In 2018, Coronado Group acquired Wesfarmers Curragh Pty Ltd (now known as Coronado Curragh Pty Ltd), including the Curragh producing mining property, from Wesfarmers Ltd.
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Summary:
Curragh is situated within the Permo-Triassic aged Bowen Basin in Eastern Australia, which covers approximately 16 million hectares. Its physiographic make-up consists of lowlands, flood plains as well as rugged plateaus and ridges. The main lithological units derive from continental and marine sedimentation with limited volcanic and intrusive rocks. The principal Resources are primarily large coal fields and secondarily natural gas.
The geological setting of the property itself consists of sediments of the Rangal Coal Measures and Burngrove Formation, both of Permian age which outcrop on the property. These units underlie alluvial Quaternary cover and minor areas ofTertiary sediments. Alluvial sediments typically have an average thickness of 10 to 15 metres, with locations of up to 30 metres of sand, clay and gravel in northern areas.
The Yarrabee Tuff marker coincides with the present lower limit of Resource estimate. Five main coal seams groups, primarily of metallurgical quality with some thermal quality coals, are mined at Curragh, as listed below:
- Cancer seam
- Aries seam
- Castor seam
- Pollux seam
- Mackenzie and Pisces seams
The Burngrove Formation typically has thick interbedded coal and tuff beds. This coal is typically high ash and is not included in either the Resources or Reserves.
The structural environment at Curragh can be fairly complex with the observed seam deformation the result of thrust faulting from the northeast with fault throws up to 30 m. Structural thickening can occur where thrust faults cause affected seams to be repeated, but in most cases the duplicated seams are not included in the Resource estimation, although such repeats of coal are often mined and included in the Resource estimation if sequencing permits such as the Pollux seam. Thrust faulting can also result in barren areas, where seams have been faulted out. North-south and east-west trending normal faults also occur but are less common than thrust faulting. The structural geology within the Resource adds some complexity to the project, as such the mine employs a strong geotechnical program to manage geotechnical risks.
The major structure that limits mining at Curragh North is the Jellinbah fault, this trends in a north west, south east direction with throws of over 100m, various splays of lesser throws (10 to 20m) trend to the north west.
Mineralization
The property, as in the Bowen Basin as a whole, does not contain any signs of metamorphic activity; the prevailing lithology is sedimentary rocks with a few igneous intrusions. The depth of host rock weathering at Curragh is on average in the order of 10 to 15 metres.
Deposits
In portions of the property, a number of these seams merge to form a single package, without any interburden strata. In the central and some of the northern part of the property the Aries and Castor seams coalesce into one coal stratum that is referred to locally as the “Mammoth” seam. The Mammoth Seam is analogous to the Leichardt seam commonly found in mining operations further north. At Curragh North the Pollux, Orion and Pisces seams coalesce into one unit which is correctly referred to as the Mackenzie seam, but in some contexts has been referred to as the “Pisces” seam even though the true Pisces seam is only one of the constituent seams of the Mackenzie assemblage. The Mackenzie seam is analogous to the Vermont seam which is commonly found in mining operations further north.
Seams of economic interest occur at depths ranging from 15m from surface down to as deep as 400m in the deepest part of the property.
Interburden host rock typically consists of regular intercalations of siltstones and mudstones, with layers of variable thicknesses. The rock and coal beds dip gently to East direction at an angle of approximately 3 degrees, with some sections displaying dip angles as high as 10 degrees in association with structural deformation.
In general, only minor instances of intrusive material have been intercepted in drill holes or mined during production at the Curragh Mine.
Igneous activity is more prevalent at Curragh North although these are not a major impact on Operations. The intrusive includes rare dykes occurring at the northern end of Curragh North deposit. There was a larger igneous intrusion approximately 500 metres long and 100 metres wide that impacted the Resources of the Aries, Castor and Mackenzie seams. Mining has proceeded past the area of impact of this intrusion.
Curragh has been subjected to moderate localized faulting more intense in southern areas that has resulted in vertical slips (displacements) as high as 20 metres, along with variations in seam thickness. Seam duplication is also common as a result of the thrust faulting but in most cases the duplicated seams are not included in the Resource estimation, although such repeats of coal are often mined.