Sedimentologicu Control of Mining Conditions in the Permian Coal Measures of the Bowen Basin, Australia

The distribution and properties of interseam and overburden rocks in coal mines is largely controlled by conditions at the time of their original deposition. Within the developed areas of the Bowen Basin, depositional environments range from fluvial through upper and lower detaic, to marginal marine and intertidal facies. Each environment has a characteristic association of lithologies with specific range of properties, and each lithology has a characteristic geometry. Fragmentation problems are associated with ancient sand channel systems, where the difficulties encountered depend on the dimension and shape of channels, their continuity, orientation to mining face and associated sediment bodies formed as levees or interdistributary muds. Stability problems in spoil, pit floor and highwalls are usually associated with mudstones which contain swelling clays derived from the original Permian volcanic source. This clay problem is aggravated by deep Tertiary weathering. Case studies are presented of detailed analyses and prediction of geomechanical properties on a mine site scale. These are used in investigating or forecasting fragmentation and stability hazards. The studies incorporate detailed field mapping, bore log data and computer data processing. They allow the development of detailed depositional models for specific interseam intervals within mines. As areas of depositional environment are identified they allow the construction of maps of similar mining conditions and the determination of the most suitable mining techniques.