The northern and southern tailings dams at Cadia, with the breach in the northern tailings dam embnakment visible.
Cracks were identified in the northern tailings dam embankment on Friday, which was followed by a slump later that day resulting in a "limited breakthrough of tailings material".
The breakthrough has been contained within the southern tailings dam, and no environmental damage has been encountered.
There were no injuries and Newcrest said it didn't believe there was any threat to safety.
Landholders and residents downstream of the dams are being kept informed.
Newcrest stressed that the tailings material comprises finely ground rock, water and a low level of benign processing reagents, but no cyanide, mercury or arsenic.
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.
As a precaution, the company stopped depositing tailings into both dams late on Friday, resulting in the suspension of all mining and processing.
Geotechnical analysis has commenced on possible repair options of the failure zone, but the company is also looking into 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 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," Newcrest managing director and CEO Sandeep Biswas said.
Newcrest said full-year Cadia guidance of 680,000-780,000 ounces of gold and 70,000 tonnes of copper would be adversely impacted, but it was too early to know the extent of the impact.
Cadia had only just recovered from a seismic event on April 14 last year, which halted underground operations for several months.
RBC Capital Markets analyst Paul Hissey said the incident was particularly unfortunate, given how hard Newcrest had worked in recent years to demonstrate operational consistency.
"Investors will likely focus on the portfolio concentration given the contribution Cadia makes to the overall business; the asset provides A$12 billion in our sum-of-the-parts net asset value of $17 billion, while it also contributes circa 60% of EBITDA," he said.
"We believe that the value of this asset is such that the cost of any technical solutions/re-engineering will not be insurmountable, and as such we would assume at this point in time that the closure is only temporary, while further risks are assessed and the company satisfies any additional regulatory requirements."
Newcrest shares slumped by more than 5% to $20.48, the lowest level since late July.
*Kristie Batten is editor of www.miningnews.net
