Recognition of Original Carbonate Mineralogy and Determination of Ore Genesis in Robat Mine (Khomein-Arak) Carbonates

The studied area is located at the middle structural zone of Sanandaj-Sirjan in Malayer-Esfahan axis. Lower Cretaceous sequence disconformably overlay the Triassic-Jurassic sequences. The sediments have been folded during Middle Cimerian (Bajocian-Batonian) and Laramian (Upper Cretaceous) orogenic phases. The carbonate sequences are the host rock of Pb and Zn mineralization in Robat area. The true thickness of the sequence in south and north slopes of Aregijeh Mountain are 256 m and 230 m respectively and in the south slope of BarAftab Mountain is 408 m.Major and trace elements such as Ca, Mg, Sr, Na, Fe, Mn, Sr/Na, Sr/Mn, Sr/Ca and δ18O and δ13C isotope values in carbonates are used for recognition of original mineralogy. Trace elements and oxygen and carbon isotopes indicate a mixed calcite-aragonite original mineralogy. Petrographic and geochemical studies indicate that carbonates affected mostly by meteoric diagenesis in an open system. Paleotemperature calculation, based on lightest oxygen value, indicates that the diagenetic temperature was about 75ºc. The genetic types of ore deposits in Robat area is a kind of diagenetic-epigenetic forms, controlled by hydrothermal fluids at low temperature, similar to the Mississippi Valley Type deposits (MVT). The model of ore formation is illustrated below: The passage of meteoric waters through fractures and faults removed Pb, Zn and Mg from shale layers and precipitated the elements in the limestone rocks. The shale layers above the limestone sequences played as a feeder trap for lead and zinc deposits. Siliceous (jasperoid) and dolomitic alteration are the main alterations in the area.