Fifty people are to lose their jobs at Newmont Waihi Gold's Martha Mine as it suspends work after a slip there last month.
The staff are part of Macmahon Contractors (NZ) Limited.
Newmont said there was a slip at the north wall of the pit in early April.
It said geotechnical engineers had advised it might be possible to gain access to the area of the slip but more time was needed to make that decision.
The company said, because of the time needed to do that, the contract with Macmahon was being terminated.
Newmont external affairs co-ordinator Kit Wilson said it could be 12 months before they knew more.
"The problem is that that investigation is going to take some time. We think it could even take up to a year," he said.
"There's at least a month's work ahead for those staff. We have to reform some of the landforms, look after some equipment...
"The idea being that this is not closure, we're just not mining at the present time and there's always the possibility that things will reopen."
Mr Wilson said underground mining and milling would continue as normal.
He said if job cuts could have been avoided, they would have been.
The mayor of the Waihi area said the loss of 50 jobs at the local goldmine was a bitter blow.
John Tregidga, who heads the Hauraki District Council, said it was disappointing as the workers and their families were part of the local community.
But he said he was hopeful that part of the mine will reopen in 12 months' time.