Multi-isotope identification of key hydrogeochemical processes and pollution pathways of groundwater in abandoned mining areas in Southwest China

Acid mine drainage (AMD) is considered one of the serious environmental issues in the mining area. Understanding the key processes and pathways of hydrogeochemical evolution is critical for the effective control of AMD pollution. Hydrogeochemical analysis along with environmental isotope tracing was utilized to provide information regarding the hydrogeochemical process of groundwater pollution by using the multi-aquifer of abandoned Dashu pyrite in Southwest China as an example. Using the deuterium excess parameter d of groundwater and the results of 2H, 18O, and T analysis, the water–rock interaction intensity was determined. The distribution characteristics of d-T revealed that the groundwater primarily originated from the Quaternary reservoir platform groundwater and that there was a close hydraulic connection among the aquifers. The results of ion analysis and sulfur isotope tracing indicated that the sulfur in groundwater was primarily derived from gypsum dissolution, whereas the sulfur in mine water was primarily derived from pyrite oxidation. The results of the hydrogeochemical inversion indicated that mining activities altered the water level and flow conditions, promoted water–rock interactions, altered the hydrogeochemical process, and caused aquifer and mine water cross-contamination. The findings provide theoretical guidance for identifying the pollution sources and critical hydrogeochemical processes that affect groundwater in depleted mining areas of multi-aquifers and also provide technical support for developing water source control and prevention techniques.