The occurrence of anthracites in an area characterized by lower rank coals in the Upper Silesian Coal Basin of Poland

Abstract

The results of petrographical-geological and chemical examinations on anthracites, semianthracites and medium-low volatile bituminous coals from Jastrzebie in the Upper Silesian Coal Basin of Poland are presented. The coking coals mined in this region exhibit volatile matter V daf = 18–26%, free swelling index FSI = 3–8 and reflectance R m = 1.10–1.35% and are inertiniterich coals ( I = 25–63%). Coal Seam 504 of the Anticlinal beds (Namurian B) has been affected by thermal metamorphism and contains both coking coals and coals of higher rank. According to the criterion of Polish Standards this coal seam varies from anthracite (V daf <10%) to semianthracite (V daf = 10–14%) in rank. The carbon content is slightly lower and the hydrogen content a little higher than those of typical anthracites and semianthracites. The reflectance values ( R m = 1.56–2.62%) are generally lower than the R m values proposed by the International Committee for Coal Petrology as boundary values for anthracites and bituminous coal. The magnitude of anisotropy and microhardness were also examined. Examinations of optical properties prove that the metamorphism exhibited by the coals is the result of elevated temperature and variable pressure. The analyses of the maceral composition indicate that there is a decrease in the inertinite content in anthracites. Vitrinite exhibits the features of thermally altered coal. The micrinite content shows a little variation. In coking coals, a strongly fluorescing bituminous substance with the optical features of exsudatinite was found. The constructed geological section of Coal Seam 504 shows distinct regular changes in chemical and physical properties as well as the petrographic composition which may be caused by the heat flux of a magma intrusion, not localized so far.