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Workers on their day off stand next to armored buses during a rest stop while riding from Freeport McMoRan Inc.'s Grasberg copper and gold mining complex towards Timika in Papua province, Indonesia, on Thursday, April 23, 2015. Freeport is the world's largest publicly traded copper producer. Photographer: Dadang Tri/Bloomberg via Getty Images

Workers on their day off stand next to armored buses during a rest stop while riding from Freeport McMoRan Inc.'s Grasberg copper and gold mining complex towards Timika in Papua province, Indonesia, on Thursday, April 23, 2015. Freeport is the world's largest publicly traded copper producer. Photographer: Dadang Tri/Bloomberg via Getty Images