Major and trace element geochemistry of CO2-rich groundwater in the volcanic aquifer system of the Eastern Sikhote-Alin (Russia)

Abstract

The largest CO2-rich mineral water resource in the Sikhote-Alin ridge of Eastern Russia at Gornovodnoe village was studied. The high-pCO2 groundwaters are cold (5.8–10 °C) with pH 5.9–6.5, TDS varied from 1.2 to 2.7 g/l and belong to Ca–Mg (Ca–Na)–HCO3 type. New data on geology, mineralogy, hydrogeology and hydrogeochemistry, in conjunction with isotope data of water and gas phases, have provided a much better understanding of the origin of this distinctive groundwater. It was found that this water is of meteoric origin, but its unusual chemical composition is controlled by interactions of CO2-rich groundwater and the aquifer materials. The dissolved CO2 gas makes the water slightly acidic (at about pH 6.2) which increased the leaching of many trace elements from host volcanic rocks typically considered immobile at these pH values. 3He/4He ratios and δ13C indicate that mantle degassing is important as a source of deep exogenic fluids. The cold CO2-rich groundwater of the Eastern Sikhote-Alin ridge is the result of interactions between fresh groundwater of meteoric origin, mantle gases and the host volcanic rocks. It thus highlights connectivity between deep and shallow fluids along with deep fractures related to ancient terrane boundaries.