Celestine deposits in the oligo-miocene Qom formation of the Abardej anticline, Central Iran: stratigraphic distribution, geochemistry, S-O-C isotopes and fluid inclusions

Celestine deposits of the Qom Formation of the Abardej region are located in the southern (Abardej mine) and northern (Kazemabad, Abardej and Qaleh-Boland mines) margins of the recumbent Abardej anticline. This paper offers the first detailed description of Sr mineralization hosted within its late Oligocene-early Miocene, sedimentary assemblages. To better understand their origins, integrative and hierarchical approaches were employed with baseline petrographic, mineralization, fluid inclusion and sulfur-oxygen-carbon isotope studies performed on both ore and gangue mineralogy. These extensive evaporite-hosted deposits, are dominated by both celestite and strontianite Sr mineralization, and were hosted by layered carbonate and marl in the Qom Formation c-d members, exhibit widespread replacement of anhydrite, gypsum, dolomite and Oligo-Miocene foraminifera. Parallel secondary stratigraphically controlled textures include the formation of pervasive Diagenetic Crystallization Rhythmites (DCR) which exhibit comparable Sr enrichment. Introductory geochemical analysis highlights weak middle rare-earth elements (MREE) celestite mineral enrichment. Fluid inclusion microthermometry from generation II celestites records average homogenization temperatures of 268 °C, and average salinities of 13.94 wt% NaCl eq. O-C isotopic studies suggest that brine CO2 was sourced from marine carbonates with values varying across a narrow range from 8.3 to 14.1‰ and 18.2 to 0.3‰, respectively, reflective of a Cenozoic seawater source. Geological, mineralogical and geochemical characteristics presented in this study area remain consistent with a sedimentary-diagenetic origin for Abardej anticline hosted celestine deposits.