The coal was mined from the Wellington Seam in the Early Campanian Northfield Member of the Upper Cretaceous Extension Formation (Nanaimo Group). The seam is very irregular and is split into a lower and an upper portion by a rock parting ranging from 0 to 2.2 metres (average 1 metre) in thickness. The upper coal averages 25 centimetres thick while the lower portion of the seam averages 55 centimetres thick. The Wellington Seam is underlain by east Wellington sandstone and is overlain by conglomerate. Refer to the Bebans mine (092GSW026) for a description of the Wellington Seam.

The seam dips approximately 10 degrees north-northeast striking west-northwest, and extends approximately 1.2 kilometres along strike and 0.55 kilometres downdip. A further 0.8 to 1.2 kilometres of Wellington seam extends beneath the sea.

The area contains a number of small north-northwest trending faults.