Hydrochemistry and noble gas geochemistry of geothermal waters in Chungcheong Province, South Korea

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.