Mineralogy and geochemistry of Mn-Fe deposits associated with ophiolitic sediments in north of Chalderan, NW Iran

Some Fe and Fe-Mn deposits are found within sedimentary pelagic rocks and radiolarian cherts of the Khoy ophiolite. Mn-Fe mineralizations in Safo area north of Chalderan City are examples of them. In Safo area, deposition of manganese occurred as lense-like orebodies in different horizons within pelagic rocks. They are stratiform and have syn-sedimentary origin. Mineralogically, braunite, pyrolusite, bixbyite, and hematite are the main minerals present in ore and calcite, quartz and barite are principal gangue minerals.The banded, massive and disseminated textures are seen in ore bodies. Geochemical and geological evidence indicates that deposition of ore minerals took place from submarine hydrothermal solutions (exhalative) on the neotethyan oceanic basin during late Cretaceous time. The Mn/Fe ratios in this deposit are highly variable and ranges from 1.35 to 31.7 with an average of 8. This mean ratio is many times higher than that of mid-ocean metalliferous sediments. The high ratio of Mn/Fe and Si/Al, very low content of trace metals specially Co, Ni and Cu, low values of Y and Ce, and high values of SiO2, Mn, Fe, Ba and Sr provide good evidence for Mn enrichment by exhalative hydrothermal fluids and also for insignificant contribution of hydrogenetic processes in formation of this deposit. The study of correlation coefficients among different oxides and elements show that there are no meaningful relationships among Cu, Co and Ni in exhalative hydrothermal solutions rich in Si, Mn and Fe.