An Anglo American spokesperson has informed Safe to Work that elevated gas readings that occurred at the Grosvenor mine site last month “may have been an indicator of a brief ignition event.”
“While underground access at the mine has remained restricted, this has not been able to be confirmed,” the spokesperson said.
Mining activities at the Grosvenor underground coal mine, near Moranbah in Queensland, had come to a halt since May 6 after an underground methane gas explosion injured five men.
Anglo American reconnected gas monitoring equipment and started re-entry stages to the mine in mid-May, but the company decided to withdraw personnel from the underground environment again last month after an increase in gas levels were recorded.
“We made the decision to withdraw personnel from the underground environment last month in line with our risk management processes, and have been working with our expert technical advisors to assess and respond to the situation since then,” the spokesperson said.
Anglo American states that the increased gas levels are a direct result of oxidation of coal while mining activities remain suspended.
As coal is excavated, the weight of the overlying ground originally supported by the coal becomes supported only by the remaining pillars or walls. This causes the mine void walls to compress and the overlying rock to crack and tilt into the void.
In longwall mines, the rock immediately above the void typically collapses into the void as mining progresses, forming a layer termed a ‘goaf’.
Anglo American is currently monitoring the gas levels closely.
“Since ceasing longwall mining activities on 6 May, we have been closely monitoring the resulting levels of various gasses to ensure the ongoing safety and integrity of the mine.
“The suspension of longwall mining elevates the risk of oxidation of the coal in the longwall goaf environment. During normal longwall mining operations this risk is very low.”
The Anglo American spokesperson noted that the oxidation is currently under control.
“The steps we are taking to address the coal oxidisation and heating risk at Grosvenor are tracking as expected, and we believe that the oxidation in the goaf is currently under control.”