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IRON SULPHIDE FROM TONSTEIN FROM 713 COAL SEAM OF JEJKOWICE TECTONIC TROUGH UPPER SILESIAN COAL BASIN (POLAND)

Zdzislaw Adamczyk, Agnieszka Klupa, Andrzej Harat

Abstract

Tonsteins are rocks which, due to their origin, mineral make-up and structure, are valuable petrographic benchmarks in the monotonously formed Carbon coal-bearing formation of the Upper Silesian Coal Basin in Poland. Mineralogical study of tonsteins is important with relation to learning more about their tuffogenic protolith. It can also serve as one of the criteria when differentiating tonstein horizons with a similar texture: structure, granulation, directions and intensity of transformations of the tuffogenic material. The present publication presents research conducted on samples of tonstein taken from the 713 coal seam in four coal mines located in the Jejkowice trough in the Upper Silesian Coal Basin (Poland). Microscopic tests were performed in transmitted and reflected light as well as using a scanning electron microscope with the functionality of determining the chemical make-up of the sample in a microarea. The mineral make-up of tonstein has been found to include: quartz, biotite, feldspars and accessory minerals (mainly zircon, iron sulphides and apatite), devitrified volcanic glass, fragments of vulcanites and grains of coal. Biotite contained in the tonstein was the subject of separate research. The present publication presents the result of tests on iron sulphides. In the tonstein tested iron sulphides occurs in the form of single crystals and as inclusions in the biotite and organic matter. The Chemical composition shows little variation in the form of occurrence of iron sulphides. Individual crystals of pyrite have a chemical composition close to stoichiometric (FeS2). The remaining forms (inclusions in biotite) belong to the FeS - FeS2 series. It should be noted that the iron sulphides usually contained admixtures of Co, Cu, Pb, Zn and, sporadically, Ag, Au and Ni. The results show that iron sulphides in tonstein are represented by pyrite and pyrrhotite. The study have shown the idiomorphic inclusions of pyrrhotite with submicroscopic galena and sphalerite in biotite most likely represented primary unaltered or slightly transformed pyroclastic grains. All form of pyrite are most likely syngenetic with tonstein and coal seam.

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DOI resolver: doi.org/10.5593/sgem2017/11/s01.058

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