SECTION 2 Existing Environment 4 2. Existing Environment 2.1 Regional Geology The following provides a general description of the geology along the entire tunnel alignment. More detailed descriptions of the geological conditions for each tunnel section are provided in the ground models prepared by GHD (Aug, 2020) and Golder (Sept, 2021). These are included in Attachment A of this report. The proposed works are located towards the Southern part of the Coromandel Volcanic Zone, a Miocene to early Pliocene andesite-dacite-rhyolite, subaerial volcanic sequence. The Coromandel Ranges are flanked to the west by the Firth of Thames, a Northward continuation of the Hauraki Rift, and to the east by the Pacific Ocean (Braithwaite & Christie, 1996). Figure 2 Regional Geologic Setting (Braithwaite & Christie, 1996) The most extensive geological unit in the area is the Waiwawa sub-group (7.9-5.6 Ma) of the Coromandel Group. This unit comprises andesite and dacite lava flows and tuff breccias, and dacitic ignimbrite, tuff and siltstone. Hydrothermal alteration has been reported. A well-defined NNE structural alignment and subsequent erosion has exposed both younger Omahine subgroup (6.7-6.6 Ma) which will be intercepted partway along the dual tunnel alignment and Kaimai subgroup (5.6-3.9 Ma) rocks which lie to the east of the portal area. The Omahine subgroup comprises andesite and dacite, intrusive andesites and lava flows, with minor intercalated tuff and tuff breccia. The Kaimai subgroup comprises andesite and
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