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 6 AECOM 3.0 Geochemical Assessment 3.1 Introduction The geochemical assessment of ore, tailings, and rock produced from the proposed mining components was carried out using: • statistical comparison of analytical results for Martha, Favona, Trio, WUG, Gladstone and Correnso rock samples; • Static, kinetic and column testing; and • predictive modelling of impacts to water quality. Existing geochemical data has been sourced from various technical reports that is summarised as follows: • Appendix A for Martha, Favona, Trio, and Correnso operations, as well as the consented Project Martha (comprising MOP4 and MUG) • Appendix B for Wharekirauponga 3.1.1 Characterisation Philosophy The following steps were undertaken to characterise ore and rock trace element composition: • Initial screening of ore and rock for a broad range of major and trace elements and potential contaminants of environmental concern. • Additional elements where they had previously been present in elevated concentrations in rock and ore from the Waihi operations, where consent conditions stipulated discharge concentrations, and / or where they had previously been depressed in rock and ore from current and previous operations. The specific intention of this comparison was the identification of potential contaminants of interest which may require rock management practices that differ from those currently undertaken by OGNZL. The geochemical composition of ore has been used to determine the likely composition of the mine tailings that would be produced from ore processing. To achieve this, mine tailings produced from Martha mine ore were used as the basis for assessment, with compositional differences between Martha, Gladstone and Wharekirauponga ore assumed to result in proportional differences in tailings composition. A similar approach is used to predict likely effects to decant and seepage quality from the storage facilities as a result of the deposition of mine tailings from the planned operations in the current and future storage facilities. 3.2 Geochemical Testing The following analytical testing methods are used to characterise ore and rock samples from selected boreholes distributed across the proposed mining areas: • Multi-element analysis - whole rock testing for a range of trace and major elements to allow characterisation of the rock for potential contaminants that may leach and adversely influence water quality. • Static testing – whole rock testing for parameters indicative of the potential for acid generation. • Kinetic testing – accelerated weathering of select crushed rock samples to assess the rate of potential acidification and contaminant release. • Column testing – on-site weathering of selected crushed rock samples exposed to atmospheric conditions and to assess management practices. The testing methodologies and analytical results are detailed in Appendix A and B.
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