Application of electron microprobe studies to determining genesis of chromite mineralization in the Qaranaz - Alamkandi area, west of Zanjan

The studied chromite mineralization in the Gharanaz-Alamkandi area is located in the west of Zanjan province and Sanandaj-Sirjan zone. The outcrops rock units consist of amphibolite, granitic gneiss, marble, amphibol schist, garnet mica schist and also ultrabasic sequences. Chromite mineralization occurred as lenzoid, veinlets and disseminated within the peridotite rocks such as serpentinized dunite, serpentinized harzburgite and serpentinit. Olivine, orthopyroxene, clinopyroxene, serpentine, asbestos, chromite and magnetite are the main minerals at these rock units. Mineral chemistry of olivines indicate that the olivines in the peridotites are rich in magnesium and show forsterite composition. Clinopyroxene in the peridotites of the study area are iron- magnesium-calcium rich with mainly are augite in composition. Orthopyroxene minerlas show mainly brunzite composition with minor amounts of hypersthene composition. The mineral chemistry of chromspinels indicate that the chromite mineralization in the study area is podiform type which enriched in Cr and Mg and depleted in Ti. In addition, the mineral chemistry studies in this area show that the host rocks of chromite mineralization and dunite- lherzolite sufferd at least 20% and 40% partial melting, rspectively. On the other hands, it can be state that both of partial melting and depleted mantle melthad important role in the formation of peridotite in the study area. According to this study, it can be note that the chromite mineralization in the study area is ophiolite type mineralization and formed from a boninitic magma in the supra subduction zone during the subduxtion of Proto-Tethys ocean beneath the Iranian block Precambrian-Cambrian time.