Geologically the Mandalong Area is located in the south-west of the Newcastle Coalfield, a geological subdivision of the north-eastern Sydney Basin. The coal deposits of this area are contained within sedimentary rocks of the Late Permian Age Newcastle Coal Measures, which are characterised by complex patterns of splitting and coalescence of the various coal seams.

The significant coal seams within the Area are the Wallarah, West Wallarah, Great Northern and Fassifern Seams. The term “West Wallarah Coal Seam” was introduced by Centennial Mandalong and has been used at Mandalong Mine to define the coal seam formed by the westerly convergence of the Wallarah and Great Northern Seams.

Other significant units, which lie within the stratigraphic section, are the Awaba Tuff Formation, which lies between the West Wallarah and Fassifern Seams, and the Munmorah Conglomerate, which sits within the Triassic Age Narrabeen Group sediments between 80 m to 110 m above the West Wallarah Seam and Wallarah-Great Northern Seams. This conglomerate beam has a significant impact on the subsidence profile for the Mandalong Mine due to its spanning potential.

Centennial Mandalong has approval to use longwall mining and bord-and-pillar mining methods to extract up to 6.5 Mtpa of ROM coal from the West Wallarah and Wallarah-Great Northern Seams.

The proposed mine plan within the Southern Extension Area encompasses a total of 40 longwall panels ranging in length between approximately 1,000 and 3,500 metres, depending on seam conditions and site constraints, and ranging in width between 160 and 200 metres.

During the MOP (Mine Operations Plan) Term Mandalong will develop and extract Longwall 21 to 24A. Following the completion of mining in ML 1433, secondary extraction will commence in the Southern Extension Area (i.e. within ML 1722 and ML 1744).

All ROM coal from Mandalong Mine is delivered via underground and surface conveyor systems to either the CES or the Delta Entry Site for coal crushing and sizing.

Coal from the underground operation is sized underground by a 4,000 tonnes per hour (tph) sizer and fed to an underground surge bin. Coal from the bin is delivered to either the Cooranbong or Delta coal clearance systems. The Cooranbong clearance system transfers coal underground by 1,200 mm conveyor belts to a 2,000 t capacity ROM bin on the surface. The Coal Handling Plant (CHP) processes up to 700 tph.

Coal from the ROM bin enters the CHP and is then discharged via a syntron feeder onto a conveyor belt where a magnet removes metal prior to being discharged into a rotary breaker at the CHP to reduce the size of coal to less than 200 mm. Large pieces of stone are separated in the breaker and discharged into a separate stone bin with a 50 t capacity. The coal is then conveyed into an intermediate 400 t capacity storage bin where it is fed via syntron feeders through a crushing and screening plant to reduce the size of the coal to less than 31 mm.

Final product is then conveyed to a 2,000 t product bin, from where it is drawn off by Eraring Power Station as required. Transfer to Eraring Power Station is via the Eraring Energy Overland Conveyor which is owned and operated by Eraring Energy.

The CHP upgrades completed in 2010 utilise a changeover gate and chute arrangement to supply either the existing ROM bin or 2,000 tph aerial conveyor. This conveyor transfers coal to either 100,000 t ROM stockpile or dual truck loading bin. ROM coal transferred into the truck loading bin is loaded onto haulage trucks at the base of the bin by a telescopic chute fitted with automated loading and override safety controls. When coal levels in the truck loading bin are near to full, coal is directed by the changeover gate arrangement onto a 2,000 tph aerial conveyor, which discharges coal onto the 100,000 t coal stockpile.

Coal is loaded from the 100,000 t stockpile by front end loader onto coal haulage trucks. The loaded trucks use the truck weighbridge on the haul road to determine the load weight and then transport coal via the haulage road to Newstan Colliery for washing and export.

A small amount of coal reject is generated from the processing of coal at the CES CHP. This coal reject is periodically transported to the Newstan Colliery Reject Emplacement Area (REA). Management of the REA is covered in the Newstan Colliery MOP (Mine Operations Plan).

Residue coal material cleaned out from surface drains, washdown bays, gross pollutant traps and the settlement ponds is transferred to the 100,000 t ROM stockpile and entrained into product coal.