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38-570: It starts at kilometre 586, at the sluice of Geesthacht , where the Elbe forms the border between Lower Saxony and Schleswig-Holstein . It continues downstream, then forming the border between Lower Saxony and Hamburg , before fully entering Hamburg territory. In Hamburg the Unterelbe forms two anabranches , Norderelbe and Süderelbe , the latter now partially a cut-off meander. Where Norderelbe and Süderelbe used to reunite, at kilometre 634 there

76-529: 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

114-745: A carpet or rubber matting, which trap the heavy minerals, gemstones, and other valuable minerals. Since the early 2000s more miners and prospectors are relying on more modern and effective matting systems. The result is a concentrate which requires additional processing. In the Somerset Levels , sluice gates are known as clyse or clyce. Most of the inhabitants of Guyana refer to sluices as kokers. The Sinhala people in Sri Lanka, who had an ancient civilization based on harvested rain water, refer to sluices as Horovuwa. Placer mining#Sluice box Placer mining ( / ˈ p l æ s ər / )

152-416: 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

190-407: 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

228-552: A simple, hand-operated, chain pulled/lowered, worm drive or rack-and-pinion drive , or it may be electrically or hydraulically powered. A flap sluice, however, operates automatically, without external intervention or inputs. Sluice gates are one of the most common hydraulic structures used to control or measure the flow in open channels. Vertical rising sluice gates are the most common in open channels and can operate under two flow regimes: free flow and submerged flow. The most important depths in designing of sluice gates are: In

266-481: 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

304-443: 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

342-423: 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

380-799: 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

418-495: 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

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456-460: 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

494-405: Is a stub . You can help Misplaced Pages by expanding it . Sluice A sluice ( / s l u s / SLOOS ) is a water channel containing a sluice gate , a type of lock to manage the water flow and water level. It can also be an open channel which processes material, such as a river sluice used in gold prospecting or fossicking . A mill race , leet , flume , penstock or lade

532-753: Is a bay called the Mühlenberger Loch  [ de ; nds ] . This marks the beginning of the section of the Unterelbe which called the Niederelbe . After leaving Hamburg it forms the border between Lower Saxony and Schleswig-Holstein, again. The end it defined by the Kugelbake in Cuxhaven at kilometre 727.73. It continues further into the Wadden Sea as the Außenelbe , where it passes

570-429: Is a sluice channeling water toward a water mill . The terms sluice , sluice gate , knife gate , and slide gate are used interchangeably in the water and wastewater control industry. "Sluice gate" refers to a movable gate allowing water to flow under it. When a sluice is lowered, water may spill over the top, in which case the gate operates as a weir . Usually, a mechanism drives the sluice up or down. This may be

608-413: 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,

646-446: 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

684-466: 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)

722-624: 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

760-495: 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

798-502: 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

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836-485: 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

874-590: The Hamburg islands Scharhörn and Nigehörn . 53°36′N 9°35′E  /  53.600°N 9.583°E  / 53.600; 9.583 This Hamburg location article is a stub . You can help Misplaced Pages by expanding it . This article related to a river in Lower Saxony is a stub . You can help Misplaced Pages by expanding it . This article related to a river in Schleswig-Holstein

912-462: 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,

950-564: 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

988-565: 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

1026-492: 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

1064-481: 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

1102-545: 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

1140-462: 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

1178-464: The mountains of the United States, sluices transported logs from steep hillsides to downslope sawmill ponds or yarding areas. Nineteenth-century logging was traditionally a winter activity for men who spent summers working on farms. Where there were freezing nights, water might be applied to logging sluices every night so a fresh coating of slippery ice would reduce friction of logs placed in

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1216-511: 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

1254-430: 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

1292-403: 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

1330-453: 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

1368-416: The sluice the following morning. Sluice boxes are often used in the recovery of black sands , gold , and other minerals from placer deposits during placer mining operations. They may be small-scale, as used in prospecting , or much larger, as in commercial operations, where the material is sometimes screened using a trommel , screening plant or sieve. Traditional sluices have transverse riffles over

1406-814: 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

1444-416: 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

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