Rare earth elements geochemistry, O and S isotopic compositions, and microthermometric data of barite from the Kuh–Ghalagheh deposit, Markazi Province, Iran

The Kuh–Ghalagheh barite deposit is located 43 km southwest of the city of Mahallat in Markazi Province, Iran. The barite mineralization occurs as a stratabound, lenticular massive orebody in siliciclastic rocks of Eocene age. Barite is accompanied by calcite, Fe- and Mn-oxides, quartz, and minor malachite. The concentration of total REEs (∑REE) is very low in barite, ranging from 0.38 to 6.26 ppm. Chondrite-normalized REE patterns show enrichment of LREE relative to HREE, and dominantly negative La, Gd, and Ce anomalies. The δ18O and δ34S isotopic values of the barite samples fall within narrow ranges of +4.0 to +5.6‰ and +26.2 to +27.8‰, respectively, which do not match those of contemporaneous seawater (Eocene). This suggests that isotopically modified seawater sulfate is the source of oxygen and sulfur in barite. Three types of aqueous, aqueous–carbonic, and carbonic fluid inclusions were found in barite, suggesting that two immiscible fluids (aqueous and carbonic) were involved in the deposition of barite. Salinity values in the aqueous fluid inclusions ranged from 1.57 to 13.40 wt% NaCl equivalent. The aqueous–carbonic inclusions have salinity values ranging from 9.43 to 16.84 wt% NaCl equivalent. The salinity ranges of the aqueous and aqueous–carbonic inclusions show that two fluids have mixed, one with moderate salinity (>15 wt% NaCl equivalent) from basinal origin and a second with low salinity (