GHD | Oceana Gold NZ Ltd | 12552081 | Geochemical Assessment Wharekirauponga Underground Mine (WAI985-000-REP-LC-0013) 22 The ABA data is visualised on Figure 16 which assesses the likelihood of the spoil material to be acid generating based on the net acid generation (NAG) pH and the neutralisation potential ratio (NPR) (GARD, 2021). The data shows that the majority of the spoil is currently categorised as potentially acid forming (PAF). The vent shaft material appears less acid producing than the Willows Access Tunnel alignment data and the WUG Mine data. When looking at the data in the context of depth to surface, core representative of the Willows Access Tunnel alignment and the WUG Mine spoil generally appears more susceptible to oxidation and the generation of ARD compared to material representative of the vent shaft. The PAF characterisation of the Willows Access Tunnel alignment is likely a function of the oxidised state of the rock, with material closer to the surface being more oxidised than the deeper material whereas the WUG Mine spoil is likely a function of the rhyolitic material closest to the orebodies. Figure 16 NPR/NAH pH Diagram for WUG Mine and Willows Access Tunnel 4.3.2 Column Testing The purpose of the column tests is to investigate the onset of acid producing conditions and leachate water quality from the spoil material associated with the WUG Mine. Column testing was considered necessary to determine any geochemical differences in spoil leachate between WUG Mine spoil and the existing Waihi dataset, to provide greater confidence in the water quality predictions and, should there be any difference, provide guidance as to any amendments required to the current waste management practices. Three separate columns were set-up on site using core material representative of waste rock and/or access tunnel/stope lining material from the WUG Mine. One column consists of material surrounding the T-Stream Vein (Drill Site 2) and two columns consist of material associated with the EG-Vein (Drill Site 4 (Northern area) and Drill Site 1 (Southern area) (Figure 5). Full column specifications are described in Appendix B. The rock sample selection criteria were based on the following: Core intervals were selected from cores spatially distributed across the projected areas of interest;
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