Oxygen, sulfur, and strontium isotope and fluid inclusion studies of barite deposits from the Iglesiente-Sulcis mining district, Southwestern Sardinia, Italy

Abstract

This paper deals with barite from stratiform, karst, and vein deposits hosted within Lower Paleozoic rocks of the Iglesiente-Sulcis mining district in southwestern Sardinia. For comparison sulfates from mine waters are studied. Stratiform barite displays δ34S=28.8−32.1‰, δ18O=12.7−15.6‰, and 87Sr/86Sr=0.7087, in keeping with an essentially Cambrian marine origin of both sulfate and strontium. Epigenetic barite from post-Hercynian karst and vein deposits is indistinguishable for both sulfur and oxygen isotopes with δ34S=15.3−26.4‰ and δ18O=6.6−12.5‰; 87Sr/86Sr ratios vary 0.7094–0.7140. These results and the microthermometric and salinity data from fluid inclusions concur in suggesting that barite formed at the site of mineralization by oxidation of reduced sulfur from Cambrian-Ordovician sulfide ores in warm, sometimes hot solutions consisting of dilute water and saline brine with different δ18O values. The relative proportion of the two types of water may have largely varied within a given deposit during the mineralization. In the karst barite Sr was essentially provided by carbonate host rocks, whereas both carbonate and Lower Paleozoic shale host rocks should have been important sources for Sr of the vein barite. Finally, δ34S data of dissolved sulfate provide further support for the mixed seawater-meteoric water composition of mine waters from the Iglesiente area.