The aim of this study is to prove the effectiveness of two electrical geophysical prospecting techniques, namely electrical resistivity tomography (ERT) and induced polarization (IP), in locating thin vein structures of metal sulphides embedded in Palaeozoic materials underlying a sedimentary cover. For this purpose, a Quaternary basin known as La Garza was selected, located in the mining district of Linares-La Carolina (Southern Spain). Galena (PbS) veins appear abundantly throughout this area, hosted in the Palaeozoic granitic bedrock. The studied veins show thicknesses from 0.5 to 2.0 m, and most present a vertical planar distribution. The veins lose their continuity below the sedimentary cover due to normal fractures that control the subsidence of the basin. During the 1980s, geophysical research campaigns were carried out in La Garza using vertical electrical sounding and failed in detecting the hidden veins. For this reason, to carry out this study, a closed regular mesh was designed, composed by eight ERT and IP profiles, with variable lengths between 315 and 411 metres. An electrode spacing between 5 and 7 metres was selected, thus allowing the granite bedrock to be reached without significantly reducing the resolution capabilities of the method. Even though ERT and IP are well-known geophysical techniques for mapping ore deposits, this is a case study that shows the advantages of the simultaneous use of both techniques (ERT and IP), over their individual application. ERT allows for reconstructing the morphology of the basin and the fractures that control it due to high-resistivity contrast between the overlying sedimentary cover and the underlaying granitic basement. However, it cannot provide any insights about their degree of mineralization. At this point, it is the IP technique that makes it possible to differentiate which are the mineralized structures. Some of these fractures produce high (above 50 mV/V) and moderate (below 50 mV/V) chargeability values, suggesting the existence of several unexploited metal veins. Furthermore, the derived models enable researchers to analyse the morphology of this sedimentary basin controlled by normal faults.

This work analyzed the effectiveness of two electrical geophysical methods in characte-rizing tailings dams. A large flotation cell used for sludge thickening in the concentration plant of the Federico Mine (closed in 1985) within the old mining district of La Carolina (southeastern Spain) was selected for this research. In addition to the direct information provided by the geology of the study area and the surface exposure of the waste deposits, information regarding the construction of this mining structure was available, which helped in the interpretations of the geophysical survey data. In this study, two geophysical surveying methods were used simultaneously: Electrical resistivity tomography (ERT) and induced polarization (IP). Six profiles were acquired, processed, and interpreted. The length of the profiles allowed the obtaining of data reaching maximum investigation depths ranging between 7 and 65 m. These profiles provided information for a detailed analysis of the internal characteristics of the deposited materials. The lateral and vertical observed variations are linked to different degrees of moisture content. The study also defines the geometry of the top of the bedrock and the tectonics that affect the pouring/dumping hole. Old flotation sludge has resistivity values that range between 1 and 100 Ωm (i.e., wet waste 1–30 Ωm, dry waste 30–100 Ωm), while phyllites in the rocky substrate have resistivities larger than 200 Ωm and can even reach va-lues greater than 1000 Ωm. Between the waste and unaltered phyllites, there is a supergene alteration zone (weathering) with resistivity values between 100 and 200 Ωm. The IP method was used to detect the presence of metals in the accumulated waste in the pond by analyzing the presence of large chargeability anomalies. Anomalies were detected in four of the profiles, which ranged from low (i.e., between 0 and 8 mV/V) to medium (i.e., between 8 and 18 mV/V) and high values (i.e., 18 and >30 mV/V).

We assess the effectiveness of complementary geophysical techniques to characterize a Jurassic dolomite confined aquifer at Loma de Ubeda, Spain. This aquifer, which is penetrated by wells in the 100–600-m depth range, is confined by Triassic clays (bottom) and Miocene marls (top). The Jurassic dolomite is characterized by prominent seismic reflectors of high amplitude. Thus, it is readily differentiated from the low-amplitude reflectors of the confining clay-rich Triassic and Miocene materials. Electrical resistivity tomography (ERT) allowed us to detail the characteristics of the aquifer up to a maximum depth of 220 m. Lateral changes in facies and small faults have been identified using ERT. Time-domain electromagnetic (TDEM) is an excellent complement to the two above-mentioned techniques in order to widen the analyzed depth range. We acquire TDEM data with different configurations at multiple study sites while simultaneously varying measurement parameters. In doing so and by comparing the effectiveness of these different configurations, we expand the use of TDEM for aquifer characterization.