Just how Oceana Gold will react when one of its mine safety "trigger levels" is exceeded in its proposed new pits needs to be detailed, hearing panel member Cr Duncan Butcher said.
The request came after Oceana Gold's geotechnical engineer Robert Bertuzzi, at the second day of the resource consent hearing into extending the life of the Macraes mine's operation, explained how movement of the west wall of the mine along the Footwall Fault was expected to be reactivated with the proposed mining of the Southern and Round Hill east pits.
Similar movement had been successfully managed with stop-start mining procedures and extensive monitoring at the mine's other pits, and had receded when mining ceased, he said.
"The consent conditions (proposed by Oceana Gold) trigger levels and alert levels are designed to give advance warning of any change in mechanism which could lead to progressive type failure."
However, he questioned the need for all mining to cease, as a proposed Waitaki District Council condition suggested.
Cr Butcher said the panel needed to see a management plan detailing the procedure.
"You're saying trust us with our management plan. We'll carry on doing what we've done before, but we need to be more confident the procedure is there," Cr Butcher said.
Civil engineer Trevor Matuschaka said in his evidence, mining of Round Hill southern pit would need to be subject to "rigorous" monitoring with a comprehensive management plan that included a set of conditions to control mining.
"There will also have to be the ability to adjust the sequence and extent of mining, depending on the movement of the Footwall Fault and observations and performance of the adjacent facilities." The new tailings storage facility would be constructed in stages and would be similar to existing facilities.
Erosion and sediment control practices, based on 20 years of experience, had worked well and he believed similar practices would be "satisfactory" for the project.
Opus International principal consultant Wendy Turvey said many archaeological sites at the mine would be impacted by the proposed works.
However, she believed the proposed mitigation measures and a separate agreement with the Historic Places Trust as well as the conditions required by the trust, would provide for the long-term protection of affected sites.
"These instruments together form a comprehensive mitigation package that address the adverse effects of the proposal on historic heritage."
The company had agreed with Historic Places to undertake an archaeological survey of the whole Oceana Gold Macraes Estate. It was to start this summer.
Traffic engineer Andrew Carr said while the road realignments proposed would increase the length of people's journeys, it was only slight and unlikely to be perceived by drivers.
The hearing continues this afternoon.
Ocean Gold hearing - Day 2
Applicant: Oceana Gold.
For: Resource consents to extend the life of the Macraes mine.
Panel: Otago Regional councillors Louise Croot (chairwoman) and Duncan Butcher and independent commissioner David McMahon.
Submitters: Oceana Gold: Opus International principal consultant Wendy Turvey, Pells Sullivan Meynink geotechnical engineer Robert Bertuzzi, Engineering Geology Ltd civil engineer Trevor Matuschaka and Traffic Design Group traffic engineer Andrew Carr.
Macraes Phase III Project
• Close existing mixed tailings impoundment and southern pit impoundment.
• Construct a new tailings storage facility called Top Tipperary.
• Construct a new dam on Camp Creek for water storage.
Mining Round Hill - Southern Pit
• Continuation and expansion of Frasers Underground Mine.
• New waste rock stacks and extensions to existing rock stacks.
