GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 11 . 1. Introduction The current Waihi life of mine plan, including Project Martha, is to complete production by 2030. Studies conducted over 2016 to 2020 by Oceana Gold NZ Limited (OGNZL) have identified two new mining opportunities. The understanding of these opportunities has advanced to a point where OGNZL is ready to lodge resource consent applications for its next project, the “Waihi North Project” (WNP). The WNP is expected to extend the life of mine to at least 2038. It comprises development of a new open pit mine (the Gladstone Open Pit (GOP)), and a new underground development (the Wharekirauponga Underground Mine (WUG)). Additional tailings storage facilities and rock storage is also proposed. GHD was commissioned by OGNZL to deliver a number of studies relating groundwater and surface water for the WNP. This report focuses on the hydrogeological (groundwater) aspects of GOP and the new rock and tailings storage facilities of the Waihi North Project. Hydrogeological (groundwater) assessment of the underground elements of the WNP are provided in GWS (2022a; 2022b), FloSolutions (2022) and Valenza Engineering (2022). 1.1 Background 1.1.1 WNP overview The detailed description for WNP is provided in the Assessment of Environmental Effects prepared by Mitchell Daysh Limited (Mitchell Daysh, 2022). The general WNP project area is shown in Figure 1.1 and key features in Figure 1.2 and Figure 1.3, comprising: – Gladstone Open Pit (GOP): A new pit near the existing processing plant and centred over Gladstone Hill. This pit will be converted to a tailings storage facility (TSF) once mining is complete. – Northern Rock Stack: A new rock stack (Northern Rock Stack (NRS)) at the Northern Stockpile area, north of the existing Tailings Storage Facility 2 (TSF2). Rock sourced from Gladstone, surplus to the volume needed to construct the proposed Tailings Storage Facility 3 (TSF3) embankment and backfilling activities, will be stored at the proposed NRS. – Tailings Storage Facility 3: A new tailings storage facility (TSF3) to the east of existing tailings storage facilities TSF2 and TSF1A. This new facility is to provide tailings storage for the WNP in addition to that provided by the proposed Gladstone open pit and existing TSFs. – Willows Rock Stack (WRS) at the new Wharekirauponga underground mine (WUG): With associated surface infrastructure, including a WRS to be located on farmland (owned by OGNZL) at Willows Road (Willows Rock Stack; WRS), with underground access to the existing Processing Plant at Waihi. Note: A new underground mine, Wharekirauponga, is proposed to be located approximately 11 km north-west of the current Processing Plant as part of the WNP (Figure 1.1). Site infrastructure supporting the mine will be located on private farmland located at the end of Willows Road. WUG surface infrastructure and tunnels from Willows Road are components of the WNP, but effects to groundwater from these aspects of WNP are not part of this assessment and are addressed by GWS (2022a; 2022b2021). 1.1.2 Relationship to other mine activities In February 2019, consents were granted for Project Martha, comprising the Martha Underground (MUG) Mine and a small cutback of the north wall of the Martha Open Pit called Phase 4 (MOP4). This project description assumes the following relationships between the previously consented Project Martha, TSF1A and 2, the Water Treatment Plant (WTP) and the WNP: – MUG will operate in parallel with the WNP. – Martha Open Pit 4 (MOP4) will be mined in parallel with the WNP. Rehabilitation of the Martha Pit after closure will comprise development of a pit lake and surrounding parkland facility for recreational use. – Continued treated water discharge limits as per the existing discharge permit (AUTH971318). – TSF1A is consented to 1,182 mRL. This results in a total proposed crest raise of 8 m from the current crest height of 1,174 mRL.
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