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The Geology and Mining Operations of the Kiirunavaara Mine, Kiruna, Sweden

Last Updated: 31st Dec 2018

By Nathalie Brandes

The Kiirunavaara Mine is an underground iron mine operated by Luossavaara-Kiirunavaara Aktiebolag (LKAB). The ore body is the largest known massive magnetite body (Meyer, 1988) and is the largest underground iron mine in the world (Ferrer-Coll et al., 2012). The mine is located in Norrbotten County in northern Sweden (Smith et al., 2013) at the city of Kiruna, which was founded in 1900 as a result of the mining operations in the area (Sievertsson, 2012).

The Kiruna District includes several Karelian (2.5-2.0 Ga) and Svecofennian (1.9-1.88 Ga) metavolcanics and metasediments (Smith et al., 2009; Smith et al., 2013). The rocks overlying the Archaean basement are first the Greenstone Group, which consists of >1.9 Ga tholeiitic to komatiitic volcanics (Ekdahl, 1993; Martinsson, 1997), then the Middle Sediment Group (Witschard, 1984), followed by andesitic volcanic rocks of the Porphyritic Group, and finally the syenite, quartz syenite, and sediments of the Kiirunavaara Group, which host the Kiirunavaara ore deposit (Smith et al., 2009; Martinsson, 2004). These rocks might have originally been basalt, trachyandesite, rhyodacite, and rhyolite altered by metasomatism (Martinsson and Perdahl, 1995; Bergman et al., 2001). All these rocks are intruded by the 1.9-1.8 Ga Haparanda and Perthite-Monzonite granitoids (Skiöld, 1987) as well as the 1.7 Ga Lina granitoids (Skiöld, 1988; Bergman et al., 2001). Around the same time of the intrusions, deformation and greenschist to amphibolite facies metamorphism affected the rocks (Skiöld, 1987; Bergman et al., 2001). The rocks of the region also underwent scapolitisation and albitisation (Frietsch et al., 1997).

The Kiruna District is the type locality for Kiruna-type iron oxide-apatite deposits (Vogt, 1927; Geijer, 1931; Smith et al., 2009). While sharing many similarities with iron oxide copper gold (IOCG) deposits, Kiruna-type ores are recognised as a distinct, but possibly related, type (Williams et al., 2005). There is debate concerning the origin of Kiruna-type deposits. Several researchers believe the ore resulted from the an oxide melt enriched in volatiles (Geijer, 1931; Asklund, 1949; Nyström, 1985; Nyström and Henriquez, 1994; Naslund et al., 2002). Others suggest magmatic fluids involved in exhalative deposition (Oreskes et al., 1995; Bookstrom, 1995; Sillitoe, 2003). Barton and Johnson (1996, 2000) propose that evaporite derived brines were drawn into a hydrothermal system and promoted ore formation. Timing and emplacement of the Kiirunavaara ore system has been dated to 1.88 to 1.87 Ga (Romer et al., 1994; Smith et al., 2009; Smith et al, 2013). Shortly after emplacement, the ores underwent metamorphism and hydrothermal alteration (Romer et al., 1994).

The Kiirunavaara ore body trends 4 km north-south, is at least 2 km deep, and averages 80 m wide (Sievertsson, 2012). It dips 60° to 70° to the east (Cliff et al., 1990). The ore is mostly low phosphorus high iron content magnetite, although about 20% of the ore body includes high phosphorus, apatite-rich magnetite (Kuchta et al., 2004). In addition to apatite, other gangue minerals include actinolite, calcite, and minor amounts of micas, chlorite, pyrite, chalcopyrite, talc, anhydrite, gypsum, titanite, and allanite (Nordstrand, 2012).

LKAB was established as a company in 1890 (Kuchta et al., 2004; Sievertsson, 2012). Mining at Kiruna began in 1898. Ore was extracted using an opencast method until 1952, when underground mining began. The mine currently employs the sublevel caving method for ore extraction (Kuchta et al., 2004). Both remote control and driver operated equipment is used in the mining operation. Primary crushing of the ore is conducted underground, after which it is hoisted to the surface for processing, which includes magnestic separation and flotation. The ore is then pelletised and sent to the harbour at Narvik, Norway, to be shipped to customers (Kuchta et al., 2004; Magnusson, 2012).

The city of Kiruna was founded in 1900 to serve the LKAB mining operations. LKAB’s first managing director, Hjalmar Lundbohm, is considered the city’s founder. He tasked Per Olof Hallman to devise a city plan that fit well with the local topography. Unfortunately, the Kiirunavaara ore deposit extends under the city Hallman designed. In the 1950s, ground surface deformation was recorded near the mine and has been slowly progressing towards the city. Beginning in 2004, LKAB and the municipality of Kiruna have been slowly moving the town away from these deformation zones. Historic buildings are moved while others are purchased for market value. Over time, Kiruna will migrate to nearby areas not underlain by ore, all paid for by LKAB (Sievertsson, 2012).


References:
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Barton, M.D. and Johnson, D.A., 1996, Evaporitic source model for igneous-related Fe oxide-(REE-Cu-Au-U) mineralization: Geology, v. 24, p. 259-262.

Barton, M.D. and Johnson, D.A., 2000, Alternative brine sources for Fe-oxide (-Cu-Au) systems: Implications for hydrothermal alteration and metals in Porter, T.M., ed., Hydrothermal iron oxide copper-gold and related deposits: a global perspective: Australian Mineral Foundation, p. 43-60.

Bergman, S., Kübler, L., and Martinsson, O., 2001, Description of the regional geological and geophysical maps of northern Norrbotton County (east of the Caledonian orogeny): Sveriges Geologiska Undersökning, Ba 56, 110p.

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Cliff, R.A., Rickard, D., and Blake, K., 1990, Isotope systematics of the Kiruna magnetite ores, Sweden: Part I. Age of the ore: Economic Geology, v. 85, p. 1770-1776.

Ekdahl, E., 1993, Early Proterozoic Karelian and Sveco-fennian formations and the evolution of the Raahe-Ladoga Ore Zone, based on the Pielavesi area, central Finland: Geological Survey of Finland, Bulletin 373, 137p.

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Smith, M.P., Gleeson, S.A., Yardley, B.W.D., 2013, Hydrothermal fluid evolution and metal transport in the Kiruna District, Sweden: Contrasting metal behaviour in aqueous and aqueous-carbonic brines: Geochimica et Cosmochimica Acta, v. 102, p. 89-112.

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