How do riffles work?

Answer 1

Basically riffles in a sluice box are an obstruction to the waterflow running down through the trough, as the water goes over the riffle a low pressure area develops allowing for the heavy minerals in the gravels, namely gold, silver, platinum etc. to drop from suspension and remain trapped on the down stream side of the riffle. there are many type of riffles used in gold and mineral palcer mining, from simple sheepskins, (Jasons Golden Fleece) blankets, rocks where a type of riffle used in ancient times by the Romans and Egyptians, wooden slates and poles used by early gold miners of the Cariboo Gold Rush 1859, today riffles can be anything from expanded metal, to floating angle iron riffles, as well the drop riffle such as the Le Trap sluice box uses, and the Drop Down Rifflefrom Greywolf Highbankers, but they all work some what on the same principal, gravity separation. Gold being 19.3 times heavier than water and on average 3 to 4 times heavier than most other gravels.