The Mazarrón Pb–(Ag)–Zn mining district (SE Spain) as a source of heavy metal contamination in a semiarid realm: Geochemical data from mine wastes, soils, and stream sediments

The Mazarrón epithermal ore deposits (SE Spain) formed in Miocene time in relation to the emplacement of dacitic–rhyodacitic domes. The Pb–(Ag)–Zn ore deposits are of the high sulphidation vein and stockwork type. There are two main mining sites: San Cristóbal–Perules (adjacent to the town of Mazarrón) and Pedreras Viejas. The area is located in the southern realm of a Miocene marine basin surrounded by mountains in its western, eastern and southern flanks. A main seasonal river (Rambla de las Moreras) crosses the basin from North to South and is strongly affected by contaminated sediments from the San Cristóbal–Perules mining site. The mine tailings are extremely rich in Pb (mean = 12,400 μg g−1) and Zn (mean = 6100 μg g−1), whereas As concentrations are also very high (mean = 650 μg g−1). Our geochemical survey also covered anthropic soils, stream sediments and the so-called almagres deposits (red alum calcines). All these environmental matrices have also very high concentrations of Pb, Zn, As, and Cd compared to our local or world baseline concentrations. The calcines are rich in As (mean = 450 μg g−1), and the main environmental concern relates to the wrong use of these materials as agricultural soils at discrete sites in the district. Besides, the anthropic soils of the district are very rich in Pb (mean = 2550 μg g−1) and Zn (mean = 1870 μg g−1). On the other hand, the seasonal river Rambla de las Moreras receives contaminated sediments from the San Cristóbal–Perules old mining site and mine wastes, which results in high concentrations of As (mean = 120 μg g−1), Pb (mean = 2700 μg g−1) and Zn (mean = 1090 μg g−1) in the sediments. These high concentrations of dangerous contaminants in an area close to a town of 35,000 inhabitants and adjacent to significant agricultural activity may pose a risk to human health.