High carbon monoxide levels are likely to keep Vale SA's Carborough Downs coal mine closed for the foreseeable future, mining unions say.
Earlier this month the miner was forced to shut down the coking mine and declare force majeure after it detected irregular levels of carbon monoxide, the International Business Times reports.
In a statement to Vale in May, the Queensland State Inspectorate for Mines ordered the immediate evacuation of all workers from the mine due to elevated levels of carbon monoxide gas in a longwall area of the underground coal mine, the miner said.
Around 7 700 tonnes of production has been lost since 29 May.
This is not the first time excessive gas levels have been detected at the mine, with the CFMEU issuing a warning over a similar incident in 2010.
According to the CFMEU, workers will not be allowed back into the mine until gas levels decline, the ABC reports.
"At this stage it is remaining static because of the injection of inert gases, it is masking what it's actually giving off," the CFMEU's Tim Whyte said.
"Somewhere along the line more monitors will have to go in that area to find exactly what's there and we don't send people back in the mines until we know … exactly what's there."
This is the second time in a month that Vale has been forced to suspend operations at one of its mines.
It was also forced to suspend nickel operations at its Southern Province project on New Caledonia following an accident at the sulphuric acid plant.