sluicing

Sluicing is a mining technique used in placer mining to separate valuable minerals, notably gold, from sediment by passing water through a sluice box. A sluice box is a long trough fitted with riffles and mats that trap heavier particles while lighter material is flushed away. The technique relies on the density difference between gold and surrounding material. Miners feed a stream of gravel into the upper end; water flow carries lighter material away and the heavier particles settle behind the riffles. Sluicing became widespread during 19th-century gold rushes and remains in use for small-scale operations, often in the form of highbankers or portable dredges. Design variations include different riffle configurations, carpet materials, and underflow controls. Pros include high recovery for coarse to mid-sized gold and relatively low equipment cost; cons include sensitivity to water quality, silt buildup, and breakage of riffles; environmental concerns involve turbidity and disturbance to aquatic habitats.

In linguistics, sluicing is a type of ellipsis in which all material of a clause is deleted except for a wh-phrase. For example: “Someone called, but I don’t know who.” The remaining wh-word is interpreted with the residual clause understood from context. Sluicing is studied to understand how languages permit omission and how the missing material is recovered, often analyzed as covert movement or structure beneath the surface. It appears in many languages and varies in whether the wh-phrase undergoes overt movement or remains in place.