<P> Nuggets are gold fragments weathered out of an original lode . 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 origin). Other precious metals such as platinum form nuggets in the same way . A later study of native gold from Arizona, 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 . </P> <P> Nuggets are usually 20.5 K to 22K purity (83% to 92%). 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, for example "865 fine" means the nugget is 865 parts per thousand in gold . The common impurities are silver and copper . Nuggets high in silver content constitute the alloy electrum . </P> <P> In literature, there are two nuggets that claim their status as the biggest gold nuggets in the world: the Welcome Stranger with the Canaã nugget 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 2,520 troy ounces (78 kg; 173 lb) and returned over 2,284 troy ounces (71.0 kg; 156.6 lb) 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 2,218 troy ounces (69.0 kg; 152.1 lb). It was melted down in London in November 1859 . </P> <P> 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 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, 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 5,291.09 troy ounces (165 kg; 363 lb) 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 1,506.2 troy ounces (46.85 kg; 103.28 lb) and 1,393.3 troy ounces (43.34 kg; 95.54 lb), which were also found at the Serra Pelada region . </P>

Where was the biggest gold nugget ever found