Flood basalt-related Fe–Ti oxide deposits in the Emeishan large igneous province, SW China

Abstract

In the Panzhihua–Xichang region (Sichuan Province, SW China), there are a number of world-class magmatic Fe–Ti oxide deposits. They are hosted as conformable masses in lower parts of layered mafic–ultramafic intrusions that are part of the end-Guadalupian (∼ 260 Ma) Emeishan large igneous province. The ore-bearing Panzhihua, Hongge, Baima, Taihe and Xinjie intrusions are spatially and temporally associated with flood basalts and granitoids in the province. New mineralogical data for Fe–Ti oxide ores in the Hongge and Baima intrusions, combined with an overview of previously published data, provide a better understanding on the formation of these enigmatic deposits. Geochemical and Sr–Nd isotopic data confirm a genetic relation between the intrusions and high-Ti Emeishan flood basalts. Parental magma compositions, estimated using the most Mg-rich cumulus olivine in the intrusions, are characterized by slight to moderate degrees of fractionation (MgO = 7.2–11 wt.%). Occurrences of rare Cr-bearing titanomagnetite (Cr 2O 3 = 1.2–10.7 wt.%) in the Panzhihua, Hongge and Xinjie intrusions are consistent with early crystallization of Fe–Ti oxides. Oxide-silicate equilibria and low V concentration (< 4800 ppm) in magnetite are consistent with relatively high oxygen fugacity. Flood basalt-related origin, early Fe–Ti oxide crystallization and relatively high oxygen fugacity, are characteristic of Fe–Ti oxide deposits in the Panxi region but are fundamentally different from those hosted in highly-differentiated, upper parts of large layered intrusions (e.g. the Bushveld Complex). Similar Fe–Ti oxide deposits have not been documented in other well-studied large igneous provinces to date, but a number of Fe–Ti oxide ore occurrences worldwide are potentially similar to this type of flood basalt-related oxide deposits.