How do sluice boxes separate cassiterite from waste material?

Sluice boxes, also known as palongs, separate cassiterite from waste material through gravity separation based on the density of the minerals.1

In this process, a slurry of mud, water, and tin-bearing sand is directed into the sluice box, which is positioned on a downward slope. The interior of the box features baffles or riffles placed at intervals along its length. As the slurry flows over these obstacles, the current is agitated, which prevents lighter waste material from settling. Because cassiterite is a heavier mineral, it falls to the bottom of the box and is trapped behind the baffles, while the lighter waste material is carried away by the water flow to tailings dumps. Periodically, the flow is stopped to collect the accumulated crude concentrate.123