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Kiruna, Kiirunavaara, Luossavaara
Sweden
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The Kiruna, or Kiirunavaara and Luossavaara magnetite-apatite orebodies are located adjacent to the town of Kiruna in the Norbotten area of northern Sweden (#Location: 67° 50' 8"N, 20° 11' 3"E).

These deposits are located within the northern Fennoscandian Shield, which in the Kola Peninsular of Russia, Finland, northern Sweden and Norway, largely comprises Archaean and Palaeoproterozoic rocks. The Meso- and Neoarchaean Kola and Karelia cratons in the east are composed of 3.5 to 2.9 Ga gneissic tonalite-trondhjemite-granodiorite (TTG), followed by 2.9 to 2.6 Ga greenstones, calc-alkaline volcanic rocks and further TTG magmatism, with consolidation after the last major stage of granitoid intrusion at 2.65 Ga. The early Palaeoproterozoic interval, between 2.5 and 1.9 Ga, was characterised by extensional/intracratonic rifting and sedimentary basin evolution, with recurrent mantle derived magmatic activity, resulting in numerous komatiitic eruptions, layered intrusions (komatiitic, picritic and tholeiitic to calc-alkaline) largely over the partly concealed Norrbotten craton to the west of the Kola and Karelia blocks, with little indication of new felsic crust during this 2.5 to 1.9 Ga period. The large layered intrusions (hosting significant Cr, Ni, Ti, V and/or PGE mineralisation, largely in Finland and the Kola Peninsular) represented a major magmatic input between 2.45 and 2.39 Ga, sometimes with associated high grade metamorphism of the intruded rocks, while major basaltic and komatiitic stages (with intercalated arenites) which occurred between 2.2 and 2.0 Ga were associated with extensional pulses.

A change took place between 1.96 and 1.75 Ga, during the commencement of assembly of the Nuna/Columbia supercontinent, when calc-alkaline andesites and related volcaniclastic sedimentary rocks were deposited in subaerial to shallow water settings, mainly over the Norrbotten craton. These rocks were underlain by significant granite, syenoid, dioritoid and gabbroid intrusions. This phase involved strong reworking of older crust within the Karelian and Norrbotten cratons. It included major batholithic development of S-type granite, migmatite and pegmatite in the core of the amalgamated Norrbotten-Karelian craton from 1.85 to 1.75 Ga, and north-south oriented A- and I-type diorite to granite batholiths extending into, and mainly within, the Svecofennian terrane to the south. It was followed, or overlapped with the interprerted accretion of several volcanic arc complexes associated with an interpreted subduction zone along the SW margin of the Norrbotten and Karelian cratons. Lahtinen et al. (2005) suggest this phase of subduction involved five partly overlapping pulses and the amalgamation of several microcontinents and island arcs onto the southwestern margins of the combined Archaean Karelian and Norrbotten cratons.

The major magnetite-apatite deposits at Kiirunavaara and Malmberget, as well as the epigenetic copper-gold deposits of the region (see the separate Norrbotten Region record for other deposits in the region), are hosted by the geographically restricted 1.89 Ga Kiirunavaara Group (formerly Kiruna Porphyries) and equivalents that overlie Archaean basement of the Norrbotten craton in the Kiruna-Gällivare district (Weihed et al., 2005). These deposits are located ~250 km to the northeast of the northwest-southeast trending Proterozoic to Archaean basement boundary and inferred subduction zone. Prior to the initiation of subduction, the same district lay within a northeast-trending extensional rift trough (Wanhainen and Martinsson, 2010). The volcanic rocks of the Kiirunavaara Group, have trachyandesitic to rhyodacitic compositions, and are taken to represent an early and chemically distinct phase compared to the dominant calc-alkaline andesites and related volcaniclastic sedimentary units of the subduction complex to the southwest. The Archaean basement, supracrustal rocks and an up to 10 km thick pile of Palaeoproterozoic sedimentary and volcanic rocks to the southwest of, and lapping onto the Archaean cratons, were multiply deformed and metamorphosed during the intrusion of voluminous 1.92 to 1.87 Ga granitoids with associated gabbros. This was followed by a 1.88 to 1.86 Ga quartz monzonite-adamellite-granite suite (interpreted to be comagmatic with the Kiirunavaara Group volcanic rocks), and then by the generation of anatectic A- and I-type granites during another major stage of deformation and metamorphism between 1.82 and 1.77 Ga (Billström et al., 2010 and sources quoted therein). These two sets of granitoids have calc-alkaline to alkali-calcic compositions (Wanhainen and Martinsson, 2010).

In the Norbotten region surrounding Kiruna, the regional early Palaeoproterozoic succession of greenstones, porphyries and clastic sediments described above, rests unconformably on deformed, 2.8 to 2.7 Ga, Archaean basement. The stratigraphically lowest member is the ~2.5 to 2.3 Ga Kovo Group, which includes a basal conglomerate, tholeiitic lava, calc-alkaline basic to intermediate volcanic rocks and volcaniclastic sediments (Martinsson, 1997). The Kovo Group is overlain by the ~2.2 to 2.0 Ga Kiruna Greenstone Group, which is dominated by mafic to ultramafic volcanic rocks with associated tuffaceous and interbedded sedimentary rocks and comagmatic intrusions. The stratigraphically lowest members of this group are minor clastic and chemical sediments (including banded iron formations) comprising sedimentary breccia, red-stained arenites and partly silicified carbonate rocks.

These Palaeoproterozoic greenstones are unconformably overlain by volcanic and sedimentary rocks, comprising several related stratigraphic units. These units regionally exhibit considerable variation in lithological composition, due in part to rapid changes from volcanic- to sedimentary-dominated facies. The Porphyrite Group and the Kurravaara Conglomerate are the lowest stratigraphic units of this succession in the Kiruna area. The former represents a volcanic-dominated, and the latter a mainly epiclastic unit (Offerberg, 1967), deposited as one or two fan deltas (Kumpulainen, 2000). These volcanic and sedimentary units, overlie Kiruna Greenstone basement 4 km to the west of the deposit. They are in turn overlain to the east by the Kiirunavaara Group that hosts the bulk of the iron mineralisation of the region, and comprises a thick pile of numerous trachyandesitic lava flows (traditionally named syenite porphyry) and overlying pyroclastic rhyodacite (traditionally referred to as quartz-bearing porphyry). This volcanic sequence is followed in turn by the Hauki and Maattavaara quartzites which constitute the uppermost Svecofennian units in the area (Martinsson, 2004).

Large-scale fluid migration of variable salinity took place in the Norbotten region from ~2 Ga, during the multiple stages of pre- and synorogenic magmatism, metamorphism and deformation resulting in regional scapolite, K feldspar-phlogopite, albite and albite-carbonate alteration (Billström et al., 2010). Regional scapolite has been variously attributed to felsic intrusions (Ödman, 1957) and to mobilised evaporites from supracrustal successions (Tuisku, 1985; Frietsch et al., 1997; Vanhanen, 2001). Around 40 iron oxide-apatite deposits are known within northern Norrbotten, with ~1600 Mt of ore having been mined from 10 of these during the last 110 years. These deposits are mainly restricted to the volcanic rocks of the Kiirunavaara Group, with very few occurrences known outside the immediate Kiruna-Gällivare area (Billström et al., 2010). Individual deposits have an average content of Fe and P varying between 30 to 70% and 0.05 to 5%, respectively. Beside magnetite and hematite, most deposits contain significant amounts of apatite and are generally strongly enriched in LREE (Frietsch and Perdahl, 1995). Within the Kiruna district, there is a progression upwards from albite-rich sodic alteration at depth, to intermediate potassic (K feldspar-sericite) to sericite-quartz at shallower levels. In the footwall of the main, conformable, tabular magnetite-apatite body at Kiirunavaara, the dominant assemblage is magnetite-albite-actinolite-chlorite, with the density of veins carrying these minerals increasing towards the base of the ore.

The tabular Kiirunavaara or Kiruna orebody is ~4.4 km long, up to 90 m thick, and extends down dip for at least 2 km to ~1.5 km below the surface. It follows the contact between a thick pile of trachyandesitic lava and overlying pyroclastic rhyodacite. To the north, the much smaller Luossavaara ore is situated in a similar stratigraphic position. The trachyandesite lava occurs as numerous lava flows which are strongly albite-altered and rich in amygdales close to the flow tops. A U-Pb age of 1876±9 Ma was obtained for titanite occurring together with actinolite and magnetite in amygdales (Romer et al., 1994). A potassic granite is present at deeper levels in the mine on the footwall side of the ore, and several 1880±3 Ma dykes of granophyric to granitic character cut the ore. A suite of rhyodacite dykes also cut the orebody, but are in turn brecciated by late magnetite. Some of these dykes are composite in character also including dolerite.

The orebody is primarily composed of magnetite, with intergrown apatite (mainly as fluorapatite), and accessory actinolite, biotite, calcite, quartz, titanite, diopside and albite. Rare earth minerals are enriched in the ore. The ore is bimodal, with high (>1 to 4% P) and low (<0.05% P) apatite ore. The apatite-rich ore is locally banded and predominates in the hanging wall and peripheral parts of the deposit, and in varying amounts in the footwall, whereas the apatite-poor variety is found close to the footwall, as slightly irregular and branching bodies of massive and fine-grained magnetite ore (Billström et al., 2010). Magnetite-actinolite veining/brecciation is found in both the hanging wall and footwall, including large blocks of volcanic wall rocks that may be partially or wholly replaced by actinolite. Blocks of wall-rock within the ore may be replaced by albite or have albitite rims.

The Kiruna deposit follows the contact between the underlying pile of trachyandesitic lava and hanging wall pyroclastic rhyodacite. The hanging wall is locally affected by biotite-chlorite alteration, commonly accompanied by weak enrichment of copper, cobalt and molybdenum. Postore alteration is evident in dykes that transect the deposit, and are altered to K feldspar, sericite and disseminated hematite, while hematite ±quartz, barite and/or fluorite veins cut the ore. The upper and lower contacts of the small, conformable magnetite-hematite (Per Geijer ores) lenses at the top of the rhyodacite are occupied by breccias of volcanic clasts in a hematite, magnetite and/or apatite matrix, with highly K feldspar-sericite-silica altered wall rocks (Billström et al., 2010; Hitzman et al., 1992). Billström et al. (2010), conclude that most features of the Kiirunavaara ores are compatible with both a magmatic magnetite intrusive origin, and over-printing by hydrothermal processes. In the deposit area, there is evidence of pre-ore metasomatic magnetite-albite-actinolite-chlorite alteration and mineralisation, followed by massive, columnar jointed magnetite-apatite ore with the characteristics of a magnetite magma, overprinted by further metasomatic magnetite mineralisation and associated alkalic alteration.

The deposit originally contained more than 2 Gt @ approx. 61% Fe, 0.97% P, 0.03% S, 0.07% Mn.

The descritions of Kiruna and its regional setting is largely summarised from Billström et al., 2010.

The most recent source geological information used to prepare this decription was dated: 2000.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


Kiirunavaara

    Selected References
Andersson, J.B.H., Bauer, T.E. and Martinsson, O.,  2021 - Structural Evolution of the Central Kiruna Area, Northern Norrbotten, Sweden: Implications on the Geologic Setting Generating Iron Oxide-Apatite and Epigenetic Iron and Copper Sulfides: in    Econ. Geol.   v.116, 30p. doi:10.5382/econgeo.4844
Bauer, T.E., Andersson, J.B.H., Sarlus, Z., Lund, C. and Kearney, T.,  2018 - Structural Controls on the Setting, Shape, and Hydrothermal Alteration of the Malmberget Iron Oxide-Apatite Deposit, Northern Sweden: in    Econ. Geol.   v.113, pp. 377-395.
Billstrom, K., Eilu, P., Martinsson, O., Niiranen, T., Broman, C., Weihed, P., Wanhainen, C. and Ojala, J.,  2010 - IOCG and Related Mineral Deposits of the Northern Fennoscandian Shield: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.4 pp. 381-414
Billstrom, K., Evins, P., Martinsson, O., Jeon, H. and Weihed, P.,  2019 - Conflicting zircon vs. titanite U-Pb age systematics and the deposition of the host volcanic sequence to Kiruna-type and IOCG deposits in northern Sweden, Fennoscandian shield: in    Precambrian Research   v.321, pp. 123-133.
Broughm, S.G., Hanchar, J.M., Tornos, F., Westhues, A. and Attersley, S.,  2017 - Mineral chemistry of magnetite from magnetite-apatite mineralization and their host rocks: examples from Kiruna, Sweden, and El Laco, Chile: in    Mineralium Deposita   v.52, pp. 1223-1244.
Carlon C J,  2000 - Iron Oxide Systems and Base Metal Mineralisation in Northern Sweden: in Porter T M (Ed), 2000 Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.1 pp. 283-296
Cliff R A, Rickard D  1992 - Isotope systematics of the Kiruna Magnetite ores, Sweden: Part 2. Evidence for a secondary event 400 m.y. after ore formation: in    Econ. Geol.   v87 pp 1121-1129
Cliff R A, Rickard D, Blake K  1990 - Isotope systematics of the Kiruna Magnetite ores, Sweden: Part I. Age of the ore: in    Econ. Geol.   v85 pp 1770-1776
Frietsch R  1982 - On the chemical composition of the ore breccia at Luossavaara, Northern Sweden: in    Mineralium Deposita   v17 pp 239-243
Frietsch R  1978 - On the magmatic origin of the iron ores of the Kiruna type: in     Econ. Geol.   v73 pp 478-485
Frietsch R and Perdahl J-A,  1995 - Rare earth elements in apatite and magnetite in Kiruna-type iron ores and some other iron ore types: in    Ore Geology Reviews   v9 pp 489-510
Geijer P  1960 - The Kiruna iron ores: in Grip, et.al., (Ed.s), 1960 Sulphides and Iron Ores of Västerbotten and Lappland, Northern Sweden, Guide Book to Excursion No. A27 and C 22, IGC Geological Survey of Sweden    pp 24-38
Hallberg, A., Bergman, T., Gonzalez, J., Larsson, D., Morris, G. A., Perdahl, J. A., Ripa, M., Niiranen, T. and Eilu, P.,  2012 - Metallogenic areas in Sweden: in Eilu, P., 2012 Mineral deposits and metallogeny of Fennoscandia, Geological Survey of Finland,   Special Paper 53, pp. 139-206.
Martinsson, O., Billstrom, K., Broman, C., Weihed, P. and Wanhainen, C.,  2016 - Metallogeny of the Northern Norrbotten Ore Province, northern Fennoscandian Shield with emphasis on IOCG and apatite-iron ore deposits: in    Ore Geology Reviews   v.78, pp. 447-492. doi.org/10.1016/j.oregeorev.2016.02.011
Parak T  1985 - Phosphorus in different types of ore, Sulfides in the Iron deposits, and the type and origin of ores at Kiruna: in    Econ. Geol.   v80 pp 646-665
Romer R L, Martinsson O, Perdahl J A  1994 - Geochronology of the Kiruna iron ores, and hydrothermal alteration: in    Econ. Geol.   v89 pp 1249-1261
Storey, C.D. and Smith, M.P.,  2017 - Metal source and tectonic setting of iron oxide-copper-gold (IOCG) deposits: Evidence from an in situ Nd isotope study of titanite from Norrbotten, Sweden: in    Ore Geology Reviews   v.81, pp. 1287-1302.
Westhues, A., Hanchar, J.M., Whitehouse, M.J. and Martinsson, O.,  2016 - New Constraints on the Timing of Host-Rock Emplacement, Hydrothermal Alteration, and Iron Oxide-Apatite Mineralization in the Kiruna District, Norrbotten, Sweden: in    Econ. Geol.   v.111, pp. 1595-1618.


Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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