ABSTRACT

Fifteen water and gas samples from hot spring sites in Chungcheong Province, South Korea, were analyzed to determine their chemical compositions and noble gas isotopic ratios. These hot spring water samples were grouped into three chemical types: Ca-HCO₃, Ca(Na)-HCO₃, and Na-HCO₃. The wide range of ³He/⁴He ratios in the hot spring waters (0.036–1.76 × 10^–6; R/Ra = 0.026–1.26) indicates that the He originates from both mantle and crustal sources in the forms of ³He and ⁴He, respectively, with ⁴He dominating. The ⁴He/²⁰Ne isotopic ratios and the concentrations of mantle-derived ³He suggest that geothermal waters originate from a common, deep-seated source containing mantle-derived and crustal He that mixes with shallow groundwater containing atmospheric noble gases as it rises to the surface.