Geochemical behaviour of vanadium in iron—titanium oxides

The following geochemical rules-of-thumb seem to hold for vanadium: 1. (1) Magnetites as a group have higher V contents than either hematites or ilmenites. 2. (2) In magnetite—hematite pairs, however, the hematite has the higher V content. 3. (3) In magnetite—ilmenite pairs, the magnetite is usually richer in V than the ilmenite, although the enrichment factor is highly variable, between 1 and 20, and in one particular case even clearly < 1. 4. (4) In hematite—rutile pairs, the rutile strongly concentrates V. This behaviour of V is understandable from the interplay of two simple considerations, namely: (a) under most conditions in which magnetite and/or ilmenite are stable at high temperatures V is dominantly three-valent, and substitutes mainly for Fe3+; and (b) when the oxygen fugacity is close to that defined by the magnetite—hematite equilibrium, V changes to valency 4+, and proxies mostly for Ti4+, in hemo-ilmenites, ilmenohematites, or rutile