Gangue mineralogy and deportment of titanium (Ti) and vanadium (V) in the Kiirunavaara iron ore deposit, Northern Sweden

The Paleoproterozoic Kiirunavaara Fe oxide-apatite intrusive body has long been known as the most productive iron ore deposit of Europe. Because of the production in the mine is advancing deeper levels and demand for iron ore is increasing, the importance of understanding the deposit from both mineralogical and geochemical point of view is obvious. Among other it is thus important to characterise the abundance and chemical composition of ore and gangue minerals in terms of their variable impact as potential Ti-V hosts, which might be critical elements for production in the future. For this purpose, 55 samples from deeper parts of the orebody were studied combining optical microscopy, SEM-based MLA, and EPMA. Three minerals with stoichiometric Ti-contents have been identified: titanite, ilmenite, and rutile. Moreover, phlogopite hosts Ti in significant amounts (Ø 4300 ppm). For the P-poor parts of the orebody (B-type ore), ilmenite and rutile form the major Ti-hosts in Fe-rich intervals (Fe > 66 wt. %), whereas titanite is predominant in P-poor intervals with slightly lower Fe contents. In contrast, Ti-minerals are fairly rare in P-rich zones of the orebody (P > 0.1 wt. %, D-type ore) and, if present, represented by titanite. Magnetite, being the major commodity at Kiirunavaara, has not revealed any significant Ti contents in its crystal structure. However, Ti is associated with magnetite in the form of Ti-rich exsolution lamellae, being restricted to magnetite crystals in B-type ore (Fig. 1). Incorporation of V has been exclusively detected in magnetite and titanite, revealing average concentrations of c. 600 ppm and 650 ppm respectively. Due to the exploration and grade control drilling the Ti-grade increases with depth. Consequently also the abundance of Ti-bearing silicate (titanite, phlogopite) and oxide (ilmenite, rutile) rises. In the future, additional flotation steps besides the reverse apatite flotation may be required to ensure their efficient elimination during the beneficiation process. It also appears unreasonable to mechanically separate the Ti-rich exsolution lamellae and lattice-bound V from the magnetite sinter feed product of the Kiruna Mine.