June 2022 G-14642.71-006-R-Rev0_FINAL v 6.4.1 Ground conditions ......................................................................................................................................................................22 6.4.2 Key geotechnical issues ........................................................................................................................................................ 25 7.0 MAIN TWIN ACCESS TUNNELS .................................................................................................................................................. 26 7.1 Geotechnical Investigations .................................................................................................................................................... 26 7.1.1 Regional geological model ................................................................................................................................................ 26 7.1.2 Subsurface investigations .................................................................................................................................................... 26 7.1.3 Key geotechnical issues ........................................................................................................................................................ 29 7.1.3.1 Tunnel geology ......................................................................................................................................................................... 29 7.1.3.2 Groundwater ..............................................................................................................................................................................30 7.1.3.3 Tunnelling conditions.........................................................................................................................................................30 8.0 WAIHI ACCESS TUNNEL ................................................................................................................................................................... 31 8.1 Proposed Portal....................................................................................................................................................................................31 8.2 Alignment Options...........................................................................................................................................................................32 8.3 Available Geological Data...........................................................................................................................................................33 8.3.1 Geological setting........................................................................................................................................................................33 8.3.2 Geomorphology ............................................................................................................................................................................33 8.3.3 Information provided by OceanaGold.......................................................................................................................34 8.4 Preliminary Geological Model Based on Available Information .............................................................. 35 8.5 Key Geotechnical Issues.............................................................................................................................................................. 36 9.0 WHAREKIRAUPONGA UNDERGROUND MINE ............................................................................................................. 37 9.1 Background ............................................................................................................................................................................................37 9.2 Proposed Underground Mine Development.............................................................................................................37 9.3 Review of the Geotechnical Assessment ..................................................................................................................... 39 9.3.1 Data available for PFS design........................................................................................................................................... 39 9.3.2 Discontinuities............................................................................................................................................................................... 39 9.3.3 Laboratory test results............................................................................................................................................................. 39 9.3.4 Rock mass characterisation...............................................................................................................................................40 9.4 Assessment of proposed mining methodology.....................................................................................................40 9.5 Recommended Additional Work for the Next Design Stages ...................................................................42 9.6 Ventilation Shaft Closure at Completion of Mining .............................................................................................43 10.0 CONCLUSIONS ....................................................................................................................................................................................... 43
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