Melt-rock interaction driving extreme titanium and vanadium enrichments during the multi-stage post-magmatic evolution of chromite from the Mirdita Ophiolite, Kosovo

Chromitites associated with rodingite from the Deva mining district (Mirdita Ophiolite, Kosovo) display thick reaction rims at the chromite – silicate matrix contact, whose most peculiar feature is an anomalous enrichment in titanium (Ti) and vanadium (V) in chromian spinel, and the presence of abundant rutile, ilmenite and titanite. The integration of textural and mineralogical observations, minero-chemical data and statistical analysis, through Principal Component Analysis (PCA), reveals a complex evolution of the chromitite body and its host rocks. Primary chromitites formed in a supra-subduction zone forearc environment, from melts with boninitic affinity. Subsequent intrusion of a mafic body and its interaction with the chromitites led to significant enrichments in Ti, V and minor Ga, Ni and Mn in chromite, the former being, at lower temperature, partially exsolved to form Ti-phases. During a later serpentinization event, affecting the ophiolite mantle rocks, the circulation of reducing hydrothermal fluids caused the rodingitization of the mafic intrusion, replacing primary silicates with hydrogrossular, clinopyroxene and chlorite. Serpentinization and rodingitization only marginally affected the chromitite body, through local re-enrichment of the previously depleted spinel rim in Al, liberated by plagioclase break-up. The study highlights the complexity of superimposed magmatic and low-temperature processes capable of modifying chromite chemistry and highlights the importance of integrated approaches to unravel their individual contributions.