Kemi mines chromite deposit is part of Kemi layered intrusion. According to Huhtelin (2015) in the central part of the intrusion the main chromite layers length is around 1,9 km and average thickness is 40 m, decreasing outward from the center. The intrusion is estimated to be 3-4 km deep according to the geophysical seismic reflection surveys.

The Kemi layered intrusion has a lenticular shape, that is around 0,2-2 km wide and 15 km long according to Huhtelin (2015). Tectonic movements have tilted the intrusion to dip about 70 degrees to the northwest. The intrusion was metamorphosed during the Svecokarelidec orogeny.

The chromite layer is mainly between metaperiodate layer on the hanging wall side and basalt contact series on the footwall side. The basalt series consist of mylonitic talc-chloritecarbonate schist, talc-carbonate rock, metapyroxenite and irregular concentrates of gabbro. The basement granitoid is in contact with the talc-carbonate rock.

The ore body has been fragmented into a group of smaller ore bodies. The main orebodies illustrated in are: in northern part Pohjois-Viia (PV), in the middle Elijärvi (EL), in the western part both Surmaoja (SO) and Nuottijärvi (NJ). Smaller ore bodies are Mätäsoja (MO) to southwest-, both Länsi-Viia- (LV) and Itä-Viia- (IV) between EL and PV. The last smaller ore body is Viianmaa/Perukka (VP) to northeast from the main ore bodies. (Huhtelin, 2015).

Kemi mine started as an open pit mine and after that mining transited to underground. Underground mine was constructed in four years, between the years 1999 and 2003. Underground mining was started two years before the open pit mining was finished in 2003.

The infrastructure for underground mining has been built to the footwall side, which is mainly hard granite. Underground mining started from level 550 and continued upwards towards bottom of the crown pillar on level 275 (Rikberg 2019). Currently Outokumpu is investing for expanding the underground mine to the level 1000, where new main level and drift is being built.

Mining method for underground mining has been from the beginning to the present-day underground benching with back fill. Kemi mine’s used stope high to be 25 meters, -width varying from 12 to 18 meters and separation based on the used backfill. Stopes filled with mixture of waste rock and slurry are categorized as primary stopes and stopes filled with waste rock as secondary stopes. Mining staff changes stope width with waste rock and pillars for stabilization of the mining area.

During 2018–2021, Kemi mine is carrying out a Deep Mine project to increase the resource efficiency of the mine. The project is about the depth extension and building underground mine infrastructure from 500-level to 1,000-level (meters) below surface. The area of the mine site has not been expanded.

The ongoing Deep Mine expansion project, expected to be finalized by the end of 2022, ensures the ore availability at Kemi mine for the coming decades.

Current mining method: Sublevel Stoping.
New mining method: Sub Level Caving.

The ore is crushed is concentrated in the plant as lumpy ore and fine concentrate products. Lumpy ores with sizes 10 – 120 mm are separated from the crushed ore using sink and float separation method. The sink and float method is based on differences in specifics gravities. The fine concentrate is separated from the crushed ore by using rod mills and spiral concentrators. Spiral concentrators separate the material by specific gravities. The tailings from the concertation are pumped to the spoil reservoir. In the reservoir the solid material is separated from the water and the water is pumped back to the concentration process (Salmi 2018).

As all used concentration methods are based on the gravitational separation, there is no usage of chemicals during the concentration of the ore. According to Salmi (2018) the annual productions are approximately for upgraded lumpy ore 400 000 tons and for fine concentrate 850 000 tons. The mine’s effects to the surrounding environment are s ........