Mercury Source: Artisanal and Small-Scale Gold Mining (ASGM)

Small amalgamation mills, locally referred to as 'cocos' (above), are often used in small-scale mining operations to crush and grind the ore. Mercury is placed directly in the 'cocos' to amalgate with any gold particles liberated during the milling process.

Miners will pan the ore concentrates to separate the gold-mercury amalgam from the non-target minerals (left).

Artisanal and small-scale gold mining (ASGM) is considered one of the world's largest emitters of mercury into the environment, accounting for approximately one-third of all global emissions. Miners use mercury to amalgamate gold. During the amalgamation process, mercury can be released directly into adjacent aquatic ecosystems because of poor care and handling of the liquid mercury. Mercury vapor is also released into the atmosphere when the mercury-gold amalgam is burned. The release of mercury creates a high risk of human exposure and also impacts adjacent terrestrial and aquatic ecosystems.

BRI's Tropical Program is working with the U.S. Department of State to identify techniques to improve mining efficiency while also reducing the reliance on mercury to extract gold. The project is being conducted in collaboration with Paul Cordy of the University of British Columbia and includes a combination of miner training activities and workshops designed to introduce appropriate technologies to miners. The project is focused in the Andean Region of South America.

The gold-mercury amalgam is then passed through a cloth and squeezed into ball, releasing excess mercury that is often collected for reuse. (Photo credits Paul Cordy)

Mercury in the Artisanal Small-Scale Gold Mining Process

To extract gold dust from the earth, artisanal miners add mercury to the silt. This can be done in an apparatus known as a ball-mill (mercury is poured into large drums that contain silt, as shown at left). The gold particles attach to the mercury, which acts like a magnet to the precious metal. The result is a solid mercury-gold amalgam that can be separated out by screening the silt.

The mercury-gold amalgam is then heated to vaporize the mercury, leaving the gold nuggets behind. Because this process is often conducted in the open air, usually close to family dwellings, anyone in the near vicinity is at risk of inhaling the airborne mercury. Excess mercury that is left in the silt (known as mine tailings) finds its way into local waterways during disposal.













Global Distribution of Mercury Emissions

Source: United Nations Environment Programme’s Global Mercury Assessment 2013: Sources, Emissions, Releases and Environmental Transport.

National and International Efforts to Reduce Mercury Emissions

The U.S. Environmental Protection Agency is working toward finding solutions to the mercury issue related to small-scale gold mining.

The new Minamata Convention on Mercury and other international efforts provide collaborative opportunities to build awareness and create solutions for this global problem.