Hydrochemical Characteristics andFormation Mechanisms of an AntimonyMining Activity Area in the Upstream WaterSource of Danjiangkou Reservoir, China

Antimony (Sb) is a major environmental pollutant that is widely present in nature and possesses toxicity and potential carcinogenicity.The mining of antimony ore can affect the quality of the water environment and the safety of drinking water for residents in the area.Taking the Gaolinggou antimony mining area in the Danjiangkou water source for the Middle Route of South-to-North Water Diversion Project (MRSNWDP) in China as the research object, systematic hydrochemical samples and hydrogen and oxygen isotope samples were collected for comprehensive hydrogeochemical analysis.The results show that: (1) The pH range of surface water in the study area is 3.09-8.30,with a mean of 7.21, indicating an overall neutral condition, while some local areas are acidic.The range of TH is 243.00-439.00mg/L, with a mean of 314.69 mg/L.The TDS ranges from 262.00 to 598.00 mg/L, averaging at 384.38 mg/L.The dominant cations are Ca 2+ and Mg 2+ , while the dominant anions are HCO 3 -and SO 4 2-.The hydrochemical types vary frequently in space, including HCO 3 SO 4 -CaMg, SO 4 HCO 3 -CaMg, HCO 3 -CaMg, and SO 4 -CaMg.For groundwater, the mean pH is 7.52, with TH and TDS ranging from 269.00-542.00mg/L and 291.00-652.00mg/L, respectively, averaging at 426.67 mg/L and 504.67 mg/L, both slightly higher than those of surface water.The dominant cations and anions are Ca 2+ and HCO 3 -, respectively, with hydrochemical types mainly HCO 3 -CaMg and HCO 3 SO 4 -CaMg.The mine water has a pH value of 8.03, indicating a weakly alkaline condition with the highest TDS content.It is rich in SO 4 2-, Ca 2+, and Mg 2+ , and the hydrochemical type is SO 4 HCO 3 -CaMg.(2) The hydrochemical characteristics in the study area are primarily controlled by rock weathering, with carbonate and silicate weathering and dissolution as the main processes.Positive cation exchange occurs in the water bodies.Surface water is significantly affected by mining activities, while groundwater is influenced