercury content ranges from background for the Kuril-Kamchatka region (1.0 – 1.5 х 10-6 %) in non-altered rocks to high and outstanding content (n x 10-2 %) in hydrothermal clays and monomineral pyrite samples. Data on sources, migration conditions and concentration mechanisms were acquired. Mercury is transported to the surface as a constituent of a deep-earth hydrothermal fluid and is concentrated at thermodynamic barriers in hydrothermal clays, in siliceous sinters (silica gel) and in soils with elevated salinity due to earth silicon, sulfates and other compounds precipitated from the steam-water mixture. Newly-formed iron sulfides (pyrite), silicate gel and peat, which is found on surface of deposits and derived from plants that decayed under siliceous sinters, are good sorbents of mercury in geothermal conditions under atmospheric pressure and temperatures varying from 20°С to 150°С. Mercury concentration levels in solid deposits and its distribution character in hypogene zone of geothermal deposits indicate the thickness and probable depth of occurrence of a heat source.