EGL Ref: 9018 22 June 2022 Page 6 WAI-985-000-REP-LC-0006_Rev0.docx This report shall only be read in its entirety. The GOP TSF is a lined TSF constructed in the void remaining after mining. The liner proposed includes partial backfill of the pit with PAF material to create the surface on which to place the pit liner. The material used for the backfill could be material from the GOP or could use material from Martha Open Pit Phase 4 (MOP4 i.e. Project Martha). If GOP overburden material is to be used it will need to be temporarily stockpiled. Underground mining requires backfill as part of the ore extraction process. Backfill for the MUG mine is currently being sourced from material being stored in the Polishing Pond Stockpile. However, with the increased production from the GOP and WUG mines the Polishing Pond Stockpile will be required for the storage of ore. Additional stockpiling capacity is therefore required for the storage of backfill for the MUG and WUG mines. As well as providing permanent storage of overburden materials not used in Storage 3 construction, the proposed new NRS can provide this additional storage for backfill of the MUG and WUG mines. It also provides storage of material required for the partial backfill of GOP required as part of the liner construction works to form the TSF. Material characteristics The overburden material from GOP and material from MOP4 is the primary material that will need to be managed in a stockpile. The chemistry of MOP4 material is the same as the existing materials that have been managed onsite to date. The GOP includes some material that has higher acid forming potential and higher mercury content. The current overburden management controls for PAF material will inherently manage the mercury. AECOM has recommended that high mercury (>3.5 mg/kg) NAF is not used in NAF zones which perform a liner function (Zones A, G, H) or where exposed to the surface (i.e., surface of Zone I). Stockpiling requirements Currently at the Development Site there is potential to store up to 1.0 Mm3 (million cubic metres) of NAF material in the existing Northern Stockpile and potential to store up to 1.5 Mm3 of PAF material in the Central Stockpile (0.9 Mm3) and in the East Stockpile (0.6 Mm3). This is not sufficient to manage the overburden materials from GOP, MOP4, MUG and WUG together. The total volume of overburden material scheduled from the GOP is 18.7 Mt or approximately 9.3 Mm3. MOP4 produces 6.2 Mt or approximately 3.1 Mm3 of overburden. Total overburden scheduled from MUG is 6.2 Mt or approximately 3.1 Mm3. Total overburden schedule from WUG is 3.5 Mt or approximately 1.8 Mm3. MUG and WUG material will be required for backfill of the underground, however, stockpile capacity is required to manage the movement of materials. Most of the material from WUG will be managed at the Willows Rock Stack however some material associated with the development of the Wharekirauponga Access Tunnel development will likely require stockpiling at the Development Site. For GOP there is 2.5 Mm3 of NAF material with low mercury that will be used for Zone A lining of Storage 3 or be stockpiled for rehabilitation
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