How about another. Gold settled out to it's depth while settling was still possible. It is/or was at a certain depth circumferentially. As one land mass causes another to lift, that layer gets closer to the surface, at times leading to simply picking it up.
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Also, when a giant meteor strikes the earth it punches a hole in the earths crust. The result is a huge pool of molten earth with a lot of the material coming from below the surface of the earths crust. Many of the largest copper, nickel mines are in fact located in areas of meteor impact sites.