trunk
A flume or sluice in which ores are separated from the slimes in which they are contained.
trunk: gravity separation channel for ore and slime
A trunk is a open-channel separator, typically 12 to 20 feet long and 2 to 4 feet wide, through which a mixture of crushed ore and fine waste material flows under gravity. Water carries the slurry downslope while the trunk's geometry and controlled water velocity allow heavy ore particles to settle and concentrate toward the bottom, while lighter clay, silt, and other slimes remain suspended and flow toward the overflow end.
The trunk works by exploiting particle density and settling rate. Ore minerals, mostly oxides and sulfides with densities between 2.5 and 5.0 g/cm³, settle faster than slimes (density near 2.0 g/cm³ or less). The operator controls the water supply to maintain a velocity fast enough to carry slimes but slow enough to let ore drop. A slight grade, usually 1 to 2 percent, aids the transport without creating turbulence that would re-suspend settled material.
The separated ore exits through a discharge box at the lower end, while the slime-laden overflow spills across a weir or lip at the far end. Some designs include riffles, V-shaped grooves, or baffle plates on the floor to trap and guide heavier particles backward. Operators must manage water balance carefully: too much flow washes ore away; too little allows slimes to settle and blocks the channel.
Trunks are a high-volume, low-cost alternative to mechanical classifiers and hydrocyclones, requiring only gravity, water, and gravity, with no moving parts to maintain. They are most common in alluvial gold and tin operations, where the ore density advantage over slime is substantial. In hard-rock milling circuits, they appear less frequently because the ore and waste densities are often closer, reducing separation efficiency.
The name reflects its resemblance to a wooden trough or trunk carried as cargo, though its industrial form is typically concrete or steel. Trunks have been in use since the 1800s in stream-bed mining, and remain standard equipment in small to medium-scale operations in regions with reliable water supply and no electric power infrastructure.