Robinson, SL & Finucane, SJ 2019, 'Key outcomes of functional benchmarking for waste rock landform closure at a Western Australian iron ore mine', in AB Fourie & M Tibbett (eds), Proceedings of the 13th International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 871-882.
The initial closure design for a waste rock landform (WRL) at an iron ore mine in the Mid West region of Western Australia (WA) was based on a traditional linear slope design, but this changed to a concave slope design when new studies demonstrated that this would provide better long-term stability and protection against erosion. As the use of concave slopes in WRL closure is still relatively new in WA, and tall concave slopes are not common in the Mid West region, a benchmarking study was conducted to increase stakeholder confidence in the revised closure design.
The benchmarking study examined key lessons from six mines in WA where tall concave slopes had been implemented or were proposed as part of WRL closure, and six mines where linear slopes had been implemented or were proposed. The latter sites were included to provide information on WRL closure in the Mid West and adjacent Pilbara regions.
As a result of this study, it was found that a high standard of WRL closure implementation occurs when waste rock and topsoil characterisation, closure risk assessments, surface drainage studies, erosion modelling and other investigations are conducted as part of closure planning. Further, it was found that the likelihood of achieving acceptable WRL closure outcomes increased significantly when well-qualified and experienced operators along with an appropriate fleet were utilised for the closure earthworks, and careful attention was paid to construction controls and tolerances.
The outcomes of the study were used to refine the closure risk assessment and risk management measures proposed for WRL closure at the iron ore mine for which the benchmarking was conducted. Subsequently, the revised WRL closure design and an updated Mine Closure Plan were approved by the WA mining regulator. In issuing this approval, the regulator stated that the exercise was “particularly useful and should be encouraged throughout industry’ and was a ‘potentially powerful agent for use in mine closure [planning]”.
This paper summarises the benchmarking methodology and discusses the key findings of the benchmarking study, including the main success factors and key challenges associated with the use of concave slope designs in closing WRLs. The way in which the study outcomes were used to refine the WRL closure design and closure risk assessment for this iron ore mine is also discussed.
Keywords: waste rock landform closure, functional benchmarking, iron ore mine closure
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