سنگ نگاری، ژئوشیمی و ژنز کانسار کرومیت کوهی (افیولیت ملانژ رباط سفید)، شمال‌شرق ایران

Major rock units of Robat Sefid ophiolitic complex are Late Cretaceous in age. The abundance of rock units in this area in ascending order are: dunit, harzburgite and pyroxenite), gabbro and diabasic dikes (mostly rudenginized). Chromite lenses are generally covered by a few centimeters to several meters of ultramafic rocks mainly of dunite. Primary disseminated and massive textures are abundant in chromite ores and secondary brecite, pulapart and kataclastic textures are present. These textures and dunite pods are confirming that chromite deposits of investigated area are in syngenetic type. Tectonic activities and specially NE-SE direction faults are the major factor for dispersion of chromite lenses. Geochemical analysis indicate that Kuhi chromite deposits samples have an average values of Cr2O3 (49.54%), MgO (20.29%), TiO2 (19.0%) and Al2O3 (2.44 to 7.9%), as well as the ratio of Cr / Cr + Al ranges from 0.86 to 0.95 (average 0.81). These indicate that chromite samples are high in Cr & low in Al type.  The percentage of Cr2O3 and MgO in the chromite samples, indicate high partial melting in magma crystallization. Lower amounts of Al2O3 and TiO2 in chromite deposits with their stratigraphic positions in ophiolitic sequence indicate deep chromite zones of the upper mantle- origin of magma. Due to the amounts of major oxides, Kuhi chromite deposits are in Podiform shape which are probably derived from island arc and boninite magmatic series which are associated with Supra-Subduction zones (SSZ). Depletion in Ti and enrichments in Th of samples conform that magma source is related to subduction zone.