a centrifuge bowl having a base and a peripheral wall surrounding an axis passing through the base and generally upstanding from the base to an open mouth;

a mounting arrangement for rotating the bowl around the axis;

a feed duct having a discharge mouth adjacent the base of the bowl for feeding the slurry into the bowl during rotation of the bowl so that, during rotation of the bowl, the intermixed particulate materials flow over the peripheral wall of the bowl from the base for collection of heavier particulate materials on the peripheral wall and for discharge of the lighter particulate materials in the slurry from the open mouth;

a launder for collecting the lighter particulate materials in the slurry discharged from the open mouth;

an annular recess having a mouth at the peripheral wall over which the materials pass when fed from the supply duct as the materials pass to the open mouth of the bowl for collection of the heavier materials in the annular recess;

the annular recess comprising an annular upper wall and an annular lower wall each extending generally outwardly from the peripheral wall;

the annular upper wall and the annular lower wall including at least portions thereof which converge together toward a base of the annular recess spaced outwardly of the peripheral wall;

fluidizing openings in the annular recess at or adjacent the base at angularly spaced positions for fluidizing said heavier materials in the annular recess;

a plurality of valve controlled discharge ports in the annular recess at angularly spaced positions for generally radially outward discharge of collected heavier materials from the annular recess for substantially continuous operation;

and an annular ring extending continuously around the annular recess;

the annular ring having an annular inner portion mounted at the mouth of the annular recess leaving a space above and below the ring for passage of materials into the recess from the bowl;

the annular ring having an annular outer portion extending from the inner portion generally radially outwardly into the recess to a position between the converging portions of the walls of the recess;

wherein the outer portion has an outermost face facing outwardly to the base and the discharge ports therein with the outer portion being shaped and arranged relative to the recess that the space between the outermost face and the discharge ports is open to cause the outermost face to act as a control surface of the materials in the recess at the discharge port.