زمین‌شیمی و زایش کانسار باریت رباط پائین، خمین، استان مرکزی

The Robat-Paein barite deposit is located about 30 Km northwest of Khomein city, in the Sanandajـ Sirjan zone. The Lower Cretaceous carbonate sequences are the host rock of barite mineralization in the Robat-Paein­ deposit.­­ These carbonate sequences consist mainly of massive bedded orbitolina-bearing limestone (undergone dolomitization in some areas) as well as marl, shale and thinly bedded limestone. ­In this region, epigenetic mineralization occurred as vein, open space filling, fracture filling, massive and replacement textures in carbonate host rocks. The low ratios of Al2O3 (0.1-0.12 wt%), TiO2 (0.01-0.3 wt%), and a relatively high Sr concentration (average 3180 ppm) in the samples of Robat-Paein­ barite deposit could be a sign for presence of ­low temperature­ hydrothermal­ ore-bearing fluids. The enrichment of ­LREE/HREE indicate that­ chlorine-rich fluids were­ dominant during mineralization,­ compared to that­­ of ­fluorinated fluids.­­ According to transportation, LREE hydrothermal solution is made by complex chloride, because they are more soluble chlorides and can be deposited in the final stages.­­­­ The REE patterns of­ the­­ Robat­-Paein barite is analogous to continental margin low temperature hydrothermal barites of California SCCB­. The negative Ce anomalies (Ce/Ce*­= 0.26-0.91), strong positive Eu anomalies (Eu/Eu* between 1.83-3.06), high Ce/La ratios (Ce/La­=1.05), low Y/Ho ratios (Y/Ho between 4-7.14) are the indicative of deposition in continental setting­.­ ­­Based on the field observation, as well as mineralogical and geochemical studies, it seems that the Robat-­Paein deposit could be classified as a MVT deposit.