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Of that, 2.5Mt would come from slot mining techniques, while the other 23.8Mt would come from highwall mining.
“Slot mining is where a slot (trench) is cut into the coal seam at an optimal position where the seam is close to the surface to minimise stripping ratios,” Fat Prophets said.
“Coal recoveries from creating the slots are expected to be in the 95% region. Slot mining run-of-mine operations would extract 2.5 million tonnes of coal.
“From the slot a highwall miner would bore into the coal seam, creating a drive while extracting the coal. Coal recoveries from the highwall operations are anticipated to be in the 51% region.”
Advantages of highwall mining include low capital cost compared to traditional open cut or underground operations, better control over the quality of the coal being extracted and more flexible and greater coal production rates.
The loss in recoveries between the two mining methods is a result of the requirement of highwall mining to leave supporting pillars between each drive to sustain the ceiling.
The high recovery rates for Duchess Paradise and its close proximity to infrastructure on the west coast would set it up for a 10 year life with approximately 30.3Mt of run of mine coal, Fat Prophets said.
It is expected to come on stream in 2013.
The coal seam thickness at Duchess Paradise for the P1 seam varies in the range of less than one metre to more than three metres.
“The use of highwall mining in this incident is beneficial due to the flexibility of the highwall miner to operate in a variable seam thicknesses environment,” Fat Prophets said.
