<blockquote>
<p>, it gets eroded. But what puts it back together? It's not like gold is magnetic and attracts itself
It doesn't need to attract itself - being &quot;tumbled&quot; down stream will at some point result in one gold grain being on the bottom of the stream, on a larger rock [anything] grain, then a second gold grain (&quot;flake&quot;, even) being dropped on top of it, then a third [anything] grain landing on the two and impact-welding them together.
Gold (native silver, native copper too) is malleable ; most rock-forming minerals aren't.
The concentration of gold into particular layers (mm-scale and smaller) in the stream sediment may promote a similar aggregation process by shear when the sediment fails and slumps down-slope.</p>
</blockquote>
<p>When you're talking about alluvial gold (which seems to be the context of your question), it is normally distributed down-slope from the outcrop of the ore, then once it reaches the bottom of a local gulley, down-stream from there. That doesn't happen in &quot;one mighty leap&quot;, but in hundreds of thousands of mm-scale hops.</p>

CC BY-SA 4.0
2024-11-21T01:41:47.320Z
2024-11-21T01:41:47.320Z
Rockdoctor
<p>After being ground down and eroded into powder on the surface, it's hard for me to see how gold dust collects again after being subducted and mixed with melted rocks by convection.</p>
<p>I know that gold is heavier, so does it sink down and collect in  a thin shell of gold between the heavy iron core and the light silicon mantle?</p>
<p>Or what?</p>

CC BY-SA 4.0
2024-11-19T07:01:44.650Z
What makes you thing gold nuggets can't form on, or near the surface? Not all surface gold is "powder". Natural liberation of gold from near surface deposits doesn't necessarily involve grinding. Weathering & erosion (physical & chemical) of the matrix can result in gold fragments dropping out.
Fred
CC BY-SA 4.0
2024-11-19T07:11:13.387Z
@Fred Okay, it gets eroded. But what puts it back together? It's not like gold is magnetic and  attracts itself.
Miss Understands
CC BY-SA 4.0
2024-11-20T08:54:53.433Z
Very related question: [Why are minerals found in "large" quantities and not scattered throughout the earth as individual atoms?](https://earthscience.stackexchange.com/questions/2778/why-are-minerals-found-in-large-quantities-and-not-scattered-throughout-the-ea/2786) but would be interesting to get a more specific answer
JeopardyTempest
CC BY-SA 4.0
2024-11-20T11:31:35.297Z
@JeopardyTempest That article doesn't say either. They only talk about an unspecified "trap" that makes the particles of one element find each other. == Well, I guess nobody knows.
Miss Understands
CC BY-SA 4.0
2024-11-20T12:34:10.123Z
I just saw that [Why do gold deposits form only in certain areas of the earth?](https://earthscience.stackexchange.com/questions/2393/why-do-gold-deposits-form-only-in-certain-areas-of-the-earth/2397) is even more on topic to your direct question.  I agree the answers are incomplete.  But it seems that there's pretty heavy agreement at least that water movement underground tends to concentrate gold and other dissolvables ([here's more about what a trap is](https://en.wikipedia.org/wiki/Petroleum_trap)) (also the same idea, above ground, is why prospectors focus on waterways)
JeopardyTempest
CC BY-SA 4.0
2024-11-20T12:36:23.643Z
(Though I think most of us would agree it's gotta at least not be the same kind of trap at least, or gold would be in the same places as oil.  So that answer sounds less secure than the hydrological ones.  But yeah, hopefully someone who knows more on this particular subject will pop in at some point at least)
JeopardyTempest
CC BY-SA 4.0
2024-11-20T12:39:53.003Z
One more related question from yet another comment followon... [this first answer to In what geological situations can I find gold?](https://earthscience.stackexchange.com/a/532/6298) is quite interesting and probably the most informative of all of the ones around
JeopardyTempest
CC BY-SA 4.0
2024-11-21T21:19:42.090Z
what makes you think it does?
John
<rocks><subduction><convection><condensation>
How does gold condense into nuggets deep in the Earth after being mixed with dirt and spread out on the surface?
Miss Understands
# How does gold condense into nuggets deep in the Earth after being mixed with dirt and spread out on the surface?

(Asked by: username_0 on 2024-11-19)

After being ground down and eroded into powder on the surface, it's hard for me to see how gold dust collects again after being subducted and mixed with melted rocks by convection.

I know that gold is heavier, so does it sink down and collect in a thin shell of gold between the heavy iron core and the light silicon mantle?

Or what?

**Tags:** rocks, subduction, convection, condensation

> **Comments:**
> **username_1**: What makes you thing gold nuggets can't form on, or near the surface? Not all surface gold is "powder". Natural liberation of gold from near surface deposits doesn't necessarily involve grinding. Weathering & erosion (physical & chemical) of the matrix can result in gold fragments dropping out.  
> **username_0**: @username_1 Okay, it gets eroded. But what puts it back together? It's not like gold is magnetic and  attracts itself.  
> **username_2**: Very related question: [Why are minerals found in "large" quantities and not scattered throughout the earth as individual atoms?](https://earthscience.stackexchange.com/questions/2778/why-are-minerals-found-in-large-quantities-and-not-scattered-throughout-the-ea/2786) but would be interesting to get a more specific answer  
> **username_0**: @username_2 That article doesn't say either. They only talk about an unspecified "trap" that makes the particles of one element find each other. == Well, I guess nobody knows.  
> **username_2**: I just saw that [Why do gold deposits form only in certain areas of the earth?](https://earthscience.stackexchange.com/questions/2393/why-do-gold-deposits-form-only-in-certain-areas-of-the-earth/2397) is even more on topic to your direct question.  I agree the answers are incomplete.  But it seems that there's pretty heavy agreement at least that water movement underground tends to concentrate gold and other dissolvables ([here's more about what a trap is](https://en.wikipedia.org/wiki/Petroleum_trap)) (also the same idea, above ground, is why prospectors focus on waterways)  
> **username_2**: (Though I think most of us would agree it's gotta at least not be the same kind of trap at least, or gold would be in the same places as oil.  So that answer sounds less secure than the hydrological ones.  But yeah, hopefully someone who knows more on this particular subject will pop in at some point at least)  
> **username_2**: One more related question from yet another comment followon... [this first answer to In what geological situations can I find gold?](https://earthscience.stackexchange.com/a/532/6298) is quite interesting and probably the most informative of all of the ones around  
> **username_3**: what makes you think it does?  

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## 1 answers

### Answer by username_4 on 2024-11-21. Score: 0

> , it gets eroded. But what puts it back together? It's not like gold is magnetic and attracts itself
> It doesn't need to attract itself - being "tumbled" down stream will at some point result in one gold grain being on the bottom of the stream, on a larger rock [anything] grain, then a second gold grain ("flake", even) being dropped on top of it, then a third [anything] grain landing on the two and impact-welding them together.
> Gold (native silver, native copper too) is malleable ; most rock-forming minerals aren't.
> The concentration of gold into particular layers (mm-scale and smaller) in the stream sediment may promote a similar aggregation process by shear when the sediment fails and slumps down-slope.

When you're talking about alluvial gold (which seems to be the context of your question), it is normally distributed down-slope from the outcrop of the ore, then once it reaches the bottom of a local gulley, down-stream from there. That doesn't happen in "one mighty leap", but in hundreds of thousands of mm-scale hops.


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