Sibanye-Stillwater owns the Keliber project through its subsidiary, Keliber Oy. The shareholders of Keliber Oy are Sibanye-Stillwater (79.82%), Finnish Minerals Group (20%), a state-owned company tasked with managing the mining holdings of the Finnish state, and a group of Finnish shareholders (0.2%).
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Summary:
Deposit type
The lithium-bearing pegmatites belonging to the Kaustinen lithium province belong to the LCT group of pegmatites. They also belong to the albite-spodumene subgroup based on the pegmatites’ high spodumene and albite content (Cerny and Ercit, 2005). LCT pegmatites are very coarse-grained rocks with similar geochemical affinities to granites that are often considered the source rocks to pegmatites. LCT pegmatites are highly enriched in lithium, and tantalum, and this suite of elements gives them their name and distinguishes them from other rare caesium element pegmatites (Bradley and McCauley, 2016).
Mineralogy and geo-metallurgy
All of the pegmatites that have been discovered and evaluated to date within the Kaustinen area have very similar mineralogy: they are dominated by albite (37 - 41%), quartz (26 - 28%), K-feldspar (10 - 16%), spodumene (10 - 15%) and muscovite (6 - 7%). Internal pegmatite zonation as seen in many other similar LCT-type pegmatites is absent from the Kaustinen pegmatites, with spodumene being the only lithiumbearing mineral that is of economic interest. Other lithium-bearing minerals such as petalite (LiAlSi4O10), lepidolite (K(Li,Al)3(Al,Si,Rb)4O10(F,OH)2), montebrasite-amblygonite (LiAl(PO4)(OH,F) - LiAl(PO4)F), Lithiophilite (Li(Mn,Fe)PO4: LiFePO4 – LiMnPO4), Zinnwaldite (KLiFeAl(AlSi3)O10(OH,F)2) and Elbaite (Tourmaline) (NaLi2.5Al6.5(BO3)3Si6O18(OH)4) have been only found in minor or trace quantities.
Despite spodumene mineralisation being generally homogeneously distributed throughout most of the pegmatites, the inclusion or incorporation of host rock xenoliths and wall rock material through dilution will impact the metallurgical recovery of spodumene during flotation and metallurgical processing. This will require careful selective mining supported by optical or density sorting methods to mitigate the impacts of dilution on the recovery of spodumene.
Syväjärvi geology
The Syväjärvi deposit is located beneath a cover of sandy till that attains an average thickness of 5 m. Outcrop within the project is restricted to an isolated exposure of a host lithology: plagioclase porphyrite (metavolcanic). The geological model describing the attitude and thicknesses of the various pegmatites and contact relationships with host rocks was derived entirely from surface drilling. Here six modelled spodumene-bearing pegmatites veins have intruded into mica schists, metagreywackes and metavolcanics following a broad antiformal structure forming “saddleback” type reefs. This has resulted in a series of shallow northerly plunging pegmatite veins, the largest of these attaining thicknesses of up to 20 m in places. The strike length totals 365 m for all veins, extending approximately 720 m down dip and to a maximum depth below surface of 160 m.
Rapasaari geology
The Rapasaari Lithium deposit is covered by a variable cover of till/overburden ranging from 3 m to 20 m in thickness, and thus outcrop is rare. In some cases, till is also overlain by peat that can reach thickness of up to 2 m. The Rapasaari deposit represents a curvilinear, structurally controlled series of thirty-three individually modelled pegmatites that exhibit variable thicknesses, resulting in a series of bifurcating and boudinaged lenses and veins that follow a south-easterly plunging synformal structure.
The three largest modelled pegmatites vary in thickness from 10 m to 20 m, with most of the minor (modelled) pegmatites having thicknesses of less than 10 m. The strike extent totals 1 250 m for all veins - approximately 730 m in the primary dip orientation (east – west) - and to a maximum depth below surface of 240 m.
Länttä geology
The Länttä deposit is covered by a relatively thin veneer of surficial sediments and till ranging from 1 m to 7 m in thickness. The deposit was discovered following road excavation work in the 1950s. Drilling completed by historical operators (Suomen Mineraali Oy and Partek Oy ) and Keliber delineated two parallel- trending pegmatite veins with a 400 m north-easterly strike and steep south-easterly dips to a maximum depth of 180 m below surface, extending approximately 100 m southeast of the outcrop location.
Emmes geology
A majority of the Emmes deposit is located under Lake Storträsket close to the village of Emmes. Overburden thickness are highly variable reaching 10 m thickness under the lake and as much as 20 m closer to the village. Drilling to date has delineated a single pegmatite vein 400 m long, striking southeastnorthwest with variable dips to the southwest, to a distance of 110 m from the outcrop and a depth of 170 m below surface.
Outovesi geology
The Outovesi deposit was discovered by Keliber in 2010 and is covered by surficial till sediments that average 10 m in thickness. Keliber’s drilling delineated a single pegmatite vein some 400 m long and reaching a maximum thickness of 10 m. The pegmatite strikes northeast-southwest for a modelled length of 360 m, with variable dips to the northwest. The vein dips steeply (~80°) to a depth of 75 m below surface.
Leviäkangas geology
The Leviäkangas lithium pegmatite deposit is located in the Kaustinen Municipality of western Finland some 5 km south of Kaustinen town It comprises three separate spodumene pegmatite veins that are conformably intruded into a mica-schist host rock. There is a possibility that these bodies may belong to one vein that has been structurally dislocated. The strike of the pegmatite veins varies between north and north-northwest. The veins are dipping to the west at an angle between 50°and 60°. The thickness of the veins varies from a few metres to 12 m.
The overburden is formed by till with some peat at the surface at Leviäkangas and varies in thickness from 5 m to 10 m.
Close to, and at the contact with, the wall rocks, the spodumene in the pegmatite is altered to muscovite. This persists for a few tens of centimetres up to one and a half metres. In addition, there are a few narrow (0.5 – 3 m) internal waste zones in the pegmatite where the spodumene is replaced by muscovite so that the Li2O grade is below the cut-off grade.
Spodumene typically occurs as coarse grained, light greyish-green lath-shaped crystals between two and 10 cm long and orientated perpendicular to the contacts of the veins with the wall rock. The pegmatite consists predominantly of albite, quartz potassium feldspar (orthoclase), spodumene and muscovite.
Tuoreetsaaret geology
The Tuoreetsaaret lithium pegmatite deposit is also located in the Kaustinen Municipality of western Finland. This deposit was discovered by Keliber using a combination of geological, geochemical and geophysical data that led to the first intersection by diamond core drilling in March 2020. The deposit comprises five lithium-bearing pegmatite vein-like bodies intrusive into a set of rock units including intermediate meta-tuffite, plagioclase porphyrite, mica schist and sulphide-bearing mica schist. The hanging wall is generally formed by intermediate meta-tuffite and the footwall by mica schist and sulphide-bearing mica schist. Plagioclase porphyrite generally forms the middling between the pegmatite veins. The pegmatite veins and their wall rocks are covered by 5 m to 10 m of glacial till with peat at the top.