Engineering & Mining Journal

MAR 2019

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REGIONAL NEWS - ASIA MARCH 2019 • E&MJ 15 Polymetal Adds 2 nd POX Line at Amursk Polymetal International has started con- struction of a second pressure oxidation (POX) line to process refractory gold con- centrates at its Amursk facilities in Rus- sia's far southeast. Designated POX-2, the project site is immediately adjacent to the current Amursk POX plant within the city of Amursk and will share some of the external infrastructure (gas main, access road, water main) with the existing POX facility. Additional electricity supply will be provided via a new dedicated pow- er line from the regional grid. POX-2 is designed to process dou- ble-refractory concentrates, which contain micron-sized gold particles encapsulated in sulphides (pyrites and arsenic pyrites) together with high concentrations of or- ganic carbon. High carbon content drives high-sorption activity (preg-robbing) and dictates the use of high-temperature (240°C) pressure oxidation compared to the medium-temperature (200°C) oxidation utilized at the existing Amursk POX facility. Pressure oxidation was selected as the most feasible processing technology for double-refractory ores. It is able to achieve gold recoveries of 96% by utilizing high temperatures, elevated pressure, and oxy- gen to recover encapsulated gold, while con- ventional cyanidation methods would result in sub-optimal recovery rates of 20%-40%. Completed metallurgical tests on high-carbon concentrates from Polymet- al's Kyzyl and Mayskoye mines have con- firmed a recovery rate of 96%. Throughput capacity at the POX-2 plant will be 250,000 metric tons per year (mt/y) to 300,000 mt/y of concentrates. The de- sign of the facility will enable processing of feed with different properties without im- pacting any of the design parameters. The plant also will have some capacity to treat third-party refractory concentrates, a mar- ket that has grown considerably in Russia and globally in recent years. Pre-production capital expenditures for POX-2 are estimated at $431 mil- lion and will be entirely funded out of Polymetal's operating cash flows. Hatch Inc., Toronto, Canada, is responsible for the basic engineering, detailed engi- neering, POX procurement support, and the supply of custom-made equipment for high-pressure and acidic processing areas. Polymetal Engineering is respon- sible for other processing areas, general site layout and infrastructure. Processing concentrates from Polymet- al's mines at Kyzyl, Nezhda, Mayskoye, and Voro, POX-2 is expected to generate significant economic benefits, as all of its refractory concentrates will be retained for in-house processing as opposed to selling to third-party off-takers. POX-2 gold pro- duction will average about 500,000 oz/y. An estimated total of 4.3 million mt of con- centrate containing 9.3 million oz of gold will be processed over a period of 23 years. Eldorado Elects to Resume Heap Leaching at Kışladağ Eldorado Gold announced in late January that it will resume mining, crushing, stack- ing, and heap leaching at its Kı ladağ gold mine in western Turkey. Work on a previ- ously announced mill project (E&MJ, De- cember 2018, p. 29) has been suspended. In October 2017, Eldorado reported that laboratory test work indicated that lower recoveries were expected from the zone of mineralization around the base of the Kı ladağ open pit. Subsequently, the company suspended mining in the pit in the first quarter of 2018. Following a year of engineering and test work, Eldorado announced in October 2018 it would proceed with the mill project. Fol- lowing that announcement, gold recovery from the leach pad increasingly exceeded expectations, and the company then fo- cused test work and analysis on the viability of resuming mining and heap leaching. Test work to extract maximum value from material already placed on the heap- leach pad and the remaining reserves was ongoing throughout 2018. Approximately 900,000 mt of ore were placed on an in- ter-lift lined test pad in the first quarter of 2018. Later in the year, results from this pad were showing recoveries of ap- proximately 58% from an extended leach cycle approaching 250 days, compared to approximately 40% recoveries from the original 90-day column tests. In early 2019, the company analyzed the new data and developed revised heap leaching plans, showing improved eco- nomics for the heap leaching scenario. As a result, it decided to resume mining and heap leaching. Benefits from the decision are ex- pected to include improved economics when compared to the mill project, with increased production and free cash flow over the next three years and a significant reduction in capital development costs. Construction and financing risks will be lower, as mining and heap leaching will not require external funding. Mining for heap leaching will restart by the end of the first quarter of 2019. Current guidance is based on mining and stacking an initial 22 million mt of ore grading more than 1.1 g/mt gold during the next three years, as well as continuing to leach material currently on the pad. Using high temperatures, elevated pressure and oxygen, POX will recover more gold.

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