CLOSE WINDOW Gold doesn't grow on trees! All of the techniques used to find and extract gold have an impact on their location. See how gold mines around the world have changed the environment. South Africa North America Brazil Australia Brazil Photograph by Michael Nichols In the 1980s Brazil saw its greatest gold rush. Miners there have dumped some 1,500 tons of poisonous mercury into the Amazon River system to chemically extract gold from the Earth, killing fish populations along the river and threatening the health of Brazil's human population. TOP   © 2000 National Geographic Society. All rights reserved.