How a Suction Dredge Works

A modern gold suction dredge is like an underwater vacuum cleaner. It uses a suction system, which draws gold-bearing materials up through the suction hose and deposits them in a floating sluice to be processed.
The sluice box contains horizontal ridges or bars, (riffles)  to catch the heaviest particles (gold) in the slurry as they are  washed down through the sluice box. After the slurry has passed the sluice box the material is discharged over the side of the dredge.

The Gold Dredge and Dredging for Gold
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In the beginning of the Gold Rush, the miners were limited because they could only work the areas that were accessible to hand tools along the banks of the streams and rivers. Their equipment was limited to gold pans, sluice boxes and rockers. As time progressed and as they became more experienced, they realized that the deeper gavels in the riverbeds were often richer than the surface gravel along the banks. In the early 1900s, several crudely built steam powered dredges were active on some of the northern rivers of California. The divers worked futility on the bottom of the rivers with heavy diving helmets and cumbersome diving suits. Although history reveals that dredging has been in existence throughout the world for many years, it is just recently that it has reached such a high degree of popularity due to advanced technology in dredging equipment. Dredges of today are lighter, more portable and more efficient than ever. A small portable backpack dredge of today can weigh as little as forty pounds and cost around eight hundred dollars. It can process as much gravel as a larger three hundred-pound dredge, some twenty years ago. One of the most exciting features of this type of dredge is that it allows the prospector to penetrate areas that were otherwise impossible to reach with heavier and more cumbersome equipment. They are also far more efficient than the machines of old. It is not uncommon to see a dredge profitably working the tailings of some of the old mines and tailing dumps. There are three basic types of dredges on the market today. They include surface dredge, submersible dredging tube and the underwater submersible dredge. The surface dredge is the most popular, efficient and versatile gold recovery machine.