GHD | Oceana Gold (New Zealand) Limited | 12537997 | Gladstone Pit TSF 10 2.3 Geotechnical properties The following presents a summary of tailings and pit wall geotechnical properties. The tailings properties presented are based on tailings from Martha Pit and Martha Underground (MUG). However, tailings deposited into the GOP TSF will primarily be from the processing of ore from the WUG. The WUG tailings are expected to be similar to the MUG tailings, with a slurry density of 45% solids and a P80 of 53 microns. 2.3.1 Tailings 2.3.1.1 Index properties The Waihi operations tailings are fine-grained silts of generally low plasticity. Occasional lenses of coarser sands are noted in the historical cone penetration test (CPTu) data. The tailings typically show fines content (less than 75 microns) in the range between 41% and 96%, with clay contents between 13% and 20%. Plasticity index varies from 0 to 22%. The range of gradation of Waihi tailings are shown in Figure 4. Figure 4 Particle size distribution range for Waihi tailings 2.3.1.2 Hydraulic properties Oedometer tests were conducted by OGNZL on tailings from TSF2 in 1992. Based on these oedometer tests, the coefficient of hydraulic conductivity was estimated for the material at vertical effective confining stresses in the range of 1 kPa to 1000 kPa (Figure 5). It is observed that permeability reaches a value as low as 1 x 10-10 m/s at the maximum confining stress. In addition to the oedometer testing, in 2010 two constant head permeability tests were conducted (flexible wall permeameter). Similar tests were conducted in 2017. The results show that coefficient of permeability of the Waihi tailings varies from 1 x 10-9 m/s to 1 x 10-11 m/s, at equivalent vertical effective stress from 112 kPa to 900 kPa, respectively. There is unlikely to be a material change to the tailings from the 1992 and 2010 testing, however, additional testing is recommended at the detailed design phase to confirm the tailings properties. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.0001 0.001 0.01 0.1 1 10 100 % Passing Sieve size (mm) Gravel Sand Silt Clay
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