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Gold nugget

From Wikipedia, the free encyclopedia
"Gold nugget" may also refer to the catfishBaryancistrus xanthellusor the mango cultivarGold Nugget.
Alaskan gold grains

Agold nuggetis a naturally occurring piece ofnativegold.Watercoursesoften concentrate nuggets and finer gold inplacers.Nuggets are recovered byplacer mining,but they are also found in residual deposits where the gold-bearingveinsorlodesare weathered. Nuggets are also found in thetailingspiles of previous mining operations, especially those left bygold miningdredges.

Formation

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A large gold nugget fromNevada County,California

Nuggets are gold fragments weathered out of an originallode.[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 ofsupergeneformation viain-situprecipitation,cold weldingof 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 ofhypogeneorigin).[2][3]

Other precious metals such asplatinumform nuggets in the same way. A later study of native gold fromArizona,US, based onlead isotopesindicates that a significant part of the mass in alluvial gold nuggets in this area formed within the placer environment.[4]

Composition

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Nuggets are usually 20K to 22K purity (83% to 92% bymass). Gold nuggets inAustraliaoften 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 theirfineness,for example "865 fine" means the nugget is 865 parts per thousand in gold by mass. The common impurities aresilverandcopper.Nuggets high in silver content constitute the alloyelectrum.[5]The chemical composition of supergene gold nuggets can reveal the characteristics of the primary ore.[6]

Largest nuggets

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A large gold nugget from theKuskokwim Mountainsof central Alaska. 6.6 x 2.0 x 1.1 cm. Weight: 77 grams
Main article:List of gold nuggets by size

Two gold nuggets are claimed as the largest in the world: theWelcome Strangerand 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 atMoliagul,Victoria, Australia in 1869 by John Deason and Richard Oates. It weighed gross, over 2,520troy ounces(78 kg; 173 lb) and returned over 2,284 troy ounces (71.0 kg; 156.6 lb) net.[7]The Welcome Stranger is sometimes confused with the similarly namedWelcome Nugget,which was found in June 1858 at Bakery Hill, Ballarat, Australia by the Red Hill Mining Company. The Welcome weighed 2,218troy ounces(69.0 kg; 152.1 lb). It was melted down in London in November 1859.[8]

The Canaã nugget, also known as thePepita Canaa,was found on September 13, 1983, by miners at theSerra PeladaMine in the State of Para, Brazil. Weighing 1,955 troy ounces (60.8 kg; 134.1 lb) gross, and containing 1,682.5 troy ounces (52.33 kg; 115.37 lb) of gold,[9][10]it is among the largest gold nuggets ever found,[11][12]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 5,291.09troy ounces(165 kg; 363 lb) that broke during excavations.[13]TheCanaãnugget is displayed at the Banco Central Museum in Brazil along with the second and third largest nuggets remaining in existence, weighing respectively 1,506.2troy ounces(46.85 kg; 103.28 lb) and 1,393.3troy ounces(43.34 kg; 95.54 lb), which were also found at the Serra Pelada region.[14]

The largest gold nugget found using ametal detectoris theHand of Faith,weighing 875troy ounces(27.2 kg; 60.0 lb), found inKingower,Victoria, Australia in 1980.

Historic large specimens include thecrystalline"Fricot Nugget", weighing 201troy ounces(6.3 kg; 13.8 lb) – the largest one found during theCalifornia Gold Rush.It is on display at theCalifornia State Mining and Mineral Museum.

The largest gold nugget ever found in California weighed 1,593troy ounces(49.5 kg; 109.2 lb). It was found in August 1869 inSierra Buttesby five partners – W.A. Farish, A. Wood, J. Winstead, F.N.L. Clevering and Harry Warner.[15]

TheVictoria, Australia gold rushof the early 1850s produced a number of large nuggets. They include theWelcome Nuggetwhich weighed 68.98kilograms(152.1 lb) which is considered to be the second largest gold nugget ever found.[16][17][18]Another find, the Lady Hotham, which weighed 98.5pounds(44.7 kg), was found by a group of nine miners on September 8, 1854, in Canadian Gully, Ballarat at a depth of 135 feet (41.2 m).[19]The Lady Hotham was named after the wife of the Governor,Sir Charles Hothamwho 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 134pounds(61 kg), 93.125pounds(42.241 kg), and 83.5pounds(37.9 kg) were also found in Canadian Gully at a depth of 55 to 60feet(17 to 18 m).[15][20]Another nugget, the Heron, was found in 1855 in Golden Gully in the Mount Alexander goldfield. It weighed 1,008troy ounces(31.4 kg; 69.1 lb) 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.[21]

On 16 January 2013, a large gold nugget was found near the city ofBallaratin Victoria, Australia by an amateur gold prospector. The Y-shaped nugget weighed slightly more than 5kilograms(11 lb), measured around 22 cm high by 15 cm wide, and has a market value slightly below 300,000Australian dollars,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 thatVictoria's goldfields were exhausted in the 19thcentury.[22][23]

See also

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References

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  1. ^Butt, C. R. M.; Hough, R. M.; Reddy, S. M.; Verrall, M. (August–September 2006)."Origin and weathering of gold nuggets"(PDF).Geochimica et Cosmochimica Acta.70(18): A78.Bibcode:2006GeCAS..70Q..78B.doi:10.1016/j.gca.2006.06.259.RetrievedAugust 18,2012.
  2. ^Gold nuggets reveal their inner secrets,Phys.Org, 2007,retrievedAugust 11,2012
  3. ^Hough, R. M.; Butt, C. R. M.; Reddy, S. M.; Verrall, M. (2007). "Gold nuggets: supergene or hypogene?".Australian Journal of Earth Sciences.54(7): 959–964.Bibcode:2007AuJES..54..959H.doi:10.1080/08120090701488289.
  4. ^Kamenov, G. D.; Melchiorre, E. B.; Ricker, F. N.; DeWitt, E. (2013)."Insights from Pb Isotopes for Native Gold Formation During Hypogene and Supergene Processes at Rich Hill, Arizona".Economic Geology.108(7): 1577–1589.Bibcode:2013EcGeo.108.1577K.doi:10.2113/econgeo.108.7.1577.RetrievedAugust 9,2014.
  5. ^McLaren, J. Malcolm.Gold: Its Geological Occurrence and Geographical Distribution.
  6. ^Horbe, A. M. C., Martins-Ferreira, M. A. C., & Lima, R. S. (2019). Supergene gold characterization by geochemistry, grain morphology and Au-Ag-Cu-Te classification. Journal of South American Earth Sciences, 95, 102315.
  7. ^Dunn, E.J. (1912).Memoirs of the Geological Survey of Victoria.
  8. ^"Famous Australian Nuggets".Australia.RetrievedFebruary 16,2013.
  9. ^Marcello M. Veiga; Stephen M. Metcalf; Randy F. Baker; Bern Klein; Gillian Davis; Andrew Bamber; Shefa Siegel."GMP – Manual for Training Artisanal and Small-Scale Gold Miners".Global Mercury Project.United Nations Industrial Development Organization (UNIDO). Archived fromthe originalon 4 March 2016.Retrieved25 October2014.
  10. ^"Maior pepita de ouro exposta do mundo está em Brasília".Governo do Brasil(in Brazilian Portuguese).Retrieved5 November2017.
  11. ^"Top 5 largest gold nuggets in the world".Arizona. 29 March 2011.RetrievedJanuary 17,2013.
  12. ^"UCSB Science Line".RetrievedJune 22,2013.
  13. ^Branco, P.M. (2008).Dicionário de Mineralogia e Gemologia São Paulo, Oficina de Textos, 608 p. il.
  14. ^Carlos Cornejo & Andrea Bartorelli (2010).Minerals & Precious Stones of Brazil.
  15. ^abHurley, Thomas Jefferson (1900).Famous Gold Nuggets of the World.New York?.
  16. ^"Gold Nuggets – Museum Victoria".Archived fromthe originalon March 17, 2008.Retrieved2013-06-23.
  17. ^"World's Biggest Gold Nuggets".Discovery Channel Australia. Archived fromthe originalon 2013-04-30.Retrieved2013-06-23.
  18. ^"Welcome Nugget: 153 years since discovery".The Courier.Fairfax Regional Media. 9 June 2011.Retrieved2013-06-23.
  19. ^"BALLARAT".Geelong Advertiser and Intelligencer (Vic.: 1851 – 1856).Vic.: National Library of Australia. 12 September 1854. p. 4 Edition: DAILY.Retrieved28 April2013.
  20. ^"MORE LARGE MASSES OF GOLD".Geelong Advertiser and Intelligencer (Vic.: 1851 – 1856).Vic.: National Library of Australia. 8 February 1853. p. 1 Edition: DAILY., Supplement: SUPPLEMENT TO THE GEELONG ADVERTISER AND INTELLIGENCER.Retrieved28 April2013.
  21. ^"Historical Finds and Discoveries".Australia. Archived fromthe originalon February 22, 2010.RetrievedFebruary 17,2013.
  22. ^Gold nugget found near Ballarat
  23. ^Sky News, Gold Find: Novice Prospector Earns Big Bucks, 17 January 2013
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