June 2022 G-14642.71-006-R-Rev0_FINAL 33 8.3 Available Geological Data 8.3.1 Geological setting 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 Age1F 2, 2F 3 (refer Figure 19). The Portal and Willows Connection are founded in the Waipupu Formation, which is a phyric andesite and dacite with minor tuff breccia, crystal tuff and lacustrine sediments, extensively hydrothermally altered. The alignment options pass below valley floor alluvium consisting of pumiceous, rhyolitic and andesite sand, gravel and silts up to the Waihi Fault. The alignment may also encounter the Whiritoa Andesite which is lithologically similar to the Waipupu Formation, but is not extensively hydrothermally altered. Basement rock in the area comprises Jurassic Age Manaia Hill Group sandstone, siltstone and conglomerate at more than 1000 m depth below the tunnel alignment options. 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 19: Waihi geological map showing the proposed tunnel alignment options. aw = Waipupu Formation, ah = Whiritoa Andesite and tm = alluvium, red lines = extensive hydrothermal alteration. 8.3.2 Geomorphology Most of the Waihi Access Tunnel corridor north of the Waihi Fault (Figure 19) underlies steep farmland and heavily bush covered terrain. Topographic highs reach to 300 to 500 m above sea level separated by incised streams. The project area south of the Waihi Fault underlies gently sloping farmland. The portal of the tunnel alignment options (refer Section 8.1) will be situated in a topographic high formed from Waipupu Formation andesite at approximately 140 m above sea level (asl). The alignment then follows beneath the terrace alluvium of the Ohinemuri River at 2 Edbrooke SW, 2001, Geology of the Auckland Area, Institute of Geological and Nuclear Sciences 1:2500,000 geological map 3. 1 Map Sheet and 74-page document. 3 Braithwaite RL, Christie AB, 1996: Geology of the Waihi area, scale 1;50,000. IGNS geological map 21.
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