The oxidation state of vanadium in titanomagnetite from layered basic intrusions

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.