WEST Wallsend colliery in the Newcastle coalfield, New South Wales, has already been targeted as a strategically important asset for new owner, Swiss-based company Glencore International.
A three-million-tonnes-per-annum mine on the doorstep of the port of Newcastle, West Wallsend was part of the Oceanic Coal group of assets bought from HIH Insurance for $138 million in July; well below the book value of $180 million. Some analysts had been tipping a price range as low as $100-120 million for the mines and associated infrastructure. Glencore also recently purchased Pasminco’s coal interests inherited from its takeover of Savage Resources, for $69 million.
West Wallsend is attractive because of its proximity to port facilities, its measured resource totalling around 136 million tonnes, and the fact that the mine has only recent seen some much needed capital investment. New operations manager Glen Lewis, previously mine manager at Cumnock, said he believed there was a lot of potential to be realised at West Wallsend.
The mine was originally operated as a bord and pillar mine, converting under then BHP management to longwall mining in 1989 at an extraction height of 2.5m. After further ownership changes and an amalgamation of adjacent coal leases, the mine inherited a nearby resource with a single seam up to 6m thick. A decision was made to move from longwall operations at 2-2.4m to a working height of up to 5m about three years ago.
In describing the main challenges of the transition at a conference in Sydney in June, ex-mine manager Neville Hamilton said the main benefit of converting to thick seam longwall mining was a 40% reduction in development mining, and increased resource utilisation. Despite this, the challenges of thick seam mining were significant. Most difficult to quantify was the influence of overlying sandstone/conglomerate strata which generated cyclic loading and windblast problems.
The same sort of strata had been a major contributing factor to “catastrophic roof failures” at the adjacent Newstan mine, which had provided invaluable insight for West Wallsend, Hamilton said. “Through a process of exploration, monitoring, analysis and formal risk assessment, it has been established that a longwall width of 150m in West Wallsend’s specific circumstances allows the risks of cyclic loading and windblast to be effectively managed,” he said.
Originally the general consensus of opinion on managing the strata was “go wide and break it up”, Hamilton said. But the only significant factor that could be influenced to reduce roof failures related to cyclic loading was longwall panel width. A conservative width of 125m was adopted, followed by a “controlled increase in panel width to 150m”
Narrowing the extraction width had resulted in roof strata “hanging up”, significantly increasing the risk of windblast. In specific circumstances the competent beams in the roof strata could cantilever back into the goaf before failing in a major goaf fall, generating windblast activity measuring over 300kph. Several million dollars have been spent to put in place a structured management plan, including the installation of a maingate monorail system to allow minimal employee exposure if windblasts occur.
Equipment capacity will continue to pose an ongoing problem to the new management because the longwall system easily outstrips the mine’s coal clearance system capacity.
“The propensity of the coal face to spall, causing overload of the AFC and stage loader makes it difficult to design a cutting procedure to effectively smooth face loading. The use of flippers and operator vigilance is generally the best approach,” Hamilton said.
Lewis said the immediate focus of the mine’s new management will be on the operation’s production and maintenance strategies to improve equipment availability.
“The main focus will be the output per unit shift to improve both on development and the longwall,” Lewis said. “It is a high-tech longwall being put into an older mine so there are a lot of bottlenecks throughout the system we need to work on. The main one is the capacity of the out-bye conveyor belt system — primarily the drift conveyor. It is our main bottleneck at the moment. I don’t think we’re getting the most out of what we’ve got. When we’ve done that we’ll see if we can justify something else.”
To June 1999 West Wallsend produced 2.8mt run-of-mine, while the new budget for 1999-2000 is 3.2mt ROM.