File: WAI-985-000-REP-LC-0050-Rev0.docx This report shall only be read in its entirety. 1.0 INTRODUCTION Oceana Gold (New Zealand) Limited (OGNZL) proposes to develop a new mining project named the Waihi North Project (WNP) to extend the mine life in Waihi by developing a new open pit and underground mine (Ref. 1). OGNZL has engaged Engineering Geology Limited (EGL) to undertake this ground settlement assessment for the project elements which potentially have ground settlement effects. This assessment considers ground settlement effects caused by ground dewatering resulting in direct consolidation of soil and rock materials. In this report ground “settlement effects” refer to both “settlement” and “tilt”. The term “settlement” applies to the widespread and relatively minor vertical displacement of the ground surface caused by dewatering. The term “tilt” refers to differential settlements in the ground surface cause by dewatering (i.e. differences in settlement over short distances). Extensive knowledge of ground settlement effects has been developed around Waihi through the monitoring undertaken for the effects associated with Martha Open Pit, and the Favona, Trio and Correnso Underground mines. This report reviews these past effects in assessing the settlement effects for the Waihi North Project. 1.1. Waihi North Project The WNP elements (Ref. 1) are shown on Figure 1, Figure 2, and Figure 3 and comprises: • The mining of a new open pit near the existing Processing Plant, centred over Gladstone Hill, the Gladstone Open Pit (GOP). This pit will be converted to a tailings storage facility once mining is complete; • A new tailings storage facility to the east of existing Tailing Storage Facility (TSF) - Storage 1A (TSF1A), called Storage 3 or TSF3 in short; • New rock stack (the Northern Rock Stack or NRS) at the Northern Stockpile area adjacent to the existing TSF – Storage 2 (TSF2); • Reconsenting of the existing Water Treatment Plant (WTP) treated water discharge consents; • Upgrading of the existing WTP to double the water treatment capacity; • A new underground mine, the Wharekirauponga Underground Mine (WUG), located approximately 11km north-west of the current Processing Plant under 23 June 2022 OCEANA GOLD (NEW ZEALAND) LIMITED WAIHI NORTH PROJECT GROUND SETTLEMENT REPORT EGL Ref: 9049
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