The redox conditions prevailing during the formation of vanadiferous titanomagnetites from three layered intrusions (Bushveld; Koillismaa; Skaergaard) have been estimated from the valence state of vanadium using synchrotron X-ray absorption near edge structure spectroscopy (XANES). Using a high energy-resolution X-ray emission spectrometer, we show that vanadium occurs mostly as V3+, with minor V4+. The most concentrated samples (up to 2.4 Wt% V2O3) contain approximately 10% of vanadium as V4+. Both V3+ and V4+ occur in the octahedral site of the spinel structure. Considering the low magnetite/melt V4+ partition coefficients, this suggests that vanadium ores crystallized under specific oxidizing conditions.
IRD, UR T058, F-75480 Paris 10, France; Univ Paris 06, CNRS, UMR 7590, IMPMC,IPGP, F-75252 Paris, France; Univ Paris 07, CNRS, UMR 7590, IMPMC,IPGP, F-75252 Paris 05, France; Univ Pretoria, Dept Mat Sci & Met Engn, ZA-0002 Pretoria, South Africa; European Synchrotron Radiat Facil, F-38043 Grenoble, France; Observ Midi Pyrenees, CNRS, UMR 5562, Lab Dynam Terr & Planetaire, F-31400 Toulouse, FranceArticleEnglish