Petrological character of lignite (brown coal) from Badenian salts in the Bochnia Mine (Southern Poland)

Abstract

The salt deposit in Bochnia is located in the marginal zone of the Carpathian Foredeep. The salt succession, composed of rock salt deposits, with claystone, mudstone and zuber interbeds was, in its original location, ca. 80 m thick. The carbonized organic material described herein occurs within three salt units: in the southern salts, in the middle salts, and in the northern salts. There are two petrographic forms of coal in the Bochnia rock salt succession: xylite and gelitic coal. Xylites are fragments of fossil wood. Externally, xylite demonstrates a fibrous texture, and can be splintered along the fissility with uneven transverse fractures. The fragments are strongly gelified and show a zonal structure: their internal parts are made of highly cracked textinite, although the external part of the xylite fragments is built of ulminite. The gelitic coal was found in the form of lenticles, formed exclusively of euulminite. Their main mineral components include metasideronatrite (Na2Fe[OH] [SO4]2 H2O) and anhydrite while their subsidiary components are gypsum, pyrite and halite. The degree of carbonization shows that, the plant material from the Bochnia rock salt deposit is an ortholignite with xylitic and gelitic varieties.