Lacustrine laminated sediments (laminites) present in Late Miocene formations of the Hõ Âjar Basin, SE Spain, display well developed loop bedding, a structure consisting of bundles of laminae that are sharply constricted at intervals, giving a morphology of loops or links of a chain. The laminite sequences, which are interbedded with turbidite marlstones, were accumulated on the bottom of a permanently strati®ed lake developed in a rapidly subsiding basin limited by 010°and 105°normal faults. As deduced from both macro-and microdeformational analyses, the basin evolved under an extensional stress ®eld throughout the Late Miocene. Four main types of loops, simple and complex loops with subcategories, have been recognized within the laminite sequence. Simple loops of type 1 show the best de®nite pattern, quite similar to`pinch and swell structures', a type of boudinage typical of stretching of alternating beds where the competence contrast is not strongly marked. The remaining loop types display contortion and occasional breakage of laminae (microfaulted edges) indicative of microdeformation near the boundary between the ductile-brittle deformational ®elds. The distribution of the various loop types across the laminite sequence re¯ects an interplay between progressive lithi®cation of the laminites as sedimentation progressed and tectonic stresses which affected the sediment sequence. Accordingly, a mechanism of deformation under an extensional stress ®eld, ultimately related to the creep movement of the main basin faults which resulted in successive seismic shocks of low magnitude, is proposed to explain the formation of loop bedding in the laminites.

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Mining of massive (Cu, Pb and Zn) sulphide bodies in the Iberian Pyrite Belt (SW Spain) has generated a great number of abandoned waste deposits such as mine ponds. These represent large accumulations of reactive minerals and subsequently, emission sources of trace elements and formation of acid drainage. Even if they have been restored, monitoring studies are required to evaluate the corrective effects and how they may change over time. This work presents the results of a monitoring study carried out at Mine Concepción mine pond, based on mineralogical (XRD), geochemical (INAA, X-ray fluorescence, ICP-MS) and geophysical (electrical resistivity tomography) techniques. In it, a series of relevant parameters have been well delimited, such as the infilling thickness and its variation and, the position, geometry and absence of water leakages through the base of the mine pond. Additionally, the existence of an internal, remnant flow of acid waters that tends to come out through the pond dyke has been identified. Chemistry of these waters indicates that oxidation processes affecting the Mina Concepción mine tailings are generating acid drainage waters which could potentially release substantial amounts of trace elements to the river Odiel. Thus, giving that not complete sealing is accomplished by the restoration capping and rainfall water infiltrates into the pond materials, at least the sealing of the dyke through which leakages occur should be revised.

Mining activity in the Iberian Pyrite Belt, on the south‐west of the Iberian Peninsula, has generated a great amount of mine tailing ponds, which once the extractive activity is finished, are abandoned and become a serious environmental problem. Here we present the results of applying the electrical resistivity tomography (ERT) technique to characterize the abandoned mine ponds in two sites: Monte Romero and Mina Concepción. ERT has allowed us to determine both the general geometry of the pond’s base and the maximum thickness of the mine tailings. In all cases, the resistivity contrast between the infilling and the bedrock is high enough to clearly define the bottom pond boundary. The low‐resistivity values (lower than 5 Ωm) obtained for the infilling are explained by the high concentration of pyrite in the tailings and the occurrence of acid waters. Whereas the Monte Romero mine pond is almost completely saturated with water, in Mina Concepción it has been possible to identify the presence of inner acid water flows, the outlet of which through the damaged dyke originates a spilling of acid waters to the Odiel River. No low‐resistivity water flows through the base of the ponds into the bedrock have been observed, indicating a good isolation of the base of the studied mine ponds.

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