A large gold dredge uses a mechanical method to dig up material (sand, gravel, dirt, etc.) using steel "buckets" on a circular, continuous, steel "bucketline" at the front end of the dredge. The material is then sorted/sifted, using water. 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 cylinder has many holes drilled into it to allow undersize material (including gold) to fall into a sluice box. The material that is washed or sorted away is called tailings. The rocks deposited behind the dredge (by the stacker) are called "tailing piles." The holes drilled 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).

 

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