WAI-985-000-REP-LC-0056 Revision 0 Page 18 of 21 Waihi North Project – Tailings and Rock Storage – Functional Need Assessment 5 NORTHERN ROCK STACK The proposed NRS will be constructed to the north of the existing TSF2 and will provide for the temporary storage of up to 7M m3. Depending on the condition of the material placed this is up to 14M tonnes of earth and rock fill storage. This rock stack is required to be able to effectively manage the progressive removal of 18.7M tonnes of overburden material from GOP and material from the development of the Wharekirauponga Access Tunnel. The rock stack acts as a stockpile to provide for the staged development of TSF3 and GOP TSF and backfill material for MUG, managing the placement of material in different zones and specifications, at different times, and through wet and dry periods. Sufficient stockpile capacity is essential for an effective operation. NRS is located immediately adjacent to the existing conveyor loadout. The conveyor delivers the overburden earth and rock from GOP across the Ohinemuri River and then it is trucked to NRS or TSF3. The area is already partially developed, with the Northern Stockpile constructed in the late 1990’s for the storage of non-acid forming rock as part of the Martha Mine Extended project. The area contains access roads, water management infrastructure and other operational infrastructure. Northern Stockpile has previously realigned the tributary of the Ohinemuri River at its toe. Further realignment is required to form the larger footprint of the Northern Rock Stack. Existing storage locations offer insufficient capacity for effective management of the material coming from GOP. The current stockpile capacity is limited with the Central and East Stockpiles setup to take PAF material and are relatively full. There is potential capacity for 2M tonnes of PAF storage primarily in the Central Stockpile with a small capacity remaining in the East Stockpile. The Northern Stockpile currently can only provide for NAF material. There is approximately 2M tonnes of NAF storage in the Northern Stockpile. Overall, there is not sufficient stockpile capacity near to the loadout to manage the material coming out of GOP. In addition to meeting capacity requirements, the storage location needs to meet a variety of parameters including: • A location within feasible pumping distance of the water treatment plant • Proximity to mining operations, to reduce material haulage and rehandling costs to efficient and economic levels • Geotechnical stability and hydrogeological suitability (the proposed site of NRS has been the subject of studies since 1994 and EGL have noted the benefit of comprehensive geotechnical investigations in their final summary of risks and mitigation measures). In its options assessment EGL (2022) identify the proposed Northern Rock Stack as the preferred means of storage for rock generated from Mine scheduling has shown that the maximum profile of the NRS is reached mid-way through the project and then decreases as material is reclaimed for construction and backfill. There is no other location within OGNZL’s current landholding that is large enough or sufficiently close to the underground portal and overland conveyor to be able to accommodate the volume of rock effectively that the NRS will be required to store.
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