Oceana Gold Waihi North Project Waihi North Project Geochemical Assessment – Geochemistry of Tailings and Overburden, Treatment and Mitigation Revision 0 – 17-Jun-2022 Prepared for – Oceana Gold (New Zealand) Limited – Co No.: 2274246 AECOM Table of Contents Glossary i Executive Summary i 1.0 Introduction 1 1.1 Background 2 1.1.1 The Gladstone Open Pit 2 1.1.2 Wharekirauponga Underground Mine 2 1.1.3 Tailings and Rock Storage Facilities 3 1.2 Report Structure 4 2.0 Geology and Mineralogy 5 2.1 Local Geology 5 3.0 Geochemical Assessment 6 3.1 Introduction 6 3.1.1 Characterisation Philosophy 6 3.2 Geochemical Testing 6 4.0 Rock 7 4.1 Introduction 7 4.2 Rock Composition 7 4.2.1 Distribution of Trace elements in the Rock Material 7 4.3 Rock Acid Generating Potential 12 4.3.1 Static Testing 12 4.4 Rock Leaching Potential 16 4.4.1 Gladstone Open Pit 16 4.4.2 Wharekirauponga Underground Mine 17 5.0 Gladstone Sump Water Quality 17 5.1 Sulphate Generation Rate of Gladstone Open Pit Walls 18 5.2 Gladstone Open Pit Runoff Water Quality 19 5.3 Geochemical Modelling 20 5.4 Key Assumptions 21 6.0 Rock Management 21 6.1 Introduction 21 6.1.1 Rock Management Strategy Philosophy for PAF Material 23 6.2 RTSA Temporary Disposal and WRS 24 6.2.1 Limestone Dosing Requirements 24 6.2.2 Key Assumptions 24 6.3 Permanent Rock Disposal 25 6.3.1 NRS and Embankment Seepage Water Quality 26 6.3.2 Permanent Rock Disposal to Gladstone Open Pit 28 6.3.3 Placement and Compaction of Rock 30 6.3.4 Estimated Backfill Rock Porewater Quality 31 6.4 Estimated WUG Underground Water Quality 32 7.0 Mine Tailings and Tailings Management 35 7.1 Introduction 35 7.2 Laboratory Analytical Work 35 7.2.1 Statistical Analysis of Ore Geochemistry 35 7.2.2 Tailings Leaching Potential 35 7.3 Estimated TSF Water Quality 50 7.3.1 TSF Pond Water Quality 51 7.3.2 TSF Porewater Quality 54 8.0 Conclusions 57 9.0 References 59 10.0 Standard Limitations 60 Appendix A Whole Rock Geochemistry Dataset A A A1. Geochemical Assessment A-1 A2. Rock A-4
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