Mineralogy and Deportment of Ti in the Deeper Part of the Kiirunavaara Deposit with Special Focus on Ti-rich Exsolution Lamellae

The Kiirunaavara deposit in northern Sweden, ranks among the largest iron oxide-apatite deposits globally, which serve as the fundament of European steel production. As mining operation progresses to deeper parts of the ore body, understanding the mineralogical variability of trace elements becomes essential for sustainable and efficient processing. Titanium is one of the trace elements that may occur in iron ores, either within various discrete minerals or as exsolution lamellae. These lamellae develop along the crystal lattices of magnetite and cannot be completely removed from the magnetite. As a result, the titanium content of the ore increases, leading to several issues, particularly a decrease in ore quality, reduced furnace efficiency, and increased slag viscosity. This thesis therefore investigates the distribution and mineralogy of Ti-bearing phases, with a particular focus on Ti-rich lamellae within magnetite in B ores at greater depths of the Kiirunavaara deposit (1365–1700 m). The study examines their occurrence, spatial distribution with depth, and deportment. In order to understand the distribution of Ti, a total of 36 samples from B- and D-type ores, as well as brecciated low Fe ore were collected from 5 exploration drill holes in the deposit ranging from depths of 1365–1700 m. After being as polished thin sections, these samples were analysed utilizing an integrated analytical workflow combining optical microscopy, SEM-based TESCAN Integrated Mineral Analyzer, Raman spectroscopy and electron probe microanalysis. Consequently, it was established that Ti primarily occurs as discrete oxide (ilmenite, rutile) and silicates (titanite) phases. In B1 ore types, rutile and ilmenite are dominant and are associated with high Fe concentrations (Fe > 66 wt%), whereas B2 ore type is characterized by relatively lower Ti concentrations (50-66 wt% Fe). Simultaneously, a sample was collected from the P-high interval part of the ore body (D-type), where Ti-bearing minerals were also observed to be very rarely distributed, with titanite in particular being the most abundant Ti mineral in the low Fe grade ores. While Ti-rich lamellae, mainly composed of ilmenite, were found to be extensively distributed within magnetite grains, with their abundance and morphology varying according to the ore type. Compared with low Fe grade ore, these lamellae are shorter and less dispersed in B-type ore. These lamellae were observed in thin sections using SEM-TIMA, which also proved highly effective in precisely determining the association of Ti-bearing minerals with main ore phases and gangue minerals.The findings obtained throughout the study highlight that Ti deportment becomes increasingly complex with depth and emphasize the need to take Ti-rich inclusions into account in order to optimize processing and mine planning strategies in the Kiirunavaara deposit. Keywords: Kiirunavaara deposit, Ti deportment, Ti-bearing minerals, exsolution lamellae, optical microscopy, SEM–TIMA.