gold dredge
   HOME

TheInfoList



OR:

A gold dredge is a
placer mining Placer mining () is the mining of stream bed (Alluvium, alluvial) deposits for minerals. This may be done by open-pit mining, open-pit (also called open-cast mining) or by various surface excavating equipment or tunneling equipment. Placer minin ...
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 seeking gold: just offshore from the beach of
Nome, Alaska Nome (; ik, Sitŋasuaq, ) is a city in the Nome Census Area in the Unorganized Borough of Alaska, United States. The city is located on the southern Seward Peninsula coast on Norton Sound of the Bering Sea. It had a population of 3,699 recorded ...
, for instance. A large gold dredge uses a mechanical method to excavate material (sand, gravel, dirt, etc.) using steel "buckets" on a circular, continuous "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 A trommel screen, also known as a rotary screen, is a mechanical screening machine used to separate materials, mainly in the mineral and solid-waste processing industries.Stessel et al. 1996, pp. 558-568. It consists of a perforated cylindrical d ...
called "the screen") that is sloped downward toward a rubber belt (the stacker) that carries away oversize material (rocks) and dumps the rocks behind the dredge. The cylinder has many holes in it to allow undersized material (including gold) to fall into a sluice box. The material that is washed or sorted away is called
tailings In mining, tailings are the materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are different to overburden, which is the waste rock or other material that overlie ...
. The rocks deposited behind the dredge (by the stacker) are called "tailing piles." The holes 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 antiquity. The concept is that the gold in sand or soil will settle to the bottom because gold is heavy/dense, and dirt, sand and rock will wash away, leaving the gold behind. The original methods to perform
placer mining Placer mining () is the mining of stream bed (Alluvium, alluvial) deposits for minerals. This may be done by open-pit mining, open-pit (also called open-cast mining) or by various surface excavating equipment or tunneling equipment. Placer minin ...
involved gold panning, sluice boxes, and rockers. Each method involves washing sand, gravel and dirt 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. Gold dredges are an important tool of gold miners around the world. They allow profitable mining at relatively low operational costs. Even though the concept is simple in principle, dredges can be engineered in different ways allowing to catch different sizes of gold specimen. Hence the efficiency of gold dredges differs greatly depending on its specifications.


History

By the mid to late 1850s the easily accessible placer gold in California was gone, but much gold remained. The challenge of retrieving the gold took a professional mining approach to make it pay: giant machines and giant companies. Massive floating dredges scooped up millions of tons of river gravels, as steam and electrical power became available in the early 1900s. The last giant gold dredge in California was the Natomas Number 6 dredge operating in
Folsom, California Folsom is a city in Sacramento County, California, United States. It is commonly known for Folsom State Prison, the song "Folsom Prison Blues" by Johnny Cash, as well as for Folsom Lake. The population was 80,454 at the 2020 census. Folsom is pa ...
that ceased operations on 12 Feb 1962 as cost of operation began exceeding the value of the gold recovered. Many of these large dredges still exist today in state-sponsored heritage areas ( Sumpter Valley Gold Dredge), or tourist attractions ( Dredge No. 4 National Historic Site of Canada). Gold dredges were used in New Zealand from the 1860s, although the earlier dredges were of primitive design and not very successful.''Gold Mining: Dredging'' from Te Ara: Encyclopaedia of New Zealand
/ref> Much of the New Zealand dredge technology was developed locally. The first really successful bucket dredge for gold mining was that of Choie Sew Hoy, also known as Charles Sew Hoy, in 1889. This dredge was able work river banks and flats, as well as the bottoms of streams. It became the prototype for many similar dredges, and led to a boom in gold dredging in the
South Island The South Island, also officially named , is the larger of the two major islands of New Zealand in surface area, the other being the smaller but more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman ...
; in
Otago Otago (, ; mi, Ōtākou ) is a region of New Zealand located in the southern half of the South Island administered by the Otago Regional Council. It has an area of approximately , making it the country's second largest local government reg ...
rivers like the
Shotover River The Shotover River ( mi, Kimiākau) is located in the Otago region of the South Island of New Zealand. The name correctly suggests that this long river is fast flowing, with numerous rapids. The river flows generally south from the Southern Alps ...
,
Clutha River The Clutha River (, officially gazetted as Clutha River / ) is the second longest river in New Zealand and the longest in the South Island. It flows south-southeast through Central and South Otago from Lake Wānaka in the Southern Alps to the P ...
and the Molyneaux River, and in
West Coast West Coast or west coast may refer to: Geography Australia * Western Australia *Regions of South Australia#Weather forecasting, West Coast of South Australia * West Coast, Tasmania **West Coast Range, mountain range in the region Canada * Britis ...
rivers like the Grey River (where the last gold dredge worked until 2004). A New Zealand born mining entrepreneur, Charles Lancelot Garland, bought the technology to New South Wales, Australia, launching the first dredge there, in March 1899, resulting in a major revival of the alluvial gold mining industry. Gold dredges also operated, extensively, in Victoria and in Queensland. From Australia, in turn, gold dredging technology spread to New Guinea, at the time an Australian territory, in the 1930s. Due to the remote locations of the goldfields and absence of roads in New Guinea, parts of dredges were carried to site by air and the dredge was assembled there.


Today

In the late 1960s and through today, dredging has returned 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 to the giant dredges of the 1930s.Fairbanks, Alaska
Gold Dredge
Today dredges are versatile and popular consisting of both floating surface dredges that use a vacuum to suck gravel from the bottom and submersible dredges.
Small gold dredges
Large dredges are still operating in several countries of South America (Peru, Brasil, Guyana, Colombia), Asia (Russia, China, Mongolia Papua-New Guinea) and Africa (Sierra Leone). In 2015, gold miner Tony Beets reconstructed a 70-year-old dredge (as seen in the popular TV series,
Gold Rush A gold rush or gold fever is a discovery of gold—sometimes accompanied by other precious metals and rare-earth minerals—that brings an onrush of miners seeking their fortune. Major gold rushes took place in the 19th century in Australia, New Z ...
, on the
Discovery Discovery may refer to: * Discovery (observation), observing or finding something unknown * Discovery (fiction), a character's learning something unknown * Discovery (law), a process in courts of law relating to evidence Discovery, The Discovery ...
channel.). As of 2016, this is the only operating large dredge in the Klondike. However, he is currently working on fixing up a second dredge 33% larger than the first one. In Season 7 Episode 20, titled Dredge vs Washplant, it was shown that in a 2-day test the running costs of the dredge were approximately 25% of those of running a washplant and feeding it with heavy equipment. Environmental impact studies show no clear positive benefits from suction dredging and potential negative impacts on stream systems. Small scale suction dredging in rivers and streams remains a controversial land management topic and the subject of much political turmoil.


References


External links


Nusa Penida
Canada and Alaska

from
Oakland Museum of California The Oakland Museum of California or OMCA (formerly the Oakland Museum) is an interdisciplinary museum dedicated to the art, history, and natural science of California, located adjacent to Oak Street, 10th Street, and 11th Street in Oakland, Cali ...
('page not found' 4 November 2022)
Parks Victoria's visitors guide to Cock's gold dredge
at El Dorado, Victoria, Australia
Gold Dredges in Indonesia
for small scale mining. 5/31/2022
Dredge No. 4
Parks Canada
Engineering New Zealand - Gold Dredge Development
{{Mining equipment * Dredges Excavators
Dredges Dredging is the excavation of material from a water environment. Possible reasons for dredging include improving existing water features; reshaping land and water features to alter drainage, navigability, and commercial use; constructing da ...