Gangue Mineralogy of the Leveäniemi Iron Oxide-Apatite Deposit in the Svappavaara Area, Northern Sweden

The Leveäniemi deposit is one of three deposits currently in production by Luossavaara Kiirunavaara AB (publ.), that operates iron ore mines in Norrbotten, northern Sweden. The gangue mineralogy of Leveäniemi is similar to that of the well-known Kiirunavaara deposit, but more complex with regards to the textural and mineral chemical variability of amphiboles and other gangue minerals. The dominant ore mineral in the Leveäniemi deposit is magnetite. The total Fe-resource is 120 Mt at an average grade of 44.1% Fe, according to the 2023 PERC report. Raw ore material from the Leveäniemi open pit is stockpiled as either magnetite, or Fe-ore mixed material, and further divided based on iron and vanadium grade.  The current Svappavaara beneficiation process face challenges with increased alkali, silica and magnesium contents in the magnetic concentrates and thus the final pellet products. The main reasons for that are magnetite inclusions of grain sizes <40 µm in gangue minerals, and fine iron ore-gangue intergrowths. This study addresses the in-situ gangue mineralogy by spatially characterizing the occurrences and compositions of common gangue minerals associated with iron oxides in the deposit, with special emphasis on alkali- and magnesium-bearing silicate minerals. The findings potentially enable improved stockpiling and more stable downstream processing. Representative sampling and subsequent preparation of polished thin sections was done from a set of drillholes, selected in a profile striking from north to south in the ore body. The thin sections were investigated by optical microscopy, followed by micro-analyses using a scanning electron microscope (SEM) and an electron probe microanalyzer (EPMA) on sections from a selection of sub-samples.  Magnesium-rich calcic amphibole was observed as the most common gangue mineral in the deposit. It shows extensive elemental substitutions of aluminum and alkali and is typically intimately associated with magnetite. Thus, amphibole is suggested as a significant source of magnesium to the final ore concentrate. Other common gangue minerals are quartz, apatite, carbonates, clay phases, clinopyroxene and biotite. The main source of potassium was found to be biotite, and spatial variations were observed in the contents of magnetite inclusions in the biotite. The main source of sodium in the final ore concentrate is suggested as a mix of frequently occurring minerals, generally low in sodium i.e. amphiboles, and less frequently occurring, but Na-rich gangue minerals i.e. scapolite and plagioclase. Even though the general metamorphic grade is uncertain, the ore and area in general appear to have experienced a low-T hydrothermal event adding Cl and CO2, generating scapolite and clay minerals.