The clayey failures fillings associated with N100 degree centigree-110 degree centigree E fractures at the El Berrocal Uranium mine (Sierra de Gredos, Spain): Characterization, genesis and retention capacity of radioactive and other elements

The clayey failures filling associated with the N100 degree centigree-110 degree centigree E fractures, at the El Berrocal U mine, have been studied in relation to the natural radionuclide migration/retention processes in a fissured granitic environment. The fracture filled with pyrite, chalcopyrite, sphalerite, galena-bearing quartz, later mineralized by pyrite, pitchblende, carbonate and barite also belongs to that fracture set. According to the data obtained by X-ray diffraction, thermal and thermogravimetric analyses, EDX coupled to both scanning and transmission electron microscopes and cation exchange methods, the clayey failures fillings are essentially composed of quartz, sericite, illite, Ca/mg beidellite, K-feldspar, albite, apatite and occasional kaolinite. Traces of monazite, torbernite, autunite, other unidentified Ca, Y, Ce, La and REE phosphates, ferric sulfates, jarosite, gypsum, barite, calcite Pb silicates, Fe-oxyhydroxides, gibbsite, Al gels and REE silicate complex gels have been also detected in the <2 mu m fraction. From a geochemical point of view, the <2 mu m fractions, in relation to the <60 mu m fractions, are very positively anomalous in U, Th, V, Cu, Zn, Sn, Ni, As, Ba, Ca and organic C. Furthermore, Cl is present, in important amounts, in almost all of the essential and accessory minerals and mineraloids in the <2 mu m fractions. (Author) 28 refs