Geochemistry and the origin of the Shamsabad manganese- bearing iron deposit, Markazi Province

The Shamsabad manganese-bearing iron deposit is located 36 km south-east of Arak city, in the Sanandaj-Sirjan Zone. In order to determine the origin and ore-forming processes of the deposit, in addition to petrographic and mineralogical studies, geochemical studies for major, trace and rare earth elements (using LA-ICP-MS method) were done on ore samples. The ore is lens form and strataband, occurring in thick-bedded to massive, orbitolina-bearing Early Cretaceous limestones. Hematite, limonite, goethite and pyrolusite are the main ore minerals. Hematite is more abundant than other minerals. The colloform texture and lamination of the ore are evidences for volcanic-sedimentary origin of the deposit, and deposition in a marine environment. The presence of todorukite as a primary mineral is indicative of the hydrothermal mediated mineralization. The high Mn/Fe and Si/Al ratios, As, Ba, Cu, Pb and Zn enrichments, and depletion of Co and Ni are similar to hydrothermal deposits. The normalized REE patterns and low ΣREE values (31.40 ppm in average) support that Shamsabad deposit is of hydrothermal origin. Negative Ce and positive Eu anomalies indicate that low temperature hydrothermal fluids have an important role in mineralization. The Co/Ni, Co/Zn, La/Ce, LaN/NdN, DyN/YbN, Y/Ho ratios, and the discriminative diagrams for trace element concentrations are in the range of hydrothermal deposits. this study, it is suggested that the Shamsabad deposit is deposited from submarine hydrothermal fluids.