Origin and evolution of vanadium (V) enrichment in Azıtepe (Alaşehir-Manisa) meta-gabbroic rocks in Menderes massif (Western Turkiye)

Abstract

The Azıtepe meta-gabbroic intrusions, located in Alaşehir, Manisa (western Turkiye), represent part of the Late Neoproterozoic gabbroic bodies that emplaced along the northern margin of Gondwana within the central Menderes Massif, and host Fe-Ti-(V) oxide mineralization. These gabbroic intrusions generally originated from a tholeiitic mantle source, and have minimal evidence of crustal contamination, as indicated by high Nb/U (30–166.7) and Nb/Th (9.37–58.3) ratios, along with low Pb concentrations. However, the mechanisms governing vanadium (V) enrichment in such Fe–Ti–(V) systems, particularly the role of metamorphic overprinting in V redistribution, remain poorly understood. This study aims to determine the processes responsible for V enrichment in Fe–Ti–(V) oxide minerals within the Azıtepe meta-gabbroic intrusion by evaluating V partitioning and mineral hosts in relation to magmatic and metamorphic controls. The ore mineral paragenesis includes Ti-magnetite, magnetite, ilmenite, rutile, hematite, goethite, pyrite, chalcopyrite, and pyrrhotite. In this study, V mineralization is observed in oxide minerals such as magnetite, Ti-magnetite which are influenced by both magmatic crystallization and subsequent metamorphic alteration. The Azıtepe meta-gabbroic rocks generally show enrichments in Fe₂O₃_(t) (10.2 to 18.5 wt%) and TiO₂ (2.04 to 6.50 wt%). The V concentrations of the studied rocks range from 355 to 473 ppm in meta-gabbros while varying between 217 and 628 ppm in amphibolites. EPMA (Electron probe microanalysis) data indicate that V is preferentially incorporated into magnetite rather than ilmenite in meta-gabbros and garnet-free amphibolites, likely due to its compatible ionic radius and charge relative to Fe³⁺, a behavior that supports its preferential partitioning into magnetite under moderate to high fO₂ conditions. The formation conditions of magnetite–ilmenite pairs in meta-gabbro and amphibolite samples from the study area were evaluated using EPMA-derived equilibrium data processed through the MagMin_PT software, and its application was extended to metamorphic samples in this study. The studied samples' log fO2 values (−13.7 to −28.1) may be pointed out moderately to strongly reducing conditions with textural context guiding interpretation. In garnet-bearing amphibolites, however, variations in metamorphic conditions (P, T, fO₂) and/or hydrothermal alteration may have mobilized previously magnetite-hosted V, facilitating its redistribution into silicate minerals such as garnet, chlorite, and clinozoisite. These results suggest that V enrichment in the Azıtepe meta-gabbroic rocks is primarily controlled by magmatic processes under moderately oxidizing conditions, with secondary redistribution during metamorphism, highlighting the potential of such intrusions as significant sources of Fe–Ti–V mineralization in post-collisional tectonic settings.