Placer mining

Henry Sandham - The Cradle

A placer mine at Alma in 1880 - DPLA - d36682f6190c8624b01556dfa53bc802 (cropped)

De re metallica p 282

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Placer gold-mining, Korea, c1900

Blei-und-Gold

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Goldwaschrinne

Placer mining is a method of mining that involves the extraction of valuable minerals or other geological materials from the earth's surface from placer deposits. These deposits form a mineralized package that is of economic interest to the miner. Placer mining is used when the metal or mineral is found in loose materials, such as sand or gravel, which is not bound to any other material. This type of mining is distinguished from traditional mining methods that require tunneling into the earth and is one of the simplest methods of extracting minerals.

Overview

Placer deposits are composed of relatively loose material that makes tunneling difficult, and so most means of extracting it involve the use of water or dredging. The word placer derives from the Spanish word placera, meaning "alluvial sand." It refers to mining the precious metal deposits (particularly gold and gemstones) found in alluvial deposits—deposits of sand and gravel in modern or ancient stream beds or occasionally glacial deposits. The metal or gemstones, having been moved by stream flow from an original source such as a vein, are typically only a minuscule portion of the total deposit.

Methods

The methods of placer mining vary greatly depending on the region, the material being mined, and the technology available to the miner. The most common methods include:

• Panning: Panning for gold is the simplest and oldest method of placer mining. Gold panning involves filling a pan with the sand/gravel from the placer deposit and, in water, separating the gold from the other materials as gold is much denser.

• Sluicing: A sluice box is more effective and processes more material than panning. Water is directed through a sluice box so that the heavier gold particles fall to the bottom and are trapped by riffles.

• Dredging: Dredging involves using a suction hose to vacuum gravel from the bottom of a body of water. Modern dredges are highly efficient and can process a lot of material quickly.

• High banking: This method combines sluicing and dredging, where water is pumped to sluice boxes located near the digging site.

Environmental Impact

Placer mining can have a significant impact on the environment. The use of water in mining can lead to the disturbance of local ecosystems and the sedimentation of rivers and streams, which can affect fish and other wildlife. Additionally, the use of toxic chemicals, such as mercury in the gold extraction process, can lead to water pollution and health hazards for local communities.

Regulation

Due to its environmental impact, placer mining is subject to regulations in many jurisdictions. Regulations may require miners to obtain permits, adhere to environmental standards, and reclaim mined land. The goal of these regulations is to minimize the environmental impact of mining activities and ensure that the land can be used for other purposes in the future.

Conclusion

Placer mining remains an important method of extracting valuable minerals and metals from the earth. Its simplicity and cost-effectiveness make it an attractive option for small-scale miners and prospectors. However, the environmental impact of placer mining necessitates careful management and regulation to protect local ecosystems and communities.