Hydrothermal Clays at the Surface of Thermal Anomalies as a Control Factor for Temperature and Geochemical Parameters of Geothermal Deposits (South Kamchatka)

Abstract

Studies were done at the Pauzhetskoye and the Nizhne-Koshelevsky geothermal deposits (South Kamchatka). Hydrothermal clays at the Verkhne-Pauzhetskoye thermal field and the Nizhne-Koshelevskoye thermal anomaly previously surveyed with a set of geological-geophysical and hydrogeothermal rules were sampled layer by layer by means of clearings, driving prospecting holes and manual core drilling. It is established that hydrothermal clays form a continuous stratum from 1.1 to 1.7 meters thick and from 0.015 to >> 0.125 km2 in area. Chemical characteristics and mineral composition of clays and clay-derived gray sand are given. Grades of Au, Hg, Pb, Cu and other elements are defined for each layer of clay. Variances in element distribution both along the strike and in vertical cross-section of hydrothermal clay strata are shown. The variances are due to temperature, physical-chemical and hydrogeochemical conditions of clay formation in certain sections of thermal fields. One of the basic mineral-concentrators of ore elements in hydrothermal clays apart from sulfates of Ca, Fe, Mg, Ba and Al, and (probably) alumosilicates is pyrite. The paper briefly deals with characteristics of its morphological properties, formation conditions and composition. Differences in sorption properties of pyrite in relation to physical-chemical and temperature conditions of the geothermal environment are demonstrated. Thus, the stratum of hydrothermal clays occurring at the surface of thermal anomalies is established to be of significance as a rather thick independent geological body and is not only a water-confining and heat-insulating layer but also serves as a dynamically active temperature and geochemical barrier within the structure of a geothermal deposit.