U:\2021\BM210482_IBo_Waihi_North_Project\Documents\WNP_Freshwater_Report_May_2022\FINAL_Freshwater_Report_FOR DELIVERY_June 2022\FINAL DELIVERED 17 JUNE 2022\WAI-985-000-REP-LC-0007_Rev0_Freshwater_20220621_FINAL.docx 15.5 Effects management The effects management for freshwater ecological values at two unnamed tributary crossings will comprise: • Erosion and sediment management. • Replacement planting of riparian vegetation. 16.0 Gladstone Open Pit 16.1 Proposed Activities The proposed activities at Gladstone Open Pit (GOP) are: • Pre-stripping of topsoil from the pit footprint and storage at Southern Stockpile (capacity: 52,500 m3); • Relocating the existing Favona portal and associated infrastructure within GOP; • Installing a new crusher and interconnecting conveyor for transporting rock to the NRS; • Hauling and storing ore and/or rock at the existing polishing pond stockpile, if required; and • Construction of noise bunds or screens around the pit rim where required. The Gladstone Pit will be mined in a period of six years, comprising approximately 2.6 Mt of ore and 18.7 Mt of overburden (waste rock). The overburden generated from the development of the pit is important for the mine material balance, with much of the material being used as construction material for development of a tailing storage facility (TSF) at GOP and for the new TSF3. Post mining, GOP will be backfilled with waste rock to form a base for converting it into a tailings storage facility. This involves backfilling the pit with 5Mt of suitable rock material and the pit walls will be reworked for this purpose. It is planned that rock will be placed by paddock dumping and then compacted in place by dozing and use of mobile compactor. It is likely that limestone will be mixed with the rock in situ. Once the base layer is formed, the layer will be then covered with a geomembrane liner and tailings from the processing plant will be deposited within the pit. The pit will store 2.1Mt with a final elevation of tailings at 1103 mRL. The GOP TSF will operate under the existing TSF operating procedure. It is expected that no more than two TSFs will be in operation at any given time to balance the water treatment rate during operation. The rate of rise of the tailings in GOP TSF would be upwards of 30 m per year if full tailings stream was directed to this TSF. This would likely give rise to consolidation challenges. It is therefore planned to deposit a smaller fraction of the total tailings stream (i.e., 25% to 50%) to GOP TSF to limit the rate of rise and improve consolidation and reduce post closure settlement. Once the tailings are filled to the final elevation in the pit, settlement of tailings is expected to continue for the subsequent 10 years. Post settlement, the tailings pond will be emptied, and a 1 m layer of NAF rock will be placed over the tailings surface for closure. Finally the area will be rehabilitated. The proposed layout of the GOP is shown in 22.
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