Overburden conveyor bridge dumps of open-cast lignite mining - fabric and petrographical composition of artificial sedimentary deposits with regard to water table rebound

摘要

The most serious effect of open-cast lignite mining is the completely changed subsurface. With regard to the water table rebound after stopping the mine's dewatering system and the prediction of sediment/water reactions, the sediment distribution ofthe 4 X 6 km X 50 m extending overburden dumps have to be explored. This was carried out as a combined geophysical well logging and core analysis and shows the following results: Within main vertical units of X 10 m thickness, layers are arranged as inclined beds. These elements, created by dredgers cut operation and particle sorting processes form alternating cohesive/non-cohesive bedding, X 1 m thick. The enrichment of fine elastics in inclined beds, will act as hydraulic barrier, affecting the future flow capacity of groundwater. Except of the material subdivision of the dump, large scale floors of differing sediment compactness were detected. The resulting shift of geochemical sections and the vertical permeability profile will affect the interface of groundwater between dump and natural hydrogeological profile. The correlation of lignite-, with sulfur- and fineclastics content means a reappearance of geogenetic texture-mineral paragenesis in the overburden dumps and as prein-formation it improves well log application in its new field of inclined low consolidated sediments. The results concerning structure/layering, and distribution of texture/composition and the effect of sediment introducing and sediment sorting processes of the investigated overburden conveyor bridge dumps indicate generatizable properties of this predominant dump type oflusation lignite mining area. Thus, the new distribution of overburden sediment constituents of further dumps as relevant with sediment-water-reaction and -transmission can be determined with an considerably optimized exploration program.