Pinched sluice is a modified sluice that has been used for many years ago. In its elementary form, the equipment is inclined trough 2 feet long, narrowing from about nine inches in width at the feed end to one inch at discharge. Basically, feed consists of slurry at 55-60% solids that enters gently and stratifies as the particles flow through the sluice and crowd into the narrow discharge area. Heavy minerals migrate to the bottom and lighter minerals are forced to the top. Separation is influenced by the walls of the sluice due to drag force. In this way the resulting mineral bands are separated by splitters at the discharge.
This equipment work on the concept that as a fine material is exposed to an opening, the arc formed by the heaviest particles dropping will be much narrow than the arc formed by the lighter minerals. A divider placed perpendicular to and below the pinched outfall lets heavy materials to collect on one side and lighter particles can be collected separately. Pinched sluices are very simple inexpensive equipment and don’t need much space. Operative problems are related to the feed percent solids variations and gold content variability. Other issued to be considered is the circulating load that is problematic and special care must be taken in order to get a stable operation.
Pinched Sluice Diagram