Underground coal mining targets coal seams at various depths. Grosvenor’s target seam is the Goonyella Middle (GM) seam. The depth of cover of the GM seam across the Grosvenor site varies from 100 to 500 metres, with depth increasing toward the north-north-east of the mine plan. The thickness of the GM seam varies from four to six metres. 21 The seam gas composition is predominantly methane (more than 95%).

The GM seam is located within the Moranbah Coal Measures, the thickness of which ranges from 250 to 300 metres in the Grosvenor area.The Moranbah Coal Measures comprise nine coal seams and their associated splits. They are, in ascending order, the Goonyella Lower, Dysart Rider, Harrow Creek Lower, GM, P, Goonyella Rider, Goonyella Upper, QB and QA seams. The Moranbah Coal Measures also contain a tuffaceous marker bed known as the P-Tuff between the GM and P seams.

Above the Moranbah Coal Measures lies the Fort Cooper Coal Measures, the base of which is the Fairhill seam. Sediments overlying the Fort Cooper Coal Measures are predominantly comprised of sandstone, claystone, basalt, gravel and clays.

Grosvenor Mine is an underground longwall mine operation.

Grosvenor comprises two mining series: the eastern 100 series and the western 200 series.27 LW 101 was the first longwall in the eastern 100 series.

The 100 series longwall blocks were designed with two headings per gateroad, with the gateroad lengths varying from approximately 1.1 to 6.3 kilometres in length.

Longwall panels average approximately four kilometres in length and are approximately 300 metres wide. At Grosvenor, the longwall blocks are formed by developing two parallel roadways, known as gateroads, on either side of the proposed block. Each set of gateroads is joined every 125 metres with cross accesses called cut-throughs. The gateroads on one side of the block, called the maingate roadways, allow transportation of workers to the longwall face, the conveying of production coal, and the supply of intake ventilation. The gateroads defining the other side of the longwall block are called the tailgate roadways, and are chiefly used to carry the return air from the longwall face back to the main ventilation shaft.

At Grosvenor, coal has been typically cut by the shearer using a bi-directional cutting method, with approximately one metre of advance per shear. The extraction height ranges from 3.8 metres to 4.7 metres.

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