The Grasstree is located on the north-western flank of the Bowen Basin, a sedimentary basin comprising Permian to Triassic age geology. A veneer of more recent Tertiary and Quaternary age sediments typically overlie the Bowen Basin strata.

The relevant geology in the vicinity of the Grasstree longwall mining area includes:
- Quaternary alluvium associated with German Creek and Little Parrot Creek;
- A veneer of Tertiary sediments of the Duaringa Formation;
- Permian coal measures including the target German Creek Seam (GC seam).

The Permian coal measures include the Rangal Coal Measures, the Burngrove Formation, the Fort Cooper Coal Measures (also known as the Fairhill Formation), the Macmillan Formation and the German Creek Formation. The coal measures comprise a sedimentary sequence with interbedded coal seams, including the target GC seam. The upper profile of the coal measures has been extensively and deeply weathered. The weathered coal measures outcrop at the surface across the southern portion of the longwall mining area and much of the surrounding area, forming undulating sandy plains. In the northern portion of the longwall mining area, the coal measures sub-crop under the Tertiary sediments and dip to the east. As the coal measures dip to the east, the depth of the GC seam increases from approximately 330 m in the south-western part of the Grasstree longwall mining area to a maximum depth of approximately 540 m at the north-eas ........

A longwall is a complex system of mining equipment that incorporates hydraulic roof supports (called ‘chocks’ or ‘shields’), coal cutting and coal transport equipment. Longwall mining involves extracting rectangular panels of coal, typically around 150 m to 400 m wide, up to 7 km long and 2 m to 5 m thick. Longwall panels are defined by access roadways that are constructed around the perimeter of each longwall panel. These roadways provide access for the installation of the longwall mining equipment, mine workers, and equipment and services.

Longwall mining involves a coal shearer travelling back and forth across the width of the longwall panel, starting from the furthest point progressively removing the coal from the panel back to the main headings. The shearer cuts the coal from the coalface on each pass and delivers the coal to a face conveyor that runs along the full width of the longwall. The face conveyor transports the coal from the coalface to another conveyor in an access roadway. Coal is then transported to the surface via a series of connecting underground conveyors.

The roof at the coalface is held up by a series of hydraulic roof supports. The supported section of roof provides space for the shearer, face conveyor and man access. After each shear of coal is removed, the face conveyor, hydraulic roof supports and the shearer are moved forward.

The roof immediately above the mined seam collapses into the void (called a ‘goaf’) tha ........

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