The Collie Sub-basin is a pocket of Permian

Permian

The PermianThe term "Permian" was introduced into geology in 1841 by Sir Sir R. I. Murchison, president of the Geological Society of London, who identified typical strata in extensive Russian explorations undertaken with Edouard de Verneuil; Murchison asserted in 1841 that he named his "Permian...

 sedimentary rocks  with an area of 225 km², enclosed within much older Archean

Archean

The Archean , also spelled Archeozoic or Archæozoic) is a geologic eon before the Paleoproterozoic Era of the Proterozoic Eon, before 2.5 Ga ago. Instead of being based on stratigraphy, this date is defined chronometrically...

 rocks of the Yilgarn Craton

Yilgarn craton

The Yilgarn Craton is a large craton which constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts...

, near the town of Collie

Collie, Western Australia

-External links:*...

 in southwestern Western Australia

Western Australia

Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

., Once considered a unique basin, this area, along with the smaller Wilga and Boyup Sub-basins to the south, are now classified as outliers of the Perth Basin

Perth basin

The Perth Basin is a thick sedimentary basin in Western Australia. It lies beneath the Swan Coastal Plain west of the Darling Scarp, representing the western limit of the much older Yilgarn Craton, and extends further west offshore...

, separated from the main area by ancient earth movements and erosion. The Collie Sub-basin contains significant coal reserves

Coal

Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

, currently being mined mainly for electricity generation

Muja Power Station, Western Australia

Muja Power Station is a power station 22km east of Collie, Western Australia. It has eight coal powered steam turbines that together generate a total capacity of 854 MW of electricity. The coal is mined in the nearby Collie Sub-basin....

.