Petrography of the Neogene lignite from the Sofia basin, Bulgaria

Abstract

The lignite seam from the Sofia Neogene basin has been sampled and the petrographical composition was determined. The coals contain high contents of macerals from the huminite group. The prevailing macerals from that group were textinite, ulminite and attrinite. Phlobaphinite, densinite and gelinite were observed rarely. Dominant macerals from the liptinite group were mainly suberinite, resinite, sporinite and cutinite. The amounts of the alginate, liptodetrinite and fluorinate were insignificant. The coal was very poor of macerals from the inertinite group. Fusinite, semifusinite, macrinite, sclerotinite and inertodetrinite were represented them. The main minerals were illite, kaolinite, halloyzite, pyrite, quartz, calcite and dolomite. Anorthite, amphibole, augite, chalcopyrite, marcasite, siderite, witherite, gypsum, melanterite and jarosite were also determined. The huminite maceral amount was highest in low part of the seam and lower in the middle part. The higher amount of the liptinite macerals was located in the middle and upper parts of the seam. Inertinite macerals were distributed uniformly on the seam profile and their amount was very low in the middle part of the seam. The middle part of the seam was contained highest amount of all minerals Illite was prevailing clay mineral in the middle part and kaolinite predominates in the low and upper parts of the seam. The type of the mire was determined as mesotrophic bog forest by Calder et al. [Bull. Soc. Geol. Fr. 162 (1991) 283], according to the Ground Water Index (GWI) and Vegetation Index (VI), calculated on the base of the maceral content. According to the petrography content, the Gelification Index (GI) and the Tissue Preservation Index (TPI), the peat bog probably originated as a fresh-water raised forest swamp.