Placer mining uses water to separate valuable minerals from sediments, with gold being the most common. Placer deposits are found in streams, beaches, and gravel left by water. Panning is the most basic method, while sluicing and dredging are used for larger areas.
Placer mining is a group of mining methods that use water to separate valuable minerals or ores from surrounding sediments. It can be used to recover platinum, tin and diamonds, but most commonly gold. A very crude form of placer mining was used by gold prospectors during the California Gold Rush in the mid-1800s. Since then, technology has progressed to allow for the processing of a larger volume of material. Modern mining methods include dredging and slucing.
Placer mining gets its name from the deposits from which the material is mined. Placer deposits are concentrations of heavy minerals that form when minerals are washed, by weather or flooding, down the slope into streams. The minerals settle in one place because the stream flow isn’t strong enough to move them any further. Placer deposits are usually found in streams, on beaches, and in gravel left behind by flowing water.
The most basic, and perhaps the most iconic, method of placer extraction is panning. The only equipment a miner needs is a frying pan, usually slightly larger than the average dinner plate. The miner places a small amount of sediment in the bottom of the pan and then fills the pan with water. He or she then swirls the water around, allowing it to wash down the sides of the pan. In this way, common sediment is washed over the side while gold or other valuable materials are left behind.
Placer mining works because some precious metals tend to be denser than the sediments around them. When water is poured or poured over the sediment, the movement of the water is enough to wash the sediment away, but not strong enough to move the gold. This principle also works with very small gold flakes.
Panning is still used by hobbyists and small-scale miners, but is very labor intensive. More sophisticated methods must be used to mine large areas. Sluicing and dredging are often used both individually and in combination.
Closing requires a closed box, which is basically just a rectangular box set on a slope. The top has an opening and the bottom has a series of wooden or metal rods that break the current as water and dirt are dumped into the open top. The lighter sediment pours out of the bottom of the box, but the heavier gold is trapped by the current disruptions caused by the rods. Dredging is really just a way to collect material to drain off. It usually uses suction to suck up sediment from a stream or river bed.
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