Coal bearing strata within the Muswellbrook area form part of the Sydney-Gunnedah Basin. The coal seams mined by MCC are part of the Greta Coal Measures, the lowermost coals of the Sydney Basin. The coal measures are separated into two main formations, the Rowan and Skelletar Formations. The area is overlain by thick glacial marine deposits (diamictites) and sandstones of the Branxton Formation, while the Greta Coal Measures unconformably overlie the Carboniferous Gyarran Volcanics.

The stratigraphic sequence of coal measure succession within the mining lease area at MCC is characterised by the presence of seven coal seams over a relatively small vertical distance of about 90 metres. The economic mining interval occurs between the Fleming and Loder seams with a cumulative total of approximately 27 metres of coal, the thickest being the St. Heliers Seam at a maximum of 14 metres.

The Greta Coal Measures are overlain by marine sandstones and diamictites of the Branxton Formation. This marine transgression during deposition of the sandstone has caused elevated sulphur levels in the top portion of the Greta Coal Measures. This top section also contains associated reactive ground. This material is mined and placed low within the pit to reduce the possibility of the material forming acidic water. Water quality monitoring data from pit sumps and surface waters show neutral pH values and provide an indication of the successful management of overburden materials at the mine.

All mining activities 2021 reporting period have occurred in Open Cut 1 with operations able to occur 24 hours a day, seven days a week. The Open Cut 1 mining schedule will continue within the Northern section of the approved area during the year, mining down through the seam sequences as they present from the Fleming through to the Loder seam. Mining has continued in Strip 23. This area will be lowered to the Lower Lewis and Loder floor to remove all underground workings. Mining extended into Strip 24 and Strip 25 in Open Cut 1. At the end of mine life all UG workings will be mined out removing any fuel sources for spontaneous combustion. The mining waste is dumped in Open Cut 1 and Open Cut 2. Open Cut 1 continues to expose underground workings of the No. 2 Underground and St Heliers Collieries. Site based procedures have been developed to allow safe extraction of the remaining underground pillar coal. These procedures are reviewed to reflect the operating experience gained during mining progress. Open cut wall designs were undertaken following recommendations of a geotechnical study completed for MCC by Mining Operation Services. Mining is achieved through open cut methods using excavators, front-end loaders and rear dump trucks. The site is currently (2022) approved to conduct mining operations until 31 December 2022. The site requires a continuation of coal storage, handling and transport until 31 March 2023. Mining operations and coal processing will be completed ........

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