Talk:Gold nugget

Formation

How do they form? — Omegatron 01:15, 26 June 2007 (UTC)

I think that's a great question, from 8 years ago, and still unanswered. The descriptions in the article are quite vague. David Spector (talk) 21:25, 12 March 2015 (UTC)

Holtermann Nugget

I think this needs a mention of why the Holtermann Nugget is not regarded as a nugget, since it weighed far more than the Welcome Stranger. --Ozhiker (talk) 08:06, 24 September 2009 (UTC)

Nuggets formed by cold welding?

Someone added this assertion, which needs a good cite. I've heard this claimed, but my guess it's rare to nonexistent. Nuggets (ime) are simply masses of native gold that get washed into streams and get rounded off, and you see them in all stages from near-pristine to gold dust. On average they get broken up as they get further downstream (ime). --Pete Tillman (talk) 23:48, 28 October 2010 (UTC), gold geologist

Cold welding is well attested in the literature, and indeed used in various manufacturing processes for gold. Here are a few refs from the web:

http://books.google.co.uk/books?hl=en&lr=&id=5D2RVNM0TAQC&oi=fnd&pg=PA243&dq=gold+nugget+formation+cold+welding&ots=F16cpqd-OE&sig=rDyb6KMlxjUPAYI3Q52rjttph3U#v=onepage&q&f=false

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6X-4037XGG-F&_user=10&_coverDate=02%2F28%2F1995&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1518853972&_rerunOrigin=scholar.google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=5b913c0d82a8fbc980fd166053fc7fce&searchtype=a

Peterlewis (talk) 08:41, 29 October 2010 (UTC)

Thanks for the interesting refs. Your first (book) is about (sort-of) cold welding in early "sintering" of gold jewelry (etc) and had no mention of nugget formation that I saw. The second is applicable, but this is the idea that native gold "grows together" in the soil horizon under the influence of humic acids. Which might be worth mention, as it's an old idea that has some support.

If you find a ref for actual "cold-welding" during stream transport, I'd be interested to see it. The idea of cold-welding in a stream, with all surfaces thoroughly wetted, seems implausible to me. Thanks, Pete Tillman (talk) 19:25, 29 October 2010 (UTC)

Well, try this ref from Mongolia for a pic of a cold welded nugget

http://www.mine.mn/gold_nuggets.htm

Peterlewis (talk) 19:45, 29 October 2010 (UTC)

If you mean the bucket-line specimen, described as "battered and smoothed in the river, and consists of gold in cracks in faulted quartzite rock." -- this looks to me like native Au in a qtz vein - infact, I saw a "fresh" spl that looked (ims) much like this, from the Las Guijas district in S AZ, where the vein qtz (for some reason) was granular-appearing. A guy found it with a metal detector -- this would have been in the early 1980s, I think. Handsome piece -- I saw it at the Tucson Show, where the owner was asking mucho $$$$. But keep looking -- I'd look in my files for humate-stuff, but they're in AZ & I'm in NM for 2 weeks.

But do think about the difficulty of cold-welding 2 pieces of Au in a creek, when they're both covered with a biofilm -- I did some research on these for my MS, the films are pretty much ubiquitous -- though I don't recall about the Arctic. Cold there ;-] Not saying it's impossible, but.... Best, Pete Tillman (talk) 18:11, 30 October 2010 (UTC), Consulting Geologist, Arizona and New Mexico (USA)

Ah, I just saw ref to Lange, Ian M.; and Tom Gignoux (1999). Distribution, characteristics, and genesis of high fineness gold placers, Ninemile Valley, central-western Montana. Economic Geology, volume 94, pages 375-386. Abstract. Worth a look? --Pete Tillman (talk) 18:14, 30 October 2010 (UTC)

And maybe I'm wrong about the biofilms, see Nanoparticle factories: Biofilms hold the key to gold dispersion and nugget formation, Geology; September 2010; v. 38; no. 9; p. 843-846; DOI: 10.1130/G31052.1 Abstract.

This study demonstrates that (1) microbially driven dissolution, precipitation, and aggregation lead to the formation of bacterioform Au and contribute to the growth of Au grains under supergene conditions, and (2) the microbially driven mobilization of coarse Au into nanoparticles plays a key role in mediating the mobility of Au in surface environments, because the release of nanoparticulate Au upon biofilm disintegration greatly enhances environmental mobility compared to Au complexes only.

And here it is in English [1]:

THE GIST

   * For the first time microbes have been shown to tinker with gold deposits.
   * Bacterial biofilms dissolve gold, which makes it available for re-depositing in purer form elsewhere. 

and [2]

It sounds like the bacterial bio-films dissolve the gold into nanoparticles and redeposit them as grains that can be purer than the original source. News reports describe it as a way of growing nuggets.

And [3]

Frank Reith of the University of Adelaide and colleagues demonstrate that bacterial biofilms play a key role in mediating the environmental dispersion of gold via the formation of nanoparticles. By using state-of-the-art microanalysis techniques, they are also able to elucidate the fundamental mechanism leading to the growth of gold nuggets under Earth surface conditions.

So if you want to use this as a source -- we'll need to change the text to agree. See what you think. Best, Pete Tillman (talk) 19:55, 30 October 2010 (UTC)

I know bacteria play a key role in oxidising pyrites in gold mines, but bacterial films on gold? And by what chemical mechanism do the bateria (what species by the way?) react with the very corrosion resistant gold?? Peterlewis (talk) 22:13, 30 October 2010 (UTC)

This unsourced speculation about particles welding together in streams shouldn't be in the article. It might happen with 100% pure, dry, clean gold, or in a goldsmith shop under a hammer blow, but it's not likely to be common underwater. Where there's, you know, *water* in between the surfaces. Not to mention copper/silver sulfide partial tarnish films due to the alloyed metals.Rep07 (talk) 04:08, 12 August 2012 (UTC)

Value beyond gold content?

Are such nuggets valued for significantly more than the gold present, as collectors' items due to their rarity? If so, are there any available examples of the sort of prices large nuggets have sold for?--Jrm2007 (talk) 07:19, 25 December 2010 (UTC)

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Formation from bacterial concentration - Inconsistent between pages

This page states A 2007 study on Australian nuggets ruled out ... bacterial concentration, since crystal structures of all of the nuggets examined proved they were originally formed at high temperature deep underground.

But the page for the bacteria Cupriavidus metallidurans states that it is essential (alongside Delftia acidovorans) in the formation of gold nuggets. Am I missing something here, or are these pages contradicting each other? 192.77.12.11 (talk) 07:55, 30 October 2023 (UTC)