The mining of copper from sulphide ores, besides the metal production, generates large amounts of mine
tailings that are deposited, e.g. in impoundments. Furthermore, due to natural leaching from these
impoundments, contamination of the environment close to the deposits often occurs. In order to
characterize the internal structure and groundwater flow of abandoned mine ponds in the Iberian Pyritic
Belt, an electrical resistivity tomography study has been carried out. Two different mine ponds have been
studied: the Monte Romero mine pond reveals a homogeneous internal structure with a maximum infilling
thickness of about 4.5 metres; the La Nava mine pond has a more heterogeneous internal structure with
an infilling thickness ranging from 15 to 20 metres. In both cases, the resistivity contrast between the
infilling and the shales constituting the base of the pond is high enough to clearly define the bottom pond
boundary. Whereas the Monte Romero mine pond is nearly fully saturated in water, the La Nava one
shows a low resistivity area that defines the groundwater flow scheme inside the pond. The low resistivity
values (lower than 5 ohm · m) obtained for the mine pond infilling are explained by the high concentration
of pyrite in the tailings and the occurrence of acidic waters. No metal rich water fluxes outside the pond
have been observed, indicating a good isolation of the two studied mine ponds
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