Zeolite Mineralization in Mudstones of the East Pauzhetka Thermal Field As an Indicator of the Discharge of Alkaline Fluids in a Present-Day Hydrothermal System, Southern Kamchatka

The argillized deposits of the East Pauzhetka thermal field in the Pauzhetka hydrothermal system were found to contain a zone of intensive zeolitization which consists of medium to high silica calcium zeolite varieties, namely, laumontite, mordenite, heulandite-Ca, and stilbite-Ca. Of all these, stilbite-Ca has the highest abundance. The zeolites can be identified well enough based both on the relationship between Si and Al, which are part of the zeolite framework, and on the concentrations of non-framework cations (Ca, Mg, Na, K, Sr, and Ba). Zeolites are mostly formed in the lower horizons of hydrothermal clays and in the underlying argillized andesites, as deep alkaline chloride-sodium hydrothermal fluids are discharged and are mixed with condensates of acid (up to neutral) vapor. The resulting sequence of zeolite generation in the shallow zone where alkaline solutions are discharged reflects, to a certain degree, a change of zeolite facies in the deeper horizons of the system: from medium-silica laumontite to high silica stilbite-Ca. We have thereby a general inference as to the regressive directivity of hydrothermal metamorphic processes in the Pauzhetka system structure, from medium-temperature propylites generated during the paleo phase to the present-day low-temperature mudstones.