Origin and evolution of two contrasting thermal groundwaters (CO2-rich and alkaline) in the Jungwon area, South Korea: Hydrochemical and isotopic evidence

Yong Kwon Koh, Byoung Young Choi, Seong Taek Yun, Hyeon Su Choi, Bernhard Mayer, Si Won Ryoo

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Abstract

In the Jungwon area, South Korea, two contrasting types of deep thermal groundwater (around 20-33 °C) occur together in granite. Compared to shallow groundwater and surface water, thermal groundwaters have significantly lower δ18O and δD values (> 1‰ lower in δ18O) and negligible tritium content (mostly < 2 TU), suggesting a relatively high age of these waters (at least pre-thermonuclear period) and relatively long subsurface circulation. However, the hydrochemical evolution yielded two distinct water types. CO2-rich water (PCO2 = 0.1 to 2 atm) is characterized by lower pH (5.7-6.4) and higher TDS content (up to 3300 mg/L), whereas alkaline water (PCO2 = 10- 4.1-10- 4.6 atm) has higher pH (9.1-9.5) and lower TDS (< 254 mg/L). Carbon isotope data indicate that the CO2-rich water is influenced by a local supply of deep CO2 (potentially, magmatic), which enhanced dissolution of silicate minerals in surrounding rocks and resulted in elevated concentrations of Ca2+, Na+, Mg2+, K+, HCO3 - and silica under lower pH conditions. In contrast, the evolution of the alkaline water was characterized by a lesser degree of water-rock (granite) interaction under the negligible inflow of CO2. The application of chemical thermometers indicates that the alkaline water represents partially equilibrated waters coming from a geothermal reservoir with a temperature of about 40 °C, while the immature characteristics of the CO2-rich water resulted from the input of CO2 in Na-HCO3 waters and subsequent rock leaching.

Original languageEnglish
Pages (from-to)777-786
Number of pages10
JournalJournal of Volcanology and Geothermal Research
Volume178
Issue number4
DOIs
Publication statusPublished - 2008 Dec 30

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Keywords

  • CO-rich and alkaline
  • hydrogeochemistry
  • isotopes
  • Jungwon area, Korea
  • thermal groundwater
  • water-rock interaction

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

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