Sumitomo Coal's attempt to recover longwall equipment sealed in at LW5 south of its North Goonyella mine in central Queensland has been a bitter sweet experience.
Mining in the troubled LW5 block was abandoned in May 1999 after constant roof support problems had caused ongoing delays. After LW5 was stopped, mining operations then shifted to LW1 north which had just been developed. LW5 south was sealed off in September due to indications of a spontaneous combustion heating.
Initial reconnaissance of the sealed area late last year showed the face still standing for the first 90 chocks. A subsequent full review suggested another recovery attempt was viable. In January the seal was removed and the face was ventilated. In addition, the stage loader, conveyor boot end, maingate drive motor and 17 legs were removed.
North Goonyella's general manager, Brian Nicholls, said less than six weeks into the exercise rapid oxidation occurred setting off a trigger point. The mine evacuated and the 5 south area was again sealed off with a 20 PSI seal. The goaf was rendered inert by the mine's Tomlinson boiler.
The good news is that $2 million worth of equipment was recovered which will give the mine a complete additional set of maingate gear. The additional legs will also help in the mine's overhauling of its 294 legs on LW1 north face. A continuous process of maintenance is underway to replace 24 legs on chocks every two weeks and failing blipper valves. The problem was first identified by Joy Mining Machinery last year which audited the supports to determine why they were not setting to their rated capacity. Roughly half the legs have been replaced to date.
Mining on LW1 north has meanwhile been going relatively smoothly Apart from a six-week delay over Christmas 2.6 million tonnes of coal has been produced since June 1999.
Lying immediately ahead of the face is a 200m faulted zone. Nicholls said the AFC chain was showing some damage and has been replaced early ahead of the predicted faulted zone. Face drilling had delineated no major displacement in the fault structure apart from some displacement on maingate. The zone has been pre-injected with 42 tonnes of microfine cement from long holes drilled into the zone from the maingate.
