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placer mining造句
1. I got educated on placer mining, and heard all about the controversy over the use of water cannons . 2. Placer mining: Oldest method of recovering gold from alluvial deposits. 3. In conducting coastal open air placer mining or shore-based well drilling to exploit seabed mineral resources, effective measures must be taken to prevent pollution to the marine environment. 4. Mechanized placer mining, with special devices for washing and separating waste from valuable minerals, is used in productive alluvial deposits. 5. Placer mining is based on the FACT that heavier substances can be separated from lighter ones in water. 6. This primitive form of placer mining is still used in some places for panning gold. 7. This paper describes basic characteristics of dredging, application of dredging technology in the world beach placer mining, and dredging future.