Dissolved gas composition of groundwater in the natural spa complex ''Choygan mineral waters'' (East Tuva)

The natural spa complex ^Choygan mineral waters^, a unique deposit of natural carbon dioxide mineral waters in Siberia, is located in the Eastern Sayan Mountains. There are 33 springs discharge in this area. Spring waters are mainly HCO₃-Na-Ca type. TDS varies from 300 mg/L to 2600 mg/L and temperature ranges from 7 °C (in spring 33) to 39 °C (in spring 12), pH varies from 5.9 to 8.3, and the value of the oxidation-reduction potential is from – 170 mV to 236 mV. All studied waters were divided into two groups according to their temperature and geochemical conditions: cold fresh water with oxidizing conditions and warm slightly brackish water with reductive conditions. The gas composition of the studied waters is represented by nitrogen (28-75 vol.%), carbon dioxide (6-65 vol.%), oxygen (7-19 vol.%), radon (4-948 Bq/l). The studied gases differ not only by the content but by the different sources