Small-scale gold mining has been going on in the Amazon for decades, with huge expansion of this activity since the early 2000s. It is often done via river dredging, in which miners excavate sediments in search of small pieces of gold. To separate the gold, miners mix liquid mercury into the sediment, which forms a coating around the gold. After burning off the mercury, what’s left is solid gold that makes up 20 percent of all the gold on the world market.
This type of artisanal mining is an important source of income for local people, supporting people in regions where jobs are limited. Similar mining methods were employed during the California gold rush in the mid-1800s. Yet artisanal gold mining is generally illegal, with little regulation. Efforts for formalizing this activity are ongoing but thus far have been limited.
Gold mining causes deforestation, which converts forests to polluted ponds and mobilizes large amounts of sediment from river bottoms. The burning of the gold-mercury