Summary:
Regionally, Maules Creek is located within the Permian sedimentary sequence of the Maules Creek Sub-basin in the Gunnedah Basin of New South Wales, Australia. The Maules Creek sub-basin uncomformably overlies (onlaps) a basement surface formed by the Early Permian Boggabri Volcanics. Structurally, the seams are deposited in a generally north south orientated basin that shallows to the south but is open ended to the north. The Maules Creek Resource is situated on the western limb of the basin which dips to the east–south east at grades of 2 to 6 degrees, with areas of local steepening.
The Maules Creek Formation contains a multi-seam resource in a sedimentary section dominated by lithic conglomerate and sandstone, siltstone and minor claystone. The formation is interpreted as being deposited primarily in a braided fluvial system. The coals are generally thicker and closer together on the western side of the basin. To the east and southeast the coal seams are split by increasingly thick sections of clastic rocks, mainly conglomerates. Within the basin the coal bearing horizons, and the sediments between them, form an essentially ‘layer cake’ stratigraphy, with some gentle post depositional folding and several phases of relatively minor tectonic dislocation. Localised variations in dip angle and dip direction occur, largely due to differential compaction of strata over interseam sedimentary wedges.
The close spatial association of basement outcrops and relatively thick accumulations of the Maules Creek Sub-basin suggest that the paleo-topography of the basement strata was relatively steep. Notably, the steeply dipping nature of the Permian topography suggests that the sediment accumulation in the sub-basin may have been structurally controlled by the periodic reactivation of deep seated basement faults situated beneath the onlapping boundary of Permian Sediments. This structural arrangement resulted in a high degree of differential subsidence across the basin which caused the development of thinner and higher ash coal seams towards the western onlapping edges of the basin, with thicker accumulations towards the basins centre.
The lower coal seams at the Maules Creek Mine onlap the basement in the west. An east west trending basement ridge exists toward the central part of the tenement with the lower coal seams abutting and subcropping against this ridge. The maximum depth from surface to the Templemore Seam within the project area is in the vicinity of 400m along the eastern boundary of CL375.
The Permian strata at Maules Creek is characterised by a single constructive coal-bearing depositional episode. The generally low sulphur content, lateral continuity of most coal seams and common occurrence of thick conglomerate wedges suggest that deposition occurred in a terrestrial succession in a river dominated upper deltaic plain generated by braided rivers. The low proportion of tuffaceous and interseam layers suggest coal deposition occurred in a comparatively quiet environment that was distant to any volcanic arc. The common occurrence of thick conglomerate wedges indicates the periodic inundation of the peat bog by significant flood events. Notably, the conglomerates tend to be sheet deposits dumped in short lived depositional events. This view is supported by the limited evidence of washouts or other erosive features. Differential subsidence and sediment accumulation along the basins western margins appears to be more episodic and less consistent than the sub-basins central portion which has negatively impacted on both coal seams thickness and ash content as they approach their subcrop on the basement surface.
The complex seam splitting that characterizes the Maules Creek Deposit has resulted in the recognition of up to 16 coal seams which are further sub-divided into 59 plies. The principal coal seams, in descending order are the Herndale, the Onavale, the Teston, the Thornfield, the Braymont, the laterally inconsistent Bollol Creek, the Jeralong, the Merriown, the Velyama, the Nagero, the Northam, the Therebri, the Flixton, the Tarrawonga and the basal Templemore.
Dimensions
The tenements comprising Maules Creek cover an irregular shaped are 11 km north south and 7 km east west.
This statement covers the Maules Creek pits as well as the remainder of the coal resources within the Maules Creek leases, where there is no proposed mine plan. Resources estimated in July 2016 for the period ending 31st March 2016.
All open cut resources at Maules Creek are less than 400m from the surface. A minimum coal thickness of 0.2 m was applied to all seams. A 45% maximum ash was also applied to all resources.