GHD | Oceana Gold (New Zealand) Limited | 12537997 | Gladstone Pit TSF 18 Criteria description Criteria requirements Basis Year 10 – 440,000 t Year 11 – 440,000 t Year 12 – 440,000 t Year 13 (Q1 only) – 48,307 t Total storage capacity (assuming settled dry density of 1.1 t/m3) 2.08 Mt OGNZL schedule agreed in email dated 17th June 2021. Tailings settled dry density 1.1 t/m3 As discussed with OGNZL Specific gravity 2.75 OGNZL provided Solids content of slurry by mass 45% OGNZL provided Tailings classification Low plasticity silt; P80 = 53 microns (WUG ore) As discussed with OGNZL Tailings hydraulic conductivity Refer Figure 10 Calibration modelling completed by EGL (2019). Beach slope Nil (assume flat surface) GHD proposed. Compressibility Refer Figure 11 Calibration modelling completed by EGL (2019). Pit Geometry Minimum pit crest elevation RL 1107 m (south-west corner) OGNZL provided pit (March 2021) Pit area 18 Ha GHD measured Bench angle / bench height / berm width Above RL1110: 22/10 m/5 m RL1110 to RL1080: 55/10 m/5 m Below RL1080: 60/15 m/5 m OGNZL provided pit (March 2021) Earthworks Design Pit backfilled with ROM rock to provide a surface for lining with a geosynthetic liner. GHD proposed Total backfill volume Backfill: 2.5 Mm3 Liner sub-grade: 0.13 Mm3 GHD proposed Material type Backfill: ROM rock (PAF or NAF), 250 mm maximum particle size. Liner sub-grade: Sub-20 mm crushed and screened rock produced from select high quality rock (with high permeability) from the mining operations or Martha Phase 4 pit cutback. As discussed with OGNZL Material source Generally, from the northern rock stack (NRS) with liner sub-grade from select high quality rock from the mining operations. As discussed with OGNZL Geochemical treatment PAF backfill to be lime treated at the same rate as recommended by AECOM (2021): - No limestone amendment required for Martha and WUG PAF material likely to be exposed for a period less than 20 weeks. - 0.6% limestone amendment rate for Martha and WUG rock for 250 day lag period. As discussed with OGNZL Backfill slope 1.5H:1V (33.7) GHD proposed Bench width 10 m GHD proposed Construction fleet Mine fleet (Komatsu 785 or equivalent) where possible otherwise 40t/65t articulated dump trucks As discussed with OGNZL Stability
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