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.

中文翻译：

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Piippumäki 片状石墨前景——芬兰逆行变质区优质石墨矿床的一个例子

机载电磁异常表明，芬兰东部 Piippumäki 的片状石墨产地是在现场工作期间通过 Slingram 的电磁测量定位的。异常大小约为 0.1 × 1 km。片状石墨的主体是石英长石片麻岩和经过逆变质作用的角闪岩。这在细粒岩相（石榴石 + 堇青石 + 硅线石 + 熔体）退化为绿片岩相（绿帘石、绿泥石、钠长石和白云母）时在薄片中观察到。石墨（最大 1 毫米大薄片）存在于片麻岩的含石墨层中，并有少量散布在角闪岩中。分析的含石墨岩石的平均总硫（TS）为0.33％，总碳（TC）为6.49％，石墨碳（Cg）的平均含量为6.41％。SEM、XRD、采用拉曼光谱对片状石墨进行分析，表明该石墨几乎无缺陷，质量高，未受逆行变质作用影响。拉曼温度计测得峰值变质温度737℃，未观察到绿片岩相温度。假截面由全岩化学成分构成，表明在约 5 kbar 和 740 °C 下达到平衡，这与观察到的矿物组合相对应。