Economically significant Permian coal Seams have been formed in different Portions of the Sydney Basin, New South Wales, a linear molasse trough situated between a cratonized foreland (Lachlan Fold Belt) to the west and a mobile hinterland (New England Fold Belt) to the northeast (figure 1). The Sydney Basin is an asymmetrical synclinal structure with a faulted crystalline basement (figure 2), which is overlain by marine and terrestrial Permian sequences followed by Triassic fluvial and deltaic sedimentary rocks (Branagan et al, 1976).
The northern and northeastern portions Of the basin are tectonically controlled by southeasterly directed thrusts and high energy palaeoenvironments adjacent to the New England Fold Belt. The western and Southern portions of the Sydney Basin border against a cratonized foreland and are characteristed by a lesser rate of subsidence, formation of fewer coal seams and considerably finer grained interseam sediments compared with the northern portions. The palaeoenvironments during the Upper Permian coal measure Sedimentation have thus determined the type of interseam sediments.
The current coal mining operations in the Sydney Basin are restricted to a relatively small number of the existing coal seams in different parts of the basin.
Most collieries operate at depths ranging between 100 metres and 450 metres, operations at lesser or greater depths are exceptions.
An assessment of the mechanically Significant vectorial and scalar attributes of roof-and floorstrata of the Seams mined has to be based on the geological setting and the prevailing palaeoenvironments during their deposition. Complications have been caused by erosional episodes, during which segments of the original roofstrata have been removed from some seams and replaced by fluvially deposited sedimentary sequences.
(Figure in full paper)
The Sydney Basin was covered by extensive peat swamps chiefly during the Tartarian and most economic coal seams have been formed in that time interval. The Hunter-Bowen orogeny has either largely terminated this development or modified it.
The depositional directions measured in the Triassic Narrabeen Groups and also in the Hawkesbury Sandstone show at least two tectonic tilting phases in the Sydney Basin. Permian and Triassic sedimentary sequences in the current configuration of the basin reach a total thickness of approximately 4800 metres.
Most coal types can be found in the Sydney Basin; the northern and western districts of the basin produce highvolatile, low rank coking coals, whereas low-volatile and high ranking coking coals are found in the southern portion.
The floorstrata of the worked seams consist mainly of lutites; claystones and arenites occasionally form the floor. A variety of rocktypes is found in the roofstrata. A variety of shales usually makes up the original roofstrata.
geological system comprising the working floor, the coal seam, and the working roof. This system is typifiable according to its mode of deposition, diagenesis, and deformational history. Apart from the non-diastrophic diagenetic changes in the system, which should include in this context compaction and coalification, post- and syndiagenetic modifications have changed the mechanical attributes of rocks and rockmasses in the coal measure sequences.
