Ingots of 99.99 percent pure silver are cast at the Krastsvetmet Krasnoyarsk non-ferrous metals plant in the Siberian city of Krasnoyarsk, Russia, June 5, 2015. Krastsvetmet is one of the world's largest players in the precious metals industry. REUTERS/Ilya Naymushin

People leave a camp after a Peruvian police operation to destroy illegal gold mining camps in La Pampa, in the southern Amazon region of Madre de Dios, Peru August 11, 2015. Picture taken August 11, 2015. (Photo by Sebastian Castaneda/Reuters)

An engineer (L) talks to a driver of a dump truck loaded with gold-bearing soil at the Vostochny opencast of the Olimpiada gold operation, owned by Polyus Gold International company, in Krasnoyarsk region, Eastern Siberia, Russia, June 30, 2015. Polyus Gold International is the largest gold producer in Russia and one of the top 10 gold miners globally by ounces produced, according to the official web site of the company. Olimpiada is Polyus Gold's largest operation. (Photo by Ilya Naymushin/Reuters)

A boy carries a dog as he stands after a Peruvian police operation to destroy illegal gold mining camps in a zone known as Mega 14, in the southern Amazon region of Madre de Dios July 14, 2015. Peruvian police razed dozens of illegal gold mining camps at the edge of an Amazonian nature reserve this week, part of a renewed bid to halt the spread of wildcatting in a remote rainforest region. (Photo by Janine Costa/Reuters)

A mine worker is seen outside “The Progreso” gold mine near La Paz, November 13, 2014. According to local media, the president of the Central Bank of Bolivia (BCB) Marcelo Zabalaga said on Thursday that the falling price of oil and minerals in the international market will not affect the national economy. (Photo by David Mercado/Reuters)

Horses from the Garrison Savannah, who are involved in celebrations today to mark 50 years of Independence, are washed in the sea first thing in the morning on December 1, 2016 in Bridgetown, Barbados. Prince Harry is visiting the Caribbean marking the 35th Anniversary of Independence in Antigua and Barbuda and the 50th Anniversary of Independence in Barbados and Guyana. (Photo by Chris Jackson/Getty Images)

Rescue workers stand next to TK Bremen cargo ship which ran aground during a powerful storm, spilling oil off the coast of France's northwestern region of Brittany as it lies stranded on Kerminihy beach in Erdeven, on December 16, 2011. (Photo by Damien Meyer/AFP Photo)

Dressers make last minute adjustments to the costumes of dancers performing as horses during a press preview of American artist Nick Cave's first major work shown in Australia, entitled HEARD.SYD in Sydney, November 8, 2016. Over several days the live art performance will feature 30 “horses” dancing to live percussion beats in suits made from coloured raffia plant fibres. (Photo by Jason Reed/Reuters)