Partial Mine Closure

Western Australia

Calibre was engaged as the EPCM in 2019 for the Mine X Closure Study to develop and present an Order of Magnitude (OoM) level design, schedule, and capital cost estimate for the partial closure of Mine X.

The project involved partial closure of the Mine X pits that are expected to be exhausted in 2026. The partial closure required that the two pits ground water level and landforms be reinstated to pre-mining conditions.

Calibre investigated and analysed developed options and highlighted the technical and commercial risks to identify and recommend the central case option to be carried forward into the Pre-Feasibility Study (PFS).

Calibre explored multiple backfilling scenarios including collaborating with industry subject matter experts and undertook a trade-off assessment that identified the cost, schedule and risk of each option to help inform a preferred solution for selection.

Project need

The Client engaged Calibre as the EPCM in 2019 for Mine X Closure Study to develop and present an OoM level design, schedule, and capital cost estimate for the partial closure of Mine X deposits. Two pits feeding material to the process plant are expected to be exhausted in 2026. A closure study (partial closure) was required to document closure strategies for these two pits in line with the Company’s Mine Closure Plan.

Project solution

Calibre investigated and analysed developed options and highlighted the technical and commercial risks to identify and recommend the central case option to be carried forward into the PFS. The main areas of focus for the scope were to design the final landform including abandonment bunds, waste dumps and pits. With a focus on providing an efficient, safe and conforming final landform design solution, Calibre explored multiple backfilling scenarios including collaborating with industry subject matter experts and undertook a trade-off assessment that identified the cost, schedule and risk of each option to help inform a preferred solution for selection.

Calibre undertook significant assessment concerning reinstating the local Aquifer to pre mining conditions. Calibre also considered surface water and potential groundwater flow impacts in consultation with the client. Calibre tailored the revegetation approach to maximise access to future opportunities.

Outcomes

  • Developed a waste dump design including a PAF cell encapsulated within the waste dump.
  • Encapsulation and treatment of wastes.
  • Mine resources considered in the final design.
  • Refined the rehabilitation strategy to preserve resources in areas where resources may be accessed in the future.
  • Developed a high-level water supply and movement strategy for the aquifer recharge requirement of 80ML/day. Four alternative aquifer recharge volumes and durations were also investigated.
  • Completed scoping and estimation for the decommissioning and demolition of infrastructure as well as rehabilitation of the sites.
  • Developed high-level post-closure monitoring schedule and costing.
  • Formulated and communicated management strategies related to environmental impacts and their control.
  • Provided expert advice on mine closure and rehabilitation requirements.
  • Led design reviews, risk assessments and constructability reviews.
  • Managed the integrated management systems to third party certification requirements.
  • Provided timely advice on all environmental aspects, including legislation, regulatory approvals and compliance.