Bucket-chain gold dredgers are suitable for placer gold mining in rivers and waterways; they can be used for placer gold mining in lakes and coastal shallows; and they are employed for the re-processing of historical tailings or old mining areas to extract residual gold particles. The dredger is composed of several gravity concentrators.The concentration ratio could reach as high as 1:1000,and the recovery efficiency about 90% after series of separating.