Econ. Environ. Geol. 2001; 34(4): 329-343

Published online August 31, 2001

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

Geochemical Evolution and Deep Environment of the Geothermal Waters in the Bugok Area: Reconsideration on the Origin of Sulfate-type Geothermal Water

Yong-Kwon Koh1*, Seong-Taek Yun2, Chun-Soo Kim1, Dae-Seok Bae1 and Seong-Sook Park2

1Korea Atomic Energy Research Institute, Daejeon 305-600, Korea
2Dept. Earth & Environ. Sci., Korea University, Seoul 136-701, Korea

Correspondence to :

Yong-Kwon Koh

nykkoh@kaeri.re.kr

Received: June 27, 2001; Accepted: August 14, 2001

Abstract

The deep environment and geochemical evolution of the Bugok geothermal waters, located in the Kyeongnam Province, was re-interpreted based on the hydrochemical and isotopic data published by Yun et al. (1998). The geothermal waters of the Bugok area is geochemically divided into three groups: Geothermal water I, II and III groups. Groups I and II are geochemically similar: high temperature (55.2~77.2oC) and chemically belonging to Na-SO4 types. However, pH and Eh values are a little different each other and Group II water is highly enriched in SO4 compared to Group I water. Group III water, occurring from peripheral sites of the central part of the geothermal waters, shows temperature range of 29.3 to 47.0oC and belongs to Na-HCO3-SO4 types. The deep environment and
geochemical evolution of the Bugok geothermal waters, showing the diversity of geochemistry, can be interpreted as follows: 1) Descending to great depth of meteoric waters that originated at high elevation and reacting with sediments and/or granites in depth. The SO4 concentration of the waters has been increased by the dissolution of sulfate minerals in sediments. 2) During the continuous descending, the waters has met with the reduction environment, producing the H2S gas due to sulfate reduction. The waters has been heated up to 130oC and the extent of water-rock reaction was increased. At this point, pH of waters are increased, SO4 concentration decreased and calcite precipitated, therefore, the waters show the Na-SO4 type. 3) Ascending of the geothermal waters along the flow path of fluids and mixing with less-deeply circulated waters. The SO4 concentration is re-increased due to the oxidation of H2S gas and/or sulfide minerals in sediments. During continuous ascending, these geothermal waters are mixed with shallow groundwater.

Keywords geothermal water, deep environment, geochemical evolution, water-rock reaction, reduction

Article

Econ. Environ. Geol. 2001; 34(4): 329-343

Published online August 31, 2001

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

Geochemical Evolution and Deep Environment of the Geothermal Waters in the Bugok Area: Reconsideration on the Origin of Sulfate-type Geothermal Water

Yong-Kwon Koh1*, Seong-Taek Yun2, Chun-Soo Kim1, Dae-Seok Bae1 and Seong-Sook Park2

1Korea Atomic Energy Research Institute, Daejeon 305-600, Korea
2Dept. Earth & Environ. Sci., Korea University, Seoul 136-701, Korea

Correspondence to:

Yong-Kwon Koh

nykkoh@kaeri.re.kr

Received: June 27, 2001; Accepted: August 14, 2001

Abstract

The deep environment and geochemical evolution of the Bugok geothermal waters, located in the Kyeongnam Province, was re-interpreted based on the hydrochemical and isotopic data published by Yun et al. (1998). The geothermal waters of the Bugok area is geochemically divided into three groups: Geothermal water I, II and III groups. Groups I and II are geochemically similar: high temperature (55.2~77.2oC) and chemically belonging to Na-SO4 types. However, pH and Eh values are a little different each other and Group II water is highly enriched in SO4 compared to Group I water. Group III water, occurring from peripheral sites of the central part of the geothermal waters, shows temperature range of 29.3 to 47.0oC and belongs to Na-HCO3-SO4 types. The deep environment and
geochemical evolution of the Bugok geothermal waters, showing the diversity of geochemistry, can be interpreted as follows: 1) Descending to great depth of meteoric waters that originated at high elevation and reacting with sediments and/or granites in depth. The SO4 concentration of the waters has been increased by the dissolution of sulfate minerals in sediments. 2) During the continuous descending, the waters has met with the reduction environment, producing the H2S gas due to sulfate reduction. The waters has been heated up to 130oC and the extent of water-rock reaction was increased. At this point, pH of waters are increased, SO4 concentration decreased and calcite precipitated, therefore, the waters show the Na-SO4 type. 3) Ascending of the geothermal waters along the flow path of fluids and mixing with less-deeply circulated waters. The SO4 concentration is re-increased due to the oxidation of H2S gas and/or sulfide minerals in sediments. During continuous ascending, these geothermal waters are mixed with shallow groundwater.

Keywords geothermal water, deep environment, geochemical evolution, water-rock reaction, reduction

    KSEEG
    Jun 30, 2024 Vol.57 No.3, pp. 281~352

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