Characterization of gangue minerals in graphite from the Bahia-Minas Graphite Province, Brazil

Natural graphite is a chemically inert, non-toxic mineral with exceptional thermal and electrical properties, making it critical for electronics, steelmaking, and lithium-ion batteries. Brazil hosts significant flake, vein, and amorphous graphite deposits and is a top-four producer of graphite. This study examines gangue mineral inclusions in graphite from the Bahia-Minas Graphite Province (BMGP), Brazil’s main graphite-producing region. Graphite occurs within paragneiss and schist of the Jequitinhonha Complex and Macaúbas Group, formed under medium- to high-grade metamorphism. Using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, and in-lens secondary electron imaging, we characterize mineral assemblages and microtextural relationships between graphite and gangue phases to better understand the mineralogy and morphology of gangue mineral impurities, which may cause issues with mineral processing at a later stage. Fourteen samples reveal graphite-bearing rocks with gneissose and mylonitic textures. Kaolinite and quartz dominate gangue minerals within graphite cleavages and interstitial zones, alongside K-feldspar, jarosite, tourmaline, and sillimanite. Sillimanite and biotite confirm amphibolite-facies metamorphism, while kaolinite, smectite, and jarosite indicate retrograde alteration and low-temperature fluid infiltration. Jarosite reflects post-peak oxidation of iron sulfides under acidic conditions, marking supergene weathering or hydrothermal overprinting. In-lens SEM imaging shows stacked graphite flakes intercalated with gangue minerals. Quartz and K-feldspar exhibit mechanically entrapped morphologies, whereas kaolinite appears intergrown, suggesting early diagenetic incorporation or retrograde origin. These observations align with impurity classification models and underscore graphite’s structural sensitivity to processing. Linking gangue morphology and graphite texture informs beneficiation strategies to preserve graphite integrity and refines mineral systems models for BMGP and analogous terranes.