Engineering & Mining Journal

MAY 2017

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HEAP LEACH MAY 2017 • E&MJ 41 www.e-mj.com can be as equally attractive as their moderate-climate counterparts for, say, larger producers in need of additional production from proven reserves. A case in point is Kaminak Gold Corp., for- mer owner of the Coffee gold project in Canada's Yukon province: Kaminak was acquired by Goldcorp for $520 million in 2016 after a feasibility study for the Coffee project indicated that the mine, which would employ heap leaching, could be paid for in just two years with initial production of more than 200,000 oz/y over the first five years at an esti- mated AISC of $550/oz. The Coffee project would be part of a trio of cold-climate mines and advanced projects in the Yukon/northern Alas- ka region of North America; At latitude 65° north, Kinross' long-running Fort Knox gold mine in Alaska is currently the northernmost heap-leach operation in North America, producing 40% of its total annual production of 390,000 oz of gold from the year-round Walter Creek heap-leach facility. Fort Knox poured its seven-millionth ounce of gold in 2016. And, Victoria Gold is advancing the Ea- gle Gold project in the Yukon, developing a deposit containing an estimated 2.66 million oz in reserves at 0.7 g/t. Eagle's AISC are anticipated to be less than $700 per oz, with an annual production rate of 200,000 oz. As the authors of the conference paper point out, cold-climate operations require unique design and operational consider- ations, including possibly seasonal oper- ations, maintaining heat within or adding heat to the heap, permafrost manage- ment, leaching kinetics (especially for bioleach operations), managing ice and snow, and closure. But leach operators in more moderate climatic locales usually can't function in a set-it-and-forget-it mode, either: pro- ducers both large and small continually tweak the parameters of their existing leach setups to overcome problems aris- ing from changes in external or pad-inter- nal conditions; these countermeasures, for example, range from crushed-ore agglomeration, or applying liner 'rain- coats' to exclude excess moisture from heavy precipitation, to drilling injection wells directly into the heap to improve leach-solution access, and even to ex- ploring new methods to process ripios, or spent ore, for further metal extraction. Kinross Gold's Bald Mountain open- pit heap-leach mine in eastern Nevada and its Round Mountain mine in the south-central part of the state provide good examples of typical modifications to improve leaching efficiency and over- all performance: During a 2016 tour of Bald Mountain — one of the largest mine sites in the U.S., with a total land package of 600 km 2 — the company noted that it was considering connect- ing two of its carbon-in-column process plants to maximize the utilization of existing carbon columns; investigating leaching via secondary wells; and using material from old heaps to build new heap phases. Kinross was also looking at imple- menting overall best practices at Bald Mountain, taken from a program at its Round Mountain operation where heap leach improvement efforts have includ- ed carbon column optimization, new pad side liners, pH enhancement involving automated reagent controls at multiple pads, and solution pumping and piping optimization. It also was evaluating addi- tional future opportunities such as adding barren solution through wells to increase pH and cyanide concentrations and en- able the solution to find a different path to the ore. Beyond physical measures such as these, companies are also investigating the potential advantages of applying in- creased automation and data analysis to heap leach processes — a trend that is being driven at least in part by the avail- ability of more-sophisticated instrumen - tation and data-collection and reporting platforms. The extent to which improved instru- mentation can enhance both resource utilization and work safety was highlight- ed recently by Emerson Process Manage- ment, which notes in a case history that the Zaldivar copper mine in Chile was seeking a cost-effective way to improve leach-pad throughput with better control of sulphuric acid distribution by moni- toring pressure and pH along the leach pad. The mine anticipated that the ability to monitor any condition changes would help optimize acid management. Zaldivar is a high-altitude, open-pit mine operated by Antofagasta plc and owned jointly by Antofagasta and Barrick Gold. To solve its acid management chal- lenges, the mine installed Emerson's Smart Wireless solution consisting of 50 wireless differential pressure de- vices. The self-organizing IEC 62591 (WirelessHART) network covers an area stretching 2 km (1.5 miles) by 650 m (2,100 ft) wide and sends pressure and pH variables to the main control system. The pressure and pH data are available online for operation and control which enables managers to optimize main- tenance resources and minimize the exposure time of operators in the field. Benefits attributed to the Smart Wireless solution include reduced risk of costly pad collapse, a copper production im- provement of 7%, reduced environmen- tal impact, and a reduction of 14% in use of sulphuric acid. Payback of the investment took less than six months, according to Emerson. Additional bene- fits gained by the use of wireless devices included mitigation of the risk of losing data transmission due to cable deterio- ration — and the wireless devices can be easily moved at low cost. In another example, Barrick has in- cluded refinements to its heap-leach op- erations as an integral part of its overall 'digital reinvention' initiative announced in collaboration with network technology provider Cisco last September. The com- pany's Cortez gold mine in northern Ne- vada was chosen as the pilot site for a flagship digitization operation because it has a mix of "all the right ingredients," according to Barrick, including an under- ground mine, an open pit, a processing plant that isn't overly complex, and a mine that had already implemented some digital technology. According to a February 2017 presen- tation by Michelle Ash, Barrick's chief innovation officer, the big-picture frame- work for the company's digitalization ef- forts will include programs to enhance predictive analytics, global task manage- ment, integrated planning and a compa- ny-wide 'analytics hub' to improve overall management awareness. The company's 2016 digital objectives for its heap leaching operations included improved carbon management through operation and analytics preventing 'ounce loss,' as well as automated carbon and reagent control to reduce downtime and reagent costs. Its list of objectives for 2017, according to Ash, includes auto- mation of its heap leach operations to in- crease throughput and recovery.

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