Regional Geology
Dartbrook Mine is located in the northern part of the Hunter Coalfield and west of the Muswellbrook Anticline. The strata of the Permian Whittingham Coal Measures outcrop in the area and dip gently to the west. The underlying marine sediments of the Maitland Group outcrop approximately 3 km east of the site, on the eastern side of the Aberdeen Thrust. The Hunter Thrust, which represents the northern limit of the Sydney basin, is located further to the east (HLA-Envirosciences, 2000).

The Greta Coal Measures occur below the Maitland Group. These seams occur at depths in excess of 1,000 m at Dartbrook Mine (HLA-Envirosciences, 2000).

The Whittingham Coal Measures contain the coal bearing Jerrys Plains Subgroup and Vane Subgroup. Within the basin, these two subgroups are typically separated by the Archerfield Sandstone, which is a massive, well sorted sandstone unit. However, in the vicinity of Dartbrook Mine, there is no vertical separation between these subgroups, as the Bayswater Seam (the base of the Jerrys Plains Subgroup) has coalesced with the Wynn Seam (the top of the Vane Subgroup) (HLA-Envirosciences, 2000).

Four of the five main coal bearing formations within the Jerrys Plains Subgroup (namely the Malabar, Mt Ogilvie, Mt Thorley and Burnamwood Formations) are present at Dartbrook Mine. The coal seams within the Jerrys Plains subgroup generally exhibit a high degree of splitting, and major seams are generally represented by several plies / splits (HLAEnvirosciences, 2000).

Interburden strata within the Jerrys Plains Subgroup generally include interbedded sandstones, siltstones and mudstones with minor claystones and tuffs and occasional conglomerates and thin siderite. These strata are generally coarse-grained in the upper sequence (above the Vaux Seam) and become progressively finer with depth to the Bayswater Seam. Non-coal units in the Vane Subgroup are generally fine to medium grained sandstones (HLA-Envirosciences, 2000).

Local Geological Characteristics
The coal seams at Dartbrook Mine are characterised by gentle dips (ranging from 3 to 6 degrees) to the north-west. Local variations of up to 15 degrees have been identified. These are generally interpreted as being due to clastic wedging, seam splitting and differential compaction (HLA-Envirosciences, 2000).

Dykes and faults are generally well defined due to their presence in historical underground workings at Dartbrook Mine. Faults trend from north-west to south-east, with significant displacements being confined to the Kayuga fault zone, its north-western branch, and the west, north-western fault zone. There are two major dykes at Dartbrook Mine. The Great Wall of China dyke is estimated to be 25 m thick and the Roman Road dyke is approximately 15 m thick. Dykes tend north-east to south-west and have cinder zones of less than 1.5 m. There are seven minor dykes south of the Roman Road dyke. These are generally 0.5 to 2.5 m thick, deeply weathered and of low strength. A number of igneous plugs have been interpreted. The Kayuga plug is approximately 200 m x 400 m in size and its location has been confirmed by exploration activities.

Coal Seam Geology
The target seams for underground mining at Dartbrook Mine are the Wynn, Kayuga, Mt Arthur and Piercefield Seams. To date, mining operations have been undertaken in the Wynn and Kayuga Seams. The Kayuga Seam, one of the uppermost seams, is the target seam for the Modification. At Dartbrook Mine, the Kayuga Seam lies at depths of 20 m (subcrop) to over 300 m.

The Kayuga Seam is characterised by bituminous, high-volatile and low sulphur content coal. The seam occurs as a series of plies and splits which diverge and coalesce across the site.

The current development consent (DA 231-7-2000) was granted on 28 August 2001. DA 231-7-2000 provides approval for longwall mining activities in the Kayuga, Mt Arthur and Piercefield Coal Seams, in addition to the previously approved mining activities in the Wynn Seam. [p. 3]

Mining in the Wynn Seam commenced in 1996 and was suspended in May 2004. Ten of the approved longwall panels in the Wynn Seam were extracted during this period. Mining operations were then relocated to the overlying Kayuga Seam. Mining of the Kayuga Seam commenced in 2004 and was suspended in October 2006. Only three of the 20 approved longwall panels in the Kayuga Seam have been mined to date. [p. 4]

The extraction height for longwall mining ranges from 3.0 m to 4.5 m. The approved longwall panels are generally 200 m wide, although DA 231-7-2000 also provides approval for the option of 300 m wide longwall panels in the Piercefield Seam. [p. 37]

AQC Dartbrook Management Pty is seeking to modify DA 231-7-2000 to facilitate the re-commencement of underground mining activities at Dartbrook Mine. The Modification proposes the following:
• Bord and pillar mining activities within the Kayuga Seam (as an alternative to the approved longwall mining activities),
• An alternative method of delivering ROM coal from the mine workings to the East Site; and
• Extending the approval period under DA 231-7-2000 by 5 years (until 5 December 2027).

The proposed bord and pillar mining will result in the extraction of up to 10 Mt of ROM coal over a 10 year period. The maximum production rate in any given year will be 1.5 Mtpa. The approved longwall mining activities in the Wynn, Kayuga, Mt Arthur and Piercefield Seams will not be altered by the Modification. The total coal production from Dartbrook Mine will remain within the approved maximum production rate of 6 Mtpa.

Dartbrook Mine has been under care and maintenance since December 2006. To enable the proposed mining activities to be undertaken, the Modification seeks to extend the period of approval by an additional 5 years.

Under the approved coal clearance system, ROM coal is transferred directly from the mine workings to the East Site via the Hunter Tunnel. The Hunter Tunnel is an underground pathway between the East Site and West Site, passing beneath the New England Highway, Main Northern Rail Line, Hunter River and Dart Brook.

The Modification proposes that coal extracted via the bord and pillar mining method will be delivered to the surface via the Kayuga Entry. It will then be hauled along an existing private road network to a new shaft facility (to be constructed west of the New England Highway). The coal will be transferred down the shaft into the Hunter Tunnel, where it will be conveyed beneath the New England Highway to the East Site.

Mining Method
The Approved Mining Area for the Kayuga and Mt Arthur Seams is contained within CL 386 and ML 1497. DA 231-7-2000 allows for the coal reserves within the Approved Mining Area to be extracted via longwall mining methods. AQC proposes to conduct bord and pillar mining in the Kayuga Seam, as an alternative to the approved longwall mining. The proposed bord and pillar mining will take place within the Approved Kayuga Seam Mining Area.

Bord and pillar mining involves the shearing of coal to develop a network of roadways within the coal seam. The roadways are separated by blocks of intact coal, which are referred to as “pillars”. The pillars will be designed to remain stable in the long term, thus resulting in no perceptible surface subsidence.

Due to the geotechnical conditions at Dartbrook Mine, bord and pillar mining will be undertaken using “in-place” methods. The “in-place” mining methodology involves the progressive installation of roof support as roadways are developed. This differs from the “place change” method, where roof support is installed after the roadways have been developed.

Mine Plan
The proposed bord and pillar mine plan within the Kayuga Seam will consist of main headings and production panels. Both the main headings and production panels are networks of parallel and perpendicular roadways, which produce square shaped pillars. All bord and pillar workings will be stable in the long-term. The dimensions of the coal pillars will need to increase as depth of mining increases.

The Kayuga Seam has a maximum thickness of approximately 4.5 m. The extraction height for the Modification will vary between 3.0 to 3.5 m.

Coal Production
DA 231-7-2000 allows for the extraction of up to 6 Mtpa of ROM coal. The proposed bord and pillar mining will result in the extraction of 10 Mt of ROM coal over a ten year period (i.e. an average rate of 1 Mtpa). The maximum annual production rate from bord and pillar mining operations will be up to 1.5 Mtpa of ROM coal. The Modification does not seek to alter the approved maximum coal production rate at Dartbrook Mine.

The Coal Handling & Preparation Plant (CHPP) contains the coal washing and processing infrastructure for Dartbrook Mine. [p. 49]

The CHPP was constructed pursuant to DA N91/00424/003. The construction of the CHPP enabled the extraction of the shallower coal seams (such as the Kayuga, Mt Arthur and Piercefield Seams).

The CHPP had a maximum throughput of approximately 1,000 tonnes per hour (tph) and could deliver ROM coal at a rate of approximately 4,000 tph during peak output. The raw coal was crushed to a maximum size of 150 mm for processing then screened at 16 mm. The 150 mm x 16 mm coal was then treated in a dense medium bath, the 16 mm x 1.4 mm coal was treated in a dense medium cyclone and the fine coal was treated in coal spirals. The product coal was then crushed to 50 mm in order to meet sizing specification for export markets.

The current intention is to not utilise the CHPP for washing the coal extracted from the Kayuga Seam through bord and ........