Abstract:Qielihu ophiolite is located to the middle part of the Bangong- Nujiang suture which is rich in chromitite resources. Qielihu ophiolite is mainly composed of altered mantle peridotite, gabbro and diabase, and chromite orebodies are lenticular in the interior of mantle peridotite.The olivine Fo (90.06~90.74) and chromite Cr# (67.45~85.42) of the mantle peridotite from the Qielihu are relatively high, the whole rock is rich in MgO, LREE and large ion lithophile elements (such as Rb, Ba, etc.), and depleted in Al2O3,CaO, high field strength elements (such as Th, Ta, Ce, Nb) and PPGE (Rh, Pt, Pd). These characteristics are similar to other mantle peridotites in the Bangong- Nujiang suture zone, indicating that they have the characteristics of Abyssal mantle peridotite and Forearc mantle peridotite. Meantime, it has gone through the process of early high degree melt extraction and late melt metasomatism. The Qielihu chromitite ore has a dense massive and disseminated structure and contains many kinds of inclusions such as spinel, chalcopyrite, galena and so on. The Cr# value of chromitite is 65.5~75.8 and the Mg # value is 64.89~76.04. The equilibrium melt shows the affinity of vitreous melt. Compared with mantle peridotite, the IPGE and PPGE fractionation of Qielihu chromitite is more obvious. The ΔlgfO2 (FMQ) values of mantle peridotite and chromitite are similar, ranging from -1. 97 to 0.69, indicating that they are derived from the same tectonic setting. Compared with other ophiolites, it is considered that the ophiolite in the Bangong- Nujiang suture originated from the mid- ocean ridge environment and its formation experienced multi- stage evolution.
