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49-605: The Sumpter Valley Gold Dredge is a historic gold dredge located in Sumpter , in the U.S. state of Oregon . Gold was discovered in Sumpter in 1862. Three gold dredges were put into service in the Sumpter Valley district between 1912 and 1934. A gold dredge works by having large buckets that pull the gold-bearing earth up into its machinery to be processed, keeping the gold and spewing the waste (known as "tailings") out

98-529: A Roman alluvial gold mine at Las Médulas , Spain are so spectacular as to justify the site being designated UNESCO World Heritage status. The methods used by the Roman miners are described by Pliny the Elder in his work Naturalis Historia published in about 77 AD. The author was a Procurator in the region and so probably witnessed large-scale hydraulic mining of the placer deposits there. He also added that

147-534: A 70-year-old dredge (as seen in the popular TV series, Gold Rush , on 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

196-824: A boom in gold dredging in the South Island ; in Otago rivers like the Shotover River , Clutha River and the Molyneaux River, and in West Coast 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

245-416: A few feet, or more than ten feet (a common term for one that is over six feet +/- is a "Long Tom"). While they are capable of handling a larger volume of material than simpler methods such as the rocker box or gold panning, this can come at the cost of efficiency, since conventional sluice boxes have been found to recover only about 40% of the gold that they process. The sluice box was used extensively during

294-407: A larger volume became more common. The same principle may be employed on a larger scale by constructing a short sluice box , with barriers along the bottom called riffles to trap the heavier gold particles as water washes them and the other material along the box. This method better suits excavation with shovels or similar implements to feed ore into the device. Sluice boxes can be as short as

343-546: A major revival of the alluvial gold mining industry. Gold dredges also operated, extensively, in Victoria and in Queensland. Dredges were also used to mine placer deposits of other minerals, such as tin ore . In later years, some dredges were electrically powered. A gold dredge was working at Porcupine Flat, near Maldon, Victoria , until 1984. From Australia, in turn, gold dredging technology spread to New Guinea, at

392-481: A sluice box, being fed not by a sluice but by hand. The box sits on rockers, which when rocked separates out the gold, and the practice was referred to as "rocking the golden baby". A typical rocker box is approximately 42 inches long, 16 inches wide and 12 inches deep with a removable tray towards the top, where gold is captured. The rocker was commonly used throughout North America during the early gold rush, but its popularity diminished as other methods that could handle

441-443: A stream bed. Gold accumulations in an old stream bed that are high are called bench deposits. They can be found on higher slopes that drain into valleys. Dry stream beds (benches) can be situated far from other water sources and can sometimes be found on mountaintops. Today, many miners focus their activities on bench deposits. Deep leads are created when a former stream bed is covered over by later sediments or by igneous rock from

490-463: A three-man crew to operate the machinery and 17 more workers to complete the crew for maintenance, bookkeeping, surveying, truck driving, managing and a few other roles. The dredge operated 363 days a year; most of the men were given the Fourth of July and Christmas day off from work. One or two men had to stay on board to watch over the machine during the evenings. Dredge workers often reported hearing

539-423: A trough into the primary sluice box where it is filtered again. Both the grizzly and undercurrent are designed to increase efficiency, and were often used in combination. Sluicing is only effective in areas where there is a sufficient water supply, and is impractical in arid areas. Alternative methods developed that used the blowing of air to separate out gold from sand. One of the more common methods of dry washing

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588-799: A vein, are typically only a minuscule portion of the total deposit. Since gems and heavy metals like gold are considerably denser than sand , they tend to accumulate at the base of placer deposits. Placer deposits can be as young as a few years old, such as the Canadian Queen Charlotte beach gold placer deposits, or billions of years old like the Elliot Lake uranium paleoplacer within the Huronian Supergroup in Canada. The containing material in an alluvial placer mine may be too loose to safely mine by tunnelling, though it

637-495: A volcanic eruption. Examples existed in the goldfields of Gulgong and Creswick in Australia. The gold bearing gravel is accessed by shafts and drives similar to underground mining techniques but is typically processed as if alluvial gold. The heat associated with an igneous lava flow, in some cases, altered the gold bearing gravel so that it needed to be crushed first to extract the gold; an example of this kind of deep lead

686-398: 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. Placer mining Placer mining ( / ˈ p l æ s ər / )

735-460: Is " winnowing ". This method was most commonly used by Spanish miners in America, and only requires a blanket and a box with a screen on the bottom. The material is first filtered through the box so only the finer material is placed onto the blanket. The material on the blanket is then flung into the air so that any breeze can blow away the lighter material and leave the gold behind. While this method

784-413: Is extremely simple and requires very few materials, it is also slow and inefficient. A trommel is composed of a slightly inclined rotating metal tube (the 'scrubber section') with a screen at its discharge end. Lifter bars, sometimes in the form of bolted in angle iron, are attached to the interior of the scrubber section. The ore is fed into the elevated end of the trommel. Water, often under pressure,

833-446: Is now rarely used for profit since even an expert gold prospector can only process approximately one cubic yard of material for every 10 hours of work. A rocker box (or "cradle") is capable of greater volume than a gold pan; however, its production is still limited when compared to other methods of placer mining. It is only capable of processing about 3 or 4 yards of gravel a day. It is more portable and requires less infrastructure than

882-466: Is possible where the ground is permanently frozen . Where water under pressure is available, it may be used to mine, move, and separate the precious material from the deposit, a method known as hydraulic mining , hydraulic sluicing or hydraulicking . The word placer derives from the Spanish placer , meaning shoal or alluvial/sand deposit, from plassa (place) from Medieval Latin placea (place)

931-624: Is provided to the scrubber and screen sections and the combination of water and mechanical action frees the valuable heavy minerals from the lighter gravel. The mineral bearing ore that passes through the screen is then further concentrated in smaller devices such as sluices and jigs. The larger pieces of ore that do not pass through the screen can be carried to a waste stack by a conveyor. Large-scale sifting of placer gold from large volumes of alluvial deposits can be done by use of mechanical dredges. These dredges were originally very large boats capable of processing massive amounts of material; however, as

980-412: 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 . The rocks deposited behind the dredge (by the stacker) are called "tailing piles." The holes in

1029-495: Is the Mexican dry wash. This method involves placing gravel on a riffle board with a bellows placed underneath it. The bellows is then used to blow air through the board in order to remove the lighter material from the heavier gold. The amount of gravel that can be processed using the Mexican dry wash technique varies from 1 1/2 to 4 cubic yards per day, and can be processed at a maximum efficiency of 80%. Another form of dry washing

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1078-502: Is the mining of stream bed deposits for minerals . This may be done by open-pit mining or by various surface excavating equipment or tunneling equipment. Placer mining is frequently used for precious metal deposits (particularly gold ) and gemstones , both of which are often 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

1127-485: The California gold rush for larger scale operations. When streams became increasingly depleted, the grizzly and undercurrent variants of the sluice box were developed. The grizzly is a set of parallel bars placed at a 45-degree angle over the main sluice box, which filter out larger material. The undercurrent variety includes additional, auxiliary sluice boxes where material is initially filtered. It then travels through

1176-488: The 1860s, although the earlier dredges were of primitive design and not very successful. 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

1225-567: The Gold Dredge Gift Store and Museum, with a video featuring interviews with dredge workers, historic photos and artifacts. Tours of the dredge are provided. The dredge was part of a paranormal investigation on the 2013 television series Ghost Mine . Gold dredge 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

1274-462: The Yukon, placer deposits may be mined underground. As the frozen ground is otherwise too hard and firm to mine by hand, historically fires were built so as to thaw the ground before digging it. Later methods involve blasting jets of steam ("points") into the frozen deposits. Deep leads are accessed by techniques similar to conventional underground mining. Although this procedure is not required,

1323-432: The back by way of a stacker. Built on a shallow hull, these dredges did not need a lot of water to operate, as they moved their pond of water with them. The internal mechanics were not very sophisticated—they duplicated, on a larger scale, many of the devices used by placer mining throughout the gold rush, such as the gold pan and the sluice box. In essence, the dirt that was dug by the large electrically powered buckets

1372-422: The beach of Nome, Alaska , 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 called "the screen") that

1421-426: 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

1470-642: The early 1900s. The last giant gold dredge in California was the Natomas Number 6 dredge operating in Folsom, California 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

1519-436: The efficiency of gold dredges differs greatly depending on its specifications. 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

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1568-564: The flow of water is a great location to find gold. Gold is very dense and is often found in a stream bed. Many different gold deposits are dealt with in different ways. Placer deposits attract many prospectors because their costs are very low. There are many different places gold could be placed, such as a residual, alluvial, and a bench deposit. Residual deposits are more common where there has been weathering on rocks and where there hasn't been water. They are deposits which have not been washed away yet or been moved. The residual usually lies at

1617-405: The ghost of Joe Bush "Haunting" the dredge when the dredge was not operating due to closure or repair. Three dredges worked the valley from 1913 to 1954. Sumpter No. 3 was built substantially from parts of the first dredge, which had been idle for 10 years. Between them, the dredges traveled more than 8 miles (13 km), extracting $ 10 to 12 million worth of gold. Still, it cost more to run than

1666-424: The giant dredges of the 1930s. 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. 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

1715-535: The gold could pay for. The last dredge closed in 1954, more than $ 100,000 (~$ 900,368 in 2023) in debt. In its lifetime this dredge made $ 4.5 million at $ 35 per troy ounce. That is 128,570 troy ounces which, at the recent value of $ 1,990.00 per ounce, would be worth $ 255,854,300. The Oregon Parks and Recreation Department has preserved this historic area as the Sumpter Valley Dredge State Heritage Area . The park includes

1764-565: The gold fields, material that was carried downstream and raised the level of portions of the Central Valley by some seven feet in affected areas and settled in long bars up to 20 feet thick in parts of San Francisco Bay . The process raised an opposition calling themselves the "Anti-Debris Association". In January 1884, the North Bloomfield Mining and Gravel Company case banned the flushing of debris into streams, and

1813-492: The gold for a large part of the ancient world. Hydraulic mining methods such as hushing were used widely by the Romans across their empire, but especially in the gold fields of northern Spain after its conquest by Augustus in 25 BC. One of the largest sites was at Las Médulas , where seven 30 mile long aqueducts were used to work the alluvial gold deposits through the first century AD. In North America , placer mining

1862-481: The gold has become increasingly depleted in the most easily accessible areas, smaller and more maneuverable dredges have become much more common. These smaller dredges commonly operate by sucking water and gravel up through long hoses using a pump, where the gold can then be separated using more traditional methods such as a sluice box. In areas where the ground is permanently frozen , such as in Siberia, Alaska, and

1911-545: The local lake Carucedo had been heavily silted by the mining methods. Environmental activists describe the hydraulic mining form of placer mining as environmentally destructive because of the large amounts of silt that it adds to previously clear running streams (also known as the "Dahlonega Method"). Most placer mines today use settling ponds , if only to ensure that they have sufficient water to run their sluicing operations. In California, from 1853 to 1884, "hydraulicking" of placers removed an enormous amount of material from

1960-462: The minerals from the ground, and separating it from the non-gold or non-gems. The simplest technique to extract gold from placer ore is panning . This technique has been dated back to at least the Roman Empire. In panning, some mined ore is placed in a large metal or plastic pan, combined with a generous amount of water , and agitated so that the gold particles, being of higher density than

2009-511: The origin word for "place" and "plaza" in English. The word in Spanish is thus derived from placea and refers directly to an alluvial or glacial deposit of sand or gravel. An alternative etymology derives the English word from American Spanish placer (placer, sandbank), from earlier placel , apparently from obsolete Portuguese placel (placer, sandbank). Placers supplied most of

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2058-430: The other material, settle to the bottom of the pan. The lighter gangue material such as sand, mud and gravel are then washed over the side of the pan, leaving the gold behind. Once a placer deposit is located by gold panning, the miner usually shifts to equipment that can treat volumes of sand and gravel more quickly and efficiently. Gold panning was commonly used on its own during the California gold rush ; however, it

2107-403: The process water may be continuously recycled and the ore from which the sought-after minerals have been extracted ("the tailings") can be reclaimed. While these recycling and reclamation processes are more common in modern placer mining operations they are still not universally done. In earlier times the process water was not generally recycled and the spent ore was not reclaimed. The remains of

2156-571: 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). 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 involved gold panning, sluice boxes, and rockers. Each method involves washing sand, gravel and dirt in water. Gold then settles to

2205-453: The site of the lode. This type of deposit undergoes rock weathering. Alluvial or eluvial deposits are the most common type of placer gold, and are often the richest. They contain pieces of gold that have been washed away from the lode by the force of water, and have been deposited in sediment in or near watercourses or former watercourses. Therefore, they are mostly found in valleys or flood plains. Bench deposits are created when gold reaches

2254-549: 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. 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

2303-814: Was famous in the context of several gold rushes , particularly the California Gold Rush and the Colorado Gold Rush , the Fraser Canyon Gold Rush and the Klondike Gold Rush . Placer mining continues in many areas of the world as a source of diamonds, industrial minerals and metals, gems (in Myanmar and Sri Lanka ), platinum, and of gold (in Yukon , Alaska and British Columbia ). An area well protected from

2352-416: Was found at Forest Reefs , also in Australia. If vegetation was buried along with the old stream, by a volcanic eruption, the effect of heat and decay upon that buried vegetation can result in the presence of harmful amounts of carbonic acid gas ( H 2 C O 3 ), as occurred in the deep lead deposit at Creswick. A number of methods are used to mine placer gold and gems, both in terms of extracting

2401-453: Was sifted and sorted, and the remainder was washed over a series of riffles allowing the gold to settle and be trapped. The primary advantages that made the dredge more efficient than other methods were the volume of earth it could process and having its own water supply. The dredge that was built in Sumpter Valley could dig over 20 buckets per minute, consuming more than seven yards of earth each minute. The Sumpter Valley Gold Dredge required

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