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 22 AECOM • Covering PAF rock with NAF material to limit oxidation of sulphides either as sealing intermediate layers or as final cover. • Compaction of surface material to reduce permeability and ingress of oxygen and water. • Treatment with limestone in order to prevent the onset of acidification prior to permanent disposal. • Limiting exposure time of PAF rock and disposal before on-set of oxidation. Trace element leaching may also result from rock that is enriched in trace elements but where these trace elements are not associated with sulphides and may leach without the oxidation of sulphides. These rocks are defined as potential for trace element leaching (PTEL) and waste management practices give consideration to mitigating the potential adverse effects from this rock. Methods 2 and 3 above are effective at controlling leaching of trace elements in this regard as neutral pH and reduced water flux both limit the leaching of trace elements. The same waste management practices can therefore be adopted for waste with PTEL. The effectiveness of waste management practices for combined rock types that are PAF and PTEL is assessed by the column leaching tests which combine rock from both categories. These results are outlined in Section 4.4 and Appendix D. Figure 10 Conceptualised Rock Management
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