Cadia shutdown after dam collapse
NEWCREST Mining will fall short of its production guidance in FY18 after a tailings dam wall collapse at Cadia gold mine last month forced operations to a standstill.
While it was too early to provide an indication of damages, the miner said the dam collapse would “adversely impact guidance for FY18”.
The tailings wall breach on 9 March involved a limited breakthrough of material at the northern dam embankment, which was contained in the adjacent tailings dam to the south.
Newcrest said cracks were identified earlier that day during a regular inspection before the dam failed later that evening.
“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,” it stated.
At the time, Newcrest confirmed there were no injuries or further threats to safety, but as a precaution it would suspend all mining and processing operations at the mine until further notice.
On 27 March, after a two and a half week break, Newcrest recommenced mining operations at Cadia East with mined ore to be stockpiled at surface until processing resumes.
Newcrest said it was undertaking work on multiple recovery scenarios, including alternative tailings locations such as the old Cadia Hill open pit.
“Newcrest continues to work with the NSW regulators on permitting the Cadia Hill open pit tailings option and has commenced procurement of some of the necessary equipment to allow this possibility to be utilised if approved,” Newcrest stated.
“A prohibition notice issued on depositing tailings in the northern tailings facility remains in place.”
Newcrest managing director and chief executive Sandeep Biswas said the miner did a group wide review of all of its tailings facilities following BHP’s Samarco tailings dam disaster in Brazil in November 2015, with Cadia’s dams reviewed independently in 2016 and 2017.
“This was a total surprise to us given all of the reviews of the dam and certification that we’ve got so we will have to do a little bit of soul searching there clearly,” Mr Biswas said.
This wasn’t the first time Cadia production has taken a hit.
In April 2017, a magnitude 4.3 earthquake near Cadia forced the mine to shut for three months, which resulted in a 48 per cent drop in profits for Newcrest.
Newcrest previously declared it would produce between 680,000 and 780,000 ounces of gold and about 70,000t of copper out of Cadia in FY18; in the first half, Cadia produced 300,737oz of gold and 30,459t of copper.
The Northern and Southern (forefront) tailings dam at Cadia.
An aerial view of the failure zone.