Small-scale gold mining mostly takes place on secondary deposits. This is also called placer mining. The gold lies under a few meters of organic material, sand and clay.
On secondary deposits, pumps and motors are used. The soil is removed with a water hose of 2”, 4” or 6”. The pulp formed by the water and the soil is pumped up and escorted to either the river in case of overburden, or to a wooden sluice box in case of gold-bearing material.
The sluice box contains a longitudinal mat, where the gold is separated from the water, sand and stones. The sluice box consists of a series of tilted wooden boxes in which gold particles and other heavy minerals are trapped behind riffles and/or a metal screen, and in the fine mat that covers the bottom of the sluice box. Gold is recovered by washing the screen and the mat with water, and with applying mercury to bind with gold.
On a river, such systems with suction hoses can also be used on top of a raft. These are named balsas or dragas.