The Cadia Gold Mine in New South Wales has been temporarily closed after the failure of a retaining dam on a tailings pond on Friday 9 March 2018. Tailings ponds are used to store sediment-laden waters from mines; such waters typically contain a high proportion of fine silt and clay particles, which take time to settle out of the water. The resulting water may be fairly clean, or may contain other pollutants (typically acids, either generated by the local geology or used in the mining process), and need further treatment. The waters from the Cadia Mine are thought to have been retained by a secondary wall, preventing wider environmental damage, but the situation is considered to be sufficiently unstable to merit closing the mine until remedial work has been carried out.
Aerial photograph of the breached tailings pond dam at the Cadia Gold Mine. Central Western Daily News.
The precise cause of the event is unclear at the current time, but the Australian Workers Union has suggested that it is likely to have been related to a recent activity in New South Wales, with two Earthquakes recorded in the state one Thursday 8 March, one of them a Magnitude 2.7 event described by Geoscience Australia as 'significant'. The union has raised concerns that that the dangers of seismic activity in Australia are not taken sufficiently seriously in the mining industry.
The approximate location of the 8 March 2018 New South Wales Earthquake. Geoscience Australia/Google Maps.
While New South Wales doe suffer occasional Earthquakes, these tend to be small and infrequent, making their precise causes hard to determine. The state is far from any tectonic plate margin that might provide an obvious cause. Many ancient sedimentary beds in southeast Australia are stacked at fairly steep angles, the result of fold mountain formation during the assembly of the supercontinent of Pangea (though the mountains themselves have largely eroded away), which can make the area slightly more quake-prone than would otherwise be expected.
Witness statements can help geologists to understand Earthquakes and the geological processes that cause them; if you felt this quake you can report it to Geoscience Australia here.
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