Oceana Gold Project Quattro Project Quattro Geochemical Assessment – Tailings and Overburden, Treatment and Mitigation \\na.aecomnet.com\lfs\APAC\Christchurch-NZCHC1\Legacy\Projects\605X\60544823\6. Draft Docs\6.1 Reports\Waihi North\App D - Kinetic and Column Testing\WNP Draft v6_App D (Kinetic Column Testing)_20220504.docx Revision 5 – 07-Aug-2020 Prepared for – Anderson Lloyd – Co No.: 5719274 Column 7 (Compacted) Column 7 (adjacent to GOP) was constructed to try and replicate placement of overburden in compacted benches. Compaction was measured based on current density of operating columns and the target dry density of waste rock calculated from a standard compaction test of the selected material. The thickness of the placed material was adjusted so that the material was compacted to 2% wet of optimum at 90% of maximum dry density. When compacting the material into column, the sample was split into four equal masses and constructed in four different ‘lifts’ based on the mass and the required compaction. Column 8 (Layered) Column 8 (adjacent to GOP) involved the reuse of a portion of material from column 3 and is constructed of three layers of overburden – each approximately 150 mm. The bottom two layers consist of fresh overburden material while the top layer is the reused ‘oxidised’ material. Three kg of limestone was mixed with this top oxidised material prior to placement. The volume of limestone was calculated in order to introduce alkalinity at a rate to extend natural lag (of the fresh material to 210 days) and neutralise the already oxidised material. This column replicates conditions in which overburden is backfilled into the pit in successive layers, with the final (top) layer left to oxidise. Limestone is then placed on top of the final layer at a rate in order to extend the lag period until the material can become saturated. Column 9 (Limestone Blended - within GOP void) Prior to placement of the waste material within the column, one kilogram of limestone was mixed thoroughly within the material. The quantity of limestone was calculated in order to extend the natural lag period (estimated at 7 weeks) to a period of 210 days by adding sufficient alkalinity (in the form of limestone) to neutralise the predicted sulphate generation throughout this period. D3.3 Column Testing Analytical Results Summarised results from the column tests are shown in Figure D9 to Figure D12. Tables outlining all analytical results and figures showing the main elements of concern are provided in Attachment B. Figure D10Weekly Column Laboratory pH
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