Conditions of Ore-Mineralization and Geochemical Correlation of Rare-Elements at the Robat Pb-Zn Deposit, West of Khomein, Central Iran

Abstract

The Robat geological study area is located 32 Km west-northwest of Khomein town. From the geo-structural point of view , it is in the median part of the Sanandaj - Sirjan zone [1], and from the mineralization aspect it is part of the Malayer - Esfahan Pb-Zn metallogenic belt [2] . The main hostrock of Pb-Zn ore-mineralization at the Robat deposit is the upper parts of the orbitolina-bearing limestone at its contact with the overlying unit of marl. Ore mineralization is characterized by vein-veinlet, fracture-filling and replacement textures, associated with silica, carbonate, argillic and hematitic alterations [3] . Geochemical trends of minor elements in ore represent positive correlation of Sb, Ag, Cu, Bi, Sn, Fe, U, Th, W, V, Zr and Y with Pb and Zn. Fluid inclusion study of samples indicates that primary fluid inclusions mainly consist of liquid, having an average temperature of homogeneity in the range of 160 ° C to 270 ° C, having the most frequency in the range of 180 ° C to 190 ° C at an average of 5 to 10 wt% NaCl equivalent for salinity. Based on the graph of pressure variations versus salinity (representing paleo-depth), it is understood that ore-mineralization at the Robat deposit is estimated to have formed at less than 50 bars pressure representing depths shallower than 200 m. Fluid inclusion study renders that the low salinity could be resulted from dilution by meteoric waters, also indicating that boiling could be the major mineral precipitation process. Therefore , it is concluded , based on these studies, besides field evidence, that the Robat Pb-Zn deposit shows strong affinity with MVT Pb-Zn mineralization type.