Up to 50,000 tonnes of ore is mined from the pit every day. Photo / Greg Bowker
Work at Newmont Waihi Gold's open pit at Waihi has been halted until further notice because of concerns about the stability of its eastern wall.
The Martha Mine produces around 100,000 ounces of gold a year and workers there have been redeployed to other parts of Newmont's operation in the
town.
No neighbouring properties were at risk as the affected area was well within the mine boundaries, a spokeswoman said.
Spectators were dotted about the edge of the pit yesterday watching "shovel-size" loads of material tumble down mine walls.
Investigations into the stability of a tyre buttress on the wall were being carried out.
At the surface facilities area above the buttress, access roads on the open pit side of a massive rock crusher have been closed until further notice as a precaution.
Newmont says the eastern wall has been subject to instability for many years - during the underground mining days before 1952 the area was known to be difficult ground.
The area was named Milking Cow because water used to drip on to miners working in tunnels.
Previous remediation measures in the present open pit included the placement of large truck tyres to form a buttress against the east wall. After heavy rain some tyres have fallen from the crest of the pit down the mine wall.
"Due to the unpredictable nature of the loose tyres when they travel, they could pose a hazard to mine employees," a spokeswoman said.
She said production had not being affected because the company's mill was processing Favona gold and stockpiled ore from Martha would be available.
"We'll change the schedule. What we're not taking out now - we will take out later."
Up to 50,000 tonnes of ore is mined from the pit every day.
The shutdown follows a fire at the mill in May which cut production and cost the company nearly $50 million in lost revenue.
General manager Glen Grindlay said the old Milking Cow mining block has been closely monitored.
"The movement is within expectations and can be predicted with a high degree of confidence. Once the safety of employees can be assured normal mining activity will be resumed."
