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 at the site 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Since mid-1999, Kiruna's haulage level at a depth of 775m has been replaced by the next level down at 1,045m, which will support production until 2018.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. On 28 October 2008, LKAB approved the decision to construct a new main level at the mine. The main level will be built at an investment of around $1.7bn.

In 2008, Kiruna produced 27.5Mt of iron products.

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 sedimentary 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 2008, LKAB estimated that the current proven reserve at the mine is 602Mt grading 48.5% iron, with probable reserves of 82Mt at 46.7% iron. Measured, indicated and inferred resources add a further 328Mt-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 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 studied the options for this, with a main haulage system to be located at a depth of 1,365m.

The new main level will deepen the mine by 320m. A new haulage level will be constructed at 1,365m depth for shuttle-train traffic. New mine locomotives and cars will be bought for a 1,435mm-wide track that will be wider than the previous mine levels.

Ore will be transported via remote controlled shuttle trains to the crushing plant. The ore will then be skip-hoisted approximately 1.4km vertically in two stages to the processing plant. Mining will be carried out in ten production areas.

Each area will be equipped with an access road, ventilation and media systems, and multiple ore passes and rock chutes. Mining will be conducted in stages between the current 1,045m level and the new 1,365m level.

An estimated 615Mt of crude ore will be mined over its lifetime, resulting in nearly 375Mt of finished products including pellets and special products.

The new level will be the seventh since underground mining started. Commissioning of the first sections of the new main level is expected to take place in 2012. Based on a yearly production of approximately 19Mt of finished products, the operating life of the Kiruna mine will be increased by more than 20 years to 2030.

The company also invested $925m in a third pelletising plant at Kiruna that was commissioned on 17 June 2008. The project also included a concentrator and ancillary equipment. The world's largest grate-kiln pelletising plant, KK4 has an initial capacity of 5Mt/y of pellets, with the potential to increase its capacity to 6Mt/y. With the contribution of the pelletising plants, production capacity of LKAB increased by nearly 10Mt pellets annually. Due to market slow down, one of the pelletising plants in Kiruna was closed in December 2009.

LKAB's aim is to make Kiruna a 'one-product' operation, with the focus exclusively on pellet production. As a result, it has also invested in new flotation equipment for the Svappavaara concentrator that was inaugurated in May 2008. The flotation enables it to produce pellet feed from some higher-phosphorus Kiruna ores. The project provides around 1Mt/y of additional output through efficiency savings.