12 March 2018
Cadia Gold Mine – another tailings dam failure
On Friday a tailings dam collapse occurred at the Cadia Gold Mine, operated by Newcrest Mining, in Orange, New South Wales, Australia. Cadia is one of the largest open cur gold and copper mines in Australia. The collapse has led to the cessation of mining operations at Cadia.
The collapse appears to have occurred on the Northern Tailings Storage Facility, on a dam that links two tailings storage areas. In consequence there has as yet been no release of pollution from the tailings site, and there were no injuries. Newcrest have released this image of the tailings dam failure:-
They have also put out a detailed press release that notes the following:-
An area of the embankment slumped late Friday 9 March 2018 following the identification of cracks earlier in the day in the dam wall during a regular inspection. When such cracks were noticed the site team quickly engaged an independent geotechnical consultant to assist Newcrest’s geotechnical engineers at Cadia with an
inspection and preliminary assessment of the embankment.
As a precaution Newcrest stopped depositing tailings into both dams late in the day of 9 March 2018. To allow site management to focus on the evaluation of the event and remediation plans, Newcrest progressively suspended all mining and processing operations at Cadia, fully effective on 10 March 2018.
The area around the tailings dam has been secured, and a comprehensive geotechnical monitoring system has been implemented, involving radar and cameras, to allow real time assessment of ground movement of the dam wall. No further movement of the wall has been detected since Friday night.
The statement also includes an aerial image of the failure:
It is clear that most of the tailings behind the failed section have not collapsed, which has prevented a large-scale release of tailings into the lower pond. There will be an urgency to try to understand this failure in order to ensure that the remainder of the tailings dam is safe, and of course to ensure that the now unrestrained tailings do not start to flow.
Interestingly, mining.com reports that the collapse occurred a few days after two seismic events in this area:
Even though the accident took place just a few days after two earthquakes of magnitude 2.7 hit the area, Newcrest did not mention any connection between these events. Back in 2017, the mine had to be shut down after it was hit by a magnitude 4.3 earthquake. It took about three months to bring it back to partial production.
It would be quite surprising if this structure was not able to withstand seismic events of this magnitude.
Whilst a major environmental disaster has not occurred at this site at the time of writing, this event once again serves to demonstrate that the failure rate for tailings dams is absolutely unacceptable. As I have said before, this frequency of failure, in combination with the potential consequences of tailings releases, would not be accepted in any other area of geotechnical engineering.