The Collie Basin is a northwest to southeast trending, elongated rift structure bounded to a large degree by major faults, with a maximum throw possibly in excess of 2,000m. The basin is thus subdivided into three depressions, namely the Cardiff, Muja and Shotts Sub-basins.

The coal-bearing sequence, of Sakmarian to late Permian age, is approximately 1,200m thick and is confined by Archaean rocks dominated by granite and granite-gneiss.

The Permian sequence commences with glacial deposits and then contains three main coal-bearing members in which coal comprises less than 5% of the material. Mining at Premier would be confined to the Premier Member (equivalent to the Chicken Creek and Collieburn Members) which has 15 major seams (greater than 2.Om thick) and numerous smaller seams and seam splits.

Interburden is dominated by fine to very coarse-grained, porous sandstones with lesser interbeds of siltstone and shale. The sequence is variably overlaid by the Cretaceousaged Nakina Formation which contains reworked Permian sediments. The high proportion of sandstone in the sequence makes the Collie Basin a major reservoir of groundwater.

The Premier Deposit is essentially a broad, shallow basin with dips of between 30 and - 80. Only minor internal faulting is known with throws up to 20m recorded.

There are three types of coal occurrences (Baarda, 1966):
• Trace coal (laminae) and carbonized black and lignitic brown plant ........

Premier Coal runs a modern open cut mine employing large electric & hydraulic shovels and 240- tonne haul trucks.

Geology of the Premier Basin is considerably different allowing the use of larger mining equipment such as electric shovels, a first for the basin, and 240-tonne capacity trucks. Pits 3 and 1D exploit the Premier seams and Pit 5 exploits the Ewington seams. The Premier seams are relatively flat allowing the use of the electric shovels, while the Ewington seams are steeply dipping, requiring a benched approach using hydraulic excavators.

The Mine is supported by sophisticated geological models and mine planning systems that combine to produce detailed, optimised schedules to ensure customer expectations of quality and quantity are consistently met in a timely manner.

Coal is mined using large excavators and 240-tonne trucks. On delivery to the coal plant, the coal is passed through a simple crushing and screening plant prior to stockpiling using a stacker/reclaimer system. Coal is delivered to local power station customers by conveyor and to other customers by rail or truck.

Key to the operations is a modern maintenance workshop and a mobile maintenance function for in- pit shovel and breakdown maintenance.

The whole operation is state-of-the-art with many functions, from fleet dispatch to dozer grade control, reliant upon extensive computer systems.

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