Good chemistry

Unfortunately, mining is also hazardous. Gold miners that operate in small, informal teams – so-called ‘artisanal gold miners’ – used 1400 tonnes of mercury in 2011, according to estimates reported by the United Nations Environment Programme. Miners often add mercury to powdered rock thought to contain gold. They do this because mercury forms an amalgam with gold, meaning tiny specks of the precious metal coalesce into larger lumps that are easier to filter out. Miners then heat these lumps up, evaporating the mercury (which boils at 357°C), and leaving what is called ‘sponge gold’ behind.
http://www.rsc.org/eic/2014/12/international-development-bubble-wrap-gold-mercury