A sluice is a piece of equipment generally used in placer, or surface, mining where the emphasis is on finding gemstones, gold or tin.
A sluice at a gold mine is made up of a variety of sluice boxes that run water through the boxes as they collect gold using riffles, corrugations, mats, or other means to disturb the flow of water and material through the boxes. The heavier particles, such as gold, are trapped in the boxes, while the lighter materials are carried off with the water.
Using a sluice to recover ore or gemstones requires a great deal of water. If there is a limited water supply near a sluice, it can be necessary to build a dam or pump in order to collect the necessary amount of water.
A small sluice box operation uses a person with a shovel to lift the mined materials into the sluice as water runs over the materials.
The sluice boxes are fairly simple, generally wooden, boxes. A typical small, hand fed, sluice is 12 feet long and 10 to 12 inches high. There will be a series of four to eight sluice boxes in a typical operation, each slipping into the other so that the water and mining material flows through each box.
The riffles are pieces of wood, rubber, or metal that are set across the bottom of the sluice to collect the gold and shake the gravel and cobbles down the sluice. If the riffles are tapered, it creates an eddy that help in the gold collection.
The boxes are sloped, generally with a drop of 4 to 12 inches per 12 foot run. The slope may need to be increased if there is a shortage of water.
Some people use a blanket or burlap under the riffles to collect any fine gold that falls among the riffles.