Ore Elements in the Structure of Geothermal Reservoir: Distribution, Geochemistry and Mineralogy, Probable Sources

Abstract

Au, Ag, Hg, Pb, Zn, As, and other ore elements have their peculiarities of distribution and behavior in the frameworks of geothermal reservoir of hydrothermal systems of island arcs. It has been distinguished, that as a hole, concentration of ore and alkaline elements is much higher in hydrothermal altered rocks, than in fresh volcanics or rocks located farther away from reservoir. At the same time, metasomatites of regressive stage contain one order of magnitude more of each of these elements in comparison with metasomatites of progressive stage hydrothermal system development. This means that with time rocks of geothermal reservoir accumulate alkaline and ore elements. The latter are in minerals themselves and in native form, in composition of sulphides as isomorphic admixtures. They make intermetallic compounds, solid solutions and melts which in composition of gaseous-liquid high-temperature fluid can be transported within the zones of tectonic disturbances. In particular, geochemical barriers for the raw of ore alkaline and other elements are formed above and around thick (up to several hundred metres) zones of hydrotherms boiling up at depths up to 1500-2000 m from the day surface, Higher concentrations of Au, Ag, B, K, Li, Rb, ect. Have been recognized here in metasomatities of quartz-adularia or quartz-adularia-epidot-prennit-wairakite composition. Areas with higher concentration of the above elements have been distinguidhed in the zones ascending hydrothermal flows in uplifted blocks. A geological-geochemicla model for the development of the high temperature ore-bearing hydrothermal-magmatic system of Baranskiy Volcano (Iturup Island, the Great Kurile series) is suggested on the basis of the study of the present-day hydrothermal-magmatic systems of the Kuril-Kamchatka insular arc, being on different stages of development (progressive, extreme and retrogressive).