Abstract
Geochemical and geophysical techniques have been applied to investigate the potential environmental impact of the abandoned La Aquisgrana mine tailings, one of the most important sulfide-bearing tailings ponds of the Linares-La Carolina mining district (Spain). The geometry of the pile has been defined through geological field work and electrical resistivity imaging (ERI) surveys. The ERI profiles revealed the position of the bedrock surface below the tailings central area (more than 40m in thickness) and helped in placing drill core sampling for geochemical analysis and a piezometer installation. In the 21 extracted samples, the total content of Pb, Zn, Cu, Fe, Mn, Sr, Rb and As were determined, with significant values being found for Pb and Zn (>2000mgkg−1), Mn (>700mgkg−1) and As (>170mgkg−1). Although AMD has not been identified, water samples from the saturated zone of the tailings are characterized by elevated dissolved sulfate (2495mgL−1), Fe (20mgL−1), Mn (16mgL−1) and Zn (7mgL−1) contents, with an E.C. value of 3.3mScm−1 and pH from 5.6 to 6.9, suggesting a process of metal mobilization. Physical and chemical data obtained from drill core and groundwater samples were combined with the electrical resistivity profile of the tailings to characterize areas with higher metal concentrations. A central low resistivity area (<30Ω.m) was identified in the vadose zone of the pile, correlated with higher Fe, Zn, Pb, As, and sulfide concentrations, and with a significant increase in silt and clay content. The lowest resistivity values (<5Ω.m) were measured in the saturated zone of the tailings, related with the highest metal(oid) contents in both solid phase and water. A lower resistivity area close to the fractured zone of the bedrock suggests a preferential flow path for subsurface water infiltration. The generated geophysical–geochemical model has allowed to depict areas of the tailings characterized by high metallic and water contents that present the greater risk for contamination.
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