REE MOBILIZATION IN COMPLEX HYDROTHERMAL-METASOMATIC SYSTEMS: FLUID CHEMISTRY EVIDENCE OF ALBITITE AND CHLORITE-TALC MINERALISATIONS IN CENTRAL SARDINIA,ITALY

S. FADDA;M. FIORI;GRILLO, SILVANA MARIA;WALTER PROCHASKA

2011-01-01

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Abstract

Several Na-feldspar and talc-chlorite deposits occur in central Sardinia. The development of postmagmatic Na-metasomatism mainly involved the bulk of the local plutons to which economic occurrences of metasomatic chlorite-talc are also associated. REE-bearing minerals have been found in the unaltered granodiorites, while different amounts of REE were redistributed in secondary phases in albitites during metasomatism. REE-bearing minerals are strongly depleted in chloritized rocks. Lanthanides may be mobilized under hydrothermal activity depending upon physicochemical conditions in the fluid phase. Among ligands, carbonates appear to have increased the solubility of REE somewhat but chlorine complexes may have played the major role in the REE depletion of granites. However, other competing complexes can attain importance where their concentrations are somewhat anomalous. Preliminary analytical results for the investigated fluids appeal to an extensive leaching of REE by highly saline, halogen-rich solutions with the most striking features being the high contents of bromine.