Mineralogical and geochemical characterization of the Saray and Pınarhisar coals, Northwest Thrace Basin, Turkey

This study investigates the mineralogical and geochemical characteristics of coals from the Saray and Pınarhisar coalfields in the Northwest Thrace Basin, using optical microscopy, scanning electron microscopy, X-ray diffraction and inductively coupled plasma mass spectrometry. The Saray and Pınarhisar coals were deposited in a limnic environment. The sulfur content of the coals ranges from 0.3 to 15.3% and high sulfur contents may originate from both seawater and volcanism. Pyritic and organic sulfur are the dominant sulfur forms (1.2% and 2.7% on average, respectively). The mineral matter of the coals consists mainly of pyrite, barite, gypsum, muscovite and kaolinite, with minor amounts of quartz, butlerite, tamarugite and rozenite. The coals are enriched in trace elements, including V (61 ppm on average), Co (5.85 ppm on average), Ni (79 ppm on average), As (39.2 ppm on average), Th (3.6 ppm on average) and U (6.7 ppm on average). Based on Pearson correlation coefficients, Ti, V, Cr, Fe, Co, Ni, Cu, Se, Rb, Au, Hg, Pb and Th have mainly inorganic affinities (r_ash-elements > + 0.5) in the Pınarhisar coals; Fe, As and Au also have inorganic affinities (r_ash-elements ≥ + 0.5) in the Saray coals. The element contents and correlation coefficients indicate that the Strandja Massif, the Tethyan ophiolite belt and the oldest basement sediments were included in the sediment source region for both coalfields, while the Strandja Massif was the prevailing sediment source region for Pınarhisar coalfield.