Open information session in Pulkkila
At an open information session, 11 October 2022, organized at the Pulkkila municipal hall, information was given about Suomen Malmitutkimus Oy’s graphite studies at the Kupukka Prospect. All study phases and the most important results so far were presented, as well as information about further plans. A discussion was held with the small but active audience that had arrived, e.g., about the continuation of studies, exploration permit, landowners’ rights and the new mining law. There is an article about the event in the Siikajokilaakso newspaper, 19 October 2022.
Graphite crystallinity of the Kupukka samples was studied at GTK laboratory
At the GTK’s Mintec laboratory, the degree of crystallinity and crystallization temperature of graphite from the Kupukka area were investigated with a Raman spectrometer; two of the samples were from the drill core and one from the graphite concentrate (flotation + chemical purification). Based on the results, the degree of crystallinity of the graphite is very high, 96 – 98% (Figs. 1 and 2).
The degree of crystallinity of the graphite examined from the concentrate is the highest, which suggests that during mineral processing and beneficiation tests, graphite with the relatively highest crystallinity is enriched in the concentrate.
The crystallization temperature estimate for the drill samples was 682 – 683 ±50 (°C), which corresponds to the metamorphic grade of the study area (high amphibolite-granulite facies).
Geophysical surveys and interpretations completed in the Kupukka graphite prospect area
Geological Survey of Finland (GTK) carried out electromagnetic measurements at the Kupukka
research area during March-April 2022. The report was completed in the end of May.
Flake graphite has been drilled at one of the research sites, Valkiaisjärvi. Other selected research sites have corresponding indications at aerogeophysical maps.
According to the survey results all four measured targets have strong indications of one or more conductive structures. Theoretical 3D models were calculated to locate the upper surface of the structures and estimate other properties. The locations of three conductive structures were determined at Valkiaisjärvi, but the dip directions were not resolved with certainty. The Multakorpi research site has a unified, vertical conductive structure nearly 100 m wide (Fig. 1). Two clearly separated, narrow conductive structures with eastwards dip were identified at the Sarvikangas research site. A uniform conductive structure was observed at the Isoräme research site. The dip direction is west.
Based on the results, all identified conductive structures have good conductivity and even better than at Valkiaisjärvi, where 8.7 – 13.4 % of graphitic carbon was assayed from graphite gneiss in drill core.
The 3D models calculated from the geophysical data can now be used in planning the drilling, which is the next step in the Kupukka graphite prospect.
Geophysical surveys in the Kupukka graphite prospect area at Siikalatva start 07.03.2022
Geological Survey of Finland (GTK) has been contracted to make EM ground surveys in several areas of the Kupukka graphite prospect at Siikalatva (Fig. 1). The aim of the study is to locate the airborne EM anomalies and to get information of the structure and dimensions on the EM source, probably made by a graphite-bearing mica gneiss.
Studies on the Niinimäki Ni-Cu deposit
All the geodata of the Niinimäki intrusion and related mineralizations has been compiled and 2D-3D models created. The focus of the study has been on the northern margin of the Niinimäki intrusion, where the best known ores are located. Based on the modelling the Plate ore is basically a lower-grade extension of the Surface ore. Both ores locate in the contact zone of the intrusion dipping about 40 degrees to the north. The Plate ore may continue deeper along the contact zone (Figs. 1-3). Exploration potential in the northern intrusion contact (Surface ore – Plate ore – Plate ore extensions) is based on 1) The probable variation of the sulphide concentration thickness along the base of the dynamic magma flow and 2) The possible off-set ores in the intrusion wall rock, stratigraphically just below the intrusion (Fig. 4).
Laboratory Flotation and Chemical Purification Tests on graphite
- Flotation concentrates of around 90 % C
- Chemically purified end product up to 98 % C with a liberation degree of graphite 99.7 %
- Total carbon recovery 82.4 %
Bench scale test work was conducted on a composite drill core sample in length of 12.90 m, at the GTK Mintec laboratories, Outokumpu, during May-November 2021. The mineralogy of the sample and beneficiation of graphite by flotation and chemical purification were investigated. The aim of the work was to get preliminary information about the beneficiation potential of graphite.
The graphitic carbon grade of the sample was 5.5–5.8 %. According to MLA, the main minerals in the sample were quartz, K-feldspar, chlorite, plagioclase, biotite, pyrite, graphite, cordierite, clay minerals, garnet, and muscovite.
Totally 3 flotation tests were made on the sample. Grind size, flotation reagents and their dosages, pulp pH and flotation time were the main variables studied in these tests. Unnecessarily fine grinding was tried to be avoided to recover graphite as large flakes as possible. Therefore, grinding was mostly performed in stages. Flotation concentrates with almost 90 % C were obtained. Chemical purification tests consisting of alkali roasting and acid leaching showed that the carbon grade of the flotation concentrates could be upgraded up to 98 % with high recovery.
If the whole process, i.e., combination of flotation and chemical purification is considered, the total carbon recovery was 82.4 %. According to the MLA study, the liberation degree of graphite was 99.7 % in the final product.
The results of this test work encourage to continue the exploration within the Kupukka reservation by Suomen Malmitutkimus Oy. However, more tests would be needed to optimize the process parameters, both flotation and chemical. In addition of this test work the degree of crystallinity and crystallization temperature of graphite will be studied in near future at the GTK Mintec by Raman spectroscopy. Below images of graphite-bearing mica gneiss, graphite concentrates of different grain sizes and chemically purified graphite concentrate.
Bench scale test work on a bed rock sample containing flake graphite was conducted at the GTK Mintec laboratories, Outokumpu during May-November 2021. The mineralogy of the sample and beneficiation of graphite by flotation and chemical purification were investigated. The aim of the work was to get preliminary information about the beneficiation potential of graphite.
The graphitic carbon grade of the sample was around 0.8 %. One aim of the test work was to study if this kind of low-grade graphite-bearing rock can be concentrated. According to MLA, the main minerals in the sample were quartz, K-feldspar, plagioclase, biotite, cordierite, Fe-oxides and Fe-oxyhydroxides, garnet, and graphite.
Totally 6 flotation tests were performed on the sample. Grind size, flotation reagents and their dosages, pulp pH and flotation time were the main variables studied in these tests. Unnecessarily fine grinding was tried to be avoided to recover graphite as large flakes as possible. Therefore, grinding was mostly performed in stages. Flotation concentrates with almost 90 % C were obtained. Chemical purification tests consisting of alkali roasting and acid leaching showed that the carbon grade of the flotation concentrates could be upgraded up to 98% with high recovery.
If the whole process, i.e., combination of flotation and chemical purification is considered, the total carbon recovery was only 55.5 %. Higher total C recovery would have been expected if a flotation concentrate with higher recovery had been chosen for the chemical purification.
Based on this preliminary test work graphite beneficiation is possible also for a low-grade starting material. More tests would be needed to optimize the process parameters, both flotation and chemical. It should be noted also that the sample for this test work was from bedrock surface with some weathering and oxidation of some minerals. This may be reflected in the study results. Thus, a drill core sample is preferred for possible future test works. By drilling, probably also the sample grade would be higher (best EM anomalies locate outside graphite-bearing outcrops). The degree of crystallinity and crystallization temperature of graphite will be studied in near future at the GTK Mintec by Raman spectroscopy.
This test work, together with the previous studies in southern Savo by Suomen Malmitutkimus Oy, provides novel and important information on the occurrence and beneficiation potential of graphite, which now can be applied also to other areas in Finland with similar bedrock geology.
Below images of graphite concentrates by different grain sizes and chemically purified graphite concentrate.
Update of graphite surveys in southern Savo
During the summer of 2020, in the Puumala, Sulkava and Juva areas, outcrops were mapped in or near the regional airborne EM anomalies. Grab samples by hammer were taken from outcrops containing graphite. The aim was to obtain samples representative of the average graphite content in the outcrop. The samples were subjected to chemical analysis in two different laboratories, ALS Finland Oy and Eurofins Labtium Oy. Part of the samples were assayed for both graphitic and total carbon. Polished thin sections were prepared for microscopic studies, both from rock slices cut perpendicular and parallel to the main schistosity of the rock.
At the turn of September-October, geophysical measurements were made at a few sites to determine the electrical conductivity of the bedrock in the area. The measurements were made with portable GEM-2 equipment and the contractor was the Geological Survey of Finland (GTK), which has extensive experience in these measurements. A report of the measurements was received at the turn of the year. In early 2021, petrophysical measurements were purchased from GTK to determine the physical properties of individual samples, such as electrical conductivity, magnetic susceptibility, and density.
About the results
The host rock for the disseminated graphite occurrences is a garnet-cordierite gneiss. The most common main minerals are quartz, plagioclase, garnet, cordierite and biotite, in places also orthopyroxene and potassium feldspar. Pyrrhotite is the dominating sulphide mineral.
The graphitic carbon contents of the chemically analysed samples remained quite low, at highest slightly below 3 %. The samples do not contain carbonate so the difference between the graphitic carbon and total carbon contents is minimal. The sulphur contents of the samples are low, usually less than 1 %. However, this is since pyrrhotite in the bedrock samples is in many places partially oxidized and sulphur is dissolved away.
Based on GEM-2 measurements, the EM anomalies are located next to the observed outcrops. It is therefore possible that there are higher concentrations of graphite next to the outcrops, under the soil. The samples, measured for the petrophysical parameters, show high galvanic and inductive resistance. Sampling from outside of the outcrops would require drilling or excavation.
Based on preliminary microscopic studies, the quality of graphite is good. The length of the graphite flakes is about 1 mm in many places and up to 3 mm in some places. Impurities are minor. Below a few micro-graphs of graphite.
Continuation of surveys
Graphite samples are still subjected to chemical analyses and laboratory tests. Some places will be mapped and sampled in the field during the summer of 2021.