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:''"Gold nugget" may also refer to the catfish Baryancistrus xanthellus or the mango cultivar Gold Nugget.'' A gold nugget is a naturally occurring piece of native gold.
Watercourse A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams a ...
s often concentrate nuggets and finer gold in placers. Nuggets are recovered by placer mining, but they are also found in residual deposits where the gold-bearing veins or
lode In geology, a lode is a deposit of metalliferous ore that fills or is embedded in a fissure (or crack) in a rock formation or a vein of ore that is deposited or embedded between layers of rock. The current meaning (ore vein) dates from the 1 ...
s are weathered. Nuggets are also found in the
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 overli ...
piles of previous mining operations, especially those left by
gold mining Gold mining is the extraction of gold resources by mining. Historically, mining gold from alluvial deposits used manual separation processes, such as gold panning. However, with the expansion of gold mining to ores that are not on the surface, ...
dredges.


Formation

Nuggets are gold fragments weathered out of an original
lode In geology, a lode is a deposit of metalliferous ore that fills or is embedded in a fissure (or crack) in a rock formation or a vein of ore that is deposited or embedded between layers of rock. The current meaning (ore vein) dates from the 1 ...
. They often show signs of abrasive polishing by stream action, and sometimes still contain inclusions of quartz or other lode matrix material. A 2007 study on Australian nuggets ruled out speculative theories of supergene formation via in-situ precipitation, cold welding of smaller particles, or bacterial concentration, since crystal structures of all of the nuggets examined proved they were originally formed at high temperature deep underground (i.e., they were of
hypogene In ore deposit geology, hypogene processes occur deep below the earth's surface, and tend to form deposits of primary minerals, as opposed to supergene processes that occur at or near the surface, and tend to form secondary minerals. At great dept ...
origin). Other precious metals such as
platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...
form nuggets in the same way. A later study of native gold from
Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
, US, based on lead isotopes indicates that a significant part of the mass in alluvial gold nuggets in this area formed within the placer environment.


Composition

Nuggets are usually 20K to 22K purity (83% to 92% by
mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different eleme ...
). Gold nuggets in Australia often are 23K or slightly higher, while Alaskan nuggets are usually at the lower end of the spectrum. Purity can be roughly assessed by the nugget color, the richer and deeper the orange-yellow the higher the gold content. Nuggets are also referred to by their
fineness The fineness of a precious metal object (coin, bar, jewelry, etc.) represents the weight of ''fine metal'' therein, in proportion to the total weight which includes alloying base metals and any impurities. Alloy metals are added to increase hardne ...
, for example "865 fine" means the nugget is 865 parts per thousand in gold by mass. The common impurities are
silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
and
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
. Nuggets high in silver content constitute the alloy
electrum Electrum is a naturally occurring alloy of gold and silver, with trace amounts of copper and other metals. Its color ranges from pale to bright yellow, depending on the proportions of gold and silver. It has been produced artificially, and ...
. The chemical composition of supergene gold nuggets can reveal the characteristics of the primary ore.


Largest nuggets

Two gold nuggets are claimed as the largest in the world: the
Welcome Stranger The Welcome Stranger is the biggest alluvial gold nugget that has ever been found, which had a calculated refined weight of .Potter, Terry F. (1999) ''The Welcome Stranger: a definitive account of the worlds largest alluvial gold nugget''. I ...
and the Canaã nugget, the latter being the largest surviving natural nugget. Considered by most authorities to be the biggest gold nugget ever found, the Welcome Stranger was found at Moliagul, Victoria, Australia in 1869 by John Deason and Richard Oates. It weighed gross, over and returned over net. The Welcome Stranger is sometimes confused with the similarly named Welcome Nugget, which was found in June 1858 at Bakery Hill, Ballarat, Australia by the Red Hill Mining Company. The Welcome weighed . It was melted down in London in November 1859. The Canaã nugget, also known as the ''Pepita Canaa'', was found on September 13, 1983 by miners at the Serra Pelada Mine in the State of Para, Brazil. Weighing gross, and containing of gold, it is among the largest gold nuggets ever found, and is, today, the largest in existence. The main controversy regarding this nugget is that the excavation reports suggest that the existing nugget was originally part of a nugget weighing that broke during excavations. The Canaã nugget is displayed at the Banco Central Museum in Brazil along with the second and third largest nuggets remaining in existence, weighing respectively and , which were also found at the Serra Pelada region. The largest gold nugget found using a
metal detector A metal detector is an instrument that detects the nearby presence of metal. Metal detectors are useful for finding metal objects on the surface, underground, and under water. The unit itself, consist of a control box, and an adjustable shaft, ...
is the Hand of Faith, weighing , found in Kingower, Victoria, Australia in 1980. Historic large specimens include the
crystalline A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...
"Fricot Nugget", weighing – the largest one found during the California Gold Rush. It is on display at the California State Mining and Mineral Museum. The largest gold nugget ever found in California weighed . It was found in August 1869 in Sierra Buttes by five partners – W.A. Farish, A. Wood, J. Winstead, F.N.L. Clevering and Harry Warner. The Victoria, Australia gold rush of the early 1850s produced a number of large nuggets. They include the Welcome Nugget which weighed which is considered to be the second largest gold nugget ever found. Another find, the Lady Hotham, which weighed , was found by a group of nine miners on September 8, 1854 in Canadian Gully, Ballarat at a depth of 135 feet. The Lady Hotham was named after the wife of the Governor,
Sir Charles Hotham Sir Charles Hotham, KCB, RN (14 January 180631 December 1855)B. A. Knox,Hotham, Sir Charles (1806–1855), ''Australian Dictionary of Biography'', Volume 4, MUP, 1972, pp 429-430. was Lieutenant-Governor and, later, Governor of Victoria, A ...
who happened to be visiting the area when the nugget was found. Eighteen months earlier, in January and early February 1853, three other large nuggets weighing , , and were also found in Canadian Gully at a depth of . Another nugget, the Heron, was found in 1855 in Golden Gully in the Mount Alexander goldfield. It weighed and was found by a group of inexperienced miners who had received a supposedly empty claim. The miners found the nugget on their second day of digging; the nugget was named after one of the gold commissioners, a Mr. Heron. On 16 January 2013, a large gold nugget was found near the city of Ballarat in Victoria, Australia by an amateur gold prospector. The Y-shaped nugget weighed slightly more than , measured around 22 cm high by 15 cm wide, and has a market value slightly below 300,000
Australian dollar The Australian dollar ( sign: $; code: AUD) is the currency of Australia, including its external territories: Christmas Island, Cocos (Keeling) Islands, and Norfolk Island. It is officially used as currency by three independent Pacific Isl ...
s, though opinions have been expressed that it could be sold for much more due to its rarity. The discovery has cast doubt on the common rumour that
Victoria Victoria most commonly refers to: * Victoria (Australia), a state of the Commonwealth of Australia * Victoria, British Columbia, provincial capital of British Columbia, Canada * Victoria (mythology), Roman goddess of Victory * Victoria, Seychelle ...
's goldfields were exhausted in the 19th century.Sky News, Gold Find: Novice Prospector Earns Big Bucks, 17 January 2013
/ref>


See also

*
Gold mining Gold mining is the extraction of gold resources by mining. Historically, mining gold from alluvial deposits used manual separation processes, such as gold panning. However, with the expansion of gold mining to ores that are not on the surface, ...
*
Gold prospecting Gold prospecting is the act of searching for new gold deposits. Methods used vary with the type of deposit sought and the resources of the prospector. Although traditionally a commercial activity, in some developed countries placer gold prospe ...
*
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 ...
* Beyers-Holtermann Specimen, the largest specimen of native gold ever found. Essentially reef gold thus with quartz and therefore not a nugget (which is typically alluvial gold). It contained approx. 3000 troy oz of gold, thus 25% more gold than the largest nugget. * Latrobe nugget * Nugget (coin) *
Rocker box A rocker box (also known as a cradle) is a gold mining implement for separating alluvial placer gold from sand and gravel which was used in placer mining in the 19th century. It consists of a high-sided box, which is open on one end and on top ...


References

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