June 2022 G-14642.71-006-R-Rev0_FINAL 5 4.0 SETTING 4.1 Geology The Coromandel Peninsula, south as far as Te Aroha, and including the area around and north of Waihi, is dominated by volcanic rocks of the Coromandel Group comprising andesite, dacite and rhyolite of Miocene Age (Edbrooke 2001, Braithwaite, Christie 1996) (Figure 2). Flow banded rhyolite that hosts the ore body has been assigned to the Maratoto Rhyolite and the associated lithic lapilli tuffs have been referred to the Edmonds Formation (Rhys 2019). These orebody host rock units overlie the older andesite, tuff and dacite of the Waipupu Formation and Whitiroa Andesite within which the various access tunnels will be constructed. Younger ignimbrite, locally up to about 100 m in thickness is present between the WUG portal and Willows Road Farm and volcanic ash materials are inferred to be present throughout the area as surficial soils. Basement rock in the area comprises Jurassic Age Manaia Hill Group sandstone, siltstone and conglomerate at more than 1000 m depth. The Coromandel Peninsula is located on the western side of the Taupo Volcanic Zone, which is an extensional tectonic domain dominated by northeast trending normal faults of low activity. Figure 2: Geological map showing distribution of main lithologies. The pink unit 'Mci' comprises the various Miocene volcanic rock types encountered by the access tunnels. The yellow unit ‘mQm’ comprises younger alluvium. The general project corridor (ref Figure 1) is within the white rectangle. A conceptual geological model for the main access tunnel between Willows Road Farm and Wharekirauponga (GHD 2020) has been prepared using regional geological mapping information and interpretation of surface topographic models (Appendix B).
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