The effect of the petrographic composition on the variation of CRI and CSR indices in the Pniówek deposit in the SW part of the Upper Silesian Coal Basin (Poland)

The characteristics of variation of the CRI ( Coke Reactivity Index ) and CSR ( Coke Strength after Reaction ) indices as well as the variation of the petrographic composition of coking coal in the Pniowek deposit (SW part of the Upper Silesian Coal Basin) have been presented. The area in which the research results have been obtained has a fundamental meaning to the Polish coking coal reserves, which are characterized by high variation both in quality and coalification. So far, no research related to the determination of the CRI and CSR variation in deposits that would be based on pillar samples collected from active workings has been performed for the Polish coking coal deposits. The samples have been obtained from 6 coal seams (Zaleze Beds, a part of Mudstone Series-Westphalian A), at depths between –500 and –700 m.a.s.l. The variation of CRI and CSR values has been presented both along the depth of the deposit (vertically) as well as isolines maps (horizontal variations). The relationships between the CRI and CSR index values and the parameters which are fundamental for their values, that is the R vitrinite reflectance and the petrographic composition (content of the Vt mmf vitrinite, L mmf liptinite, and I mmf inertinite macerals) have been analyzed. The examined coking coal of the Pniowek coal mine is characterized by the following values of the analyzed parameters: CRI = 19.9-60.8% (mean of 33.4%), CSR = 24.4-65.3% (mean of 49.5%), R = 0.98-1.14% (mean of 1.08%), Vt mmf = 60-81% (mean of 74%), L mmf = 4-11% (mean of 7%), I mmf = 13-31% (mean of 19%). The analysis of the variation of the coal quality parameters has not indicated evident and distinct vertical variation tendencies. When considered together with the horizontal variation in the E-W direction, in the view of the tectonics of the deposit (strike, dip, course of the main faults), it indicated a relation between the quality parameters and the direction of bed dips. In the deposit of the Pniowek coal mine, presence of coals of various quality has been confirmed. In the east, at greater depths, less coalified coal characterized by lower CRI values and higher CSR values is present. Such coal has a lesser vitrinite content and a high inertinite content. In the western direction (opposite to the dip direction), higher coalified coals, with higher CRI values and lower CSR values occur-these coals have a high content of vitrinite and low part of inertinite. Inversion of coalification has been demonstrated, as the smaller the depth the lower the reflectance of the coal should be, whereas the case in the Pniowek coal mine is the opposite. Such inversion may be related, as it has been demonstrated numerous times, to the occurrence of thermal metamorphism which modified the regional structure of coalification. No evident relationship of CSR and CRI values and the petrographic content of coal has been found, which is exhibited by low values of correlation indices. High content of inertinite in the samples characterized by relatively low values of CRI, relatively high CSR values and the lowest reflectance, however, draws attention. This runs against expectations, as usually the coal with better coking properties is characterized by the lowest content of inertinite macerals. The explanation of this relation requires further research on the inertinite macerals, especially the typically inert macerals (that is fusinite, micrinite and sclerotinite). The found relationship between the CSR and CRI values does not deviate from the data provided in literature from around the world. The correlation of the CSR index and the Pniowek coal mine vitrinite reflectance, however, is only partially consistent with the results relating to other coals. This confirms the difference of the coal in the examined area, which was exhibited many times and which should be connected to a very specific course of the coalification processes, especially the effect of thermal metamorphism.