Editing Gold nugget (section)

==Formation==
[[File:GoldNugget.jpg|thumb|upright|A large gold nugget from [[Nevada County, California|Nevada County]], California, on display at the [[National Museum of Natural History]] in [[Washington, D.C.]]]]
Nuggets are gold fragments weathered out of an original [[lode]].<ref>{{Cite journal |last=Butt |first= C. R. M. |author2=Hough, R. M. |author3=Reddy, S. M. |author4= Verrall, M. |title=Origin and weathering of gold nuggets |journal=Geochimica et Cosmochimica Acta |volume=70 |issue=18 |pages=A78 |date=August–September 2006 |url=http://crcleme.org.au/Pubs/Articles%20and%20papers/Goldsmidt_butt01004.pdf |doi=10.1016/j.gca.2006.06.259 |bibcode= 2006GeCAS..70Q..78B |access-date=August 18, 2012}}</ref> 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 (geology)|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 (geology)|hypogene]] origin).<ref>{{citation |year=2007 |title=Gold nuggets reveal their inner secrets |publisher=Phys.Org |url=http://phys.org/news111763640.html |access-date=August 11, 2012}}</ref><ref>{{Cite journal |last=Hough |first=R. M. |author2=Butt, C. R. M. |author3=Reddy, S. M. |author4= Verrall, M.  |title=Gold nuggets: supergene or hypogene? |journal=Australian Journal of Earth Sciences |volume=54 |issue=7 |pages=959–964 |year=2007 |doi=10.1080/08120090701488289 |bibcode=2007AuJES..54..959H }}</ref>

Other precious metals such as [[platinum]] form nuggets in the same way. A later study of native gold from [[Arizona]], based on [[Lead#Isotopes|lead isotopes]] indicates that a significant part of the mass in alluvial gold nuggets in this area formed within the placer environment.<ref>{{cite journal |last=Kamenov|first=G. D. |author2=Melchiorre, E. B. |author3=Ricker, F. N. |author4=DeWitt, E. |title=Insights from Pb Isotopes for Native Gold Formation During Hypogene and Supergene Processes at Rich Hill, Arizona |journal=Economic Geology |volume=108|issue=7 |pages=1577–1589|year=2013 |url=http://econgeol.geoscienceworld.org/content/108/7/1577.abstract |doi=10.2113/econgeo.108.7.1577 |bibcode=2013EcGeo.108.1577K |access-date=August 9, 2014|url-access=subscription }}</ref>