Thermal waters obtained from deep-seated hydrothermal systems can be classified based on geothermal heat sources and geochemical characteristics of hot spring waters. As it is evident that in several kinds of geothermal heat sources, “volcanic” heat sources can supply the hugest energy for the formation of deep-seated hydrothermal systems, geothermal heat sources are classified into 2 types, i.e. “volcanic; [V]” related to Quaternary volcanic activities younger than 1 Ma, and “sub- or non-volcanic; [!]” not related to Quaternary volcanic activities. From geochemical classification of hot spring waters, it is clarified that thermal waters obtained from deep-seated hydrothermal systems are derived in essence from following four “source waters”, i.e. “meteoric water; [MW]”, “sea water; [SW]”, “volcanic thermal fluid; [VF]” and “waters formed by water-rock interactions; [WR]”.
As the results, it is explained that deep-seated hydrothermal systems can be categorized thermally and geochemically into following 4 types, i.e. “meteoric-water-originated volcanic hydrothermal system; [V, MW (+VF/WR)]”, “sea-water-originated volcanic hydrothermal system; [V, SW+MW (+VF/WR)]”, “meteoric-water-originated sub-or non-volcanic hydrothermal system; [!, MW (+WR)]” and “sea-water-originated sub-or non-volcanic hydrothermal system; [!, SW+MW (+WR)]”.
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