In December 2019, an exploration permit application ML2019:0113 was submitted for the Karhunmäki 1 prospect, covering an area of approximately 965 hectares, situated ca 5 km west of the town of Lapua (Figure 1). The court process is pending.
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 (Figure 3). They are mainly psammitic and pelitic mica gneisses with graphite-sulphide interbeds. Micagneiss, metacherts, 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 graphite-sulphide interbeds have formed by recrystallisation 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 mobilised graphite lenses/layers. There are also geophysical indications of possible enriched conductors in the area.
Highlights from 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).
A metallurgical test-work program was conducted in 2019 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.
The primary objectives of the metallurgical program were to determine the metallurgical response of the sample and to characterize the graphite concentrate in terms of flake size distribution and total carbon grade. Representative head samples were extracted during sample preparation.
The KAR-MET-19001 sample was subjected to flash and rougher flotation followed by polishing and primary cleaning. Due to the encouraging results, the KAR-MET-19001 sample was subjected to another open-circuit cleaner flotation test.
The test-work produced a concentrate grade of 96.4 per cent TGC, with 51.3 per cent large/jumbo flakes (+180 micron).
Figure 1. Karhunmäki 1 ML2019:0113 exploration permit application area. Boundaries updated 16.9.2021. Click to enlarge image.
Figure 2. Bedrock metamorphism and interpreted black schist/graphite 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 lines in the study area are based on historical field observations and strong magnetic/electromagnetic anomalies. Click to enlarge image.
Figure 3. Vaasa granite and Evijärvi schist belt. The study area is marked with a red box and the green interpreted occurrences within the area are based on historical field observations and strong magnetic/electromagnetic anomalies. The pink areas are interpreted as mineralised zones containing graphite paraschist and graphite-sulphide paraschist. Click to enlarge image.
Latest Karhunmäki news
18/05/2020: Finnish Graphite Update