The La Carolina district, which is located in Jaen (Southern Spain), has experienced important mining activity for
centuries. These long-standing mining activities, which have been associated with the presence of a philonian
network of metallic sulfides, have generated vast accumulations of mine wastes—primarily tailings
impoundments—that contain high levels of heavy metals from ore concentration plants. In this paper, the
resolution of electrical resistivity imaging (ERI) is analyzed to determine the internal structure of these tailings
dams and to assess the influence of the tailings over groundwater and surface water. The “La Manzana” dam,
which is one of the largest sludge dams in the district, was selected to achieve this objective.
First, old aerial photographs that were taken prior to the existence of the tailings dam were examined. Second,
probing was performed using mechanical drilling, which enabled the identification of the features of the fill
material, the thicknesses of the mine tailings and the contact zone between the mining structure and the
basement. Third, the probe acts as a piezometer, which is an excellent tool to correlate the geophysical
prospecting techniques. The characterization of the internal geometry of this structure has been performed by
two ERI surveys, in which electric profiles were obtained under different moisture conditions. During the dry
season, this methodology has been effective for identifying the morphology of the structures, contact with the
substratum, variations in the vertical and horizontal distribution of the deposited material, and the fracture
zones, as well as the contact between the tailings and the substratum on which they are deposited. Conversely,
during the wet season, this contact was not distinct in the profile; however, variations in the saturation degree
of these deposits, preferential infiltration areas and water flow through the interior of the tailings dam were
observed. Last, the ERI survey confirmed the absence of waterproofing measures in the dump areas, which
represents a high risk of soil and water pollution in the surrounding areas.
© 2014