![]() It also has low environmental impact, as no stripping of vegetation or overburden is necessary, and all process water is fully recycled. This type of gold mining is characterized by its low cost, as each rock is moved only once. ![]() "Pay" gravel is excavated from the front face of the pond and processed through the floating plant, with the gold trapped in the onboard sluicebox and tailings stacked behind the plant, steadily filling in the back of the pond as the operation moves forward. The pond is excavated in the gravel bar and filled from the natural water table. These operations typically use a land-based excavator to feed a gravel-screening plant and sluicebox floating in a temporary pond. ![]() Other larger scale dredging operations take place on exposed river gravel bars at seasonal low water. Smaller dredges with 2 to 4-inch (100 mm) suction tubes are used to sample areas behind boulders and along potential pay streaks, until "color" (gold) appears. This has improved the chances of finding gold. ![]() Small suction dredges are much more efficient at extracting smaller gold than the old "bucket line" was. Some large suction dredges (100 hp+ 10 inch) are used in commercial production throughout the world. Corps of Engineers, the Montana Department of Environmental Quality, and the local county water-quality boards. Some states, such as Montana, require an extensive permitting procedure, including permits from the U. State dredging permits in many of the United States gold-dredging areas specify a seasonal time period and area closures to avoid conflicts between dredgers and the spawning time of fish populations. A suction dredge consists of a sluice box supported by pontoons, attached to a suction hose which is controlled by the miner working beneath the water. These are small machines that float on the water and are usually operated by one or two people. ![]() Although this method has largely been replaced by modern methods, some dredging is done by small-scale miners using suction dredges. ![]()
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