Summary:
Svappavaara comprises three deposits: Leveäniemi, Gruvberget, and Mertainen. Leveäniemi is the only pit in operation where mining re-commenced in 2014.
Deposit Geology
Leveäniemi
Porphyrite-group felsic to mafic meta-volcanics dominate in the Leveäniemi area. The volcanic host rocks in the hanging wall, historically referred to as leptites, are trachyandesite in character (Hobler 2013) and consist mainly of various amounts of biotite, feldspar, amphibole, quartz and plagioclase. The trachyandesites are generally massive in appearance but, depending on the amount of biotite, they can be granoblastic, ranging from locally weakly to moderately foliated.
The footwall is made up of a highly deformed schist, with biotite, and locally sericite, as the dominant mineral. This schist is generally moderate to strongly foliated. Lithogeochemical work suggests that the footwall schistose rocks originate from the same rock type as the relatively undeformed trachyandesite rocks in the hanging wall.
In the footwall of the deposit carbonate skarn units appear. This unit is a package of Mg rich carbonates and volcanoclastic rocks which have been strongly Ca altered. The magnetite mineralization occurs as veins/breccias in the trachyandesites and biotite schist and is related to extensive pervasive alterations including Na-feldspar, anthophyllite, biotite and scapolite. The whole formation is cut by numerous younger non-mineralized mafic dykes trending northsouth with varying dip directions. These dykes range in thickness from 10 cm to 30 m.
Gruvberget
The host rocks at Gruvberget are fine grained, mafic to intermediate metavolcanic rocks, with granoblastic to schistose texture. The hanging wall rocks, are classified as rhyodacite/trachyandesite with patchy pervasive actinolite, albite, and reddish alteration. It is also common to see more localized sericite, chlorite, and limonite alterations in the hanging wall.
The footwall rocks are partly chlorite schists, andesites and basic volcanic rocks with a higher grade of TiO2 (TiO2 = 1,1%). Like the hanging wall these rocks can be heavily altered but tend to show chlorite, biotite, and clay alterations more commonly. There are magnetite veins, one to five metres in width, often located in the chlorite schist or in the andesite.
Mertainen
The bedrock around Mertainen is dominated by altered intermediate to mafic rocks. These were historically called syenite porphyry (Geijer, 1930; Frietsch, 1957, Lundberg & Espersen, 1965) trachyte (Eriksson & Hallgren, 1975) or trachyandesite (Martinsson 2009). The deposit has two distinct lithologies based on immobile element classification. Andesitic rock occurs in the hanging wall with basaltic andesites occurring in the footwall. The units are not in direct contact, instead a graduation from andesitic to basaltic andesite is observed. This gradation could likely be attributed to the presence of brecciating mineralization. Mineralogically they are similar, being comprised primarily of plagioclase and albite with lesser and variable concentrations of alkali-feldspar, amphibole, biotite, epidote and carbonate (veining).
The Mertainen deposit is characterised as a large breccia, containing lenses or veins of massive magnetite in its central parts. A high-grade zone is surrounded by successively less magnetiterich breccias which are more extensively developed in the hanging wall (Lundberg & Esperssen, 1965). The host rock is commonly rich in amygdales and feldspar phenocrysts and may also be rich in magnetite which occurs disseminated, in patches, and in irregular veins (Lundberg & Smellie, 1979).
Mineralisation
Leveäniemi and Gruvberget
The Leveäniemi and Gruvberget deposits are hosted at the same stratigraphic position in the volcanic package. However, due to varied intensity of the deformation, Leveäniemi and Gruvberget differ in appearance. Leveäniemi has been subject to more intense folding and shearing resulting in a large, remobilised halo around the mineralisation of successively lower grades. Folding and shearing in Gruvberget is less intense and the relatively sharp contacts are preserved. Consequently, the progressive transition from massive to brecciated to banded to veined mineralisation occur over a shorter distance in Gruvberget compared to Leveäniemi. The Gruvberget and Leveäniemi deposits are offset by a structure that displaces the lithologies. Hence, the entire Svappavaara deposits were split into two fault blocks. The Gruvberget block was further sub divided into two fault blocks due to identified offsets in the volcanoclastic hanging wall packages. In the model update for 2024, the Leveäniemi fault block now also includes the very low-grade mineralisation associated with the eastern shear zone unit. This unit has been constructed as its own shell separated from the main mineralisation.
Within the Fe 15% wireframe, five grade domains have been modelled to further characterise the mineralised material. In Gruvberget and Leveäniemi, observations from core logging and statistical relationships have been used to categorise the mineralised material into the following grade domains: 1) massive domain, 2) high-transitional domain, 3) mediumtransitional domain, 4) low-grade domain, and 5) weathered domain. The cut-off grade has been determined from logging and was then statistically evaluated.
Mertainen
The Mertainen mineralisation is locally sheared and strongly brecciated resulting in a small core of high-grade mineralisation surrounded by a large halo of progressively lower iron grades. The Mertainen 15% mineralisation shell is subdivided into 1) high-grade, 2) medium-grade, and 3) low-grade mineralisation.