How does gravel pumping recover tin-bearing sand?

Gravel pumping is a primary surface-mining method used to recover tin from alluvial deposits. The process involves several key steps:

• Overburden Removal: Barren material covering the deposit is first removed using equipment such as draglines or shovels.1
• Dislodging the Ore: High-pressure water jets are directed at the deposit to break up and dislodge the tin-bearing sand.1
• Pumping the Slurry: A submerged gravel pump collects the resulting slurry of mud, water, and tin-bearing sand, raising it to a series of sluice boxes, or palongs.1
• Gravity Separation: As the slurry flows down the sloped, baffled sluice boxes, the heavier minerals—specifically cassiterite—settle at the bottom. The lighter waste material is carried over the end of the boxes to tailings dumps.1
• Concentration: The flow is periodically stopped to collect the accumulated crude concentrate.1

This method is highly effective for processing the fine-grained minerals found in ancient riverbeds and valleys.1