Séminaire

Spain has a long mining tradition, spanning from Roman times to World War II and then steadily declining in the 1960s and 1970s. The resources exploited were mainly massive sulfide deposits which are abundant in the southwest (Iberian Pyrite Belt) and southeast parts of the country, but also included the world’s largest mercury deposit (Almadén mine) in the center of Spain. This prolonged mining activity have generated over time a great number of mine infrastructure, cavities and mine waste deposits such as slag heaps and mine ponds, as a consequence of the extraction and metallurgic processes. Those deposits were mostly abandoned after mining decay and the closure of mining companies, so they have been exposed to surface processes and dynamics for virtually thirty years until, in 2002, an inventory of them was prepared in order to assess their state and hazard potential for a growing population which also gets a great deal of its economic income from tourism in coastal areas relatively close to these mine waste deposits.

The work presented here was developed through a series of research projects lead by the Universidad Rey Juan Carlos (Madrid), where the environmental assessment of mine ponds and slag heaps in the mentioned areas was undertaken by a combination of geophysical and geochemical techniques. Geophysics (mainly electric resistivity tomography) allowed establishing the state of the mine pond structures (contention dikes, bottom of mine ponds) and the presence of acid water flows. Geochemistry (major and trace elements) was performed both on mine pond tailings obtained with a soil core sampler and in nearby waters and soils. Its study, combined with texture and mineralogy of the tailings lead to: 1) the discovery of still large concentrations of economic elements in some of the mine ponds (e.g., 1000-3000 ppm Cu) that resulted from old metallurgical processes which were not able to benefit enough the target elements; 2) the assessment of important contamination levels of toxic metals (As, Sb, Pb, Cd, Zn) produced by acid mine drainage from surficial mine tailings to watercourse sediments and waters; 3) the recognition that in some cases, aeolian dispersion is the most important contaminant agent, which needs the application of basic science methods to monitoring the pollutants contents (especially mercury) and 4) the need to perform periodical monitoring studies in mining areas that are being re-converted to touristic ‘mine-parks’, such as the Don Quijote Route, which crosses areas with potential contamination where tourist activity involves open-air picnic and other recreations. Those are just a few examples of the wide variety of applications of environmental geochemistry to modern human society development.

julien.gargani@u-psud.fr