www.valenza-engineering.com 381_R_04_Rev 0 OGNZL_WUG_Phase1_Conceptual_Mitigation 3 be encountered in the tunnel), are exposed by movement on the NNE structural alignment and subsequent erosion. Kaimai subgroup (5.6-3.9 Ma) intrusives and extrusives make up the covering dome, to the CVZ and are present to the east of the portal area. These comprise lava flows and domes, tuff and tuff breccias with intercalated volcaniclastic sediments and local welded dacitic ignimbrite. Older, faultemplaced rocks of the Coromandel Group are present, locally with extensive hydrothermal alteration. These lithic and pumice-rich ignimbrites, rhyolites and obsidian-rich pumice breccia deposits and tuff will be intercepted at the termination of the tunnel in the WUG. Tauranga Group sediments infill faulted and erosional depressions. These materials comprise pumiceous alluvial gravelly sand, silty clay and peat; estuarine silt and mud interbedded with ignimbrite; and tephra from the Taupo Volcanic Zone and are the host rocks of the deposit. Structural controls are associated with the East Graben fault sequence with quartz veins within the rhyolitic flows becoming brecciated. Vein dips become steeper and sub-vertical, with a striking change from the northeast to a more northerly orientation. Northeast-trending fault is inferred in the Waiharakeke valley with strong north to northeast-trending fault block at the tunnel termination. Less prominent faulting may occur along the other valleys and, if present, may be penetrated by the proposed tunnel. The orientation of the vein systems relative to the mine plan is shown in Figure 2-1. Figure 2-1:WUG Vein System 2.2. HYDROLOGY AND TOPOGRAPHY The topography around Waihi in the Ohinemuri River valley is flat within the alluvium with isolated volcanic outliers forming small hills to the north of the township. Notable is the area of Martha open pit directly north of the town centre. These outcrops become continuous moving north into the Coromandel Ranges which reach a height of 500masl. Within the Ranges and in the WUG area the topography is deeply incised by the northeast-trending valley system and densely bush covered. There are no established vehicle access routes into the Wharekirauponga area. The WUG lies beneath two surface water catchments, with the proposed access tunnel from the catchment divide in the Coromandel Ranges to the northwest of Willow Farm southward falling within the substantial Waihou River catchment, and the tunnel and WUG to the north of the divide falling within the Otahu River catchment. The Ohinemuri River drains to the south through Waihi township before joining
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