27 September 2022 - Australian Pacific Coal Limited (AQC) entered into a binding agreement with Trepang, Tetra and M Resources in relation to a joint venture to see Dartbrook re-commissioned as a coal-producing mine.
On May 1, 2023, the binding term sheet announced in September 2022 has been renegotiated. The key terms of the restructured JV are:
- AQC retains the majority direct working interest which has increased from 50% to 80%.
- Tetra remains a direct JV participant with a 20% working interest and remains the mine Manager and Operator.
- Trepang will no longer have a direct working interest in the JV.
- M Resources will receive a 10% indirect economic interest in the JV through AQC.
AQC holds an 80% joint venture interest (70% economic interest) in the Dartbrook thermal coal project.
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Summary:
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.