Integrated assessment of major element geochemistry and geological setting of traditional natural mineral water sources in South Korea at the national scale

Abstract Springs and hot spas have been used worldwide since ancient times as sources of potable, medicinal and bathing water, as well as for industrial purposes. They also sustain spring-dependent ecosystems and provide water flow to downstream ecosystems. We investigated the major element hydrogeochemistry of traditional springs, CO2-rich waters, and hot spas in South Korea and their relationships with features of bedrock geology and structural settings at the national scale to classify water types and identify the major factors controlling the occurrence of each water type. Three criteria—mineral content, CO2(aq), and water temperature—defined six major water types. Alkaline mineral water in carbonate rocks and sedimentary rocks result from readily weatherable lithology. The majority of mineralized waters are CO2-rich or thermal waters with a wide range of mineral contents. Their occurrence was found to be mainly concentrated near faults and boundaries between Early to Middle Jurassic granitic rocks and other rocks of much older ages, and this pattern was quantitatively identified through proximity analysis. This finding indicates that younger granitic rocks provide sources of heat and deep-seated CO2, and faults link these deep sources to groundwater flow. Hydrolysis of primary silicate minerals, including feldspar and biotite, is likely to supply major and minor solutes including Mg2+, F-, and Fe to CO2-rich and thermal waters. F- concentration appears to be regulated by the saturation states of calcite and fluorite, and Mg2+ concentration in alkaline thermal water is driven by the formation of Mg-bearing secondary silicates. We demonstrated that natural mineral water in tectonically stable regions has diverse thermal and hydrogeochemical properties that are mainly controlled by their lithological and structural settings at the regional scale. These results may help elucidate the generation processes of natural mineral waters with high cultural and ecological values, leading to their sustainable use and protection.