[jandrewrogers]

Veins of heavy metals are created by the chemistry of hydrothermal systems. High-pressure super-heated water is a great solvent and will leach many things out of the surrounding rocks in a chemistry and temperature/pressure dependent way.

These hydrothermal systems can be structurally enormous and form gradients e.g. due to differences in rocks and temperature at different depths. This acts a bit like a distillation column. Every metal has different characteristic solubility and will precipitate out of solution in boundary areas where amount of metal in solution exceeds the solubility under those conditions. Since these are fluids, the solution is circulating, bringing fresh saturated solution to the boundary area.

In some regions like Nevada, there are places where very large and diverse gradients are exposed e.g. you will find copper, silver, gold, tin, mercury, lead, uranium, etc veins of various quality distributed across the same very local geological formation as different metals were deposited in different places within the same hydrothermal system.

A limitation on formation is that it typically requires a relatively large hydrothermal system with stable properties and appropriate chemistry over millions of years. The kinds of places that have large hydrothermal systems also tend to be geologically unstable.

[cmyr]

I remember reading in one of John McPhee's geology books (collected as [1], and one of the best things I've ever read) about a particular way that diamonds can form; it had a name (like a diamond jet or a diamond burst or something) but the basic idea is mesmerizing: super-heated water containing dissolved carbon would find some fissure in the surrounding rock and explosively expand into it, and in the process it would cool rapidly and diamonds would crystallize out of the solution. I'm stuck with the visual of a seam of diamonds popping into existence in an instant, which is not what we normally think of as a geological timescale.

[1] https://en.wikipedia.org/wiki/Annals_of_the_Former_World

[PKop]

Similar process here with gold

https://news.ycombinator.com/item?id=38935662

[fnordpiglet]

I’m surprised it’s not due to settling in magma. Does this mean on, say, the moon we would see a uniform scattering of elemental atoms ?

[PaulHoule]

... there's a reason why gold is a precious metal! See also https://en.wikipedia.org/wiki/Hydrometallurgy