Karhunmäki – Graphite
The Karhunmäki project area is located in Lapua municipality within the Southern Ostrobothnia region in Western Finland, ca 80km east of Vaasa. The study area was chosen because of its high metamorphism, known coarse flake graphite findings and extensive interpreted graphite schist zones based on airborne geophysics, bedrock observations and historical drilling.
In December 2019, an Exploration Permit application was submitted for the Karhunmäki 1 prospect, covering an area of approximately 965 hectares, situated near the town of Lapua in Western Finland.
The Lapua bedrock has formed under high PT conditions (high amphibolite-granulite facies) and consists of strongly deformed and migmatitic metasedimentary rocks. These metasediments are known to contain various graphite-sulphide interbeds with medium-coarse flake graphite. In general, the high PT conditions have allowed the graphitic material to naturally recrystallise, grow and purify to a possibly high quality flake graphite ore. It is also known that strong deformation/faulting/shearing together with high PT conditions have usually resulted in some kind of remobilisation, which possibly has created enriched flake graphite deposits.
The main rock type in the region is a heterogeneous rock called Vaasa granite. It has formed from mica gneisses through melting to various degrees and re-crystallization. Eastern and southern parts of the Vaasa granite complex form part of the Evijärvi schist belt where the dominant rock types are psammitic and pelitic metasediments. Chemical compositions indicate that the Vaasa granite has evolved from Evijärvi-type metagreywackes almost isochemically. In the Lapua−Alahärmä region, the main granite rock type is unoriented and its appearance is similar to intrusive rock. Garnet and quartz aggregates are common and locally there is also orthopyroxene.
Lapua is part of the Evijärvi schist belt, which consists of migmatitic metasedimentary rocks. They are mainly psammitic and pelitic mica gneisses with graphitic interbeds. Mica gneiss, meta-cherts, graphite-sulphide schists and banded metavolcanic rocks dominate in the area and its surroundings. The schist belt also contains several small tonalitic and granitic intrusions and minor volcanic-sedimentary interbeds.
The metamorphic grade in the schist area is mainly at amphibolite facies, though in the region it has in places increased to granulite facies. Vaasa granite has developed from sedimentary rocks by gradual melting under PT conditions varying between amphibolite and granulite facies.
The graphitic interbeds have formed by re-crystallisation and have mostly been mobilised into thin and irregular veins or layers. The main target area (Karhunmäki/Kiviniemi) consists of irregular fold and deformation structures, which could potentially contain small or even large scale re-mobilised graphite lenses/layers. There are also geophysical indications of possible enriched conductors in the area.
Bedrock metamorphism and interpreted black schist occurrences in Western Finland. Lapua (red box/study area) is located within a granulite peak facies area with multiple black schist and graphite schist interpretations. The green interpreted occurrences in the study area are based on historical field observations and strong magnetic/electromagnetic anomalies.
Highlights from the 2019 Karhunmäki field and test-work include:
- 33 graphite bearing boulders and outcrops were sampled over a strongly Electromagnetic (“EM”) conductive area, measuring 7.0 kilometres by 4.0 kilometres.
- The 33 samples were analysed for TGC by Leco furnace at ALS Finland in Outokumpu. The resulting grades ranged between 1.1 per cent TGC to 10.0 per cent TGC.
- Metallurgical test-work on a composite of boulder and outcrop samples taken from a highly EM conductive area measuring 1,200 metres by 700 metres, named the Kiviniemi prospect and within Karhunmäki, produced a concentrate grade of 96.4 per cent TGC, with 51.3 per cent large/jumbo flakes (+180 micron).