GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 21 . Table 2.2 Regional geology presented units in Figure 2.4 Group Symbol Geology Unit Description Tauranga Alluvium Present day alluvium: Fluvial sand, gravel and mud of streams draining to the east of the Hauraki Lowlands. (Ruahihi Formation) Alluvium River deposits: Pumiceous, rhyolitic, and andesitic sand, gravel and silt. Minor lignite. (Matua Subgroup) Whitianga Group Ignimbrite Waikino Ignimbrite: Strongly welded, glassy ignimbrite. (Ohinemuri Subgroup) Ignimbrite Owharoa Ignimbrite: Welded, pumice rich ignimbrite. (Ohinemuri Subgroup) Ignimbrite Corbett Ignimbrite: Pumice-rich lithic-crystal ignimbrite. (Ohinemuri Subgroup) Rhyolite Ruahorehore Rhyolite: Rhyolite Dome of the Homunga Rhyolite. (Minden Rhyolite SubGroup) Breccia Orokawa Breccia: Massive tuff breccia composed of andesite clasts in altered crystal-rich matrix, minor tuffaceous sandstone and siltstone. (Coroglen subgroup) Coromandel Group Dacite Uretara Formation: Andesitic and dacitic tuff breccias with minor volcanogenic siltstones. Andesite and dacite flows and domes. (Kaimai Subgroup) Andesite Matangia Andesite: Fine grained, glassy andesite flows with minor tuff breccias. Local hydrothermal alteration. (Kaimai Subgroup) Andesite Whiritoa Andesite: Andesite and dacite flows and domes with tuff breccias and lithic-crystal tuff. (Waiwawa Subgroup) Andesite Waipupu Formation: Andesite and dacite. Minor tuff breccia, crystal tuff and lacustrine sediments. Extensive hydrothermal alteration. (Waiwawa Subgroup) 2.4 Groundwater 2.4.1 Overview The hydrogeology of the area has been previously described in Section 2.2 of the GWS (2018a) report and summarised in the Project Martha AEE (OGNZL, 2018). Groundwater levels and directions are controlled by the presence and interconnections (where they occur) of the workings, vein systems and post mineralisation structures (faults and fracture zones). The shallow groundwater system in the Waihi area comprises groundwater flow through shallow soils, reworked young volcanics and weathered rock. The deep aquifer is regionally formed by andesite of the Coromandel volcanic group. Near the Martha Pit, shallow groundwater in the younger andesite deposits is separated from the deeper groundwater in the andesite rock by a weathered lower permeability upper layer of the andesite rock mass. At the location of the key components of WNP relevant to this assessment (Gladstone, NRS, TSF3, WRS), groundwater has a different setting to Martha due to faulting. The local hydrogeology for each area is distinctly different with the respective conceptual groundwater models (CGMs) discussed in detail in Sections 3 to 6. Groundwater is discussed at a regional level below. 2.4.2 Regional hydrogeology Groundwater recharge is from direct rainfall infiltration to the shallow groundwater. The recharge that remains in the shallow groundwater system, after some residence time in the aquifer, discharges locally as either springs and/or baseflow to streams or the Ohinemuri River. Recharge to the deep groundwater system occurs where the deeper volcanic units (andesite, dacite, rhyolite) are exposed at the surface, usually in topographic highs such as ridges, as well as a small amount of leakage from the shallow groundwater system. The specific recharge rates to deeper versus shallow groundwater at the site are unknown, but typical values for shallow groundwater are expected to be in the order of 22% to 40% of annual
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