Petrographical, chemical and FT-IR properties of a suberinitic coal from Aydin–Germencik area, Western Turkey

A suberinitic coal was discovered by coincidence during drilling for geothermal research in the Germencik area. Drilling activity showed that the coal was 6-m in thickness on the upper part of the Miocene-aged basal conglomerate unit, which is one of the important geothermal reservoir rocks in the Germencik area.Petrographic, FT-IR, XRD, chemical and SEM analyses were conducted to reveal the detailed properties of the suberinitic coal. The coal is composed entirely of suberinite and phlobaphinites which are part of cork tissue. These tissues also include features such as lamination and micro-folding. Well-preserved cork tissues and bark textures were observed abundantly in the coal samples. Jarosites, gelified cork tissues, are the most common alteration products observed in the coal samples. FT-IR analysis showed that suberinitic coal contains distinct peaks in the aliphatic C–H stretching bands. SEM analysis reveals suberinitic textures and framboidal pyrite inclusions, indicating metallic sulfur mineral sources.Hydrothermal fluids have important controls on the composition of the Germencik area coals. Geothermal reservoir conditions affected coal rank and caused an increase in reflectance values as well as calorific values. Framboidal pyrites probably formed by means of geothermal water and associated mineralization in the region.

•Germencik coals contain entirely of suberinite, phylobaphinites and exhibit perfect cork tissues, bark textures.•Germencik coals were influenced by hydrothermal fluids.•The coal ingredients reveal high pH and temperature conditions of the environment.•FT-IR analysis of Germencik coals exhibit aliphatic and aromatic components.•Excellent framboidal pyrites were observed by means of SEM analysis.