A mechanically operated, sloping table by which heavy and light materials are separated. The end motion imparted to the table tends to drive all minerals up the slope of the table, but a flow of water carries the light materials down faster than the mechanical motion carries them up. The heavy materials settle to the bottom and finally reach the upper end and are delivered into a proper receptacle. The Gilpin County, Imlay, and Golden Gate concentrators are the chief types.