The flake graphite prospect of Piippumäki—an example of a high-quality graphite occurrence in a retrograde metamorphic terrain in Finland

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.