El proyecto de El Berrocal: síntesis preliminar

Abstract

El Berrocal is an international research project on the natural radionuclide migration in a fissured granitic environment. This project is being carried out in the El Berrocal zone, north of the village of Nombela (Toledo). The gelogical formation studied is a granitic pluton with an epithermal vein-type mineralization comprising quartz, sphalerite, pyrite and chalcopyrite; and pitchblende, pyrite, carbonates and barite. The activities of the project are focused on the structural, lithological, geochemical, hydrochemical and hydrogeological aspects of the granite-U mineralization system, in order to establish a migration model of the natural radionuclides of the environment. The concurrence of the tectonic, hydrothermal and supergenic processes has originated several U remobilizations during the deuteric, hydrothermal and supergenic alteration phases, which affected the system. These phases are responsible of the mineralogical species and present distribution of this element within the system. The Th remobilization is much more limited, due to its different geochemical behavior. The present water-rock interaction processes account for the different types of water existing in the system, which are sulphatic, in the shallowest zones, and calcium bicarbonated in the deepest. The U contents in these waters vary from 1 to 100 ppb. The hydrogeology of the zone is controlled, at a local scale, by the topography and the fracture network, and the mineralized quartz dyke plays a major role on the groundwater flow. The isotopic analyses of the U and Th series in the infill materials seem to indicate recent sorption-desorption U processes and coprecipitation with carbonates.