Raman spectral characteristics of magmatic-contact metamorphic coals from Huainan Coalfield, China

• The geochemical behaviors of contact metamorphosed coals exhibit a somewhat different maturation pathway.
• The Raman spectroscopy can be used as a rough geothermometer in the range of 250–500 °C ± 83 °C.
• Quantitative structural information on thermally-metamorphosed coal in the Zhuji Coal Mine was systemically obtained by means of Raman analysis technology.

Normal burial metamorphism of coal superimposed by magmatic-contact metamorphism makes the characteristics of the Raman spectrum of coal changed. Nine coal samples were chosen at a coal transect perpendicular to the intrusive dike, at the No. 3 coal seam, Zhuji Coal Mine, Huainan Coalfield, China, with different distances from dike-coal boundary (DCB). Geochemical (proximate and ultimate) analysis and mean random vitrinite reflectance (R0, %) indicate that there is a significant relationship between the values of volatile matter and R0 in metamorphosed coals. Raman spectra show that the graphite band (G band) becomes the major band but the disordered band (D band) disappears progressively, with the increase of metamorphic temperature in coals, showing that the structural organization in high-rank contact-metamorphosed coals is close to that of well-crystallized graphite. Evident relationships are observed between the calculated Raman spectral parameters and the peak metamorphic temperature, suggesting some spectral parameters have the potentials to be used as geothermometers for contact-metamorphic coals.

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