Bowen Basin Geology
Geological Distribution of Coal in the Bowen Basin
Queensland's coals range in age from Carboniferous, 350 million
years (Ma) in age, to Tertiary (65 Ma). The commercially significant black
coals are restricted to deposits within sedimentary basins of Permian (280
Ma), Triassic (250 Ma) and Jurassic (200 Ma) age, located mainly in the central
and eastern portions of the state.
 Curragh Dragline  Collinsville Plant |
The coal deposits of Permian age are by far the most commercially important. Of the State's black coal inventory totalling in excess of 30 billion (x109) tonnes (measured and indicated resources), Permian coals account for approximately 75% of the total resources, including almost 100% of the coking coal and about 60% of the thermal coal resources. Permian coals within the Bowen Basin in central Queensland account for approximately 70%, of the State's coal inventory while Mesozoic coals found mainly in the Clarence-Moreton, Surat, Callide and Tarong basins make up the remainder. Shallow coal potentially amenable to open-cut mining makes up about 55% of the inventory, with the remaining 45% present at greater depths. |
The most important Permian coal basin is the Bowen Basin, which is exposed in a large, triangular-shaped area of central Queensland, 600km long and up to 250km wide. The basin extends south in the sub-surface beneath Mesozoic sediments of the Surat Basin, and connects with the Gunnedah and Sydney Basins in New South Wales.
Coal seams in the Bowen Basin exhibit major variations in rank and quality, reflecting both the depositional and tectonic history of the basin. A broad trend of increasing rank from west to east has long been recognised, and was used as a guide for coal exploration targets during the late 1950s and early 1960s.
Along the structurally disturbed north-eastern edge of the Bowen Basin, the coals range in rank from anthracite to low volatile bituminous, and deposits tend to exhibit a complex structure. Coals in the central part of the basin are medium to high volatile bituminous and include the best coking coals. Structural deformation in these deposits is generally relatively mild.
In the southwest, the coal rank falls below the coking range with a consequent loss of coking properties. The more significant deposits in this region are usually low ash non-coking coals and generally are not affected by major structural deformation apart from normal faulting. The westerly decrease in rank continues across the Springsure Shelf and into the Galilee Basin.
Coal-bearing horizons have been preserved at many stratigraphic levels throughout the Bowen Basin, but deposits of economic importance are restricted to four groups.
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The oldest coals (Group I) of Early Permian age are represented by the Reids Dome beds, a unit of highly variable thickness and lithology. Distribution is restricted to the south-western part of the Bowen Basin. In the extreme southwest of the basin, seams can be up to 30m thick, but only occur at considerable depth. Further north the seams are thinner and at shallower depth. Near surface resources of good quality thermal coal have been delineated in the Capella area, and at Cullin-la-ringo near Emerald. No Group I coal seams have been mined to date. |
Group II coal measures, also of Early Permian age, occur as several unconnected deposits located around the northern and western margins of the basin. These include the Collinsville Coal Measures in the north, the Rugby Coal Measures southwest of Moranbah, and a group of deposits in the Clermont area, including the Blair Athol and Wolfang Basins, which are structural outliers of the Bowen Basin. The Calen Coal Measures, which occur near the coast north of Mackay, are also considered to be of similar age. Coal has been mined at Collinsville and Blair Athol for many years. Collinsville produces both coking and steaming coal, while at Blair Athol the product is low rank, medium volatile, low ash thermal coal.
Group III coals of Late Permian age were deposited on the Collinsville Shelf, under conditions which varied from a marine-influenced deltaic environment in the German Creek Formation, to dominantly fluvial flood plain environments in the Moranbah Coal Measures. These formations contain most of high grade coking coal deposits mined in Queensland, extending from Kestrel mine near Emerald to North Goonyella mine, north of Moranbah.
Other mines in this group include Gregory, Crinum, Oaky Creek, German Creek, Norwich Park, Saraji, Peak Downs, Moranbah North, Goonyella and Riverside. The underground mines at Kestrel, Crinum, Oaky Creek, German Creek, Moranbah North and North Goonyella demonstrate the importance and quality of these coal measures to support viable mining operations. Seams of slightly older age occur in the Freitag Formation and Aldebaran Sandstone in the central western and south-western parts of the basin, but rarely attain a thickness sufficient to warrant consideration.
A marine transgression, which halted deposition of Group III coals in the south, did not extend into the northern part of the Basin where coal measures continued to be deposited. Volcanism at this time resulted in major outpourings of tuffaceous material, which contaminated seams in the Fair Hill Formation and Fort Cooper Coal Measures, rendering them uneconomic at present, despite their considerable thickness.
The final phase of coal deposition in the Bowen Basin in the Late Permian resulted in the formation of Group IV coals. These include the Rangal Coal Measures, Baralaba Coal Measures and the Bandanna Formation. The coals in this group are the most diverse in terms of quality, and also the most widely distributed within the basin. Group IV coals were deposited under fluviatile, lacustrine and paludal conditions.
Although the quality and rank of Group IV coals vary greatly, they are characterised by comparatively low reactives content and low sulphur. They are of major economic importance as a source of coking, PCI (Pulverised Coal Injection) and thermal coal and have been mined intensively over the past 30 years. Fourteen open-cut mines (Moura, Blackwater-South Blackwater, Curragh, Ensham, Jellinbah East, Yarrabee, Foxleigh, German Creek East, Moorvale, Coppabella, South Walker, Burton, Hail Creek and Newlands) and two underground mines (Cook and Newlands) currently work the Group IV coal seams.
The Galilee Basin, which is connected to the Bowen Basin across the Springsure Shelf, also contains large quantities of high volatile, low rank thermal coal.
Extracted from: Mutton, A. J. (Compiler), 2003: Queensland Coals 14th Edition. Queensland Department of Natural Resources and Mines