Summary:
Deposit Geology
The Kiruna mineralisation comprises the main Kiirunavaara deposit as well as the Luossavaara and Konsuln deposits. All three deposits are located at the contact between the Luossavaara formation hanging wall and the Hopukka formation footwall. The main Kiruna mineralisation is interpreted to have been offset by several faults, the most significant of which are NE-SW trending in the northern and southern ends of the deposit. These display an offset of up to ~400 m in the Konsuln area which includes the Sigrid and Viktor lenses and ~200 m in the northern end. In addition, several lenses of magnetite mineralisation occur within the Luossavaara formation at different stratigraphic levels, internally referred to as Neptunus (made up of five lenses) and Hvalrossen. Hvalrossen sits around 100 m stratigraphically above the main Kiruna mineralisation and the main Neptunus lenses are approximately 700 m above.
At Kiruna and within the Fe 15% wireframe, five primary grade domains have been modelled to further characterise the mineralised material. In Kiruna, observations from core logging and statistical relationships have been used to categorise the mineralised material into five domains: high phosphorous, massive, high-grade, medium-grade and low-grade.
The Kiruna iron oxide-apatite mineralisations are located within the volcanic and volcano sedimentary formations of the Kiirunavaara group. Iron mineralisation is found in two stratigraphic positions, with the Kiirunavaara and Luossavaara iron ore bodies and the satellite Konsuln ore body located at the contact of the Hopukka and Luossavaara formations and the Per Geijer mineralisation (Rektorn, Haukivaara, Henry and Nukutus) being located higher in the stratigraphy, at the contact of the Luossavaara and Matojärvi formations and also within the latter.
The trachyandesitic Hopukka formation forms the footwall of the Kiirunavaara and Luossavaara iron ore deposits. It is composed of intermediate lavas that commonly show plagioclase phenocrysts in a fine-grained grey groundmass. Magnetite and apatite veins or schlieren are relatively common in the trachyandesite.
Porphyritic rhyodacite of the Luossavaara formation forms the hanging wall of the Kiirunavaara and Luossavaara ore deposits. The unit consists of red, grey, or brown pyroclastic tuffs, ignimbrites, and lavas that in places show flow banding texture. In the middle part of the formation, between the Luossavaara and Rektorn ore bodies, there is at least one zone of agglomerate, which exhibits magnetite nodules (e.g., Geijer 1968).
The magnetite orebodies are crosscut by felsic dykes that are compositionally similar to the rhyodacite. These dike porphyries are present both in the footwall and in the ore, but they have not been recognized in the hanging wall. The orebodies are also crosscut by at least two generations of mafic dykes.
Kiirunavaara Mineralisation
The Kiruna orebody exhibits significant geological continuity and variability. The orebody extends approximately 7,000 m along strike, with a maximum plan width of about 1,150 m. The vertical extent of main Kiruna mineralisation ranges from -120 RL to -2,900 RL, representing a total depth of approximately 2,780 m.
The Kiirunavaara iron oxide-apatite orebody intruded the contact of the trachyandesite of the Hopukka formation (footwall) and the rhyodacite of the Luossavaara formation (hanging wall). The orebody is a thick plate that extends from the surface down to a depth of 1300-2400 m, based on current knowledge. The orebody is between 90 and 120 metres thick and dips towards the east at 55-60 degrees. The plunge is towards the north. The original surface of the deposit has been removed by open pit mining.
The Kiirunavaara ore consists of massive magnetite that is commonly very fine-grained to more coarse-grained. Hematite is much rarer. In the low-phosphorus magnetite types (referred to as ‘B-ores’) the apatite content is negligible whereas in the high-phosphorus types (referred to as ‘D-ores’) the apatite content may be up to several percent. Other commonly occurring minerals include calcite, actinolite, talc, quartz, titanite and anhydrite. Sulphides are rare, but both pyrite and chalcopyrite are present. The ore commonly exhibits a sharp, intrusive contact to the wall rocks. Magnetite veins and dikes are common both in the footwall and in the hanging wall adjacent to the main ore zone.
The Kiirunavaara orebody was most probably formed in several pulses. This is shown in the distribution of the different ore types within the deposit. In general, D-types seem to be more common in the northern part of the orebody (referred to as ‘Sjömalmen’, or the ‘Lake ore’), at the footwall and hanging wall margins and as internal zones throughout the orebody.
Although hematite is relatively rare compared with magnetite in the Kiirunavaara orebody, it is present in small concentrations throughout the orebody.
The margins of the Kiirunavaara orebody are richer in silicate minerals than the central parts, with the predominant silicate mineral being actinolite. Titanite is preferentially present near the footwall, where it is found in zones mapped as skarn. The mineral distribution is reflected in the geochemical trends, where SiO2 and MgO concentrations are higher at the margins of the orebody and in the P2O5-rich zones, and the TiO2 concentration increases towards the footwall.
Other Known Mineralisation in the Area
Konsuln is a satellite orebody of Kiirunavaara deposit approximately 600 m long and commonly 20-40 m wide in the central and southern parts, but not wider than 10 m in the northern part of the orebody. Konsuln may have been separated from Kiirunavaara by northeast oriented faults, or that it has formed from one (or more) separate ore lenses.
The Konsuln orebody strikes mainly in a northwest direction and is wider to the south. The dip is approximately 70-90° east and northeast.
The ore quality in Konsuln varies between B (Fe-rich and P-poor) and D (Fe-poor and P-rich), with more consistent and higher quality ore in the thicker southern part.
Sigrid and Viktor deposits are located east and southeast of Konsuln. In the past, these deposits have been mined by open pit methods. Underground mining methods were also used at Sigrid until 1980. Based on previous diamond drilling results the mineralisation occurs in irregular, separate lenses, and veins. The logging and geochemical data shows that the hanging wall mainly consist of rhyolite and the footwall consists of trachyandesite, although there is a mixing between these rock types especially in the footwall.
Per Geijer – potential to become Europe’s most important mine for critical raw materials.
Promising results from LKAB’s ongoing exploration in Kiruna and Gällivare were presented last spring. The deposit Per Geijer is in close proximity to existing operations in Kiruna. More extensive studies show an increase from 400 million tonnes of mineral resources with high iron content to over 500 million tonnes, and that the Per Geijer deposit contains up to seven times the grade of phosphorus as the orebodies that LKAB mines in Kiruna today. Phosphorus is one of three nutrients in mineral fertilisers necessary for food production and is on the EU’s list of critical minerals.
For the first time, LKAB reports a Mineral Resource and further extensive studies in Per Geijer of assets amounting to more than one million tonnes of rare earth metals in the form of Rare Earth Oxides, which are used to produce Rare Earth Elements (REE).