Mineral chemistry of Fe-Ti oxides from the Xinjie PGE-bearing layered mafic-ultramafic intrusion in Sichuan, SW China

Abstract

The Xinjie intrusion is a typical example of a mafic-ultramafic body that hosts both Fe-Ti oxide and Cu-Ni-(PGE) sulphide mineralization. Both the oxide-rich and sulphide-rich layers occur as part of an igneous layered sequence. The layered sequence can be divided into three cycles. Chromite mineralization occurs at the lower part of each cycle, whereas magnetite and ilmenite mineralization occur in the upper part. The intergrowth of chromite and ilmenite, and titanomagnetite and ilmenite are common in the ores. High temperatures and oxygen fugacities together with isotopic evidence of crustal contamination indicate that ilmenite-titanomagnetite grains were crystallized at greater depths, prior to assimilation of crustal materials. Two possible mechanisms can explain the oxide mineralization: (1) immiscible oxide melts formed within the magma started crystallization of olivine and chromite, and (2) formation of these ore zones by magma mixing.