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, shown in yellow in Figure 4-5, 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).
The main gangue mineral of the massive ore is actinolite, which occurs as dispersed crystals (c. 1mm in size) or as coarse aggregates forming meandering bands through the massive ore. Biotite and calcite are secondary constituents, the biotite resulting from the breakdown of amphibole and magnetite and often observed as a vein constituent cutting through the preexisting fabric. Calcite occurs interstitially and as a replacement phase in addition to being a common vein constituent (Lundberg & Smellie, 1979). The host rock is sodic in character and in many places scapolitized. Scapolite also occurs together with actinolite in magnetite veins (Martinsson & Virkunnen, 2004; Baker et al., 2015).
Mineralization
All three deposits share common characteristics to the mineralization. Magnetite is the dominantly occurring mineral followed by hematite and the iron-oxyhydroxide minerals. Typically, the main mineralization at each deposit is fine grained and massive with low amounts of gangue minerals. Iron oxides constitute 90-95% of the massive mineralization typically with amphiboles, apatite and calcite as the most commonly occurring accessory minerals. Hematite or other iron oxides are secondary minerals formed as an alteration product of magnetite. The deposits share the same contact relationship in general to the andesitic host rock, with the massive mineralization grading out into a magnetite matrix breccia followed by magnetite veining of the host rock. The breccia and veining typically share the same accessory minerals as the main mineralization.