Authors: Bennett, K; Erickson, J; Blaxland, D; Langley, A; Crouse, P; Wallace, P

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Bennett, K, Erickson, J, Blaxland, D, Langley, A, Crouse, P & Wallace, P 2022, 'Using imagery to develop a 3D resource model of waste rock landforms for closure design', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 829-842,

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Closure of large mine facilities (e.g. tailings storage facilities [TSFs]) often requires sourcing large volumes of variable material with specific characteristics. Where feasible, identifying and sourcing appropriate material in the required volumes from local waste rock landforms (WRLs) is recognised as best closure practice. However, many historic WRLs have been constructed without considering the stockpiled materials as a borrow resource for future mine closure. Material investigations that characterise the composition of the material within a WRL and delineate the extent of similar materials are often constrained to the upper surfaces of the WRL. Due to the height and variability of material within numerous WRLs, mine closure plans will often include knowledge gaps in . This paper will present how imagery has been used to produce a three-dimensional (3D) resource model of two WRLs at the Gold Fields St Ives Gold Mine, located approximately 60 kilometres south of Kalgoorlie, Western Australia, and how this has supported the closure design of three TSFs situated adjacent to the WRLs, and proposed TSF closure/rehabilitation works. The TSF closure plan requires sourcing various material types, including coarse fractured rock material for erosion protection on existing embankments, clean and competent material for construction of new roadways and spillways, and fines material with suitable physical and chemical properties to support long-term vegetative growth to cover the TSF surface. Each of these closure material types will be sourced from specific predetermined zones using the 3D resource model of the WRLs. Gold Fields and Stantec worked together to correlate mine pit geology, historical aerial imagery and aerial elevation data, and material characterisation data to develop a 3D model that provides zones of waste rock materials having the required physical, chemical, geochemical, and geotechnical properties needed for the proposed cover systems and uses. Mapping and delineating the zones of similar material, in a 3D resource model, that can then be quantified and targeted during closure planning and implementation is key to a cost-effective method of sourcing the different material types needed for closure. Delineations are produced through having a sound understanding of the site geology, enhanced by reviewing details related to the mining of the deposits from which the waste rock material was excavated, including historical aerial images and numerous material characterisation test results of samples collected near the WRL surface at targeted locations. A challenge with all closure planning projects is incorporating the information developed during the investigation and planning phases into the closure design. This paper presents the methodology behind the successful closure planning approach that has been implemented at the St Ives Gold Mine to reduce uncertainties in material volumes and establish a forward work plan for mining-specific units of waste rock that will result in effective management of this closure risk. The paper concludes with lessons learned and recommendations for how miners might plan to better facilitate future use of historic WRL material for mine closure.

Keywords: mine closure, tailings, rehabilitation, mine waste, cover, reuse, recycle

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