Textural,chemical and isotopic variations induced by hydrothermal fluids on mesozoic limestones in northwestern Sicily

The results are given of textural and compositional investigations carried out on carbonate materials outcropping in various localities in northwestern Sicily where fluorite, barite and calcite mineralizations of hydrothermal origin occur. Observation of the textural features indicate variations in the degree of calcite recrystallization and silicification that appear to be more marked in rocks that show more evident effects of mineralization. The geochemical behaviour of the minor elements indicate variations in chemical composition (increase of Mn, Fe, and Sr and removal of Mg) as a result of interactions between mineralizing fluids and host-rocks. Comparison between the isotopic compositions of oxygen and carbon in mineralized and unmineralized limestones shows that isotopic exchange took place between CaCO₃ and hydrothermal fluids. The values obtained support relatively short limestone/water contact times and moderate temperature values. It is suggested that the ore-forming solutions were essentially heated meteoric waters. Precipitation of the fluorite was caused by temperature decrease, reaction with Ca-rich wall rock, and increase in pH of initially rather acid hydrothermal solutions.This work was supported by a grant from the Ente Minerario Siciliano.