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Design revision, Reefton Open Pit Gold Mine, New Zealand


Located 7 km from the town of Reefton, the Reefton Open Pit mine was  commissioned in 2007 with an estimated mine life to 2017. The pits have been developed within 20 km of the Alpine Fault in intensely folded and sheared greywacke and argillite. Reefton is situated in the nanghau River valley region and is subject to high annual rainfall. Gold ore is railed, trucked and finally processed at the Macrae’s operation south of Palmerston, South Island. Based on current reserves the mine life is estimated until 2017.

PSM was engaged to assess and analyse the geological interactions of the existing designs and to propose revised tunnel designs allowing for the continuation of construction around the backfilled collapse cavity.

engineering AND technical Opportunities

Located in a remote region on the west coast of New Zealand’s South Island, the geology is complex. The mine is situated along the Alpine Fault in intensely folded and sheared greywacke and argillite. The area has a high average annual rainfall of 2,200 mm per annum. There was limited onsite geotechnical expertise. Mining consent regulations required establishment and maintenance of monitoring. This provided the ability to modify the mining plans in response to incipient failure.

Approach and innovation

PSM`s tailored approach included:

  • Training of site staff in data collection to maximise efficiency
  • Provision of extensive kinematic and statistical analyses
  • Provision of rigorous numerical modelling using limit equilibrium [Slide, Limitstate Geo] and finite element [Phase2] analyses
  • Provision of design: 15 m batters and 5-10 m berms.


Working closely with OceanaGold, PSM developed a sound knowledge and understanding of the company’s objectives and technical challenges. Following successful training of existing staff to collect necessary data, PSM provided ongoing monitoring.

Services: #argillite #Geotechnical #goldore #greywacke #reefton

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