Abstract
The flake graphite occurrence in Piippumäki, Eastern Finland, as indicated by an airborne electromagnetic anomaly, was located during fieldwork by electromagnetic measurements with Slingram. The anomaly is approximately 0.1 × 1 km in size. The flake graphite is hosted by quartz-feldspar gneiss and amphibolite that have been subjected to retrograde metamorphism. This is observed in thin sections as granulite facies (garnet + cordierite + sillimanite + melt) regressing to greenschist facies (epidote, chlorite, albite, and white mica). The graphite (up to 1 mm large flakes) is found in graphite-bearing layers in the gneiss, and to a minor extent disseminated in the amphibolite. The average total sulfur (TS) is 0.33%, total carbon (TC) is 6.49%, and the average content of graphitic carbon (Cg) is 6.41% for the analyzed graphite-bearing rocks. SEM, XRD, and Raman spectroscopy were used for analyzing the flake graphite, indicating that the graphite is almost defect-free, of high quality, and has not been affected by the retrograde metamorphism. The peak metamorphic temperature of 737 °C was determined by a Raman thermometer, and no temperatures of greenschist facies were observed. A pseudosection was constructed from whole-rock chemical composition and indicated equilibration at ca 5 kbar and 740 °C, which corresponds to the observed mineral assemblages.
Highlights
Natural graphite has been listed as a critical raw material by the European Union since 2011 (European Commission 2017a)
We found some new outcrops with graphite
Sulfides are present in the mica- and graphite-rich layers, which appears as a rusty surface in outcrop
Summary
Natural graphite has been listed as a critical raw material by the European Union since 2011 (European Commission 2017a). As the demand of natural graphite is increasing in the EU, it is important to identify high-quality graphite. An extensive part of the Fennoscandian shield consists of the Svecofennian domain characterized by amphibolite to granulite facies metamorphic bedrock. Since high quality of graphite can be related to high grade metamorphism, supracrustal rocks of the Svecofennian domain are a promising target for high-quality flake graphite deposits. Graphite occurrences in Fennoscandia have been studied quite extensively, e.g., by Gautneb and Tveten (2000), Pearce et al
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