It was originally anticipated the longwall would be through the faulted area and restarting longwall production last week, but it was delayed as conditions continued to prove difficult.

The problem deteriorated over the past two weeks, resulting in a 450,000 tonne shortfall, roughly 15% of the mine’s projected annual output.

“Mining has been more difficult than anticipated as conditions ultimately proved to be significantly different to the geological interpretation,” Centennial said.

An “extensive roof fall” occurred on the face that had to be reinforced, but when longwall mining resumed, a further cavity developed. The mine’s longwall face conveyor, rated at 700kW, was unable to move the additional load.

The face recovery operation was further disrupted after a surface borehole was forced open by vandals, causing an unstable underground atmosphere and resulting in all underground workers being withdrawn.

The company said the mine plan for the next longwall block included measures to mitigate the risk by relocating the longwall face equipment around such faults. A relocation face has already been driven on the next longwall block.

Centennial has already ordered a new AFC, almost three times as powerful as the current system. Rated at 2 x 850kW, the new AFC will be installed early next year on the next longwall face.

“It is expected that following the introduction of the more powerful armoured face conveyor and the new approach to managing fault zones, Newstan will return to normal production and profitability levels,” the company said.

The company was able to keep Newstan customers supplied from other operations.