Placer Mining

Placer mining is a type of surface, open-pit mining in which valuable minerals such as gold are extracted from a river or streambed using a pan, rocker, sluice, or dredger.^[1] Excavation of minerals also includes using water pressure to separate and remove the minerals from dirt, gravel, or other debris. This process is called hydraulic mining. Surface excavation and tunneling equipment are also used to accomplish excavation.

[edit] History

The Roman Empire used placer mining to extract valuable minerals located in streambeds or exposed openly on the ground. Such mineral deposits were known as placer deposits.^[2] Ores recognized at the surface were eventually followed into the ground by surface strip-mining or by digging short tunnels. Such a method became known as opencast mining and the Romans extracted various metals this way.

Placer mining was especially popularized in the framework of the many gold rushes that started in North America. The first recorded use of placer mining for gold started in the Appalachian mountain region in the 1700s. Once gold in the area became exhausted, more gold was discovered in the western part of the U.S. The California Gold Rush was sparked in 1849 when a man by the name of James Marshall discovered a dime-sized gold nugget at Sutter’s Mill.^[3] Subsequent gold rushes followed, with gold fever spreading from western California into British Columbia’s Fraser Canyon and Interior regions and then up into the Yukon with the Klondike Gold Rush.

During the Gold Rush, scores of prospectors panned for gold in creeks, streams, and riverbeds. Dirt from the riverbed was scooped into a pan and then swirled around the water and dirt, eventually pouring the water out. The gold would remain at the bottom of the pan because it was heavier than other debris. Panning became the most common and simplest method of placer mining.^[4]

In streams that yielded a number of gold nuggets, a prospector would use a device called a rocker, a long box that water and dirt were shoveled into. The box was then rocked back and forth, similar to panning, mixing the water and dirt together. The mixture of water and dirt then spilled out at the other end of the box, leaving behind any gold. Sluices were also used in the placer mining of gold.^[5] The sluice was a wooden channel or trough through which water flowed down, which had levers to control water flow. Other equipment commonly used in placer mining included shovels and picks.^[6]

The practice of placer mining did not fade away with the Gold Rush. The method is still deployed today as certain mineral types such as gold, tungsten, and tin are still located on or close to the ground’s surface.

[edit] References

1. ↑ A Glossary of Prospector's Terms, 2008-09-30.
2. ↑ Duncan, Lynne Cohen. Roman Deep-vein Mining. UNC.edu, 2008-09-30.
3. ↑ Mining History of Placer Gold. E-GoldProspecting.com, 2008-09-30.
4. ↑ Placer Mining. Library.Thinkquest.org, 2008-09-30.
5. ↑ Placer Mining. Library.Thinkquest.org, 2008-09-30.
6. ↑ Mining Words. Library.Thinkquest.org, 2008-09-30.