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 15 AECOM Figure 7. NPR/NAG pH diagram for Rock Material 4.3.1.1 NAG pH Distribution in Gladstone Open Pit NAG pH data and its relative distribution throughout the GOP is shown in Figure 8. NAG pH appears to exhibit a generally decreasing trend with pit depth. This may indicate that the capacity for rock to generate AMD will increase as the pit is advanced. It is expected that (deeper) geology occurring beneath the groundwater table has been exposed to relatively reducing conditions, limiting the natural oxidation of minerals. Conversely, oxidising conditions above the groundwater table are likely to have resulted in natural weathering of the rock, reducing the acid producing potential of this material over time.
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