Geoenvironmental characterization of abandoned copper tailings pond combining electrical resistivity imaging (ERI) and geochemical methods (Tongling, China)

Metallic mining tailings ponds are a kind of land resource which should be rehabilitated and utilized urgently but are also a crucial environmental concern due to the accumulation and emission of toxic elements. The abandoned Shuimuchong tailings pond, from the exploitation of Shizishan copper mine district at Tongling City, China, has been exposed to aeolian and water agents for almost 34 years (1990–2024) generating a huge volume of waste composed of sulfide minerals, especially in the surface layer, which eroded and dispersed further afield. In this paper, we demonstrated a successful combined approach of geophysics and geochemistry to explore geoenvironmental characterization of such deposits, including their geometry and the potential risk evaluation. Super-high density electrical resistivity imaging (ERI) surveys were carried out for characterizing the inner structure of this tailings pond, determining both the general geometry of the oxide layer and the stability of the tailings. The analysis of resistivity profiles makes it possible to visualize a low resistivity layer associated with the oxidized iron covering and provide the potential pathways of heavy metal along fractures with high resistivity. Besides, in order to investigate the variation of heavy metal concentration and soil physicochemical parameters in depth, especially associated with the oxidized iron covering, 9 solid samples were collected under the ERI lines from topsoil to subsoil at an interval of 10 cm and the surrounding soil samples were collected along the tailings dam downward to the farmland in 2 parallel lines. Furthermore, mineralogical and geochemical characterization techniques (XRD, XRF and ICP-MS) were carried out to determine the possible occurrence of heavy metals that could entail ecosystem and human risks and the assessment of heavy metal pollution. In conclusion, the permanent application of geophysical and geochemical techniques should be recommended in order to minimize the environmental impact of the tailings on the areas affected, and also to provide scientific basis for environmental restoration.