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When gold, or some other metals, such as copper, are found, they are often found in large nuggets. But, from what I understand, gold is produced in quite stochastic stellar processes. As such, shouldn't the distribution of gold and other elements be rather uniform, or at least conglomerated according to the stellar process by which they were created? Why do we see large gold nuggets? Shouldn't we find gold mixed uniformly with all the other elements created along side it in its stellar process?

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  • $\begingroup$ Because they are often precipitated, e.g., at/around hydro-thermal vents. $\endgroup$ – stali Dec 11 '15 at 21:56
  • $\begingroup$ See Also; earthscience.stackexchange.com/questions/391/… $\endgroup$ – Siv Dec 12 '15 at 9:30
  • $\begingroup$ Short answer atoms and particles of the same element have the same chemical and physical properties and react ot processes in the environment in the same way. $\endgroup$ – John May 20 at 14:24
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Some things to consider. Even if elements are formed randomly in stars that does not necessarily imply that the elements will be distributed evenly and randomly when the star explodes. Following the explosion of a star there will be a gravitational attraction between the elements created within the star which will cause clumping/agglomeration of the elements.

The other thing to consider is chemical attraction due to ionic charges and the lack or excess of electrons in the outer shells of atoms which causes atoms to chemically combine with other atoms to form molecules.

Many elements and molecules are soluble in water. When conditions change, such as temperature, pressure or chemical attraction, metals can precipitate out of solution and collect en-mass, sometimes forming nuggets.

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In addition to Fred's comments, there is growing evidence that some metallic elements, including gold, are bio-concentrated to billions of times the concentration in ambient solutions. In addition, once a minute 'nugget' or grain is established, it acts as a nucleating agent for further deposition. Another factor is the mico-environment's position on a 'pH-redox fence'. If the right combination of acidity/alkalinity and electrical potential is encountered, than extraordinary precipitation can occur, even where and when one would not normally expect it. This is particularly the case in which buried organic carbon (reducing agent) comes into contact with circulating groundwater. Over time remarkable concentrations, including sizeable gold nuggets, can precipitate from vanishingly small aqueous concentrations. Also recall that in quite mild geothermal - hydrothermal conditions, of 100 to 300 deg C, for example, the rates of chemical precipitation of 'insoluble' elements like gold, can be tens of thousands of times faster than would be seen under normal meteoric temperatures.

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There are processes that can move certain elements around (including gold) when you take water, pressurise and heat it up, such as happens in the Earth's crust. These processes will preferentially take one element relative to another. Some will take gold and leave other stuff behind. When this gold-bearing water accumulates in some place, the gold will stay there.

As an example, let's take a mixture of salt and sand. If you let water flow over it, the sand will stay behind but it will dissolve the salt and redeposit it wherever the water are going to. So in principle it's the same thing.

I made a drawing for another answer some time ago:

Why do gold deposits form only in certain areas of the earth?

When gold, or some other metals, such as copper, are found, they are often found in large nuggets.

That's not actually correct. They are not "often found in large nuggets". Whenever they are found in large nuggets it is indeed spectacular, but this is extremely rare (and becomes rares as more of those are found). Most gold is mined in very low concentrations. A good estimate for how much gold is in the rocks that are mined for is is 1 gram of gold per 1 tonne of rock mined. That's very little.

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  • $\begingroup$ Agreed, that most gold is extracted from deposits in which the metallic particles are so small as to be invisible to the naked eye. But I think Terry's question was particularly about visible chunks of gold, from milimetre sized flakes and upwards. $\endgroup$ – Gordon Stanger Dec 13 '15 at 9:46

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