Abstract: The helical sluice, or spiral, of a mineral separator used for mineral separation, has a series of take-off openings to carry off strata of dense minerals which form when a pulp of water and minerals to be separated pass through the spiral. Each take-off opening is a slot in the spiral bottom, transverse to the flow, and its effective length, or throat gap, may be varied by a tongue slidably engaged in the slot and having a splitter blade extending up from its leading end to deflect dense strata into the throat gap. A second slot is formed in the tongue to take off middlings, and this is also adjustable, by a slide.