A gold dredge is a placer mining

Placer mining

Placer mining is the mining of alluvial deposits for minerals. This may be done by open-pit or by various surface excavating equipment or tunneling equipment....

 machine that extracts gold from sand, gravel, and dirt using water and mechanical methods.

The original gold dredges were large, multi-story machines built in the first half of the 1900s.

Small suction machines are currently marketed as "gold dredges" to individuals who want to try their luck: just offshore from the beach of Nome, Alaska

Nome, Alaska

Nome is a city in the Nome Census Area in the Unorganized Borough of the U.S. state of Alaska, located on the southern Seward Peninsula coast on Norton Sound of the Bering Sea. According to the 2010 Census, the city population was 3,598. Nome was incorporated on April 9, 1901, and was once the...

, for instance.

A large gold dredge uses a mechanical method to dig up material (sand, gravel, dirt, etc.) using steel "buckets" on a circular, continuous, steel "bucketline" at the front end of the dredge. The material is then sorted/sifted, using water. On large gold dredges, the buckets dump the material into a steel rotating cylinder (a specific type of trommel

Trommel

A trommel is a screened cylinder used to separate materials by size - for example, separating the biodegradable fraction of mixed municipal waste or separating different sizes of crushed stone....

 called "the screen") that is sloped downward toward a rubber belt (the stacker

Stacker

A stacker is a large machine used in bulk material handling. Its function is to pile bulk material such as limestone, ores and cereals on to a stockpile. A reclaimer can be used to recover the material....

) that carries away oversize material (rocks) and dumps the rocks behind the dredge. The cylinder has many holes drilled into it to allow undersized material (including gold) to fall into a sluice

Sluice

A sluice is a water channel that is controlled at its head by a gate . For example, a millrace is a sluice that channels water toward a water mill...

 box. The material that is washed or sorted away is called tailings

Tailings

Tailings, also called mine dumps, slimes, tails, leach residue, or slickens, are the materials left over after the process of separating the valuable fraction from the uneconomic fraction of an ore...

. The rocks deposited behind the dredge (by the stacker) are called "tailing piles." The holes drilled in the screen were intended to screen out rocks (e.g., 3/4 inch holes in the screen sent anything larger than 3/4 inch to the stacker).

Concept

The basic concept of retrieving gold via placer mining has not changed since the beginning of the gold rush

Gold rush

A gold rush is a period of feverish migration of workers to an area that has had a dramatic discovery of gold. Major gold rushes took place in the 19th century in Australia, Brazil, Canada, South Africa, and the United States, while smaller gold rushes took place elsewhere.In the 19th and early...

. The concept is that the gold in sand or soil will settle to the bottom because gold is heavy/dense, and dirt, sand, rock, etc. will wash away, leaving the gold behind. The original methods to perform placer mining

Placer mining

Placer mining is the mining of alluvial deposits for minerals. This may be done by open-pit or by various surface excavating equipment or tunneling equipment....

 involved gold panning, sluice boxes, and rockers. Each method involves washing sand, gravel, dirt, etc. in water. Gold then settles to the bottom of the pan, or into the bottom of the riffles of the sluice box. The gold dredge is the same concept but on a much larger scale.

History

By the mid to late 1850s the easily accessible gold in California was gone, but there was still a lot of gold to be mined. The challenge of retrieving the gold took a more professional mining industry approach to make it pay: giant machines and giant companies. Massive floating dredges scooped up millions of tons of river gravels, as steam power and electrical power became available in the early 1900s. Many of these large monsters still exist today in state sponsored heritage areas (Sumpter Valley Gold Dredge

Sumpter Valley Gold Dredge

The Sumpter Valley Gold Dredge is a historic gold dredge located in Sumpter, Oregon, United States. The dredge was built during the gold rush that consumed most of the western states throughout the mid-19th century. Gold was discovered in Sumpter in 1862, but the advent of using a large machine to...

) or tourist attractions.

Today

In the late 1990s and through today, dredging has resurfaced as a popular form of gold mining. Advances in technology allow a small dredge to be carried by a single person to a remote location and profitably process gravel banks on streams that previously were inaccessible by the multi-story hundreds-of-feet-long dredges of the 1930s.
Today dredges are versatile and popular consisting of both floating surface dredges that use a vacuum to suck up gravel from the botton and submersible dredges.

External links

• Modern gold dredge techniques, for small-scale mining
• explorenorth.com Gold Dredges in the North, Canada and Alaska
• California gold dredges, from Oakland Museum of California
  Oakland Museum of California
  Oakland Museum of California or Oakland Museum is a museum dedicated to the art, history, and natural science of California located in Oakland, California....
  
  
• www.parkweb.vic.gov.au/resources05/05_1355.pdf Parks Victoria's visitors guide to Cock's gold dredge at El Dorado, Victoria
  Eldorado, Victoria
  Eldorado, or El Dorado, is a small town in the north-east of Victoria, Australia. At the 2006 census, Eldorado had a population of 287.-History:...
  
  , Australia