tossing
The process of washing ores by violent agitation in water, in order to separate the lighter or earthy particles; tozing.
tossing: violent water washing to separate ore from waste
Tossing is a gravity-based ore dressing method in which ore is agitated violently in water to exploit differences in density and particle size. The lighter gangue, clay, and weathered material suspend and wash away, leaving heavier ore particles to settle or concentrate. This process predates mechanical screening and remains useful in alluvial and placer operations where ores are already partially liberated from host rock.
The equipment is simple: a wooden or metal tub or trough fitted with a mechanical stirrer, typically an arm or paddle driven by water wheel, steam engine, or hand labor. The ore slurry is charged into the tub with enough water to create a turbulent, boiling motion. Coarser material settles quickly; finer waste stays suspended and overflows via a weir or spillway. Tossing works best on ores where density contrast is pronounced, such as cassiterite (density 6.8 to 7.0) in association with quartz and feldspar, or native gold and alluvial tin.
Variants and context
In small-scale and artisanal mining, tossing is often done by hand using a shallow pan or basket, tilted and shaken to wash fines away. Industrial tossing machines, sometimes called jigs or shaking tables in their refined forms, operate on the same principle but with controlled reciprocating or oscillating motion. The term "tozing," an older spelling, appears in 18th and 19th century mining texts and refers to identical practice. Tossing is distinct from panning, which uses slow circular motion, and from sluicing, where ore flows continuously down an inclined channel.
The main limitation is that tossing works poorly on fine ore or when ore and gangue are similar in density. It also requires a reliable water supply and can generate silt and suspended solids that require settling ponds. In hard-rock mines processing coarse broken ore from underground, tossing has been largely superseded by dense-media separation and flotation. However, in alluvial operations and in regions where mechanical sorting is expensive or impractical, tossing remains a standard first stage of concentration.
The name reflects the action itself: the ore is tossed about in water until lighter particles separate and escape. Historical practice often combined tossing with buddling, a gentler washing in shallow troughs, to produce a marketable concentrate ready for smelting or further treatment.