Abstract: A concentrator comprising an elongate vertical upwardly opening drum with an upwardly and radially outwardly inclined side wall and a substantially horizontal bottom wall, means rotatably supporting the drum on a vertical axis, drive means rotating the drum about said axis, a plurality of vertically spaced annular radially inwardly and downwardly inclined baffles at the inside surface of the side wall and cooperating therewith to define a plurality of vertically spaced annular substantially downwardly opening heavy material collecting recesses, a normally closed drain opening at the lower end of the drum, material supply means to deliver particulate material into the drum adjacent the bottom wall and including a vertical material conductor with open upper and lower ends; and irrigating means including a water supply communicating with the upper end of said conductor and delivering water into and through the conductor and vertically spaced nozzles connected with the water supply and arranged within the drum an