GENESIS ANALYSIS OF SULFATE GEOTHERMAL MINERAL WATER IN KARST AQUIFERS AT XIWENZHUANG UPLIFT, TAIYUAN BASIN

Taiyuan Basin is a Cenozoic fault basin. The formation of faults block and horst in the basin is controlled by the north-south and east-west faults. The karst thermal mineral water is mainly distributed in the area between the Sanji horst and the Tianzhuang fault. The main aquifers of karst thermal water are the carbonate of the Ordovician Fengfeng group, the upper and lower Majiagou groups. We took 18 geothermal water samples in the field, and collected the hydrochemical data of 9 geothermal water and 3 geothermal water in the existing literature. According to the analysis and test results, the hydrochemical type of karst thermal water is SO₄-Ca ·Mg type. According to the ion concentration relationship and the saturation index of the main mineral in the thermal mineral water, it can be inferred that the hydrochemical type is mainly affected by the gypsum layer. In addition to the dissolution of calcite and dolomite, the dissolution of gypsum plays a leading role in the process of groundwater dissolution and filtration. According to the mineral saturation index, Ca²⁺ produced by gypsum dissolution and the increase of geothermal mineral water temperature also lead to the saturation of calcite or dolomite, which may lead to precipitation. The effect of the dissolution of gypsum on the dissolution of calcite and dolomite has an inhibitory effect. The age of karst thermal mineral water in the Xiwenzhuang uplift is more than 20, 000 a, which is mixed with ancient water. The temperature of karst thermal reservoir is 72.6~91.1 ℃, and the depth of circulation is 2123~2663 m. Long-term water-rock interactions provide the time of conduction heating and enriched mineral components for the thermal mineral water. As the high value area of the temperature, TDS and Sr concentration in karst thermal mineral water, Xiwenzhuang uplift is the catchment area of thermal mineral water in the basin, and also the best area of regional thermal mineral water. The increasing trend of TDS and Sr concentration reflects the obvious dissolution and filtration of groundwater from recharge area to drainage area in the basin. There are occurred such a trend: cold underground water with low TDS and hydrochemical type of HCO₃-Ca ·Mg to karst thermal mineral water with high TDS and hydrochemical type of SO₄-Ca ·Mg.