French photographer Rémi Bénali traveled for two days by dugout canoe to reach the remote mining settlement of Dorlin. The miners at first suspected him of being a police officer -- his light meter looked suspiciously like a GPS unit. But once he had gained their trust, he compiled this remarkable portfolio documenting their lives.

The first stage in the process is crude: Blast away the topsoil and bombard the mud with water from high-pressure hoses to get at the gold-bearing alluvium. Then, once the lucrative concentrates have been separated from the muck, mercury works its magic, transforming gold-flecked mud and dust, through a process called amalgamation, into solid nuggets that you can hold in your hand and turn into hard cash.

But for every gram of gold that is extracted, between one and three grams of mercury are lost. Once the amalgamation process is complete, the contaminated mine tailings drain into the nearest river, where methylmercury accumulates in the tissue of carnivorous fish -- a staple of the miners' diet (not to mention that of other river dwellers). A more direct threat is the inhalation of mercury vapor. Any mercury that is still mixed in with the gold after amalgamation either evaporates or is burned off, exposing the blowtorch-wielding miner (and often his wife and children, since much of the work is done at home) to the toxic vapor.

Alternatives to amalgamation do exist. Centralized processing centers, which now operate in several countries including Venezuela, Guyane's close neighbor, can eliminate the use of mercury altogether, or at least minimize emissions by employing specially designed retorts and furnaces that allow a large proportion of it to be recycled. But as Bénali discovered, few of these benefits have reached the hidden world of the garimpeiros and the noirs marrons.