Isotope provenance of AMD and treatment options for large, abandoned mines: A case study of the abandoned Dashu pyrite mine, Southwest China

Discharge of acid mine drainage (AMD) along with heavy metals mobilization is a critical environmental concern. An urgent need is to manage or treat AMD in the minefield effectively. To this end, based on a hydrogeological investigation, the d-T (deuterium excess parameter-Tritium content) technique was adopted to trace the recharge, runoff, and discharge of AMD in the abandoned Dashu pyrite mine in China. The results reveal that AMD in the minefield originates from local precipitation and shallow groundwater and exhibits apparent seasonal runoff variations. The AMD is associated with shallow groundwater from the top of the Quaternary platform on the axis of the Dashu anticline, and protons could originate from the pyrite oxidation. Therefore, an engineering practice to purify the AMD is combined with (1) water diversion to stop AMD formation and blockage of the AMD outlets. (2) Acceleration of Fe(II) oxidation through aeration promotes the precipitation of Fe-oxide and hydroxide. (3) Neutralization of AMD using Karst water from the Maokou Formation (P₂m). This study provides a new research idea and tracing method for improving hydrogeological surveys and effectively handling environmental problems related to AMD of abandoned mines.