Geoenvironmental characterization of riverbeds affected by mine tailings in the Mazarrón district (Spain)

Abstract

This study presents the results of the geoenvironmental characterization of San Cristóbal and Las Moreras riverbeds, both affected by mine tailings in the Mazarrón district, Murcia (SE Spain). The main objective of the study was to characterize the present conditions of the riverbeds in order to identify related environmental problems. The goal is particularly relevant, because the abandoned mine wastes remain a continual source of acid mine drainage (AMD) and metal contamination, and soils and watercourses in this zone are still highly polluted. For the San Cristóbal site, the electrical resistivity tomography survey indicated a two-unit sequence, in good agreement with borehole data: an upper unit extends down to a 1.5 m depth that corresponds to the upper part of sandy tailings, and a lower unit of lower resistivity values extends down to 6 m depth corresponding with clayed tailings and riverbed deposits. At the Las Moreras site, a 2 m thick upper unit of low resistivity values and a 4 m thick lower unit of higher resistivity values were distinguished, also in good agreement with borehole data. Significant amounts of pyrite, sphalerite, and galena were determined in tailings from both sites. The alluvial materials from both riverbeds showed significant toxic metal and metalloid contents (Ag, As, Cu, Sb, Pb, and Zn). An important level of contamination by AMD from the surficial tailings to the watercourse sediments and waters also occurs. Mineral wastes, intensive agricultural activities, and the population of the town of Mazarrón overlap in the district, so both remediation and monitoring are necessary to minimize environmental impact on the areas affected, in one of the most touristic areas in SE Spain.