Charakterystyka epigenetycznych zmian węgla w pokładach w strefach uskokowych Górnośląskiego Zagłębia Węglowego

Abstract

The paper presents the findings of the changeability of the qualitative parameters of coal beds and the strength parameters of neighbouring rocks in the faulting zones of the Upper Silesian Coal Basin (the USCB) as well as relations between the geometrical parameters of faults and the intensity of their changes. The research area included the region of the main saddle and its axis constitutes the Kłodnica fault and the 405 coal seam of Załęże beds. The investigation of the qualitative parameters of coal at the interval of 1—10 m from the fault surface was done on 205 groove samples taken from 10 mines. The analysis of the coal included its basic composition, technological properties and coking, petrographic and physical qualities as well as its structure in infrared radiation (IR). The results obtained underwent statistical analysis and were presented in the form of tables and figures. The findings showed that the faulting zones in the USCB are places where there are significant reductions in strength parameters of rock mass; that is why their patency for the migration of gases and water can be intensified and as a consequence this causes a danger of fall. Under favourable conditions, depending on the nature of discontinuity, degrading and aggrading changes of coal quality are generated in these zones. The opening of fault fissures for fluid flow resulted in degradation of the coal quality, whereas in the case of their closeness, the cumulated friction heat might cause the growth of coalification simultaneously increasing the coal quality (30% and 12% of the fault population respectively). Hypergenic changes resulted in coal of the qualitative parameters close to the one derived from the zones of eluvium cover and so-called red beds. In the faulting zones of an aggrading nature, both the interval and the scale of changes in the coal parameter values were definitely smaller but only directly on the fault surface, whereas their reverse direction caused an increase in the degree of coalification (friction metamorphism). The results of the research examining the coal by means of the spectroscopy method in the IR proved the degrading and aggrading nature of coal changes in the faulting zones although the relations observed were less clear. In the tectonic breccia filling in some fault fissures, the fact that coal weathered and changed to a varying extent at high temperatures was proved. The way this happened as well as the unchanged nature of the coal parameters of the beds surrounding the breccia prove their allochtonic origin. This is connected with bed fires and transport as well as faulting breccia. In the majority of the faulting zones examined (58%), a significant diversification of coal parameter values was not observed. The changeability of their values usually did not exceed 5%, was random in nature, and did not show correlations with the distance from the fault. What also decreased in the faulting zones was the resistance to one-axis rock compression surrounding the coal beds (about 54% to 67%), including the interval up to 11 m from the fault surface. The nature and intensity of coal change points to the important relations with some geometrical fault parameters. Hypergenic coal changes were observed, among other things, in the fault fissures of the dominant NW-SE and NE-SW run direction, with a predominant throw in the direction to the SW. In line with the fall of the intensity of weathered changes, the run of faults evolved into the WNE-ESE direction. The faults of such expansion in the USCB are characterized as fragile. Because they were formed in the period of the inversion of the Upper Silesian basin in a tense regime of compressions, they show a substantial patency for fluids. The intensity of the hypergenic changes indicates a positive correlation between the amplitude of fault throws and a negative one with the depth of the bed incidence. The coal thermally and weatheringly changed is connected with the faults of the NW-SE run. The fault run next to which the aggrading coal changes dominate is close to the NWN-SES and W-E direction. Because the faults of such a run in the USCB are susceptible in nature and developed during the compressive regime, their fissures are usually closed, cumulating the friction heat. In the fault zones where there were no changes in the coal quality, the orientation of faulting surfaces did not show the privileged run direction. It is assumed that the hypergenic changes in coal beds are generally connected with the inversion of the Upper Silesian basin, which took place during the Asturian phase of the Variscian orogenesis. The climax of the weathering changes also occurred in the Upper Carbon—Lower Triassic period, however, they could have lasted up to the Paleogene.