GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 31 . 3.2 Local geology The regional geology is presented in Section 2.3. The local geology for the Gladstone area is presented in Figure 3.3 and summarised in Table 3.1, which includes the local terminology applied to the Gladstone assessment. Key geological features are summarised below from GNS (1996) and site observations (Appendix A). The proposed GOP is located in the andesite of Gladstone and Winner Hills (unit aw). It accesses the ore body referred to as the “Waihi East ore bodies” (Figure 2.3), which is located southwest of the Favona vein within the same andesite host rock. The geology in the vicinity of Gladstone is notable for weathering of the upper andesite and hydrothermal breccia between deposition events, and young volcanics on the eastern and southern flanks of Gladstone Hill (Figure 3.3). Fractures and faults which strike southwest to northeast through the andesite of Gladstone Hill and the Favona mine are evident as mineralised veins, with the mineralised zone characterised in the OGNZL leapfrog model (2021) to extend beneath the Ohinemuri River as presented in Figure 3.1. Additional fracturing may continue in the same direction beyond the mineralised zone. These fractures acted as conduits for the hydrothermal waters and were likely connected to the explosion centre for the hydrothermal breccia which is evident in a number of boreholes at the site. Subsequent volcanic activity resulted in the widespread deposition of dacite to the east and south of Gladstone Hill (Black Hill dacite; unit iu). The dacite infilled the paleo-valley present in the current day location of the Gladstone Wetland and Ohinemuri River. More recent ignimbrite materials (units hw and ho) and alluvial deposits associated with the Ohinemuri River overlie andesite to the north and west of Gladstone Hill (Figure 2.4). Additional geological units included in the OGNZL leapfrog model (2021) that have also formed the basis of the analysis include: – Ash cover and regolith materials. This is grouped with rhyolitic tuff (RT) in Table 3.1. – Volcaniclastic sediments (VC), present as a discrete layer in places above the andesite or breccia, and underlying the dacite. For the purposes of the assessment these materials are assumed to have hydraulic properties generally consistent with the dacite. Figure 3.3 Gladstone geological section (A-A’ of Figure 2.4) (URS, 2003))
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