Peculiarities of petrographic composition of coking coals in southwest part of Upper Silesian Coal Basin (Poland) as a result of thermal metamorphism influence

Abstract

Subject of the research were coal samples taken from different tectonic blocks of a coal bed, from the seams 404/2, 409/3, 409/4, and 415/3 (Namurian C) in coal mine Zofiowka. Samples from investigated seams represent middle ranked coal type B (metabituminous), characterised by a mean reflectance of vitrinite in a range of Ro = 1,12 to 1,33%. It was found that for samples collected from coal seams 415/3, 409/4, and 409/3, value of vitrinite reflectance decreases slightly with increasing distance between the sampling location and red beds that exist in the Carboniferous roof, what points on certain inversion of coal rank. All analysed coal samples from Ruda beds are characterized by certain peculiarities in petrographic composition, which are typical for thermally metamorphosed coals, in the temperature range of 400-500°C. Presence of such components as anisotropic inertinite, fluorescing bituminous substance, and more rarely pseudomorphs after macrospores characterized by intense bireflectance, were observed. Sporadically pyrolytic coal was also observed, characterised by intense anisotropy with visible Brewster crosses by cross-Nicol position. Components, which exhibit structure similar do coke, were also observed in tested coal samples. A manifestation of thermal processes could be also presence of significant amounts of carbonates in tested samples, which are present in a form of filling of cellular spaces in semifusinite, fusinite, and funginite.