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Norrbotten Region - Kiruna / Kirunavaara, Malmberget, Gruvberget, Viscaria, Aitik, Kiskamavaara

Norbotten, Sweden

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The Norrbotten Region of northern Sweden contains large reserves of magnetite-apatite ores, particularly at Kiruna (Kirunavaara with +2 Gt of 60-62% Fe), Malmberget (930 Mt @ 60-62% Fe), Gruvberget Iron (73.8 Mt @ 57% Fe. 0.87% P) and Gruvberget Copper (0.2 Mt @ 0.5% Cu) in late Palaeoproterozoic (1.88 Ga) rocks, but also copper mineralisation at deposits such as Aitik (global resource of 800 Mt @ 0.3% Cu, 0.2 g/t Au) and Viscaria (production of 13 Mt @ 2.3% Cu from a global resource of 40 Mt @ 1.5% Cu, 0.7% Zn). The small Kiskamavaara occurrence (3.42 Mt @ 0.37% Cu, 0.09% Co) is also described below. These deposits are believed to be related to the Iron Oxide Copper Gold class of deposit and lie within the broader Fennoscandian Iron Oxide Copper Gold Province.

Kirunavaara - see the separate Kiruna, Kiirunavaara, Luossavaara record.

Malmberget (#Location: 67° 12' 0"N, 20° 41' 56"E) - The Malmberget deposit is located at Gällivare, ~80 km SSE of Kiirunavaara. It comprises at least 10 mined iron ore bodies sitting within an elongate east-west zone that is 5 km long and 2.5 km wide, containing around 20 discrete bodies (Carlon, 2000). In the western and northern parts of the deposit the ore forms an almost continuous horizon over the whole 5 km long zone. Remaining reserves in 2015 were 346 Mt @ 42.5% Fe. The current (2018) underground operation is concentrated in 10 orebodies each of 5 to 245 Mt, producing 17.4 Mt of apatite iron ore per annum (Bauer et al., 2018).
  The hosts to the deposits (Geiger 1930) comprise red and grey, alkalic, syenitic and mafic metavolcanic rocks as at Kiirunavaara and are traditionally called leptites in the Malmberget area. A porphyritic texture is locally preserved in the felsic rocks, whilst amygdules are occasionally encountered, suggesting a mainly extrusive origin and a primary character similar to that of the Kiruna Porphyries. Mafic rocks are mainly found adjacent to the ores as conformable to discordant lenses and occasionally contain remnants of plagioclase phenocrysts and amygdules. Some mafic rocks are interpreted to represent dykes, although most are regarded to have been sills or extrusions (Geijer 1930). A large intrusion of post-orogenic Lina Granite occurs to the NW of the deposit and corresponds to an increasing recrystallisation of the host rocks. Dykes of granite and pegmatite are frequently found in the ores and their host rocks. Some of the pegmatites are rich in coarse-grained hematite, apatite and titanite (Martinsson and Wanhainen, 2000).
  The Malmberget orebodies are highly deformed and 'stretched', refolded and rodded into a series of dismembered shoots with complex geometry. Pre-deformation dimensions of the ore zone appear to have been similar to that at Kiirunavaara. Recrystallisation has increased the grain size of the iron oxides and apatite from 0.1 mm, as at Kiirunavaara, to 0.5 to 2 mm for the ore minerals at Malmberget, although larger porphyroblasts of magnetite may occur in hematite rich ore. Apatite banding is a common feature of the ores, which contain both magnetite and hematite. The eastern section of the deposit includes several virtually isolated bodies of magnetite ore, which generally contains lesser apatite. The main gangue minerals overall are apatite, amphibole, pyroxene and biotite. Pyrite, chalcopyrite, bornite and molybdenite are more rarely found (Martinsson and Wanhainen, 2000). The 'layering' in the apatite-magnetite at is a recrystallisation phenomena, and can be considered a 'gneissic texture', with the magnetite clearly having 'flowed' as a solid-state ductile medium. The deposit has also suffered thermal metamorphism from the adjacent post-orogenic Lina Granite (Carlon, 2000).
  The contact zones of the magnetite-haematite-apatite-actinolite iron deposits are marked by veining, brecciation of the wallrocks, iron-oxide matrix supported breccias, host-rock xenoliths within the iron oxides, wall rock clast reaction rims and clast digestion and corrosion phenomena. Magnetite matrix supported, wall rock slab-clast and explosive jigsaw clast breccias, suggest rapid decompression phenomena, while fine grain size and thin reaction rims indicate rapid deposition of iron oxides from a fluid medium. Brecciation often occurs in both hangingwall and footwall contact zones suggesting emplacement vertically rather than horizontally, and there is no silicate fusion in contact with iron oxides as would be expected with magmatic magnetite emplacement into a brittle fractured, solid metavolcanic host (Carlon, 2000).
  Structural analysis (Bauer et al., 2018) indicate an initial compressional event (D1) at around 1.88 Ga. This represents the main metamorphic event (M1) in the district and was responsible for a strong transposition of primary layering and the orebodies and led to the formation of a composite S0/1 fabric (Bauer et al., 2018). A subsequent F2 folding event at ~1.80 Ga formed an open, slightly asymmetric synform with a steeper SE limb and a roughly SW-plunging fold axis. Structural modelling suggests that the ore formed at two separate horizons. F2 folding was accompanied by stretching, resulting in boudinage of the iron orebodies. D2 related high-strain zones and syntectonic granites triggered the remobilisation of amphibole, biotite, magnetite and hematite and controlled the formation of iron oxide-copper-gold (IOCG) style hydrothermal alteration, including an extensive K feldspar alteration accompanied by sulphides, scapolite and epidote. A distinct time gap of at least 80 m.y. is indicated between the formation of iron oxides and sulphides (Bauer et al., 2018). Bauer et al. (2018) suggest brittle structures and the lack of an axial planar parallel fabric indicate upper crustal, low-pressure and high-temperature conditions during D2 deformation, inferring a hydrothermal event rather than purely regional metamorphic compression. The same authors propose that the Malmberget IOA deposit was deformed and metamorphosed during a 1.88 Ga crustal shortening eventand the deposit was subsequently affected by a 1.8 Ga folding and hydrothermal event that is related to a regional IOCG overprint.
  A string of layered, tholeiitic gabbro complexes which is composed of troctolite, magnetite gabbro and gabbronorite lie within 2 km to the south of Malmberget and Gällivare. These complexes comprise multiple, ovoid shaped alkaline to tholeiitic mafic-ultramafic intrusions that are distributed over a 10 x 6 km, ENE-WSW elongated area intruding the host mainly felsic metavolcanic rocks to Malmberget, and include the Dundret, Vassaravaara and Littikhed intrusions that vary from 3 to 4 km in diameter. The lower and outer parts of the Dundret intrusion consist of troctolite alternating with magnetite gabbro. The upper and central sections are dominated by gabbronorite with interlayers of magnetite gabbro and locally peridotite. The layering of the complex forms a bowl-like structures where the dip decreases from 60° at the margins to almost horizontal at the centre of the intrusion (Martinsson, 1994, 2000; Martinsson and Wanhainen, 2000). The gabbros have been dated as follows: Dundret - 1883±5 Ma; Vasaravaara - 1798±3 Ma; Sarlas, 2017). The felsic volcanic sequences and gabbro complexes are intruded by smaller post orogenic monzodiorite-quartz-syenite bodies (Sarlas, 2017). The close proximity of magnetite bearing felsic extrusive rocks as at Malmberget and magnetite bearing intrusive gabbroic complexes at Dundret, Vassaravaara and Littikhed, i.e., an environment of mingled mafic and felsic igneous rocks of similar age bracket, is of significance.

Gruvberget (#Location: 67° 38' 1"N, 21° 1' 14"E) - Both an apatite-iron and an epigenetic copper deposit occur at Gruvberget, ~40 km SE of Kiirunavaara. The apatite-iron mineralisation at Gruvberget is 1300 m long and up to 65 m thick and persists to depths of ~350 m. It is hosted by intensely scapolite- and K feldspar-altered intermediate to mafic volcanic rocks. Several northeast-trending meta-dolerite dykes cut the ore and its wall rocks. The ore is mostly massive, consisting of magnetite in the north, and hematite in the central and southern parts of the deposit. In the north, the ore is overlain by a narrow zone of garnet, amphibole and epidote towards the hanging wall, whilst an extensive ore breccia is developed in the footwall at the middle part of the deposit. K feldspar alteration is extensively developed east of the iron ore, resulting in a high K2O content (up to 9.8 %).Veins and schlieren of magnetite, hematite, apatite and amphibole form an extensive ore breccia in the footwall of the mid-sections of the deposit (Frietsch, 1966). LKAB commenced mining operations commenced in May 2010 extracting ~2 Mt per annum of raw ore that is processed into 1.4 Mt of pellets.
  The Gruvberget Cu deposit is the largest of the old copper mines in Norrbotten. The earliest information on the mine date from 1644 when a license to mine was granted. Between 1657 and 1684 about 1000 t of Cu was produced. Copper is the only metal reaching economic grades, while the gold content is generally very low. Copper sulphides are scattered throughout the Gruvberget area, with zones of richer mineralisation mainly developed in the footwall to the iron ore. Chalcopyrite, and less abundant bornite, are the main ore minerals, occurring disseminated together with magnetite in altered rocks, or as rich ore shoots at the contact with the iron ore. Locally, there are also veins of quartz, minor K feldspar, amphibole, garnet, and small amounts of magnetite, chalcopyrite and bornite. Molybdenite is locally present in small amounts. Druses with epidote, magnetite, pyrite, copper-sulphides and desmine (stilbite) are common within the bornite-bearing sulphide occurrences. Intense K feldspar alteration is locally developed in association with the bornite mineralisation west of the iron ore, replacing the earlier scapolite. Several of the old workings are close to meta-dolerites, and the copper mineralisation seems to be controlled by the same structures as the dykes. As the meta-diabase dykes cut the iron ore, this suggests that the copper occurrence represents a separate and later event, with the iron ore only acting as a chemical-structural trap (Lindskog, 2001; Billström et al., 2010).

Viscaria (#Location: 67° 51' 57"N, 20° 6' 56"E) - The Viscaria copper-deposit is located 4 km west of Kiirunavaara in Sweden. The mine was initially owned and operated by LKAB Viscaria AB and commenced operation in 1983. The operation was acquired by Outukumpu OY in 1985 and closed in 1997.
  The Kiruna Greenstone Group of the Kiruna-Viscaria district are characterised by low grade metamorphism (generally upper greenschist to lower amphibolite facies) with generally well preserved primary structures (Bergman et al. 2001). It has been divided into six formations based on petrographical and geochemical criteria (Martinsson, 1997), as follows from the base (after Ellice, 2014):
Såkevaratjah Formation - basaltic lavas, dolerite and locally conglomerates;
Ädnamvare Formation - komatiites, indicating a magmatic change from tholeiitic to ultramafic;
Pikse Formation - tholeitic basalts;
Viscaria Formation - a succession of volcaniclastic sediments and organic sediments (carbon shales);
Peuravaara Formation - MORB type pillow-lavas;
Linkaluopal Formation - volcaniclastics and carbonates. This upper most unit is interpreted to have been completely eroded in Viscaria deposit area, although it is well preserved to the north.
  The Viscaria Formation hosts four distinct zones of mineralisation that are referred to as D, C, B and A zones, from the base. These units are laterally extensive and can be traced for several kilometres along strike to both the NE and SW of the deposit.
  The host to the D Zone mineralisation is subdivided into the lower D1 stratigraphic unit which consists of a magnetite-bearing carbonate rock lying directly on top of the uppermost rocks of the Pikse Formation. The overlying D2 is a finely banded, tuffaceous shale with syn-sedimentary slump structures, and likely grades upwards to more massive pyroclastic tuffaceous material.
  The C Zone mineralisation is hosted by a 20 to 30 m thick black graphitic schist containing 15 to 25% C, with little sulphide content comprising minor pyrite, pyrrhotite and sphalerite which occur occur in veinlets.
  The B Zone mineralisation are subdivided into four members. The basal B1 member comprises massive, fine-grained tuff. B2 is similar in but has graded bedding structures at varying scales. B3 is tuffaceous with interbedded graphitic schists, whilst B4 is composed of coarse-grained pyroclastic material.
  The host rocks to the A Zone mineralisation varies in thickness from 15 to 25 m and is comprises a mixture of felsic ash tuff, black/graphitic schists, carbonate rocks and basaltic tuff. The lowermost section is a felsic tuff unit that is typically 3 to 5 m thick, with disseminated graphite at the base of the unit. The graphite content gradually increases upwards and grades into a black/graphitic schist. An ore-bearing carbonate unit has historically been interpreted to be hosted in a layered sedimentary tuff unit that separates the black schist from overlying pyroclastic and sedimentary units.
  The Viscaria Formation is overlain by a thick sequence of pillow lavas of the Peuravaara Formation, whilst in its upper section it has been intruded by several mafic sills, particularly to the south and at depth. These sills range in thickness from 10 to 50m and produce a more complex ore geometry (Martinsson, 1997).
  The A and B zone deposits are predominantly composed of chalcopyrite with associated abundant pyrrhotite ±pyrite ±magnetite ±sphalerite ±galena. The D and Discovery zones are predominantly composed of magnetite and chalcopyrite with only very minor associated pyrite.
  The A Zone was 3 km long, NE-SW trending and is situated between two black schist units, as described above, at the top of a large alteration zone expressed by the destruction of plagioclase and the formation of biotite. The ore zone is capped by a thin chert unit extending several kilometres beyond the economic part of the deposit. The A Zone was known to a depth of 700 m dipping at 80°E, decreasing at depth to 45 to 50°. Chalcopyrite, magnetite, pyrrhotite and sphalerite are the main ore constituents, occurring as disseminations, thin layers and more massive accumulations. Calcite is the main gangue mineral, with accessory amphibole, apatite, barite, quartz and albite (Billström et al., 2010).

Aitik - The Aitik deposit is located 15 km east of Gallivare and Malmberget and is described in the separate Aitik record.

Kiskamavaara is a small Cu-Co-Au resource located 40 km east of the Kiruna deposit. It is one of a number of small occurrences located along the major regional NNE trending Karesuando-Arjeplog Deformation Zone, interpreted to be a reactivated structure on the eastern margin of a 2.1 Ga rifting episode. The same structure passes through the Gruvberget deposit, ~30 km to the SSE to SE. It is partly associated with extensive zones of albite-carbonate alteration within a sequence that predominantly comprises intermediate to felsic metavolcanic rocks and quartzite. A granodiorite intrusion is exposed 1 km south of the mineralisation.
  The host to mineralisation is fragmental with subrounded clasts of up to 4 cm in diameter of altered intermediate volcanic rocks in a matrix mainly composed of fine grained volcanic material and varying amounts of hematite, magnetite and pyrite. Many of the clasts are strongly K feldspar altered, giving a red colouration and increasing the grain size. Texturally similar K feldspar alteration occurs as diffuse patches in the matrix fragments, suggesting the alteration, at least in part preceded clast formation. This is interpreted to indicate a hydrothermal origin with contemporaneous alteration and fragmentation related to tectonic and hydrothermal activity (Martinsson, 2011).
  The volcanic rocks have been metamorphosed at lower to medium amphibolite facies, with the andesites being subjected to intense ductile deformation, resulting in a steep and generally strong NNE-SSW foliation. In contrast, the fragmental rock has only locally undergone ductile deformation, occurring as narrow zones of mylonite or a weak to strong foliation. The deformed rocks are commonly rich in sericite (Martinsson, 2011).
  The deposit comprises three higher grade sulphide lenses within an ~900 m long and 15 to 40 m wide mineralised zone. Co-bearing pyrite is disseminated in the matrix to the fragmental rock together with magnetite and some chalcopyrite. The matrix ranges from almost massive pyrite in the core of the rich ore lenses, to peripheral disseminated magnetite-pyrite and an outer hematite-magnetite fringe. Higher Cu grades are sporadic within pyrite rich lenses, but is typically found on their periphery. Carbonate and local quartz are the principal gangue minerals, enclosing euhedral pyrite and magnetite, although the carbonates have often been removed by weathering, giving the mineralisation a vuggy appearence. Elevated gold grades of 0.1 to 0.4 g/t are related to the sulphide mineralisation, whilst molybdenite is a locally developed accessory mineral (Martinsson, 2011).
  The most prominent alteration style is a very strong K feldspar development that forms a 250 to 300 m wide zone within the fragmental rocks, the central, and sulphide rich part of which differs only in its more intense reddish colour. A carbonate rich albite rock is found east of the deposit and is interpreted to possibly represent either an altered felsic intrusion or a strong hydrothermal alteration of the andesite (Martinsson, 2011).
  The K-feldspar altered fragmental rock is enriched in K
2O (7.1 to 11.6%) and Ba (0.25 to 0.64%), whilst Ca, Na, Zn and Y are depleted. Further to the east, a common alteration assemblage in metavolcanic rocks and metadolerite comprises scapolite and associated biotite. The scapolite mainly occurs porphyroblasts although it also locally forms as veinlets. In detail, the host rock exhibit a distinct zonation from west to east that is truncated at its eastern side by a shear zone. To the west, the rock has a reddish-grey colour and is dominated by K feldspar alteration with disseminated hematite as breccia infill. Further east, sericite and minor tourmaline overprint the K feldspar and magnetite, and calcite begins to appear as breccia fill. This is followed by a zone with a strong red colouration with remnants of scapolite. Magnetite, pyrite and some chalcopyrite and calcite occur as breccia matrix but are succeeded eastward by a magnetite zone almost devoid of sulphides with traces of molybdenite (Martinsson, 2011).
  Historic resource estimates are 2.87 Mt grading 0.6% Cu and 0.09% Co (Persson, 1982); and 3.42 Mt @ 0.37% Cu, 0.09% Co (Persson, 1981; Martinsson and Wanhainen, 2000). The Co which is in pyrite, varies from 0.07 to 3.6%, averaging 0.9% (Martinsson and Wanhainen 2000). Gold was not included in these estimates, but locally varies from 0.1 to 0.4 g/t in the sulphide zones (Martinsson, 2011).

The Norrbotten district and its mineralisation and geologic and metallogenic setting are the subject of papers in the monograph: Porter T M (Ed.) "Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective" volumes 1 and 2, published by PGC Publishing, Adelaide, Australia - See abstracts by Carlon, 2000 and Nisbett et al., 2000.

The deposits and the setting of the Norrbotten district are also described in
Billström 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. - See abstracts by Billström et al., 2010 and Smith et al., 2010.

For detail consult this paper or other reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 2012.     Record last updated: 8/7/2020
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.


Malmberget

Gruvberget

Viscaria

  References & Additional Information
   Selected References:
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.
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.,  2011 - Kiskamavaara shear zone hosted IOCG-style of Cu-Co-Au deposit in Northern Norrbotten, Sweden: in Barra, F., Reich, M., Campos, E. and Tornos, F., (Eds.), 2011 Lets talk ore deposits, Eleventh Biennial SGA Meeting, Antofagasta, Chile, 26-29 September 2011,   Proceedings, v.2, pp. 470-472.
Smith M, Coppard J and Herrington R,   2010 - The Geology of the Rakkurijärvi Copper-Prospect, Norrbotten County, Sweden: in Porter T M, (Ed),  2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.4 pp. 427-440
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.
Weihed P, Arndt N, Billstrom K, Duchesne J C, Eilu P, Martinsson O, Papunen H and Lahtinen R  2005 - Precambrian geodynamics and ore formation: The Fennoscandian Shield : in    Ore Geology Reviews   v27 pp 273-322
Williams, P. J., Kendrick, M.A. and Xavier, R.P.,  2010 - Sources of Ore Fluid Components in IOCG Deposits: in Porter T M, (Ed), 2010 Hydrothermal Iron Oxide Copper-Gold and Related Deposits: A Global Perspective PGC Publishing, Adelaide   v.3, pp. 107-116.

   References in PGC Publishing Books: Want any of our books ? Pricelist
Carlon C J, 2000 - Iron Oxide Systems and Base Metal Mineralisation in Northern Sweden,   in  Porter T M, (Ed.),  Hydrothermal Iron Oxide Copper-Gold & Related Deposits: A Global Perspective,  v1  pp 283-296
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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 takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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