Oceana Gold Project Quattro Project Quattro Geochemical Assessment – Tailings and Overburden, Treatment and Mitigation \\na.aecomnet.com\lfs\APAC\Christchurch-NZCHC1\Legacy\Projects\605X\60544823\6. Draft Docs\6.1 Reports\Waihi North\App D - Kinetic and Column Testing\WNP Draft v6_App D (Kinetic Column Testing)_20220504.docx Revision 5 – 07-Aug-2020 Prepared for – Anderson Lloyd – Co No.: 5719274 subject to reducing conditions (< pH 2.5) during the flushing event resulting in speciation to soluble arsenite. It is considered that conditions conducive to these elevated arsenic conditions are unlikely to occur within placed overburden from Project Quattro (refer Section 6.0 of the main report). In contrast, the columns that have limestone applied at inception (by blending – Col9 and layering – Col8) show that limestone application is an effective measure at preventing / delaying the onset to acidity. This is particularly highlighted in Col9 where the pH remains above pH 4.5 until week 25 of operation, a pH not seen in the other columns since their inception. This is also association with depressed acidity, sulphate and trace element concentrations in the column leachate. The layered column (which includes a layer of blended limestone and oxidised material) exhibits an initial spike in trace element concentrations (associated with the already oxidised material) followed by a general reduction with time. Like the limestone dosed columns, the compacted column shows depressed long term trace element concentrations when compared to the unmitigated columns. However early ‘spikes’ in copper, molybdenum, nickel and zinc are noticeable and it is likely this is a reflection of the immediate surface on the compacted columns which is exposed to atmosphere and therefore within the zone of oxidation Once sulphate production within this area is exhausted, limited infiltration of oxygen into the compacted mass limits additional sulphide oxidation and associated trace element leaching. D3 Summary Refer to Section 4.4 of the main report for an overall summary of kinetic and column testing analysis.
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