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 ........
