ESTABLISHING and maintaining a healthy development lead, careful management of roof conditions and implementation of thorough maintenance schedules have been the main factors behind a solid first six months of operations at Oaky North, MIM Holdings’ newest longwall operation in central Queensland.

While the longwall started production three weeks later than planned on February 16, longwall production for the year ended June 30, 1999, totalled 1,476,887 tonnes, only 106,000t under budget. The mine recorded its best month in June with record tonnage of 570,731t of longwall coal, about 200,000t above budget.

What most pleases Oaky Creek general manager Peter Lynch is that “people haven’t taken their eye off the ball”. The mine went into production with a development lead of two blocks and keeping development well ahead of the advancing longwall is a key focus, according to Lynch, who dreamed up the idea of basing production bonuses on development metres. Regardless of how much tonnage is produced, if no development metres are attained bonuses are not paid. On average, the mine maintains a minimum of two longwall blocks lead, a strategy management said had numerous advantages, including being able to demonstrate continuity of supply.

“We’re competing world-wide against America and a lot of those markets are thousands of kilometres closer than we are. So one of the big selling points is that with our development lead we should be able to be a very reliable supplier,” said Oaky North mine manager, Ken McLaren.

Apart from being able to show customers a mine plan delineating developed blocks, the mine’s challenging geological conditions make it virtually imperative a good development lead is maintained.

“It allows us a big time-frame to put up a lot of secondary support, clean the roads, mesh the pillars and make sure the longwall is of a really high standard,” McLaren said. “So when the longwall goes in to mine back out we’ve got nothing to do except mine the coal.”

It is clear that from day one the idea was to capitalise on keeping development ahead. Apart from the shields Oaky North has two full sets of longwall equipment which allows pre-installation of the longwall before change-outs. The hope is to cut down relocation time to between 10 to 14 days.

Strategies for roof support have been influenced by friable roof conditions, weak floor and the presence of a synclinal trough midway along the length of the northern gateroads. Dennis Black, production/services superintendent, said this necessitated two target rates for development. “Relatively good mining conditions exist as the gateroads advance inbye toward the syncline,” he said.

“However, the ground conditions deteriorate as the gateroads advance further inbye beyond the syncline which necessitates the installation of substantial secondary support, including groutable megabolts on advance. At Oaky North our development operations advance at an average rate of 20m per shift up to the syncline. Beyond the syncline the target rate reduces to 10m per shift. However, recently introduced improvements in the strata control products we use combined with diligent installation techniques has on occasion resulted in performances upward of 50% above previous expectations, lifting the achieved average rate in these conditions to 12m per shift.

“Significant gains have been achieved in the area of strata control in the past six months which have included the introduction of the super-pin nut and high-torque drill motors to achieve significant pretension in the roof bolts during installation. We have also introduced a system of tensioning each shift the 50t groutable megabolts which we install on advance in areas of poor roof. This approach enables us to achieve the maximum benefit from the installed roof support, minimising delamination and subsequent ground movement.”

Oaky North owns three Joy 12CM12 continuous miners with two operating at any given time. The third unit is maintained as a spare panel which is manned when one of the operating units stops for planned maintenance or as a back-up in the event of a breakdown. Equipment maintenance is given a high priority which is now paying dividends in the form of increased availability and reduced component wear.

Each development unit, including the continuous miner, shuttle cars and feeder, is given a complete overhaul at the end of each gateroad.

“When we bring them back we know we can cut 4-5km without too many heartaches,” said Peter Binnie, engineering and maintenance superintendent.

On the human resources side, though the management team has been hard pressed to get the “green” workforce fully trained, standards are high and turnover rates are well below industry averages. Said Binnie: “We have gone out of our way to employ people who don’t have the stigma of the coal industry, and to do the training to the standard we require — which is a very high standard. To me, what we are achieving in this area is about 40% above anything else in the industry at the moment.”