![]() ![]() Nuggets are usually 20.5K to 22K purity (83% to 92% by mass). 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. ![]() Other precious metals such as platinum form nuggets in the same way. 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). They often show signs of abrasive polishing by stream action, and sometimes still contain inclusions of quartz or other lode matrix material. Nuggets are gold fragments weathered out of an original lode. ![]()
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