[ohum]

Is there an answer to that question? And, why is the distribution of matter not random? Maybe some sort of gravitational grouping? (eg earth's iron core, centrifugal enrichment of uranium). Or affinity for some orientation relative to field states, magnetism/diamagnetism etc.?

Like attracts?

[CBLT]

As I understand it, the distribution was decided when the earth was still hot. So the mechanics you're interested in are those of high-temperature solutions containing liquid gold, which I don't understand that much. There's other interesting phenomena too, like gold frequently occurs in quartz rocks[0].

[0] https://www.quora.com/Why-is-gold-frequently-located-in-quar...

[adrianN]

I'm not a geologist at all, but when you freeze soda you tend to get water ice infused with veins of high-sugar soda concentrate. I wouldn't be surprised if similar mechanisms tend to lump matter with similar melting points together in molten rock.