WAI-985-000-REP-LC-0056 Revision 0 Page 12 of 21 Waihi North Project – Tailings and Rock Storage – Functional Need Assessment generation, and surface drainage of TSF2 would need to be removed and reinstalled on the new downstream slope. TSF2 RL176 takes out the conveyor and loadout (currently at RL153.5). The conveyor would have to be finished (with a loadout) immediately after it crosses the Ohinemuri River. This notably reduces the level of the loadout, which was favourable for hauling to the TSF1A, Central Stockpile and East Stockpile. TSF2 RL176 downstream raise embankment requires approximately 13.2M tonnes of material. 80% or 10.6M tonnes of this material has to be placed prior to any tailings storage to be achieved. This is compared with 5.2M tonnes for TSF3 starter embankment. TSF2 is also the resting place of Pukewa’s head and shoulders previously mined from Martha Hill. Pukewa is the life force recognised by local iwi associated with the Martha Ore Body which is located at the location of the past Martha Hill, now Martha Open Pit. From a material scheduling and project economic perspective OGNZL consider raising of TSF2 to RL176 not to be feasible for the Waihi North Project. Raise of TSF1A from RL182 to 192 Raising of TSF1A 10m from the consented crest of RL182 to RL192 through steepening of the downstream slopes to the maximum safe geotechnical profile was considered. This would require full rework of the existing downstream slope requiring removal of all the existing surface drainage and rehabilitation capping layers and placement of approximately 7.8M tonnes of rock. The storage created provides for 4.8M tonnes of tailings, which combined with GOP TSF capacity of 2.1M tonnes, is not sufficient to achieve the required 8.8M tonnes for the project. This is therefore not a viable option for the Waihi North Project. Paste backfill of WUG and GOP Underground backfill using paste is a potential option for tailings disposal. To create the paste, tailings are deslimed, thickened and mixed with a binder, like cement. The benefit of paste backfill is that it utilises the underground voids created in the mining process for tailings storage. But paste backfill has a density much less than insitu ore in addition to being mixed with cement and hence only a portion of the tailings stream can be restored underground. Of over 6M tonnes of ore modelled to be mined from WUG, underground paste-fill disposal would store about half (3.3M tonnes). This falls well short of the tailings storage required for the Waihi North Project. Further paste backfill to WUG is not without notable challenges. For cost and practical reasons, pastefill is difficult to manage and to integrate into the mining schedule in the specific circumstances of the WNP: • Studies have shown that paste backfill is impractical to use as part of our planned mining methods as our stopes are small and require progressive backfill to address subsidence risks, which introduces significant additional time into the schedule due to the construction of bulkheads, and the wait time on the curing of the paste. The scheduling implications of paste backfill, alone, have rendered this option uneconomic. • The transport of paste (pumping) or tailings from plant would be technically complex and expensive due to the long horizontal distance from the Process Plant to the SFA to the underground mine. Most paste plants are located immediately above the mine which is not possible in the case of WUG due to its location. As an alternative to pumping paste from the SFA or the processing plant, studies considered the costs and practical implications of pumping thickened tails and then removing water underground (i.e.
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