A West Coast geologist warned about the threat of explosions from gas in the Pike River mine more than three years ago.
And a second mining expert says initial investigations of the mine were inhibited because of its location in Paparoa National Park.
Western Exploration director Murry Cave said in May 2007 there were several geological risks at the underground site.
They included:
A pit bottom with deep, highly gassy coals and the associated risk of "outburst", or gas or water-pressure- forced explosions, outwards at the coalface.
The presence of an active fault that needed to be crossed underground with a zone of considerable and sustained ground stresses.
A degree of uncertainty about the difficulties in accessing the resource due to geological structure, plus the risk of environmental damage from subsidence and "acid mine drainage".
Cave also pointed to explosions at Solid Energy's shortlived Mt Davy mine, which was shut down in 1998 after three miners were killed in two separate accidents.
"Mt Davy was forced to close after only a few years when it was concluded that the mine could not be safely operated due to the risk of outburst following the deaths of a number of miners resulting from outbursts," he said then.
Cave told The Press yesterday that coal in the Pike River mine was at the "higher end of the scale" for its gaseousness.
Each tonne of coal contained about 10 cubic metres of gas.
From 2000 to 2004 Cave was an adviser on the Pike River mine to the landowner, the Department of Conservation, as part of resource consent and access issues.
University of Canterbury engineering and mining geologist David Bell said the Hawera Fault zone running through the mine shaft allowed pockets of methane gas to build up. (The Press)
One place that Murry Cave's 2007 comments appear is:
ReplyDeletehttp://www.sharetrader.co.nz/showthread.php?4603-PRC-Pike-River-Coal/page6
This thread also includes rebuttals by John Dow and Peter Whittall that bear reexamining in light of the current tragedy.
John Dow's assertion that the Hawera Fault is inactive is surely wrong - it is a strand of the Alpine Fault System.
Because of (appropriate) environmental considerations this mine has been developed with much less evaluation drilling and fewer surface gas evacuation facilities than would normally be the case. I would guess that there are numerous gas-bearing fracture systems within the seam that are only found when mined into. These would be within small faults and fracture zones related to the Hawera Fault. In a properly developed mine these fractures and faults would be evaluated as fully as possible before mine development.