Geochemical and Isotopic Compositions and Geothermometry of Thermal Waters in the Magumsan Area, South Korea

Abstract

The Magumsan thermal waters of the southeastern Korean Peninsula are pumped out of six deep wells (average depth, 300 m) at temperatures of 30.8–49 °C. The thermal waters are chemically classified into two groups: NaHCO3 type (<31 °C) and NaCl (HCO3, SO4) type (>40 °C), both of which have chemical compositions that are distinct from local groundwater (Ca–HCO3 type). δ18O and δD values suggest that the thermal waters originate from meteoric water and they are isotopically fractionated by silicate hydration or H2S exchange. δ34S values (+7.0 to +15%) of dissolved sulfate in the thermal waters reflect enrichment in 34S through kinetically controlled oxidation of magmatic pyrite in the thermal aquifer and mixing with paleo-seawater. On the 3He/4He vs. 4He/20Ne diagram, the thermal waters plot along a single air mixing line of dominant crustal He, which indicates that the heat source for the thermal waters is non-volcanogenic thermal energy that is generated from the decay of radioactive elements in crustal rocks. Chalcedony geothermometry and thermodynamic equilibrium calculations using the PHREEQC program indicate a reservoir temperature for the immature thermal waters of 54–86 °C and 55–83 °C, respectively.

Analysis of Natural Organic Matter in Water from Cold and Hot Mineral Springs in South Korea Using 15T FT-ICR-MS

“…27 In general, hot mineral springs are closely related to magma or volcanic activity, but the hot mineral springs in South Korea are non-volcanic hot mineral springs in which groundwater is heated by a geothermal gradient (Jeong et al, 2019). 28 …”

“…In South Korea, hot mineral spring water is groundwater with a temperature of 25 °C or higher (Lee, 2007). 27 In general, hot mineral springs are closely related to magma or volcanic activity, but the hot mineral springs in South Korea are non-volcanic hot mineral springs in which groundwater is heated by a geothermal gradient (Jeong et al, 2019). 28 Figure 1 shows the sampling points and the characteristics (type) of the water at each point.…”

“…27 In general, hot mineral springs are closely related to magma or volcanic activity, but the hot mineral springs in South Korea are non-volcanic hot mineral springs in which groundwater is heated by a geothermal gradient (Jeong et al, 2019). 28 Figure 1 shows the sampling points and the characteristics (type) of the water at each point. Hot mineral spring waters were collected from boreholes in nine hot springs in South Korea from August 2017 to March 2017.…”

Estimation of the Deep Geothermal Reservoir Temperature of the Thermal Waters of the Active Continental Margin (Okhotsk Sea Coast, Far East of Asia)

“…Geothermal systems in non-volcanic continental margins are mostly of crustal origin and are associated with the decay of radioactive elements (e.g., 238U, 232Th, 40K), unlikely to have magmatic heat sources [10,11]. Another heat source is that developed along with interfaces between lithospheric sectors, where friction and viscous shearing forces along boundaries are converted into heat [12].…”

“…Silica and cation geothermometers, the Na-K-Mg ternary diagram, the silica-enthalpy model and the thermodynamic equilibrium method have widely been used as tools in estimating the reservoir temperatures of geothermal systems, based on chemical analyses of the thermal waters [10,13]. After a cross-validation of the results from each method in this research, suitable methods were adapted to estimate the reservoir temperature of the thermal waters, because of the different range of their applicable temperature and given chemical data condition.…”