Hydrogeochemical Processes of Carboniferous Limestone Groundwater in the Yangzhuang Coal Mine, Huaibei Coalfield, China

We examined the primary mechanisms controlling water quality evolution in the Carboniferous aquifer in the Yangzhuang coal mine (Huaibei coalfield). Q-mode factor analysis explained how the Na + and SO 4 2− concentrations gradually increase and the hydrochemical type transforms from Ca-HCO 3 to Ca·Na-HCO 3 and Ca·Na-HCO 3 ·SO 4 along the flow path. The high bicarbonate concentration appears to be due to dissolution of calcite and dolomite and an open carbonate system, while frequent water inrushes and the declining water level provide evidence for the relative closure of the Carboniferous limestone aquifer. Gypsum dissolution is the main SO 4 2− source. Inverse geochemical modeling sufficiently explained the hydrogeochemical processes that control the water quality evolution. These findings should aid the interpretation of groundwater hydrochemical evolution and groundwater quality management in the study area and other north China coalfields.