Mount Davy Mine, Greymouth, Grey District, West Coast Region, New Zealandi

Regional Level Types
Mount Davy Mine	Mine
Greymouth	- not defined -
Grey District	District
West Coast Region	Region
New Zealand	Country

Mining and exploration operations at this location reads more like a war campaign between miners and the local geology, a battle the rocks won.

Mt Davy is 20 kilometres north-east of Greymouth. While coal was known at Mt Davy since the early days, the rugged terrain prevented anyone from effectively exploring its extent. An attempt was made in 1948, with a camp, personnel, and drilling rig flown in by helicopter. Equipment, including the drilling rig had to be tied to the exposed rocky slopes of the mountain with heavy steel cables, to prevent gales dislodging it.

Drilling quickly stopped when high pressured water burst from the holes, at such a rate the project had to be abandoned. They stated the very broken Dunollie Beds overlying the Goldlight Shales are saturated with water held in cavities.

The New Zealand government owned Solid Energy decided in the mid 1990's to conduct exploratory underground workings into Mt Davy, with the aim of opening a new underground coal mine here.

It was well known the coal seams in the region contained large amounts of methane gas. Explosions had been a semi regular occurrence in many of the historic coal mines, due to a build-up of methane gas, and consequent fireball caused by an ignition source, as simple as a fall of coal. Coal miners were killed either from the depletion of oxygen, mangled in the explosions, the subsequent fire, or buried in coal dislodged during the event. It is noted to 1975, over four hundred men had been killed in coal mines in the region, with multiple fatalities often the result of methane build-ups. The Pike River Mine disaster occurred after the Mt Davy exploration.

However gas/coal outbursts simply by digging into the rock, was unheard of in 123 years of coal mining in New Zealand, although has occurred at times elsewhere in the world. Between November 1997 to July 1999, 21 outbursts of gas and coal/rock were recorded in the underground workings.

Work digging a drive began in May 1995, into the Morgan Coal Measures of the Paparoa Group, with access needing to traverse a reverse fault called R6. The Sub-Morgan Seam at the location is 5 metres thick, with the McArthur Seam 90 metres above it in the Rewanui Coal Measures. The Sub-Morgan seam was reached on the 08 October 1997.

By this stage there had been three violent outbursts, the third and largest removing 300 tonnes of coal. A second drive had been started in June 1996, and this working was not expected to suffer the same problem. It was assumed as no outbursts had occurred in Drive 1 in a similar strata, and outbursts were more likely in thick coal seams, whereas Drive 2 was accessing far smaller seams.

Drilling had to be altered in Drive 2, when high pressured gas began venting from drill holes. Then the outbursts began, the first in a coal seam less than one metre thick, and in one instance in sandstone with no coal. The next outburst dislodged 30 tonnes of coal. The event caused two fatalities, the men working the digging machine asphyxiated, and buried under tonnes of coal. Oxygen had depleted to 5% volume of air at the beginning of the event.
Work was suspended, but surprisingly only to evaluate better mining methods, and resumed in the second drive.

Each event caused a re-evaluation of mining methods. A three stage drill hole process was developed to relieve rock stress, and a surface de-gassing plant was installed. Miners operated machinery by remote control, protected by armour plating, flameproof material, 20 metres away from the rock-face, with compressed air pumped into the operating cab. A real time gas monitoring system was installed, providing readings every 60 seconds.

Outbursts continued. Across September to December 1998 the McArthur seam was explored without incident. Then after several more events, a large explosion dislodged 422 tonnes of coal. After several more small outbursts, on 01 July 1999, one dislodged 600 tonnes of coal, and mining was finally stopped, before it could reach production stage. It was determined none of the strategies implemented had any effect on mitigating the danger.

The Mt Davy deposit shows severe tectonic stress, most prominent in areas of folding. The rock is interspersed with faults, both normal and partly reverse. The bedding in the coal seam showed little cohesion. This chaotic geology had allowed the build-up of large gas reservoirs along faults and shears, in a region already known for having coal seams that were very gaseous. Miners simply had to hit a fault when digging, to potentially cause a sudden release of gas, in effect a gas explosion of tremendous force, dislodging sometimes large amounts of coal and rock surrounding it.

The mine was shut and sealed on 01 August 1999. The map shows the geographic Mt Davy, the sealed entrance tunnel in the vicinity.

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