Hydrogeochemistry of thermal waters of the Baikal Rift, South-Eastern Tuva, Russia

The spa resort of the Ush-Beldir is located in the south-eastern part of the Tuva region, Russia in the zone of influence of the Baikal rift. The Ush-Beldir territory has about 10 thermal springs and 4 exploration wells used for treatment and prevention of diseases. Hydrological and hydrochemical features of the thermal groundwaters are considered. The studied waters are thermal (T=50–83°C), alkaline (pH=9.3–10), low mineralized (TDS<370 mg/L) Na–НСО3 waters with a high content of SiO2 (up to 125 mg/L) and F (up to 14 mg/L). The correlation of F- with SiO2, НСО3–, Cl-, Na+ as well as the calculation of saturation indices of minerals, allows one plausible solute source for these thermal waters, viz. the dissolution of rock-forming aluminosilicates, most likely plagioclase, gabbro and/or amphiboles in shales.