|
Per Geijer - Nukutus, Henry, Rektorn, Haukivaara, Lappmalmen |
|
|
Norbotten, Sweden |
| Main commodities:
Fe REE P
|
|
 |
|
|
 |
Super Porphyry Cu and Au
|
IOCG Deposits - 70 papers
|
All papers now Open Access.
Available as Full Text for direct download or on request. |
|
|
The Per Geijer magnetite-hematite-phosphate deposit with by-product Rare Earth Elements (REE) is located just over 2 km NE of the Kiirunavaara iron ore mine in the Norbotten area of northern Sweden (#Location: 67° 52' 36"N, 20° 15' 32"E).
The giant Kiirunavaara deposit and the smaller Luossavaara, ~1 km along strike to the north, are principally massive, tabular, almost purely magnetite bodies with generally low phosphorus content. In contrast, the Per Geijer deposit is composed of two end members, that are predominantly magnetite and mainly hematite, with zones of mixed magnetite-hematite mineralisation, and occur at a higher stratigraphic level. Both the magnetite and hematite mineralisation is more phosphorous rich, with an average of ~2.4% P at Per Geijer, compared to 0.97% P at Kiirunavaara.
Mineralisation was first identified at Per Geijer in the late 19th century. Shallow, relatively narrow sections of the deposit have been partially mined as four separate satellite 'orebodies', namely Nukutus, Henry, Rektorn and Haukivaara which were mainly exploited during the 1960s, 70s and 80s. These orebodies yielded ~9 Mt from open pits and lesser underground operations, averaging 43.25% Fe (Grip and Frietsch, 1973). These, relatively narrow, generally <40 m thick, steeply dipping orebodies are distributed at surface over a north-south strike length of ~5 km, and width of up to ~500 m flanked by an alteration halo, as described below. The fifth body, the Lappmalmen zone, is buried, has not been mined, and was only partially known from drilling and geophysics.
Recorded historic production from individual orebodies were: Nukutus - 0.74 Mt @ 40 to 45% Fe, 4% P between 1961 and 1967 from an open pit; Henry, which was discovered in 1910 - 4.9 Mt @ 45% Fe, 4.5% P from an open pit between 1969 and 1987; Rektorn, discovered in 1887 and mined as both an open pit and underground between 1925 and 1961, with a total production of 2.5 Mt @ 33% Fe, 3.5% P, and according to Bergman et al. (2001) had a resource of 20 Mt at the same grade. Tonnages are from Martinsson (2015) and grades from (Grip and Frietsch, 1973).
More recent exploration has delineated a much larger, predominantly concealed body, presumably incorporating the Lappmalmen zone as an upper apophysis. A block model published on the LKAB website (see below) indicates a shell enclosing Measured + Indicated + Inferred Mineral Resources that is >3 km long and up to 700 m wide, with a vertical extent of 1000 to 1800 m. This shell is almost entirely concealed and is to be further tested underground via a new >2 km long drive from the existing Kiruna Mine, at a depth of ~700 m. This drive will intersect the northern margin of the 'deposit shell' in the half of its vertical extent. The previously mined shallow orebodies detailed above are assumed to be upper extensions connected/related to the larger deposit below.
For detail of the regional setting and metallogeny see the separate Fennoscandian Iron Oxide Copper Gold Province and Norrbotten Region records, as well as the Kiruna - Kiirunavaara, Luossavaara record for a description of those two nearby deposits.
In summary, the geology of northern Sweden includes a rift related ~2.3 to 2.0 Ga Palaeoproterozoic Greenstone Belt, with an accreted, subduction related Svecofennian igneous and sedimentary arc suite and extensional back-arc basin, all deposited on an attenuated Archaean basement. These rocks were deformed and metamorphosed to upper greenschist facies during the 1.9 to 1.8 Ga Svecokarelian Orogeny (e.g., Martinsson, 2015).
Basement comprises the extensive Neoarchean tonalitic-granodioritic Råstojaure Complex (Skiöld, 1979; Martinsson et al., 1999). This is unconformably overlain by the ~2.2 to 2.1 Ga Rhyacian, Palaeoproterozoic Kiruna Greenstone Group, a 2 to 4 km thick pile of tholeiitic mafic to ultramafic volcanic rocks, interpreted to be related to a Siderian to Orosirian continental rift event between ~2.5 and 2.0 Ga (Bergman and Weihed, 2020). The stratigraphic record demonstrates this event began with a transition from early clastic sedimentation to evaporites and then to 'within-plate' type volcanism, to later continental flood basalts. Subsequent crustal thinning is interpreted to have generated MORB basalts. This group has unconformable upper and lower margins. It is overlain by the thick 1.90 to 1.87 Ga Porphyrite Group calc-alkaline intermediate to felsic volcanic rocks, mainly andesitic volcanic rocks interpreted to have formed during subduction and is accompanied by clastic sedimentary rocks of mainly andesitic origin. Subduction is assumed to have been initiated by inversion and partial closure of the preceding rift.
The Kurravaara conglomerate, which overlies the Kiruna Greenstone and includes clasts of that unit, as well as calc-alkaline intermediate to felsic volcanic rocks presumed to be derived from the Porphyrite Group (Martinsson and Perdahl, 1993).
All of the iron 'ores' in the central Kiruna area are hosted by the 1.88 to 1.86 Ga Orosirian Kiirunavaara Group (previously the Kiruna Porphyries) which temporally overlaps the Porphyrite Group, and has a gradational upper contact with the Kurravaara conglomerate. The Kiirunavaara Group, has a bimodal nature and a chemical composition which Martinsson (2004) suggests implies an intraplate origin. Andersson et al.> (2021) suggest the sequence was deposited in an extensional intracontinental back-arc basin. It is subdivided into to the:
• Hopukka Formation, the lowest unit, which is dominated by amygdaloidal basalt to andesitic to trachyandesitic lava and sub-volcanic rocks (also known as the 'Syenite Porphyry' in earlier literature);
• Luossavaara Formation, ~800 m of 'felsic porphyries' with abundant 2 to 5 mm feldspar phenocrysts (Martinsson et al., 2016), interpreted to be a rhyodacitic pyroclastic unit composed of tuffs and subordinate breccia conglomerates (e.g., Martinsson 2015);
• Matojärvi Formation, a mixed volcanic and sedimentary unit comprising rhyolite, basalt, conglomerate, greywacke and schist (Martinsson
2004). The basal unit is a rhyolitic ignimbrite (Frietsch, 1979), traditionally, described as the 'Rektor Porphyry' (e.g., Geijer, 1950). The Matojärvi Formation marks a transition in the geological character of the sequence, from a volcanic → volcano-sedimentary → sedimentary sequence, represented by the progression from basal rhyolitic tuffs and ignimbrites (Geijer, 1950; Frietsch, 1979), conformably overlain by basaltic agglomerates, tuffs and lavas (Martinsson, 2004), followed by heterolithic breccia conglomerates (Andersson et al., 2017), lithic greywackes, and a phyllitic uppermost horizon (Lundbohm, 1910; Frietsch 1979). The volcanic sequence of the Orosirian Kiirunavaara Group at Kiruna is understood to have formed over an interval of no more than 15 m.y. (Andersson et al., 2021).
The volcanic period was followed by deposition of cross-bedded arenites, interrupted by bands of sedimentary breccia conglomerates situated in its basal and middle sections. This suite is the regionally correlatable 1.87 to 1.85 Ga Hauki quartzite (Martinsson, 2004).
The Kiirunavaara and Luossavaara deposits were emplaced at the contact between the Hopukka and Luossavaara formations, whilst the Per Geijer mineralisation is developed between the upper contact of the latter and the basal rhyolitic ignimbrite of the Matojärvi Formation (Andersson et al., 2021). However, the at Haukivaara and Lappmalmen deposits, at least partly, are also extend into the overlying Matojärvi Formation (Krolop et al., 2019).
Whilst no descriptions of the geology of the main Per Geijer deposit have been encountered, it is understood to be composed of the same style of mineralisation encountered in the main exposed Per Geijer orebodies that have been mined previously. To provide an insight into what this mineralisation style involves, these are summarised below as follows (after Martinsson, 2015):
Nukutus
Nukutus is the northernmost of the Per Geijer orebodies, and was discovered in 1888. Mineralisation is known over a strike length of >1.5 km, but appears to have only been exploited in a central thickened section over a length of <500 m where it is ~100 m thick, compared to the general <30 m to the north and and south. Mineralisation is mostly fine grained, massive magnetite and hematite. The principal gangue minerals are carbonate, apatite and quartz, which may also occur as rounded to more irregular blebs within the magnetite-hematite mineralisation, and locally as larger accumulations, especially at the orebody contacts where they may be partly banded. Apatite and carbonate are also found as the matrix to crosscutting breccia at the footwall contact, enclosing clasts of magnetite/hematite and silicified rhyodacite. Almost pure apatite veins cut the orebody at scales varying from mm to almost metre scales. Chalcopyrite is present in small amounts in these associations, and also occurs together with apatite and carbonate in chlorite-sericite altered basalt in the hanging wall.
Henry
The Henry deposit was discovered in 1910 and has a 'Y' shape, composed of both stratabound and transgressive lenses. The NNW-SSE trunk and north-south right arm of the structure is up to 70 m thick and represent concordant mineralisation, whilst the WNW-ESE left arm is transgressive. The Henry pit exploited the orebody over a length of ~1 km, with stratabound mineralisation tapering to the south, and being fault offset to continue as the Nukutus orebody to the north. The stratabound mineralisation is dominated by massive magnetite that has largely been altered to hematite. Locally, vuggy and skeletal massive iron oxides are found, and more rarely very fine grained magnetite with a scoriaceous texture. In both varieties, magnetite is largely altered to hematite with some goethite cavity infill. The discordant section of the orebody extends into the footwall and ends in trachyandesite of the Hopukka Formation. Iron oxides change from hematite to magnetite with increasing depth in the footwall. In the northern part of the orebody, apatite-carbonate-quartz rocks occur, similar to those found at Nukutus. These are partly banded, and in places seem to intrude the host rocks (Ginet and Kunzle, 1978). The discordant mineralisation is accompanied by strong sericite alteration, and within the amygdaloid trachyandesite of the Hopukka Formation, there is associated albite ±carbonate alteration with minor chalcopyrite in amygdales and in quartz-carbonate veins.
Rektorn
The Rektorn orebody was discovered in 1987. In the open pit, mineralisation is continuous over a strike length of ~750 m and varies from 20 to 40 m in width. It is composed of magnetite and hematite in varying proportions, with apatite that is disseminated, enriched in bands, or forms coarse-grained crosscutting veins and breccia infill. Locally, quartz and carbonate are important gangue minerals in the apatite-rich mineralised zones (Geijer, 1950). Mineralisation is mostly fine grained with magnetite partly transformed to hematite. Less commonly the ore is coarse grained with an intergranular texture of tabular magnetite grains with interstitial apatite, carbonate and some quartz.
The rhyolitic ignimbrite unit of the lower Matojärvi Formation in the hanging wall has undergone extensive K feldspar alteration and silicification, whilst sericite formed during a late pervasive alteration phase in association with shearing and as patches or lenses of massive sericite containing radiating aggregates of tourmaline. These rocks contain minor Cu-sulphides. Intercalations of fragmental siliceous, apatite-poor hematite mineralisation up to several metres in thickness are common within these silicified and K feldspar altered rhyolitic ignimbrites at the upper contact. One of these lenses of massive iron oxide mineralisation is seen to transition into a scoriaceous texture. Barite, orthite and fluorite are accessories in the altered basal rhyolitic ignimbrite unit and in the siliceous hematite ores (Lundbohm 1910). A strong sericite-chlorite alteration is developed in the sheared basaltic tuff overlying the rhyolitic ignimbrite.
In the southern part of the orebody, a 10 to 20 m wide ore breccia extends into the footwall, containing up to 50 cm wide altered fragments of rhyodacite, set in a matrix of carbonate, apatite, quartz and magnetite. Further south a banded rock with the same mineral composition occurs at the footwall contact. Several carbonate-bearing quartz veins containing minor amounts of hematite, allanite, pyrite, chalcopyrite and bornite crosscut the iron oxide mineralisation at a high angle. Towards the centre of the orebody, a branch of iron oxide protrudes at least 40 m into the footwall. The Luossavaara Formation rhyodacite in the footwall is usually altered over a width of 5 to 10 m along the contact with the mineralisation, with an assemblage of sericite, ferro-dolomite, biotite and, locally, tourmaline with occasional minor chalcopyrite and pyrite (Geijer 1950).
Haukivaara
The Haukivaara Mine is located <1 km to the SE of the Rektorn orebody and consist of 2 parallel ore lenses, each ~600 m long, largely hosted within the Matojärvi formation. The lenses have average widths of <20 m and are composed of hematite with minor magnetite. The mine has been inactive since the early 1970s.
Little information has been encountered on the blind Lappmalmen mineralisation, which was found in the 1960s to the east of Rektorn and has not been mined. Mineralisation occurs at the contact between the Luossavaara and Matojärvi formations, and extends up into the latter. According to Parák (1975), it had yielded the thickest intersection of Per Geijer mineralisation with 250 m @ 44.4% Fe, 4% P and 5% SiO2, was up to 700 m deep and is composed of Per Geijer type mineralisation. It is assumed this body forms part of the larger Per Geijer deposit.
Wall rock alteration is generally strongest in the hanging wall of the exposed Per Geijer orebodies (e.g., Rektorn, as described above), occurring as K feldspar, quartz, sericite, ankerite-calcite, chlorite and minor tourmaline, forming an up to 200 m wide upper fringe within the lower Matojärvi Formation. It is characterised by spotted K feldspar in strongly silicified felsic volcanic rocks. K feldspar alteration may be overprinted by sericite in shear zones. Hydrothermal breccias are also frequently evident in the hanging wall, composed of strongly altered clasts of mainly basalt and rhyolite within a matrix of apatite, carbonate, sericite and magnetite/hematite. Up to 10 m thick intercalations of cherty hematite ore are also common and may have a fragmental texture, mostly developed in strongly K feldspar altered and silicified rhyolite. They commonly containing some barite with minor apatite (Geijer, 1950; Martinsson, 2004; Martinsson, 2015). Most of the hydrothermal alteration appears to be related to the introduction of apatite-rich iron mineralisation (Martinsson, 2015).
Footwall rocks are generally less altered, with chlorite, biotite, carbonate, apatite and locally albite or actinolite occurring in an up to 50 m wide fringe in the underlying rhyodacite from the Luossavaara Formation (Martinsson, 2015).
The typical composition of massive iron oxide mineralisation is 40 to 50% Fe magnetite/hematite, 20 to 30% apatite, 5 to 25% carbonate and 2 to 10% quartz. However, mineralisation exhibits large variations in texture, mineral composition, influenced by the relation to wall rocks. Magnetite is commonly found as euhedral to subhedral isometric crystals, with grain sizes that vary from between 20 and 400 µm, but rarely >1 mm. It is generally associated with hematite and apatite. Inclusions of predominantly apatite, monazite, pyrite and chalcopyrite may be present locally, particularly in large >500 µm euhedral grains. Hematite replaces magnetite, occurring as irregular shapes or as pseudomorphs, and is generally associated with magnetite, apatite and sulphide minerals such as chalcopyrite and pyrite. Euhedral hematite laths with varying grain sizes, commonly >1 mm are also found (Krolop et al., 2020).
Trace element analyses (LAICP-MS) show that there are variation in the Ti content of magnetite from 24 to 3199 ppm, while V (641 to 1119 ppm) and Ni (228 to 635 ppm) are relatively constant. Co contents identify two populations of magnetite, ranging from either 63 to 88 ppm in Nukutus and Rektorn to significantly lower concentrations of 1 to 9 ppm in Lappmalmen. Hematite is generally found as Ti-poor and Ti-rich populations, with the former at ~300 ppm, while the T-rich variety carries 2.17 to 13.6%. Vanadium is relatively constant at 576 to 1961 ppm, with the exception of Henry with 83 to 357 ppm. Ni is generally lower in hematite than in magnetite but may be a high as 175 ppm. The total Co contents are below 52 ppm in all deposits.
Mineral Resources
Mineral Resources at 31 December 2022, as published by LKAB on 12 January 2023 were as follows:
Magnetite mineralisation
Measured + Indicated Resource - 136 Mt @ 52.6% Fe, 2.67% P;
Inferred Resource - 227 Mt @ 50.8% Fe, 1.95% P;
TOTAL Resource - 363 Mt @ 51.5% Fe, 2.22% P, 0.17% TREO.
Mixed magnetite and hematite mineralisation
Measured + Indicated Resource - 42 Mt @ 47.4% Fe, 2.98% P;
Inferred Resource - 109 Mt @ 45.6% Fe, 2.76% P;
TOTAL Resource - 151 Mt @ 46.1% Fe, 2.82% P, 0.21% TREO.
Hematite mineralisation
Measured + Indicated Resource - 23 Mt @ 54.6% Fe, 2.73% P;
Inferred Resource - 48 Mt @ 55.3% Fe, 2.42% P;
TOTAL Resource - 71 Mt @ 55.0% Fe, 2.52% P, 0.18% TREO.
Internal waste
TOTAL internal waste - 0.6 Mt @ 9.2% Fe, 0.79% P, 0.09% TREO.
TOTAL Measured + Indicated + Inferred Resource
TOTAL all ore types - 585 Mt @ 50.5% Fe, 2.41% P, 0.18% TREO.
NOTE: TREO = Total Rare Earth Oxide, and includes:
Light Rare Earth Oxides (LREO) - La2O3, Ce2O3, Pr2O3, Nd2O3, Sm2O3,
Heavy Rare Earth Oxides (HREO) - Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3 and Y2O3.
LREO and HREO constitute 17% and 83% of the tested apatite concentrate samples respectively.
Mineral Resources have been constrained within optimised stopes based on the mining and production of magnetite pellets and hematite concentrate. The optimisation uses a cut-off grade of 26% Fe for the magnetite dominant material, 35% Fe for the mixed magnetite / hematite material and 53% Fe for the hematite dominant material.
Testwork completed to January 2023 produced an apatite concentrate with a P2O5 grade of >34% and an associated TREO grade of between 0.84% and 0.85% TREO.
The most recent source geological information used to prepare this decription was dated: 2022.
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.
Per Geijer
|
|
|
|
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
|
Krolop, P., Jantschke, A., Gilbricht, S., Niiranen, K. and Seifert, T., 2019 - Mineralogical Imaging for Characterization of the Per Geijer Apatite Iron Ores in the Kiruna District, Northern Sweden: A Comparative Study of Mineral Liberation Analysis and Raman Imaging: in Minerals (MDPI) v.9, 14p. doi:10.3390/min9090544.
|
Krolop, P., Richter, K., Niiranen, K., Gilbricht, S., Schulz, B., Oelze, M. and Seifert, T., 2021 - Trace element composition of iron oxides in the Per Geijer deposits In Kiruna, Northern Sweden: in European Geosciences Union (EGU) General Assembly 2021, 19 to 30 April 2021. 10p. doi.org/10.5194/egusphere-egu21-1987.
|
Martinsson, O., 2015 - Genesis of the Per Geijer apatite iron ores, Kiruna area, northern Sweden: in Andre-Mayer, A.S., Cathelineau, M., Muchez, P., Pirard, E.and Sindern, S., (Eds.), 2015 13th SGA Biennial Meeting, Mineral Resources in a Sustainable World, Nancy, France, 24 to 27 August 2015; Abstract Volume, pp. 1107-1110.
|
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
|
|
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.
|
Top | Search Again | PGC Home | Terms & Conditions
|
|
