Newscrest Mining has reported to have contained a breakthrough of tailings material at its Cadia gold mine in New South Wales (NSW), Australia.

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The Northern and Southern (forefront) Tailings Dams at Cadia

The company reported late last week that "a limited breakthrough of tailings material" was identified at the Cadia northern tailings dam embankment.

With the breakthrough contained within the southern tailings dam, Newcrest is continuing to monitor the impact, reporting no environmental damage or injuries as a result of the event.

Newcrest reported that 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 these cracks were noticed, the Cadia site team 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.

Newcrest had secured the area around the tailings dam, 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.

NSW regulators were immediately notified, with Newcrest working closely with them until the review is completed, supported by independent geotechnical consultants.

The tailings material is a slurry of finely ground rock, water and a low level of benign processing reagents. Cadia uses a gravity circuit to recover gold, with the remaining gold and copper reporting to a concentrate which is exported to copper smelters. Cadia does not use a chemical reduction process to recover gold, where the gold extraction process involves the use of substances such as mercury, cyanide and arsenic.

Geotechnical analysis has commenced on possible repair options of the failure zone. Work has also commenced on multiple recovery scenarios including alternative tailings locations such as the old Cadia Hill open pit, which is already the subject of a prefeasibility study to assess suitability for tailings disposal.

The operation is 25 kilometres from the city of Orange in central west New South Wales and is 250 kilometres west of Sydney.

Managing Director and Chief Executive Officer, Sandeep Biswas, said "The safety of our people and the community, together with the highest standards of environmental compliance, are paramount and remain our focus as we investigate this event and enact our forward work plan."

Whilst it is too early in the evaluation and recovery process for Newcrest to provide an indication of the extent to which FY18 production, capital and cost guidance will be impacted, Newcrest did comment in an ASX announcement that "this event will adversely impact guidance for FY18 given the contribution of Cadia to the overall outcomes of Newcrest. Further updates will be provided to the market when available."