Since majority of tropical placers have limonite cemented layer, under which the most interesting values are, the dredge must use a cutter wheel. Many areas, where gold or diamond placers are found in South America, have undergone processes of rejuvenation. Often, all deeper layers are still maiden. While in former climates gold moves as physical particles, in lateritic environments gold predominantly moves as a solution and precipitates in areas with a specific geochemical condition. Plants play an essential role in a gold mobilization.
Many tropical plants produce cyanide.
Precipitated gold particles are very small, and are distributed like a cloud in the alluvium. The gold in such tropical placer is often distributed through a whole vertical section. The evaluation of such deposit is much more precise than an evaluation of a nuggety one.