REE geochemical characteristics and fluid inclusion studies of the Bagher-Abad fluorite deposit, central Iran

Abstract

The Bagher-Abad fluorite deposit is located ~20 km southeast of Mahallat city (Markazi Province), Central Iran. The vein, veinlet and open-space filling fluorite mineralization are in the Shemshak Formation of Upper Triassic-Jurassic age close to the north margin of the Sanandaj-Sirjan belt and Central Iranian microcontinent. The mineral paragenesis in the studied district includes fluorite (white, purple, and smoky), dolomite, quartz, calcite, barite, hematite, goethite, and a minor amount of pyrite. Low concentration of rare earth elements (REE) in fluorites (9.99 –16.75 ppm) reveal that REE of fluorites have likely originated from surrounding units. The chondrite-normalized REE patterns revealed slight enrichment of light rare earth elements (LREE) relative to heavy rare earth elements (HREE) in both early and late stage fluorites. Geological and geochemical relationships between fluorite mineralization, host rocks, structurally controlled open-space filings, chondrite-normalized REE patterns and the Tb/La-Tb/Ca diagram provide clues to the hydrothermal mineralization processes for the fluorites in this area. Based on the computed Eu and Ce anomaly values of early and late fluorite samples, it can be concluded that the studied fluorites were probably deposited under relatively high oxygen fugacity as a product of interaction between relatively low pH hydrothermal fluids and surrounding carbonates. Our thermometric results based on fluorite hosted fluid inclusions reveal two separate fluid populations-a low homogenization temperature (~103 °C) and higher salinity (up to 20.8 wt.% NaCl equiv.) and a high homogenization temperature (up to 152 °C) and low salinity (~11.5 wt.% NaCl equiv.). The Te (eutectic temperature) values indicate that other components such as CaCl2, KCl, and MgCl2, as well as NaCl were the main components of the mineralization fluids. The Bagher-Abad fluorite deposit is characterized by the post-orogenic event of the Shemshak Formation that is not associated with magmatic activity. The occurrence of open-space filling fluorite mineralization and lack of significant alteration of the associated host rocks are typical features of the studied deposit. These characteristic mineralization in the vicinity of orogenic belt support the idea that the Bagher-Abad fluorite deposit can be considered as a Mississippi Valley-type (MVT). © 2018 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany.