Oceana Gold Waihi North Project Waihi North Project Geochemical Assessment – Geochemistry of Tailings and Overburden, Treatment and Mitigation Revision 9 – 17-Jun-2022 Prepared for – Oceana Gold (New Zealand) Limited – Co No.: 2274246 A-3 AECOM A2.3 Rock Acid Generating Potential A2.3.1 Static Testing Static testing provides a mass balance for the potential acid generating and neutralising minerals and reactions but does not account for the potential rate of reactions that can significantly influence whether rock will generate ARD. Summarised static data is presented in Table 31 (proposed Gladstone), Table 32(Martha Mine) and Table 33 (Historical rock samples from Trio, Favona, Martha and Correnso) and presented in boxplots Figure 18 to Figure 23 of the main report. In general, the acid generating potential of the rock from within the proposed GOP and WUG is similar to that of historical mining areas. This includes: • Mean sulphur concentrations in the Gladstone rock ranging from 2.7% in the andesite to 3.2% in the hydrothermal breccia. • Mean sulphur concentrations in the Wharekirauponga rock ranging from 0.91% in the WUG mine to 3.7% in the WUG access tunnel. • These are comparable to the historical rock sulphur concentrations ranging from 2.1 to 3.0%. As a result the acid potential (AP) in kg CaCO3 per tonne of the Gladstone and WUG rock is considered comparable. The acid base accounting of the rock from within the proposed GOP and the WUG mine has the following differences: • The largest difference between the datasets is the lower neutralising capacity within the GOP. This is highlighted with respect to a lower overall mean acid neutralising capacity (ANC), ANC/ MPA, and neutralisation potential (NP) values within the proposed GOP rock when compared with mined rock. • The acid neutralising capacity of the WUG rock is comparable to existing mining operations as shown in Figure 25. • As a result of the similar AP and ANC in WUG rock to historical mined rock, the ANC/MPA is also comparable to previously mined rock.
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