Abstract
This study presents the results of the geoenvironmental characterization of La Matildes riverbed, affected by mine tailings in the Cartagena–La Unión district, Murcia (southeast Spain). Soils and riverbeds in this area are highly polluted. Two Electrical Resistivity Imaging (ERI) profiles were carried out to obtain information about the thickness of the deposits and their internal structure. For the mine tailings deposits of La Murla, a tributary of the El Miedo riverbed, the geophysical method imaged two different units: the upper one characterized by low resistivity values and 5–8 m thickness, correlated with the mine tailings deposits; and the lower more resistive unit corresponding to the Paleozoic metasediments bedrock. The ERI profile transverse to the Las Matildes dry riverbed revealed the existence of three different units. The uppermost one has the lowest resistivity values and corresponds to the tailings deposits discharged to the riverbeds. An intermediate unit, with intermediate resistivity values, corresponds to the riverbed sediments before the mining operations. The lower unit is more resistive and corresponds to the bedrock. Significant amounts of pyrite, sphalerite, and galena were found both in tailings and riverbed sediments. The geochemical composition of borehole samples from the riverbed materials shows significantly high contents of As, Cd, Cu, Fe, Pb, and Zn being released to the environment. Mining works have modified the natural landscape near La Unión town. Surface extraction in three open-pit mines have changed the summits of Sierra de Cartagena–La Unión. Rock and metallurgical wastes have altered the drainage pattern and buried the headwaters of ephemeral channels. The environmental hazards require remediation to minimize the environmental impact on the Mar Menor coastal lagoon, one of the most touristic areas in SE Spain.
Highlights
The Province of Murcia, situated in the southeastern most part of the Iberian Peninsula, is one of those mining areas in Spain that today still suffer from serious environmental problems due to the presence of nearly eighty abandoned mineral waste structures, especially in the Sierra de Cartagena area and La Unión town [1]
There are examples of studies on tailings ponds using (i) magnetometry, enabling us to deduce the variations of the tailings structures [3,4]; (ii) electromagnetics, used to investigate the structural and hydrogeological settings of oil sands tailings dykes [5]; (iii) seismic, to derive the internal pond boundaries by means of refraction and reflection waves [6,7]; and direct-current geoelectrical imaging surveys [8], where the electrical resistivity tomography (ERI) method is strongly affected by the variation of some important properties of tailings such as moisture, soil salinization, particle size distribution, acid mine drainage, etc. [9,10]
This study focused on an area of ~4 km2 to the east of La Unión town, where numerous mining works extend along the small headwaters of the El Miedo and Las Matildes dry riverbeds in the Sierra de Cartagena–La Unión region
Summary
The Province of Murcia, situated in the southeastern most part of the Iberian Peninsula, is one of those mining areas in Spain that today still suffer from serious environmental problems due to the presence of nearly eighty abandoned mineral waste structures, especially in the Sierra de Cartagena area and La Unión town [1]. The composition and emplacement sites of these mine wastes have generated environmental hazards related to geochemical pollution (among others), that negatively affect soils, groundwater, flora, fauna, and humans [1,2]. There are examples of studies on tailings ponds using (i) magnetometry, enabling us to deduce the variations of the tailings structures [3,4]; (ii) electromagnetics, used to investigate the structural and hydrogeological settings of oil sands tailings dykes [5]; (iii) seismic, to derive the internal pond boundaries by means of refraction and reflection waves [6,7]; and direct-current geoelectrical imaging surveys [8], where the electrical resistivity tomography (ERI) method is strongly affected by the variation of some important properties of tailings such as moisture, soil salinization, particle size distribution, acid mine drainage, etc. The ERI method has been the fundamental tool to support physical–chemical analysis in phytoremediation works on the abandoned mining ponds in the Sierra de Cartagena area. The application of geophysical, mineralogical, and geochemical techniques, together with landscape evolution studies, could allow the analysis and quantitative assessment of the pollution risk [11,12,13,14,15]
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