Oceana Gold Waihi North Project Waihi North Project Geochemical Assessment – Geochemistry of Tailings and Overburden, Treatment and Mitigation Revision 0 – 17-Jun-2022 Prepared for – Oceana Gold (New Zealand) Limited – Co No.: 2274246 50 AECOM Table 22 Trace Element Leachability Parameter Existing TSF Tailings (log Kd*) Gladstone (log Kd*) WUG (log Kd*) Changes in Leachability Arsenic 4.6 2.2 2.6 Increased leachability in Gladstone and WUG Cadmium 4.2 1.8 3.7 Increased leachability in Gladstone Chromium 5.2 4.6 2.8 Increased leachability in WUG Lead 5.1 2.8 3.6 Increased leachability in Gladstone and WUG *Kd: Partition Coefficient (Allison, J.D and Allison, T.L. 2005) 7.3 Estimated TSF Water Quality The geochemistry of the ore from WUG and GOP has the principle differences outlined in Section 7.2. Aside from these specific differences, which are accounted for as outlined below, the tailings produced from these ores are expected to be of similar characteristics to tailings currently within TSF1A and TSF2. As both current tailings storage facilities are dominated by ore from the Waihi area (approximately 70 to 100% for TSF1A and TSF2 respectively) it is unlikely that the geochemistry of the ore deposited from the WNP component of the project will differ sufficiently to materially alter what is already present. The resultant leachate should therefore not differ significantly from what has (to date) been recorded from TSF1A and TSF2. Comparison of previous assessments (URS 2001) to actual results factoring existing underdrains and decant chemistry by differences in whole ore trace element concentrations provides a reliable assessment of resultant geochemical composition for these components. The validity of this approach is dependent on the leachability of trace elements in the respective ore which will depend to a degree on ore mineralogy and metallurgical processes used in gold extraction. The approach of factoring existing seepage and decant based on ore trace element composition requires further evaluation for the TSF3 and GOP TSF which could initially receive a greater proportion of ore from GOP and WUG resulting in a greater influence of any differences in pore fluid composition from this ore. TSF3 and GOP TSF decant and porewater is therefore based on both geochemical modelling, factoring of existing facility underdrains and decant, and correction for leachability of trace elements from Gladstone and WUG ore. The mining schedule suggests that TSF1A, TSF2, TSF3 and GOP TSF could receive ore from the respective ore bodies as outlined in Table 23. The maximum values are based on the maximum proportion received in any given quarter. Table 23 Processed Ore Deposition TSF Receiving Tailings Martha Ore (MUG, MOP4 etc) GOP Ore WUG Ore TSF1A 94% 6% - TSF2 95% 5% - TSF3 Mean all sources 20% 9% 71% Maximum Gladstone (by quarter) 50% 47% 3% Maximum WUG (by quarter) - - 100% GOP TSF
RkJQdWJsaXNoZXIy MjE2NDg3