Nizhne-Shсhapinsky Thermal Springs (Kamchatka) as an Example of Magnesium Carbon Dioxide Waters

The article presents the results of hydrochemical studies of the Nizhne-Shchapinsky (Kipely) carbon dioxide thermal (39°C) springs in 2021. The springs are discharged within the Shchapinsky graben near the active Kizimen volcano. The results include macro- and microcomponent composition, isotopic composition of source water, some free gas components, and dissolved strontium. The results are discussed using previously published and archive data, taking into account the geological and structural position of the area, water–rock interaction, as well as using simple thermochemical calculations in order to explain the rare, but characteristic of the chemical composition of some carbon dioxide waters, predominance of magnesium over calcium. It has been shown that the waters of the Nizhne-Shchapinsky springs are formed as a result of mixing of two components: deeper and more heated sodium chloride water and more surface, less heated water with the composition Mg–Ca– $${\text{HCO}}_{3}^{ - }$$ , formed due to interaction with carbonate-bearing rocks and CO2 of igneous origin.