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64-578: The Waikato North Head ironsand mine, just south of the settlement, produces up to 1.2 million tonnes of ironsand a year, for use in the New Zealand Steel mill at Glenbrook . The deposit is estimated to contain more than 150 million tonnes in total. The ironsand is processed on-site with a series of separation processes with river water, before the slurry is pumped to the Glenbrook mill through an 18-kilometre underground pipe. The name Otaua

128-529: 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

192-416: 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

256-407: 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

320-465: A modest pavilion that was replaced in 1963. The bowling green entrance is an arch, with a granite memorial plaque reading: In loving memory of the men of the district who fell in two world wars 1914–18 ― 1939–45. W. C. Motion was the son of William Motion . After moving to Otaua in the 1890s he became a Justice of the Peace and active member of the community. Motion served as chairman of

384-481: 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

448-443: 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

512-423: 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

576-799: 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

640-495: 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

704-460: 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

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768-511: Is a contraction of Te Takanga-o-Tauaiwi , a reference to the falling of Tauaiwi, a descendant of Hotonui of the Tainui waka. Tauiwi was killed at Otaua by Tāmaki Māori and his body fell into a disused pit. In the mid-1700s, the area was settled by Ngāti Te Ata , an iwi formed by the marriage of Te Atairehia of Te Wai-o-Hua , and Tapaue, a Tainui warrior. The coast alongside the Tasman Sea

832-527: Is a type of sand with heavy concentrations of iron . It is typically dark grey or blackish in color. It is composed mainly of magnetite , Fe 3 O 4 , and also contains small amounts of titanium, silica, manganese, calcium and vanadium. Ironsand has a tendency to heat up in direct sunlight , causing temperatures high enough to cause minor burns. As such it forms a hazard in New Zealand at popular west-coast surf beaches such as Piha . Ironsand

896-413: 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,

960-568: Is found many places in Europe, although it was rarely used for smelting. It is often found in association with volcanic or basaltic sands. For example, it is found in Tenerife , Spain , where the magnetite grains contain a very high amount of titanium and other impurities. The typical composition is 79.2% iron oxide, 14.6% titanium dioxide, 1.6% manganese oxide , 0.8% silica and aluminum oxide , and trace amounts of chromium . It can also be found in

1024-529: Is found mixed with quartz sand that washes down from granite mountains. The magnetite in the sand contains few impurities or other metal oxides. Masa ironsand was used for manufacturing wrought iron and steel , used in everything from tools to cookware. Ironsand was used extensively in Japan for iron production, especially for traditional Japanese swords . Akome ironsand is found mixed with sand made from an igneous rock called diorite . The magnetite in

1088-467: Is found worldwide. Although the iron mineral composition of the ironsand is mostly magnetite, the sand is usually mixed with other types of sand that wash downriver or ashore from mountainous or underwater deposits. The exact composition of the sand mixture may vary drastically even in the same geographic region. In some areas the sand may contain mostly quartz , while in others the sand may be made primarily from volcanic rock such as basalt , depending on

1152-446: 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

1216-466: 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)

1280-624: 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

1344-503: Is sometimes referred to as titanomagnetite. It was produced from volcanic eruptions that occurred in the Pleistocene epoch , and is formed due to the oceanic erosion of the volcanic rock which is washed ashore by the waves to form the dunes of the black beaches. The magnetite is mixed with sand made from andesite and rhyolite . The sand mixture typically contains 5 to 40% magnetite. New Zealand had limited deposits of iron ore, but

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1408-619: Is still practiced by Japanese craftsmen today. Sluice box Placer mining ( / ˈ p l æ s ər / ) 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

1472-495: 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

1536-485: 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

1600-536: The Great Lakes , where it is often mixed with a feldspar sand and sometimes bright grains of garnet . The magnetite from these areas often contains high amounts of chromium and titanium. In the 19th century ironsand was sometimes used as blotter sand for concrete and masonry work, or more rarely as raw material for steel production; one blacksmith in Connecticut used it for making bar stock . According to

1664-562: The OED online entry for sand-iron , Jedidiah Morse (1761–1826), writing in The American universal geography (new edition, 1796 (2 vols)), stated that Jared Eliot (1685-1763) invented sand-iron, or the making of iron from black sand , in 1761. However, Japanese craftsmen have been using sand-iron, known as " tamahagane ", in sword-making for at least 1200 years. The crafting of sand-iron in " tatara " smelters, made of brick and clay,

1728-609: The River Dee , in Aberdeenshire, Scotland , containing 85.3% iron oxide, 9.5% titanium dioxide, 1.0% arsenic , and 1.5% silica and aluminum oxide. Ironsand occurs extensively on the west coast of New Zealand 's North Island . The sand makes up a large portion of the black-sand beaches on the North Island, as well as the surrounding sea floor. The magnetite in the sand contains fairly large quantities of titanium, and

1792-511: The 11th century and the 19th century, when a European miner named Felix Tegengren arrived to find the Chinese industry in shambles. Tegengren notes that ironsand was sluice mined in Henan and Fujian by local farmers and smelted over charcoal fires to make tools, but it involved a lot of work, which made it very expensive. It was only smelted where there was enough wood for the fires and cheaper steel

1856-564: The 8th century, iron-making technology developed with the use of ironsand ( satetsu ) as the raw ingredient. Because of the loose nature of the sand it was difficult to smelt in a normal bloomery , or to use in a blast furnace to make pig iron , so the Japanese developed an open-topped bloomery called a tatara . The tatara was built with a low, tub-like shape, resembling a horizontal blast-furnace, into which ironsand could be poured and contained, and smelted in stages. Unlike with other methods,

1920-850: The Otaua school committee, member of the Waipipi Road Board, director of the New Zealand Dairy Association , and a member of the Franklin County Council for the riding of Waipipi. Otaua School is a co-educational state primary school for Year 1 to 8 students, with a roll of 206 as of August 2024. The school opened in 1895 and held centennial celebrations in 1995. 37°18′23″S 174°44′27″E  /  37.306397°S 174.740826°E  / -37.306397; 174.740826 Ironsand Ironsand , also known as iron-sand or iron sand ,

1984-462: 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,

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2048-415: The charcoal was piled on top of the sand and smelted from above, keeping it from being blown about by the blasts from the bellows . Instead of brick or stone, the tatara was made of clay so that it could simply be broken apart to extract the metal bloom. This method allowed smelting of much higher volumes of ore than other types of bloomery smelting. The ironsand in Japan comes in two forms. Masa ironsand

2112-414: The coast of Taranaki faced resistance from some Māori and others in 2005 in the wake of the New Zealand foreshore and seabed controversy . A large quantity of it is shipped to China and Japan, but by 2011 New Zealand's sole manufacturing plant was producing 650,000 metric tons of steel and iron per year. New Zealand is the only country to use ironsand for industrial smelting. The typical composition of

2176-426: The deposits of ironsand were massive. It had been used by some early settlers to manufacture steel and pig iron, but the material could not be smelted in common bloomeries or blast furnaces. A few smelting companies formed in the late 19th and early 20th centuries, but were unable to process the ore with any economic success due to the sandy nature and high titanium content, which tended to form hard, brittle carbides in

2240-564: 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

2304-565: 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

2368-492: 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

2432-481: 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

2496-516: The history of ironsand in China end with inconclusive results. One source may indicate its use as early as the Tang Dynasty (~700-900 AD) while others seem to contradict this interpretation. Due to wars, invasions, famines, distrust of the government, overpopulation, a rising opium epidemic, and clashes between various tongs of miners, very little information exists about the industry between

2560-468: The late 1960s, producing the first output of steel in 1969. Ironsand is placer mined from Waikato North Head. 1.2 million tonnes is used by New Zealand Steel to create steel , in a unique manufacturing process. Mining at Taharoa produces up to 4 million tonnes for export. A previous mine existed at Waipipi in South Taranaki. A proposal by Iron Ore NZ Ltd. for further ironsand mining off

2624-545: 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

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2688-501: The loose, granular nature of the ore was difficult to keep contained in common bloomeries or blast furnaces, having a tendency toward granular flow (mimicking a liquid at larger scales) and was easily blown away by the bellow blasts, so was impossible to process using common methods of iron or steel production. Thus, innovative methods of smelting the ore were developed. The magnetite grains, however, often contain other metal impurities, such as chromium , arsenic , or titanium . Due to

2752-447: The magnetite is 82% iron oxide , 8% titanium dioxide and 8% silica ; 0.015% sulfur , and 0.015% phosphorus . In 100% concentrations of magnetite this had a maximum potential to yield ~ 58% metallic iron, although the titanium is unrecoverable by modern techniques. Ironsand is found extensively around the US, especially in the area of New York , Southern California , New England , and

2816-560: The manufacture of swords and weapons, and a chemical process of rapidly decarburizing liquid pig-iron to make wrought iron, using the oxidation properties of saltpeter (called the Heaton process , it was independently discovered by John Heaton in the 1860s). China remained the world's largest producer of iron until the 11th century, manufacturing large quantities of relatively affordable steel and iron. Donald B Wagner, an expert in ancient Chinese metallurgy, notes that attempts to trace

2880-462: 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

2944-586: The modern age ironsand is placer mined along China's southeast coast and used for smelting steel. The typical composition of this ironsand is 48.88% metallic iron, 25.84% silica, 0.232% phosphorus, and 0.052% sulfur. In Indonesia, iron sand is prevalent on the south coast of Java island . Large scale mining was not practiced in Japan until the 7th or 8th centuries. Prior to this, metals were commonly imported into Japan from China and Korea. Deposits of iron ore are thought to have been scarce in Japan, so, around

3008-470: The nature of the sand the mining operations were rarely stationary, but frequently moved from place to place. Historically, ironsand was predominantly used in East Asian cultures; most notably in China and Japan. Ironsand had moderate, localized uses in China during the late Industrial Revolution , but was a rather unimportant commodity throughout the long history of the Chinese iron-industry. Unlike

3072-511: 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

3136-430: 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

3200-403: 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

3264-409: The rest of Eurasia and Africa , there is very little archeological evidence to suggest that bloomery smelting was used in ancient China . The Chinese countryside was rich in deposits that contained both coal , a fuel that burns at a high temperature, and an iron ore containing a high content of phosphorus . Around 1200 BC the Chinese developed a method of smelting the rocky ore into pig iron, which

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3328-413: The sand contains often greater than 5% titanium dioxide , which lowers the smelting temperature. The akome ironsand is used in the tatara to make pig iron, which is then used to make items out of cast iron ( nabegane ). In the manufacture of steel, the akome was added to the tatara during the initial stage of smelting, acting as a binder and catalyst for steel production, upon which the masa ironsand

3392-453: 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

3456-408: The steel. In 1939, a commission was formed to study the properties of the ore and devise a way of smelting it on an industrial scale. The commission determined that, by sintering the sand into bigger chunks or pellets, the problems of smelting the sand in a blast furnace could be eliminated. However, at that time World War II began, and thus further development was suspended and did not resume until

3520-416: The types of minerals along the water's path. The ironsand is typically picked up along the way from beds, veins, or inclusions of magnetite, which may originate a great distance from the sand deposits, and washed downstream or along the currents with the rest of the sand. Being heavier than the other sands, it is often deposited in areas where the water experiences a sudden change in direction or speed, such as

3584-413: The widening of a river or where the waves ebb and flow against the shoreline. The ironsand is mixed with the other sands as small grains of black or dark-blue magnetite. Sand used for mining typically had anywhere from 19% magnetite to as low as 2%. The ironsand typically had to be separated from the sand mixture. Because the magnetite is usually heavier than quartz, feldspar, or other minerals, separation

3648-814: 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

3712-416: 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

3776-448: Was not readily available. Therefore, the material was considered to be economically unimportant in China. However, because the mining was safe, outdoor work, it was practiced by local farmers to supplement their income wherever it was available; in the 19th century 1,000 lb (450 kg) of sluiced sand typically sold for the equivalent of 50 to 60 US dollars (by 2016 exchange rates ~ 900--1000 dollars or 700--800 euros). However, in

3840-628: Was poured during further stages. When smelted for pig iron, 1,000 lb (450 kg) or 120 kanme ) typically yielded about 200 lb (91 kg) of pig iron, 20 lb (9.1 kg) of steel, and 70 lb (32 kg) of slag. When smelted for steel, 1,000 lb (450 kg) of sand yielded about 100 lb (45 kg) of steel, 100 lb (45 kg) of slag, and 90 lb (41 kg) of pig iron. Slag and pig iron that were not suitable for use were then melted together to form wrought iron, of which 1,000 lb (450 kg) mixed produced about 500 lb (230 kg) of iron. Ironsand

3904-520: Was settled by Ngāti Kahukōkā. Maioro, south-west of Otaua near the shoreline, is the site of a Ngāti Kahukōkā pā . The pā was first settled in the 1200s, becoming fortified with palisades in the 1400s and 1500s. Otaua developed into a European farming settlement in the 1890s, with a school opening in 1895. The 360m² Otaua community hall was built in 1898. It has since been extensively renovated with modern fittings, and now features an outdoor deck area and tennis courts. Otaua Second World War Roll of Honour

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3968-451: Was then remelted and poured into molds ( cast ) to form cast iron. Although the metal was very brittle, this method was able to produce iron in much greater volumes than bloomery smelting, and with vastly higher yields of metal per ore. By the 1st century BC the Chinese iron-industry was by far the largest and most advanced in the world. By the 1st century AD they had developed puddling for the production of mild steel , crucible steel for

4032-648: Was unveiled on the hall on 21 September 1946, commemorating the 43 local residents who had served in the war, including three who had died. Several Otaua servicemen from both wars are also listed in the Waiuku War Memorial Hall, including three who aren't included in the Otaua Roll of Honour. On 20 November 1954, the Otaua District War Memorial Bowling Green was formally opened across the road. It features

4096-472: Was usually done by washing it in sluice boxes (a method similar to gold panning but on a larger scale). Sluice separation typically yielded concentrations of magnetite ranging from 30 to 50%, depending on the type of sand and the method used. In the early 20th century a process of magnetic separation was developed that could produce concentrations as high as 70%. Once concentrated, the magnetite grains could then be smelted into various forms of iron. However,

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