Hydrothermal Clays of Kamchatka Geothermal Fields: Composition, Structure and a Role for Understanding the Evolution of Hydrothermal Systems

Argillaceous rocks and hydrothermal clays capture attention of scientists worldwide due to the fact that they possess special physical-chemical properties and widely occur in ancient and modern volcanic areas. We demonstrated at the previous stage of research (Rychagov et al., 2010: WGC-2010) that hydrothermal clays formed distinctive geological bodies in the hypergenesis zone of the large geothermal systems of South Kamchatka and were very important for study and development of geothermal deposits. They are an upper water-confining stratum and a heat shield within the system structure. It is hypothesized that the stratum of hydrothermal clays creates conditions for the formation of a complex geochemical barrier of noble, non-ferrous, ferrous and rare metals. In elaboration of this concept and for understanding the real role of hydrothermal clays in the evolution of the hydrothermal systems and in the structure of geothermal reservoirs, key sections of clay strata being formed in various physical-chemical conditions are studied in detail: near vapour-gas jets, on hot and cooling areas, on newly-formed thermal fields, beyond the thermal anomalies. Variances in composition and structure of hydrothermal clays being formed at vapour- and water-dominated geothermal deposits are shown. We suppose that the composition, structure and properties of the stratum of clays in the hypergenesis zone reflect the evolution of hydrothermal systems at a certain stage of its development and may serve as criteria for practical assessment of the temperature and fluid regimes of various-type geothermal deposits.