EGL Ref: 9215 23 June 2022 Page 42 This report shall only be read in its entirety. File: WAI-985-000-REP-LC-0002_Rev0.docx. a saturated condition which minimises geochemical risks and allows for attenuation of discharge from the surface of the TSF in extreme flood events. 6.8. Sterilisation of resource Options for disposal of tailings or rock that may potentially sterilise future ore resources need to be considered. Normally investigation of potential ore resources beneath TSFs or permanent rock stacks are undertaken to demonstrate that they will not prohibit access to future ore resources. 7.0 REVIEW OF TECHNOLOGIES FOR TAILING DISPOSAL 7.1. Tailings Technologies The Global Industry Standard on Tailings Management (GISTM, Ref. 18) recommends that projects consider and evaluate different options for disposal of tailings and this should include the available technologies for disposal of tailings. They include: • Conventional slurry tailings • Thickened tailings • Paste • Filtered tailings Comments on these options follow. 7.1.1. Conventional slurry tailings Conventional tailings are pumped to a TSF as a slurry using centrifugal pumps after minimal thickening following processing of the ore to remove gold and silver. This is the conventional technology used at most gold mines. The tailings are pumped and deposited at a high water content. Water separates from the solids upon deposition in the TSF and ponds on the tailings surface. Additional water is released from the tailings as they settle and consolidate. Most of this water rises and ponds on the surface of the tailings. The ponded water is pumped back for re-use in the Process Plant or to a water treatment plant before release. The tailings have a lower density and are weaker than thickened or paste tailings, although they do gain considerable strength and density as they consolidate. They are more susceptible to liquefaction than thickened or paste tailings. Conventional slurry tailings require larger embankments than thickened or paste tailings to safely retain the tailings and pond water and drains to intercept seepage. The Waihi Operation has had large quantities of mine pit overburden to dispose of. This has allowed construction of conservatively designed downstream construction embankments that can safely contain slurry tailings and associated runoff from extreme rainfall events. 7.1.2. Thickened tailings Tailings can be thickened to reduce water content and volume of material that needs to be disposed. This is achieved by special tanks and flocculants. Thickened tailings require pumping by positive displacement (piston) pumps as the solids concentration increases. The advantages in comparison with conventional slurry tailings include that they can occupy a smaller footprint, have higher strength, the retaining embankment can be smaller, require less
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