C- and O-isotope and fluid inclusion studies of carbonates from pyrite and polymetallic ore deposits and associated country rocks (Southern Tuscany, Italy)

Abstract

A total of 42 C- and O-isotopic analyses on 35 samples of carbonates from pyrite and polymetallic deposits of southern Tuscany and associated country rocks are presented. Hydrothermal calcites and dolomites in the ore deposits show a wide range of isotopic compositions, which probably accounts for multiple sources of carbon and oxygen. Calculated isotopic compositions for COH species in equilibrium with calcites are similar to those measured in present-day geothermal fluids of the nearby Larderello-Travale field, suggesting a common link for all late- to post-Apenninic hydrothermal manifestations in the area. The isotopic compositions of country rocks range from typical marine values to lower values, the isotopic depletion likely accounting for metamorphic and hydrothermal effects related to the Mio-Pliocene Apenninic event. In contrast, 10 samples of similar rocks from non-mineralized areas of northern Tuscany show no isotopic evidence of metamorphic and hydrothermal alteration. Data from fluid inclusions indicate important relationships between calcite-forming fluids and sphalerite-forming fluids in the ore deposits here studied.