The Kiirunavaara ore body consists of magnetite ore with magmatic intrusions. The ore body stretches about 4km along the strike in the N 10° E direction with an average width of around 80m, dipping at about 60° SE towards the Kiruna city (Nordqvist and Wimmer, 2014). The average iron content for the ore body is 64% (Nordqvist and Wimmer, 2014), but the grade varies, and the iron content can reach up to 69% (Rutanen, 2011). In general, the ore quality is better in the middle part of the ore body and poor near the hanging wall and footwall contact (Henrikki Rutanen, personal communications, 2015).

In Kiruna, mining takes place in an underground mine with a current main haulage level 1,365 metres below ground.

The Kiirunavaara mine has a continuous and massive ore deposit which allows a standard mine design layout.

Most of the mining at the Kiirunavaara mine is done via transverse SLC layout; i.e. cross cuts are oriented perpendicular to the strike of the ore body. Longitudinal SLC is practiced in some areas where the ore width is narrow; i.e. the drifts and cross cuts are parallel to the strike of the ore body. The general mine layout at the Kiirunavaara mine has evolved over a long period; its hybrid layout can adapt to ore width and shape. Some transverse drifts transform into longitudinal drifts near the hanging walls, allowing better recovery. Other transverse drifts branch to accommodate either the ore shape or to handle disturbed mining areas with the objective of reducing development costs. In general transverse SLC layout is preferred over longitudinal SLC layout due to rock mechanics related issues (Patricia Boeg-Jensen, Personal communication, 2015).

The sublevel interval in the Kiirunavaara mine is 29m (floor to floor) and drift spacing is 24.7m (centre to centre) (Susanne Karppinen, personal communication, 2015). The drift spacing is 21m (centre to centre) for blocks 38 and 41 (Susanne Karppinen, personal communication, 2015). The production drift is 7m wide and 5.2m high (Jonsson, 2015).

The Kiirunavaara mine uses a standard SLC ‘silo-shaped’ ring design; it has normally 8 drill holes with 54m long mid holes (60m in some cases) and side holes with a side angle of 73° (Wimmer, 2014). The diameter of production holes is 115mm (Wimmer, 2014). The distance between two adjacent holes at the end of the bore hole can be a maximum of 4m (Susanne Karppinen, personal communications, 2015).

The greater mining depth has necessitated the development of the new method, raise caving. Both the method and the machine concept, which is an essential part of the mining method, have been developed by LKAB in close collaboration with Montanuniversität Leoben, in Austria. Large-scale testing will begin next year in the Kiruna mine.

Raise caving, as opposed to sublevel caving, is a method that enables mining of the orebody from bottom to top, instead of from top to bottom. In other words, the sequence is reversed, and the technology shift has several advantages, not least in terms of safety.

The ore is processed above ground in three concentrating and pelletising plants.

Sorting
Sorting is a dry process in which the ore is crushed and screened in order to magnetically separate types of rock that are not iron ore. The iron content in the crushed ore is increased from approximately 45 percent to around 62 percent.

Concentrating
To further purify the ore after sorting, the crushed ore is ground finer still in a concentrating process. Kiruna has three concentrating plants. In the concentrating plants the crushed ore goes through several stages of grinding and magnetic separation using water in order to release and remove impurities before the concentrated product (slurry) goes on to the processing plants to be made into pellets. The iron content has then increased from around 62 percent to around 68 percent.

Pelletizing
LKAB currently has three pelletizing plants in Kiruna. Kiruna produces both blast furnace pellets and pellets ........