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 Figure D9 NPR/NAG pH diagram for overburden within Columns D3.2 Column Treatment A summary of the testing treatment of each column is provided below. Field measurements were taken from the column leachate on a weekly basis by OGNZL staff throughout the column’s operation. Leachate was periodically (generally every second or fourth week) collected and sent for analysis to R J Hill Laboratories Limited. Columns 1 & 4 Columns 1 (adjacent to GOP) & 4 (within GOP void) were not treated and were run under ‘optimal’ field acid producing conditions. That is no lime dosing and free draining. Columns 2 & 5 (Saturated) Columns 2 (adjacent to GOP) & 5 (within GOP void) were initially not treated and were run under ‘optimal’ field acid producing conditions (free draining), until they had been in operation for an 11 weeks period and until the leachate had a pH < 3. These columns were then saturated to mimic the effect of prolonged exposure followed by groundwater saturation. Columns 3 & 6 (Limestone Dosed) Columns 3 (adjacent to GOP) & 6 (within GOP void) were initially not treated and were run under ‘optimal’ field acid producing conditions (free draining), until they had been in operation for an 11 weeks period and until the leachate had a pH < 3. A volume of limestone (CaCO3) was then calculated based on the exposure period, the leachate sulphate concentration, and mass of rock within the column. This volume of limestone was applied to the top of the columns at week 11. An additional volume of limestone was added at week 30.
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