Abstract
The legacy of the mining industry has left a large number of tailing ponds in the Cartagena–La Unión mining district exposed to water and wind erosion, which causes serious environmental and health problems and requires remediation. Before applying any remediation technique, an intensive sampling of the materials infilling the pond is required to determine the geochemistry of the pond, which will condition the remediation process. However, sampling the large number of tailing ponds that compose the district could be expensive. Thus, the main objective of this study is to evaluate the usefulness of electrical resistivity tomography (ERT) as a non-invasive tool to provide an image of spatial subsurface resistivity distribution and its relation to the physicochemical composition of near-surface mine wastes. To achieve this objective, three short ERT profiles were conducted, and 12 samples in each profile were collected at different depths for its geochemical characterization. Several non-linear regression models were fitted to predict physicochemical properties and metal concentrations from electrical resistivity measures. As a result, a high resistivity area was depicted in the ERT profiles G2 and G3, while the low resistivity ERT profile G1 was also obtained in accordance with the site’s surficial characteristics. Relationships among low resistivity values and high salinity, clay content, high metal concentrations, and mobility were established. Specifically, calibrated models were obtained for electrical conductivity, particle sizes of 0.02–50 µm and 50–2000 µm, total Zn and Cd concentration, and bioavailable Ni, Cd, and Fe. The ERT technique was shown to be a useful tool for the approximation of the location and distribution of the highest ranges of fine particle sizes, moisture, and, to a lesser extent, metal accumulation in the near-surface waste materials.
Highlights
The mining of metalliferous mineral deposits and associated smelting and metal processing activities have led to perturbations in surface environments [1]
The geochemical characterization showed that metal concentrations, especially for Zn, Pb, and Cd, in the surface area of the El Gorguel tailing pond exceed the legal reference level, with Cd being the most available and water-soluble metal in the pond, especially in the G1 area
The electrical resistivity tomography (ERT) method has been a useful tool for supporting geochemical surveys for identifying subareas with different materials within tailing ponds
Summary
The mining of metalliferous mineral deposits and associated smelting and metal processing activities have led to perturbations in surface environments [1]. In the Cartagena–La Unión mining district (South-East, Spain), the legacy of more than 2500 years of intensive mining activity has left a large number of tailing ponds that generate environmental impacts due to leachates with high concentrations of sulfides and metallic elements [1,4,5,6,7]. Their wastes are characterized by significant amounts of metals such as Pb, Zn, Cu, and Cd, high salinity, acidic pH levels, and low soil organic matter content [8]. It has been demonstrated that plant cover provides physical protection to minimize wind erosion and the surface runoff of soil materials [10]
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