Geology, fluid inclusions, sulfur isotopes, and Rare Earth Element signatures of the Ain Mimoun barite vein-type ore-deposit, Northeastern Algeria

The barite-vein type of Aïn Mimoun ore-deposit, located in the Saharan Atlas (North-eastern Algeria), is hosted in Albian-Aptian carbonates rocks, and controlled by NE-SW and E-W trending-faults. The vein mineralization mainly consists of barite, associated with galena, sphalerite, grey copper, chalcopyrite, and pyrite. Microthermometric analyses of fluid inclusions indicate moderate to high temperatures (∼105 °C–∼185 °C) and high salinities (20–25 % NaCl equiv.), with eutectic temperatures suggesting H2O-NaCl-CaCl2 brines. The presence of Na+ and Ca2+ in the solutions suggests interaction of the mineralizing fluids with the carbonate-hosted rocks and Triassic formations. The δ34S values of barite (15.7 ‰–26.6 ‰) indicate a sedimentary origin of sulfur, probably involving thermochemical sulfate reduction (TSR) processes. Two isotopic groups are distinguished: white barite associated with sulfides (15.7–17.4 ‰), reflecting sedimentary sulfates, and translucent barite (21.4–26.6 ‰), suggesting prolonged interaction with evaporites. Chondrite-normalized rare earth element (REE) spectra reveal an enrichment in light rare earth elements (LREE), negative cerium anomalies (Ce/La: 0.10–0.81), and positive europium anomalies (35.52–188.62 ppm; Eu/Eu∗: 54.71–88.14), characteristic of hydrothermal deposits created in oxidizing conditions. These data suggest a hydrothermal epigenetic origin for the barite-vein type of Aïn Mimoun ore-deposit, classified as Mississippi Valley-Type (MVT). The mineralizing fluids were deep basinal brines migrating along fault zones, interacting with Cretaceous carbonate-hosted rocks and Triassic evaporites, contributing to the barite precipitation processes.