Geochemical, structural and morphological characterization of vein graphite deposits of Sri Lanka: Witness to carbon rich fluid activity

Sri Lanka is endowed with high purity vein graphite deposits with extensive mineralization in the tectonically weakened zones of the basement high-grade rocks. Distinctly different crystal shapes of graphite are found even within a single vein and it is controversial in interpreting prevailed fluid activities and crystallization process to form such a variation. Therefore, this study was carried out to interpret the origin of vein graphite using geochemistry, crystal-morphology, and structure of the crystals. Sampling was conducted on four different depths at the Kahatagaha-Kolongaha mine, Sri Lanka. Characterizations of graphite were carried out by micro-Raman spectroscopy, X-ray diffraction spectroscopy, scanning electron microscopy, and inductive couple plasma mass spectroscopy. The results indicate that the genesis of the vein graphite is related to a single phase of fluid activity and the fluid was mostly pure with possible trace impurities. Further, it was revealed that the thickness of the veins, interaction with host rocks and mobility of the impurity elements have influenced the formation of different morphologies of graphite in a single vein.