Hydrogeochemical Characteristics and Formation Mechanisms of the Geothermal Water in the Qingdong Coal Mine, Northern Anhui Province, China

The hydrogeochemistry of geothermal fluids provides insight into the occurrence, formation, and circulation of geothermal resources. We collected 13 geothermal water (> 34 °C) and 11 common groundwater samples (< 20 °C) from the Qingdong coal mine in China. The geothermal water samples had higher TDS, Ca 2+ , and SO 4 2− contents, by 1.22-, 1.28-, and 1.25-fold, respectively. The hydrochemical facies of the geothermal water samples was 92% SO 4 ·Cl–Ca.Mg and 8% SO 4 ·Cl–Na, whereas the common groundwater samples was 73% SO 4 ·Cl–Ca.Mg and 27% SO 4 ·Cl–Na. Moreover, hydrogen and oxygen isotopic analysis revealed that atmospheric precipitation and water–rock interaction were the sources of the geothermal water. The chemical composition of the geothermal water is dominated by ion-exchange interactions and the dissolution of carbonates and silicates. Overall, geothermal water in the study area is characterized by optimal hydrodynamic conditions and more intense ion-exchange interactions than common groundwater. Moreover, the formation of geothermal water is controlled by hydrogeological and structural conditions, and by the infiltration of atmospheric precipitation, heating by deep circulation, and transportation by water-conducting faults (F 11 ) to shallow coal strata. These results will facilitate the development of geothermal resources and the construction of green ecological mines, which will provide considerable economic and social benefits.