The last giant gold dredge in California was the Natomas Number 6 dredge operating in Folsom, California that ceased operations on as cost of operation began exceeding the value of the gold recovered. Massive floating dredges scooped up millions of tons of river gravels, as steam and electrical power became available in the early 1900s. The challenge of retrieving the gold took a professional mining approach to make it pay: giant machines and giant companies. The rocks deposited behind the dredge (by the stacker) are called "tailing piles." The holes in the screen were intended to screen out rocks (e.g., 3/4 inch holes in the screen sent anything larger than 3/4 inch to the stacker).īy the mid to late 1850s the easily accessible placer gold in California was gone, but much gold remained. The material that is washed or sorted away is called tailings. The cylinder has many holes in it to allow undersized material (including gold) to fall into a sluice box. On large gold dredges, the buckets dump the material into a steel rotating cylinder (a specific type of trommel called "the screen") that is sloped downward toward a rubber belt (the stacker) that carries away oversize material (rocks) and dumps the rocks behind the dredge. The material is then sorted/sifted using water. Small suction machines are currently marketed as "gold dredges" to individuals seeking gold: just offshore from the beach of Nome, Alaska, for instance.Ī large gold dredge uses a mechanical method to excavate material (sand, gravel, dirt, etc.) using steel "buckets" on a circular, continuous "bucketline" at the front end of the dredge. The original gold dredges were large, multi-story machines built in the first half of the 1900s. A gold dredge is a placer mining machine that extracts gold from sand, gravel, and dirt using water and mechanical methods.
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