Kiruna Iron Ore Mine

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With an ore body 4km long, 80m thick and reaching a depth of 2km, LKAB's Kiruna is the world's largest, most modern underground iron ore mine. Since mining began here over 100 years ago, LKAB has produced over 950Mt of ore, yet only one third of the original ore body has been extracted.

Since mid-1999, Kiruna's haulage level at a depth of 775m has been replaced by the next level down at 1,045m, which will support production until 2018. The operation employs 1,800 people, of whom 400 work in the mine.

In 2006, Kiruna produced about two-thirds of LKAB's total output of 23.3Mt, of which 16.9Mt were pellets. The company's sales of iron-ore products also totalled 23.3Mt, of which 15.9Mt were pellets.

The ore seam at Kiruna is 4km long, 80-120m thick and reaches a depth of 2km. Kiruna Mine is the largest and most modern underground iron ore mine of the world.

The Kiruna orebody was formed at around 1,600Ma ago following intense volcanic activity. Iron-rich solutions precipitated the iron on to a syenite porphyry footwall. Then the ore bed was covered by further volcanic deposits, quartz porphyry, and sedimetary rocks. Later the whole body was tilted to its current dip of 50 to 60°.

The ore contains a very pure magnetite-apatite mix, black ore contains less apatite than grey ore. Containing more than 60% iron, the ore is of extremely high quality. Magnetite means, the ore contains enough iron to become magnetic. This rare feature of this ore was used hundreds of years ago to make the first compasses.

Very few people work underground. The seams are drilled by remote operated drills. Huge Finnish-built driverless wheel loaders, follow computer-controlled routes and only stop at piles of broken rock to collect the ore. At this point an operator sitting in front of a TV screen on the surface loads the ore and carries it to shaft where is is dropped to the 1,045m level where it is crushed and then hoisted to the surface to be processed.

A recent article in the Daily Telegraph (September 25, 2004) states that a geological forecast says that fissures area spreading from the mine and it is feared that in 20 years time the whole town will disappear into the mine.

The mine is divided into eight production areas, each containing its own group of ore passes and ventilation systems. Mining the ventilation shafts for the current production level was carried out by SIAB using Indau 500 raise borers, while Skanska Raise Drilling developed a total of 32 ore passes between the 775 and 1,045m levels using Tamrock and Robbins raise borers. Alimak developed two special units based on its RCM-6 system to reinforce the ore passes with cable bolts and shotcrete as necessary.

Ore is mined using sublevel caving, with sublevels spaced at 28.5m vertically. With a burden of 3.0–3.5m per ring, this yields around 8,500t for each blast. LKAB subsidiary Kimit AB supplies the explosives and prepares the holes for blasting.

The main haulage level at Kiruna lies at a depth of 1,045m, with the mine's ore-handling systems capable of handling 26Mt/y of run-of-mine rock. Seven 500t-capacity shuttle trains, controlled from the 775m level, collect ore from ten groups of ore passes and deliver it to one of four crushing stations. -100mm ore is then skip hoisted in two stages to the 775m level and then to surface.

Electric-powered, remote-controlled drilling and ore handling equipment supplied by Atlas Copco and Tamrock is widely used. After blasting, load-haul-dump machines (some of which are fully automated) carry the run-of-mine ore to the nearest ore pass, from which it is loaded automatically on to one of the trains operating on the 1,045m level.

After primary crushing, sampling using a Morgårdshammer automatic sampler to obtain the apatite and magnetite contents, and hoisting to surface, the ore is processed in Kiruna's complex of a sorting plant, two concentrators and two pellet plants to give pellet and sinter fines products. Some ore is moved by rail to LKAB's Svappavaara plant for pelletisation. Products are hauled by rail to the ports of Narvik (Norway) or Luleå for shipment.