An underground bord and pillar mine is on the horizon for Ensham, together with future plans for a high capacity underground mine as part of the Ensham Central project.
The Ensham Central project is awaiting final approval following the acceptance of the draft environmental assessment by the Environmental Protection Agency in December 2006.
In the meantime, the Queensland coal miner plans to trial various mining methods to make the most of current reserves.
Ensham technical general manager Colin Moffatt said Ensham was currently investigating the feasibility of pullback and high wall mining at its Emerald mine, in addition to pressing ahead with extensions to pit operations and plans for a trial underground mine.
“As the coal resource gets deeper we need to look at all the alternative options for managing the resource over the life of the mine,” Moffatt said.
“Having said that, we have long-term contracts with customers and cannot simply rely completely on the cheapest mining method (ie draglines) when we have orders to fill, so we will use a combination of equipment and methods.”
Ensham made a major advance in the efficiency of its operations in January this year when it commissioned its new Bucyrus 8750 Dragline 4. Although still in the early stages of production, the company said the dragline was meeting or exceeding performance expectations and had dramatically reduced overburden removal costs.
In addition to the major investment in a fourth dragline, Ensham has also changed its day-to-day mining operations. This included winding back truck and shovel operations and reconfiguring the mine haul fleet to offset the problems brought on by the worldwide shortage of mining truck tyres.
Ensham operations general manager Peter Westerhuis said tyre usage had become an important factor in openpit operations.
“We’ve had to do some calculations on TKPH [tonnes per kilometre an hour] and alternatives to mine haul trucks because of the unavailability and cost of high TKPH tyres,” Westerhuis said.
“This is a problem for us because there is an enormous heat build-up in the tyres as they travel along haul roads from pits furthest from the crushing plant.
“We are now stockpiling coal outside the pits along the haulage road and using road trains to take the coal the rest of the way. This way the dump trucks only travel a short distance at slow speed up the ramp so the tyres are not subjected to the same heat cycling and they last much longer.”
Ensham has also decommissioned its small fleet of centre dump trucks as the operating cost per tonne was not stacking up with alternatives.
“These trucks are getting older and more costly to maintain, so we have taken them out of service in favour of the road trains,” Westerhuis said.
“The future challenges for us as a mature mine are to look at all the alternative options for managing the remaining resource. Strip ratios are determined by the depth of the resource and as the coal gets deeper costs increase proportionately.”
Westerhuis said Ensham either had to rely more on draglines and less on truck and shovel to uncover coal or use alternate mining methods to access the deeper seams.