EGL Ref: 9049 23 June 2022 Page 10 File: WAI-985-000-REP-LC-0050-Rev0.docx This report shall only be read in its entirety. to the Mataura Stream, alluvial terrace deposits exist consisting of silty gravel and sands. These materials directly overlie the andesite (Ref. 36). 3.6. Wharekirauponga Dual Tunnel alignment GHD (Ref. 28) has interpreted the available information along the Wharekirauponga Dual Tunnel from Willows Access Tunnel to WUG mine indicating that the tunnel passes at depth primarily through the Waipupu Formation andesite (aw) and Whiritoa andesite (ah), passing various geological lineaments or faults. The sections indicate that the Whakamoehau andesite (Ref. 31) overlies the Waipupu and Whitianga andesite over part of the alignment, however the tunnel is unlikely to intersect this unit at depth. This is shown on the plans in Figure 22 to Figure 26 and sections in Figure 27 to Figure 30. This mapping is based on the GNS 1:50,000 geological map (Ref. 24, 28). 3.7. WUG Mine geology At WUG the host rock is assigned to the Maratoto Rhyolite (Ref. 24, 27, 29, 30, 31). The epithermal quartz veins occur in the rhyolite flow and breccias that form a dome complex (Ref. 31). The Maratoto rhyolites are overlain by tuffs of the Edmond Formation (24, 30, 31). The rhyolites infill a north-east trending graben (down thrown) structure (Ref. 30). The rhyolites overlie andesites of the Waipupu Formation or Whitianga Group andesites (Ref. 24, 27). The mineralised sequences are partially overlain by strongly magnetic, fresh andesite flows, rhyolitic tuffs and recent ash deposits (Ref. 22). The andesites are interpreted to be Whakamoehau andesite (Ref. 31). The fault structures of the graben trend approximately north-northeast (not inferred to be active) with a series northwest-striking faults interpreted to be crosscutting the rhyolites (Ref. 30). The geology at WUG is shown in a simplified form in Figure 31 and Figure 32, with a rhyolitic profile of pyroclastic deposits indicated to overlie a notable thickness of (lava) flow deposits, with pyroclastic deposits again beneath the flows before reaching the underlying andesites. The WUG Mine will be in the rhyolite flows and pyroclastic deposits. The ventilation shafts are positioned over the declines as they approach the mine from the south. They may be wholly within the Whitiroa andesite or pass through the Whakamoehau andesite at the surface and into the rhyolites at depth (26, 27). Further ground investigation is required to confirm the ground profile at these locations. 4.0 WAIHI DEWATERING AND GROUNDWATER LEVELS 4.1. Historical Dewatering Extensive underground mining was undertaken at the Martha Mine from 1893 until 1952. The workings were generally in the area of Martha Hill, which is now Martha Open Pit and modern Martha Underground. Dewatering the original mine was required down to the full depth of workings, approximately RL540m. The historic dewatering occurred over many decades, longer than the recent phase of mining (1989-2021). By the time the recent phase of mining commenced in 1989 the groundwater levels had returned to near pre-mining levels.
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