Identifying hydrogeochemistry evolution mechanism in high-sulfur non-ferrous metal mining areas via hydrochemical characteristics and isotopic evidence

Pollution of surrounding groundwater by mining activities and closed mines is a serious public concern around the world. To elucidate the hydrogeochemical evolution mechanism in high‑sulfur non-ferrous metal mining area, an aquifer system in Tongling of China was investigated as an example. Based on the results of hydrogeochemistry and stable isotopes，the hydrochemical evolution of aquifers is significantly influenced by water-rock interaction, while evaporation has contributed less to the hydrochemical components of groundwater. Inverse hydrogeochemical modelling demonstrated that carbonate minerals, gypsum, pyrite, halite and clay minerals as well as CO₂(g) and O₂(g) were admitted as major reactants along the flow path from the closed mine to the active mine, and mineral dissolution or precipitation and ion exchange were potential reactions. Principal component analysis confirmed that the dissolution of carbonate and sulfide predominated in hydrogeochemical evolution of groundwater. The oxidation and dissolution of sulfide are the primary factor to form acidic water, while the dissolution of limestone and dolomite will neutralize acidic water. In parallel, the leaching and ion exchange processes in the southern flow area of the mining mine are more intense, and the contribution to the chemical components of groundwater is significantly greater than that in the western flow area, which provides a reference for the zoning blocking of acid mine drainage. Although the fissure water flowing from the closed mine to the mining mine is neutral, considering the fact that the fissure water will aggravate the mine drainage and the water quality will deteriorate, active measures should be taken to identify crack channels as far as possible to reduce the risk of acid mine drainage diffusion through minimizing the hydraulic connection between them. These findings could understand the hydrogeochemical characteristics of high‑sulfur non-ferrous metal mines, thus effectively prevent groundwater pollution in the mining regions.