Isotope–Hydrogeochemical Features of the Thermomineral Waters of the Issyk-Kul Artesian Basin

This article presents new data on the chemical composition, content, and distribution patterns of stable oxygen and hydrogen isotopes in the natural waters of the Issyk-Kul intermountain artesian basin. The complex geological and hydrogeological conditions of the study region have led to a variety of thermomineral waters in terms of chemical composition, TDS, and temperature. The results have shown that the studied waters of the region have an initial meteoric origin with a clearly defined high-altitude effect and the fractionation of isotopes is determined by secondary superimposed processes. The geological and tectonic structure of the study region contributes to the formation of mineral waters of various chemical compositions: carbon dioxide waters with insignificant TDS are formed within rocks and open cracks; carbon dioxide–nitrogen or nitrogen–methane waters with a TDS of more than 2.0 g/L (sometimes significantly higher, up to 35.0 g/L) are formed when the thickness of the sedimentary cover is significant. Ion-salt geothermometers were used to estimate the deep temperatures of the formation of thermomineral waters, which showed a wide range of temperature values (from 21.4 to 144.8°C), which indicates different conditions for the formation of the studied waters.