A two million tonne rockfall this week at Oceana Gold's Martha pit mine at Waihi in the central North Island appears likely to result in lengthy delays to any reopening of the pit, which has been closed for more than a year.
The slip was down the same benched face as a smaller slip in April last year, which closed the Martha pit.
Six days before Tuesday's rockfall, Oceana had publicly predicted and warned a larger slip was ‘‘expected soon'' in the same area.
No staff were in the pit and a part of the public walkway around the pit rim has subsequently been closed.
Oceana purchased the historic mine, which includes expanding underground operations, from Newmont in May last year for $132million, just weeks after the first slip closed the pit.
Oceana Gold spokesman Kit Wilson estimated in the latest rockfall, at 5am on Tuesday, about two million tonnes of rock slipped down the north wall of the mine.
‘‘This slip was not unexpected. In fact, we advised the local community late last week that we believed there would be an event of this nature over the next few days,'' he said.
Oceana shares were unchanged at $4.52 yesterday.
Mr Wilson said since Oceana formally took ownership last November, there had been ‘‘restricted mining activities'' in the Martha pit, but Tuesday's rock fall was independent of those activities, being directly linked to last year's slip.
He said more movement was being detected in the area and Oceana expected more, smaller, rock falls as the slip stabilised.
Mr Wilson said Oceana had already begun construction of a new haul road to access the Martha pit, but that work was now on hold while the situation was assessed.
Mr Wilson said remediation work would be required, but it was too early to predict a timeframe, options or costs involved.
He said the fall of rock was in an area which had been monitored extensively, including the use of a radar system that can detect very small movements, meaning the event could be anticipated in the expected area.
‘‘Members of the public may have heard the rock falling, but there was no danger to them at any time,'' he said.
Gold production from Waihi, all underground, was just under 70,000oz during calendar 2015.
This year, Oceana planned to spend $10 million to $12 million at Waihi on 34km of exploration drilling around the mine, and a mine optimisation study was expected to be finished by the second half of 2016.
Mr Wilson said while plans were under way to re-enter the Martha pit, the latest slip meant those plans would have to be modified and re-entry ‘‘may take a while longer''.
‘‘Our plan was always to resume work in the mine if this could be done safely,'' he said.
Following the April 2015 slip, there had only been limited work in the open pit, all of it well away from any potential rock fall area, Mr Wilson said.
●Oceana's first quarter trading results are due out tomorrow.
