A sluice is defined as a channel through which controlled amounts of diluted slurry. Sluice box and riffles are one of the oldest forms of gravity separation equipment. The size of this equipment is variable and range from small and portable metallic models to large units. Small models are employed for prospecting purposes. In general, sluices can be made of wood, aluminum, steel or plastic. A typical sluice section is 360 cm long and 30 cm wide. As a rule, a long narrow sluice is more efficient than a short wide one. The sluice must slope 10 to 30 cm per 360 cm (12 feet) depending on the water available, the coarse particle to be processed and the possible gold particle size.
To perform efficiently, a sluice needs large amounts of water. Enough water must be added to the feed to build up a sand bed in the bottom of the sluice. For maximum recovery, the flow should be turbulent, yet not forceful enough to wash away the sand bed. Russian studies have shown that recovery increases with the frequency of cleaning. For clean up, clear water is run through the sluice until the riffles are clear of gravel. A pan or barrel is placed at the discharge end to prevent loss of concentrate. Starting from the head of the sluice, riffles are carefully washed into the sluice. According to the model, any bottom covering is removed and washed into a separate container. Clean up continues until all riffles are washed. Large particles of gold should be removed by hand, and then the concentrate is washed out of the sluice or dumped into an appropriate container. The concentrate can be smelted or cleaned more by panning. After clean up, the sluice is reassembled and more ore is processed.
Schematic view of sluice