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 (~260Ma) 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=7.2-11wt.%). Occurrences of rare Cr-bearing titanomagnetite (Cr 2O 3=1.2-10.7wt.%) in the Panzhihua, Hongge and Xinjie intrusions are consistent with early crystallization of Fe-Ti oxides. Oxide-silicate equilibria and low V concentration (<4800ppm) 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. © 2010 Elsevier B.V.