minerals Article The Disappearance of Coal Seams Recorded in Associated Gangue Rocks in the SW Part of the Upper Silesian Coal Basin, Poland Justyna Ciesielczuk * , Monika J. Fabia ´nska , Magdalena Misz-Kennan, Dominik Jura, Paweł Filipiak and Aniela Matuszewska Institute of Earth Sciences, University of Silesia, 60 B˛edzi´nskaStr., PL-41-200 Sosnowiec, Poland; [email protected] (M.J.F.); [email protected] (M.M.-K.); [email protected] (D.J.); pawel.fi[email protected] (P.F.); [email protected] (A.M.) * Correspondence: [email protected]; Tel.: +48-323689336 Abstract: Coal seams in the Upper Silesian Coal Basin vanish within the Carboniferous Upper Silesian Sandstone Series and below an unconformity marking the Carboniferous top surface. Changes in the geochemical, mineralogical, petrological and palynological characteristics of gangue rocks associated with the vanished seams record what happened. The observed changes could have been caused by (1) coal-seam paleofire, (2) peat combustion, (3) igneous intrusion, (4) metasomatism and/or (5) weathering. Multifaceted research on samples collected at the Jas-Mos mining area, a part of the operating Jastrz˛ebie-BzieCoal Mine that are representative of different geological settings in the northern and southern parts of the mining area, point to intra-deposit paleofire as the most plausible reason for the disappearance. Biomarkers enabled recognition of differences in heating Citation: Ciesielczuk, J.; Fabia´nska, duration and oxygen access. Coal seams in the south burned quickly with abundant oxygen supply. M.J.; Misz-Kennan, M.; Jura, D.; Seams in the north pyrolyzed for an extended time under conditions of limited oxygen. Though Filipiak, P.; Matuszewska, A. The other methods used proved less sensitive, all confirmed low (100–150 ◦C) paleotemperature heating. Disappearance of Coal Seams Overall, the reason for the local disappearance of the coal seams, making their exploitation difficult Recorded in Associated Gangue and unprofitable, can be assigned to a variety of different processes in a complex overlapping history Rocks in the SW Part of the Upper Silesian Coal Basin, Poland. Minerals of variable weathering, heating due to local endogenic fires and, probably, earlier peat combustion. 2021, 11, 735. https://doi.org/ 10.3390/min11070735 Keywords: disappearing coal seam; thermal alteration of gangue rocks; paleofire; Upper Silesian Coal Basin Academic Editor: Shifeng Dai Received: 20 May 2021 Accepted: 3 July 2021 1. Introduction Published: 7 July 2021 Coal and coal-bearing rocks in the south-western part of the Upper Silesian Coal Basin (USCB) of Early Pennsylvanian (Namurian BC) age underwent changes resulting Publisher’s Note: MDPI stays neutral in the partial/complete disappearance of coal seams over an area of ca 500 km2. This with regard to jurisdictional claims in disappearance is associated with gangue rocks of various colors, typically located above published maps and institutional affil- the seams. Maximum noticed thickness reduction up to disappearing was observed in coal iations. seam No. 505, which, with a regular thickness of ca 5 m, shows this most clearly—though the problem concerns coal seams Nos. 415/1 and 510 [1], 504, 505 and 506 [2–4] and 406/4 [5], exploited in both the Polish and Czech parts of the USCB. The coal there, if any, is grey-black, dull, heavily cracked, brittle and without a banded structure. The altered, Copyright: © 2021 by the authors. variably colored coal-bearing rocks are characterized by increased fracturing, porosity Licensee MDPI, Basel, Switzerland. and reduction of physical and mechanical properties [6,7], all a reflection of oxidation This article is an open access article and heating. distributed under the terms and Changes in the gangue rocks accompanying the vanishing coal seams may have been conditions of the Creative Commons caused by weathering and thermal alteration of coal-bearing sediments locally preserved Attribution (CC BY) license (https:// below a regional unconformity marking the Carboniferous top surface and within intra- creativecommons.org/licenses/by/ Pennsylvanian disconformities [8]. General (geological) and detailed (petrographical, 4.0/). Minerals 2021, 11, 735. https://doi.org/10.3390/min11070735 https://www.mdpi.com/journal/minerals Minerals 2021, 11, x 2 of 31 Minerals 2021, 11, 735 2 of 30 below a regional unconformity marking the Carboniferous top surface and within intra- Pennsylvanian disconformities [8]. General (geological) and detailed (petrographical, ge- ochemical, palynological) descriptions of these variably colored beds indicate weathering geochemical,effects and/or palynological) thermal transformations, descriptions the of theseorigin variably of which colored is not clear, beds indicateas subsurface weathering map- effectsping and and/or sample thermal collection transformations, is possible only the from origin boreholes of which and issingle not clear,outcrops as subsurface in operat- mappinging coal mines. and sample As exploitation collection avoids is possible regions only possibly from boreholeslacking coal, and these single parts outcrops of mines in operatingare abandoned coal mines.and inaccessible. As exploitation avoids regions possibly lacking coal, these parts of minesSeveral are abandoned underground and inaccessible. outcrops with vanishing coal seams and weathered and/or thermallySeveral altered underground gangue rocks outcrops of various with vanishing types and coal irregular seams geometries and weathered occur and/or in the thermallymining areas altered between gangue Jastrz rocksębie ofin Poland various and types Karviná and irregular in the Czech geometries Republic occur (Figure in the1). miningAnomalies areas favoring between reduced Jastrz˛ebiein coal-seam Poland thickness and Karvin andá in incr theeasing Czech Republiccoalification (Figure occur1). Anomaliesmainly in the favoring coalfield reduced of the coal-seam Jas-Mos, thicknessa part of the and Jastrz increasingębie-Bzie coalification Coal Mine occur (Figures mainly 2 inand the 3). coalfield of the Jas-Mos, a part of the Jastrz˛ebie-BzieCoal Mine (Figures2 and3). FigureFigure 1.1.Subsurface Subsurface structuralstructural mapmap ofof thethe CarboniferousCarboniferous coal-bearingcoal-bearing Paralic,Paralic, Upper SilesianSilesian Sandstone and Mudstone SeriesSeries in in the the western western part part of of the the Upper Upper Silesian Silesian Coal Coal Basin Basin (USCB) (USCB) (after (after [9,10 [9,10]]; simplified).; simplified). Areas Areas with vanishingwith vanishing coal seams coal seams and associated altered gangue rocks at the top of the Carboniferous units are shown in pink. 1: Jas-Mos mining and associated altered gangue rocks at the top of the Carboniferous units are shown in pink. 1: Jas-Mos mining area, a area, a part of the Jastrzębie-Bzie Coal Mine; 2: Mudstone Series, Westphalian AB (CwAB), with bottom isolines (coal seam part of the Jastrz˛ebie-BzieCoal Mine; 2: Mudstone Series, Westphalian AB (CwAB), with bottom isolines (coal seam 405); 405); 3: Upper Silesian Sandstone Series, Namurian BC (CnBC), with bottom isolines (coal seam 510); 4: Paralic Series, Na- BC 3:murian Upper A Silesian (CnA), Sandstonewith bottom Series, isolines; Namurian 5: bottom BC isolines (Cn ), in with km bottom a.s.l.; 6: isolines isolines (coal of average seam 510); random 4: Paralic vitrinite Series, reflectance Namurian Rr A A(%); (Cn 7: ),isolines withbottom of average isolines; vitrinit 5:e bottomcontent isolines(%); 8: fault; in km 9: a.s.l.;thrust. 6: isolines of average random vitrinite reflectance Rr (%); 7: isolines of average vitrinite content (%); 8: fault; 9: thrust. Minerals 2021, 11, x. https://doi.org/10.3390/xxxxx www.mdpi.com/journal/minerals Minerals 2021, 11, x 3 of 31 Minerals 2021, 11, 735 3 of 30 405); 3: Upper Silesian Sandstone Series, Namurian BC (CnBC), with bottom isolines (coal seam 510); 4: Paralic Series, Na‐ murian A (CnA), with bottom isolines; 5: bottom isolines in km a.s.l.; 6: isolines of average random vitrinite reflectance Rr (%); 7: isolines of average vitrinite content (%); 8: fault; 9: thrust. Figure 2. Structural sketch map of the coal seam No. 505 in the Jas‐Mos mining area, a part of the Jastrzębie‐Bzie Coal Figure 2. Structural sketch map of the coal seam No. 505 in the Jas-Mos mining area, a part of the Jastrz˛ebie-BzieCoal Mine, Mine, and its disappearance (based on geological documentation of Jastrzębie‐Bzie Coal Mine, simplified). 1: isoline of the andbottom its disappearance of coal seam (basedNo 505 on in geological m a.s.l.; 2: documentation subcrop of 505 ofcoal Jastrz˛ebie-BzieCoal seam below Miocene Mine, claystone; simplified). 3: coal 1: isoline rank and of the quality— bottom ofisolines coal seam of the No average 505 in m volatile a.s.l.; 2: matter subcrop content of 505 (V coaldaf %), seam vitrinite below reflectance Miocene claystone;Rr % and coal 3: coal types; rank 4: unexploited and quality—isolines coalfield, 5: of daf theexploited average coal; volatile 6: altered matter associated content (V gangue%), vitrinite rocks and reflectance vanishing Rr coal% and seam coal 505; types; 7: fault 4: unexploited and thrust; coalfield, 8: geological 5: exploited cross‐ coal;section 6: altered lines; 9: associated outcrops gangueof coal seam rocks 505 and in vanishing testing gallery coal seam47 (samples 505; 7: N1–8 fault andin blue) thrust; and 8: in geological south corridor cross-section II below lines;coal 9:seam outcrops