TOPSHOT - Escondida copper mine miners on strike block a road in Antofagasta, Chile, on February 15, 2017. Workers at the world's largest copper mine, BHP Billiton's Escondida in Chile, began an indefinite strike on February 9 to demand pay increases, prompting concerns on world commodity markets. / AFP / Martin BERNETTI (Photo credit should read MARTIN BERNETTI/AFP/Getty Images)

TOPSHOT - Escondida copper mine miners on strike block a road in Antofagasta, Chile, on February 15, 2017. 
Workers at the world's largest copper mine, BHP Billiton's Escondida in Chile, began an indefinite strike on February 9 to demand pay increases, prompting concerns on world commodity markets. / AFP / Martin BERNETTI        (Photo credit should read MARTIN BERNETTI/AFP/Getty Images)

Escondida copper mine miners on strike block a road in Antofagasta, Chile, on February 15, 2017. Workers at the world's largest copper mine, BHP Billiton's Escondida in Chile, began an indefinite strike on February 9 to demand pay increases, prompting concerns on world commodity markets. / AFP / Martin BERNETTI (Photo credit should read MARTIN BERNETTI/AFP/Getty Images)

Escondida copper mine miners on strike block a road in Antofagasta, Chile, on February 15, 2017. 
Workers at the world's largest copper mine, BHP Billiton's Escondida in Chile, began an indefinite strike on February 9 to demand pay increases, prompting concerns on world commodity markets. / AFP / Martin BERNETTI        (Photo credit should read MARTIN BERNETTI/AFP/Getty Images)

Miners of the Escondida copper mine, on strike, block a road outside of Escondida, some 145 km northeast of Antofagasta, Chile, on March 8, 2017. Workers at the world's largest copper mine, BHP Billiton's Escondida in Chile, began an indefinite strike on February 9 to demand pay increases, prompting concerns on world commodity markets. / AFP PHOTO / Martin BERNETTI (Photo credit should read MARTIN BERNETTI/AFP/Getty Images)

Miners of the Escondida copper mine, on strike, block a road outside of Escondida, some 145 km northeast of  Antofagasta, Chile, on March 8, 2017. 
Workers at the world's largest copper mine, BHP Billiton's Escondida in Chile, began an indefinite strike on February 9 to demand pay increases, prompting concerns on world commodity markets. / AFP PHOTO / Martin BERNETTI        (Photo credit should read MARTIN BERNETTI/AFP/Getty Images)

Escondida copper mine miners on strike block a road in Antofagasta, Chile, on February 16, 2017. Workers at the world's largest copper mine, BHP Billiton's Escondida in Chile, began an indefinite strike on February 9 to demand pay increases, prompting concerns on world commodity markets. / AFP / MARTIN BERNETTI (Photo credit should read MARTIN BERNETTI/AFP/Getty Images)

Escondida copper mine miners on strike block a road in Antofagasta, Chile, on February 16, 2017. 
Workers at the world's largest copper mine, BHP Billiton's Escondida in Chile, began an indefinite strike on February 9 to demand pay increases, prompting concerns on world commodity markets. / AFP / MARTIN BERNETTI        (Photo credit should read MARTIN BERNETTI/AFP/Getty Images)

Escondida copper mine miners on strike block a road in Antofagasta, Chile, on February 16, 2017. Workers at the world's largest copper mine, BHP Billiton's Escondida in Chile, began an indefinite strike on February 9 to demand pay increases, prompting concerns on world commodity markets. / AFP / Martin BERNETTI (Photo credit should read MARTIN BERNETTI/AFP/Getty Images)

Escondida copper mine miners on strike block a road in Antofagasta, Chile, on February 16, 2017. 
Workers at the world's largest copper mine, BHP Billiton's Escondida in Chile, began an indefinite strike on February 9 to demand pay increases, prompting concerns on world commodity markets. / AFP / Martin BERNETTI        (Photo credit should read MARTIN BERNETTI/AFP/Getty Images)