The Aitik mine is one of Europe’s largest open pit copper mines. It is located 20 km east of the municipality of Gällivare, in the northernmost part of Sweden and 60 km north of the Arctic Circle. The mine is operated by Boliden AB and is often described as one of the most efficient mines in the world given its profitability despite having extremely low copper grades (Boliden 2015).

The Aitik Cu-Au ore is interpreted as a deformed and metamorphosed porphyry Cu-Au deposit with an IOCG-type hydrothermal overprint (Wanhainen et al. 2012).

Footwall rocks include two rock types, namely, feldspar–biotite–amphibole gneiss and the porphyritic intrusion of quartz monzodiorite. Both rock types show porphyritic texture, the former having amphibole phenocrysts while the latter is plagiophyric. The rocks within the ore zone transition from biotite gneiss, to biotite schist, to muscovite schist towards the hanging wall. Biotite and muscovite schist/gneiss both contain garnet porphyroblasts and is mainly differentiated by the amount of ferromagnesian minerals. Tourmaline occurs as fine-disseminations and as porphyroblasts. The hanging wall is comprised of three rock types, namely, feldspar–biotite–amphibole gneiss, metadolerite and occasionally amphibolite. Several pegmatite dykes cut the deposit, primarily in the hanging wall and ore zone. The dykes range from 0.5 to 20 m in width, which may be mineralized if situated within the ore zone.

Chalcopyrite, pyrite and pyrrhotite are the main sulphide minerals in Aitik, whilst bornite, chalcocite and molybdenite constitute minor components. Oxides such as magnetite and ilmenite are also found throughout the deposit. Ore minerals occur as disseminations, veinlets, patches and clots, and also in several types of veins together with varying amounts of other minerals such as quartz, biotite, amphibole, garnet, tourmaline, barite, zeolites (stilbite and chabazite) and thaumasite (Wanhainen and Martinsson, 2003).

Mineralization exhibits a north-northwesterly plunge, which reaches up to 800m below surface in the northern part and a depth of 400 meters in the southern part (Bergmann, 2001; Wanhainen 2005). Zonation of copper and gold distribution is observed within the deposit. Wanhainen et al. (2003) reported copper enrichment (>0.6% Cu) within 100-300 m, which decreases at deeper levels, i.e., 0.4–0.6% Cu at 400–600 m depth. On the other hand, gold-rich areas (>0.6 ppm) only exist at the deeper levels (400–600 m depth) and typically associated with amphiboles (Wanhainen et al. 2003).

Several alteration minerals are present in the ore body and are probably associated with several pulses of hydrothermal activity. Most extensive within the ore zone is biotite and K-feldspar alteration, commonly accompanied by garnet porphyroblasts of spessartine-almandine composition. Biotite is altered to sericite towards the hanging wall. Pervasive K-feldspar- epidote alteration is mainly restricted to the footwall and hanging wall contacts but may occur sporadically within the ore zone (Monro 1988). Albite-scapolite alteration associated with amphibole-pyroxene veins sporadically occurs within the deposit (Bergman et al. 2001).

Two other minor deposits are present within the Aitik mine area. The Salmijärvi deposit, found in the southern end of the Aitik open pit, have a similar mineralization style as the main deposit but of lower grade. Amphibole-biotite gneisses and local diorite hosts the mineralization. On the other hand, Liikavaara deposit is located in the eastern part of the mine area. Mineralization in Liikavaara is hosted by volcanosedimentary rocks of mainly andesitic composition and dominantly controlled by quartz-(calcite)-(tourmaline) veins. Ore minerals are chalcopyrite, pyrite and pyrrhotite, with significant amounts of magnetite, molybdenite and scheelite (Warlo et al. 2017).

At Aitik mine near Gällivare ore is mined from an open pit mine. A prerequisite for open pit mining is that the ore body reaches the surface, and is not covered with thick earth or rock layer. The mining is done with so-called pallet mining. Earth and rock layers above the ore (waste rock) is taken away freeing the ore below in horizontal slices called pallets.

Holes for blasting are drilled with electric drills from Bucyrus and Atlas Copco. Hole depth: 16-17 m Hole diameter: 311 mm Drill attern: 7x9 m Between 200-300 holes are drilled for each round of blasting. A normal blast round produces around 700 000 tonnes of rock for extraction.

Boosters are loaded into the holes followed by emulsion explosives. Explosives: Emulsion explosives (Kemitti-610) from Forcit, about 1 tonne of explosive is used in each hole.

With the help of shovels from Bucyrus, P&H, Komatsu and wheelloaders from Caterpillar, the blasted rock is loaded on to trucks for further tranportation. The largest trucks, CAT 795F, holds about 313 tonnes. A bucket can hold 45 m³ rock (Komatsu 26 m³). The ore is transported to the crusher and the waste rock to a waste rock dumpsite. The machines are equipped with the positioning system Minestar.

The crushers in the open pit are located at 165 and 285 meters below ground level. Each crusher has a capacity of up to 8 000 tonnes/ hour. Each day, around 100 000 tonnes of ore are crushed. The crushed ore is transported by conveyor belts through an intermediate stockpile and then to the ore storage located by the concentrator.

There are seven conveyors with a total length of 7 km for the transportation of ore from the crusher to the ore storage. 3,5 km of the route is in a tunnel. The conveyors have a capacity of up to 8 000 tonnes/hour and can go up to 4,8 meters/second.

An ore storage area with a capacity of 200 000 tonnes, equivalent to two days operation, is located beside the concentrator. The building is 90 meters high and 60 meters is above ground level.

When the ore enters the mill, water is added and then grinded into the two mills. The grinding technique is called autogenous, ie the ore grinds itself without the addition of external material. There are two grinding lines, each line consisting of a primary and a secondary mill. Each grinding line has a capacity of 2 200 tons of ore/hour, a total of 36 million tons/year. Primary mills are 12 meter in diameter and 14 meter long. The electric motor driving the mills is of 22,5 MW (30 570 hp).

Screw classifiers in the grinding circuit ensure that the milling is sufficient. Finished ore slurry then flows to a common mixer, reagents are then added to allow the flotation of the mineral chalcopyrite. The flotation circut consists of flotation cells with a total volume of 5 340 cubic meters. Remaining material are pumped to the tailing pond for disposal.

The concentrate are dewatered with a thickener and then through a press filter. The finished product is known as copper concentrate and contains of 28% copper, 8 g/t gold and 250 g/t silver.

Copper concentrate is now ready for transport by truck to the rail terminal in the southwest corner of the industrial area. It is then loaded on rail wagons and transported to the smelter in Rönnskär, Skellefteå.