Some states, like Montana, need a comprehensive licensing procedure, including U.S. gold dredging areas to avoid conflicts between dredgers and fish populations spawning time. State dredging permits specify a seasonal time period and area closures in many of the U.S. A suction dredge consists of a pontoon-supported sluice box attached to a suction hose controlled by an underwater miner. Small machines that float on the water are typically operated by one or two people. While this method has been largely replaced by modern methods, small-scale miners use suction dredges to make some dredging. Less dense material flows like tailings out of the box. The material is transported by the current through the volt where behind the riffles settles gold and other dense material. At the top of the box is placed gold-bearing material. In order to channel water flow, the box is placed in the stream. In order to allow gold to drop out of suspension, the riffles are designed to create dead zones. Essentially, a sluice box is a man-made channel with riffles at the bottom. It has long been a very common practice for prospecting and small-scale mining to use a sluice box to extract gold from placer deposits. Usually the panning material is removed from stream beds, often at the inside turn in the stream, or from the stream’s bedrock shelf, where gold density allows it to concentrate, a type called placer deposits. It quickly settles down to the bottom of the pan as gold is much denser than rock. The pan is submerged and shaken in water, sorting the gravel gold and other material. Large, shallow pans are filled with gold-containing sand and gravel. Gold panning is mainly a manual gold separation technique from other materials. Placer deposits are composed of relatively loose material that makes tunneling difficult, so most extraction methods involve water or dredging. Placer mining is the technique of extracting gold accumulated in a placer deposit.
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