Vanadium Enrichment and Exsolution Microtextures in Fe-Ti Oxides from Mafic Intrusions in Québec, Canada

Magmatic Fe-Ti oxide deposits are an important source of Vanadium, yet the mechanisms controlling V enrichment and redistribution remain debated. This study investigates vanadium-bearing titanomagnetite from two contrasting mafic intrusions in Québec, Canada: the layered Lac Doré Complex and the massif-type Lac Saint Jean Anorthositic Suite.

Both intrusions reveal complex lamellar exsolution textures, including trellis-, sandwich- and cloth-textured ilmenite intergrowths. These structures reflect two distinct exsolution pathways that operated under different thermal and redox conditions. Coarse ilmenite lamellae with trellis and sandwich intergrowths formed through high-temperature oxy-exsolution under super-solvus conditions, where magnetite became progressively oxidized. In contrast, subsolvus re-equilibration at lower temperatures produced typically cloth-textured ulvöspinel, which was subsequently replaced by fine-grained ilmenite during continuous cooling.

Electron microprobe and LA-ICP-MS analyses reveal systematic variations in TiO2, FeO, and Fe2O3 contents in titanomagnetite, reflecting magmatic differentiation and variable redox conditions. Vanadium distribution is closely linked to the ratio of Fe2+/Fe3+, with V preferentially incorporated as V3+ under moderately oxidizing conditions via coupled substitution with Fe3+ in octahedral magnetite sites.

During exsolution processes, vanadium becomes locally redistributed between magnetite and ilmenite lamellae. The observed textures provide a spatial record of this redistribution and demonstrate that both magmatic and postmagmatic processes influence vanadium partitioning between mineral phases. These findings have direct implications for the formation and economic assessment of vanadium-bearing Fe–Ti oxide layers in mafic systems.