Kiruna Iron Ore Mine, Sweden

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Since mid-1999, Kiruna's haulage level at a depth of 775m has been replaced by the next level down at 1,045m, which will support production until 2018.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.

GEOLOGY AND RESERVES

The Kiruna orebody was formed at around 1,600Ma following intense volcanic activity with the precipitation of iron-rich solutions on to a syenite porphyry footwall. The ore bed was then covered by further volcanic deposits (quartz porphyry) and sedimetary rocks before being tilted to its current dip of 50–60°. The ore contains a very pure magnetite-apatite mix, containing more than 60% iron and an average of 0.9% phosphorus. Black ore contains less apatite than grey ore.

The original reserve at Kiruna was some 1,800Mt. As of the end of 2004, LKAB estimated that the current proven reserve at the mine is 657Mt grading 48.3% iron, with probable reserves of 140Mt at 46.5% iron. Measured, indicated and inferred resources add a further 500Mt-plus to the inventory, with exploration continuing to identify further resources at depth.

MINING

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.

CURRENT AND FUTURE PROJECTS

Although the current 1,045m haulage level was originally expected to serve the mine until at least 2015, higher production rates will mean that a new level and shaft-hoisting system will need to be operational by 2012.

LKAB is now studying the options for this, with some type of main haulage system that will be located at a depth of 1,365m.

The company is also investing $925m in a third pelletising plant at Kiruna, with commissioning scheduled for 2008. The project also includes a concentrator and ancillary equipment. The world's largest grate-kiln pelletising plant, KK4 will have an initial capacity of 5Mt/y of pellets, with the potential to increase its capacity to 6Mt/y.

LKAB's aim is to make Kiruna a 'one-product' operation, with the focus exclusively on pellet production. As a result, it is also investing in new flotation equipment for the Svappavaara concentrator, which will enable it produce pellet feed from some higher-phosphorus Kiruna ores. The project will provide around 1Mt/y of additional output through efficiency savings.

Click here for printable version