I was reading Does gold come from outer space?(BBC News). If the majority of gold on Earths surface does come from space would it tend to be equally distributed on comets and asteroids, or would tend to collect in pockets?

As I understand it, for the most part it seems that nuggets and pockets of gold on Earth tend to develop from erosion factors, it seems unlikely that these same effects would be present in Space, and that any catastrophic event (i.e. planetary destruction) would tend to disrupt any existing high density areas of gold.

Is there any known process that would tend to create high density grouping of gold elements in space?


1 Answer 1



Planetary Differentiation is the key here. When enough smaller asteroids smash together and form a big enough body, the heavy stuff sinks to the bottom (iron and other metals), middle layers tend to be formed of silicates (i.e. sand and rocks), and the lighter stuff floats on top (water, methane). (Mind you, the examples here are based on the composition we find in our solar-system. Other stars have significantly different make-ups.)

Once that's occurred, if a body were to be broken up (by a fast-moving asteroid, pulled apart by a gravity-well, etc), there'd be some chunks of metals, some rocky silicates, and some icy masses. Some might even be all three. And as it turns out, this is just the kinds of asteroids we find in space — some are rocky, some are metal-rich, some (like comets) are icy.

Gold is HEAVY. Around twice as heavy as iron. Gold will be more strongly differentiated by gravity (particularly since it doesn't react chemically with much). Same sort of thing with other heavy metals — lead, uranium, platinum, etc.

This is why there's some hope about asteroid mining — the hard part of mining is often getting to the valuable metals through the dirt and waste-rock. Some asteroids are mostly metal — no digging required.

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    $\begingroup$ But most gold-bearing ores (and many others) are created through hydrothermal processes. In the case of gold, most of the early deposits were then concentrated by erosion & deposition (placer gold). $\endgroup$
    – jamesqf
    Feb 26, 2016 at 20:15
  • $\begingroup$ @jamesqf Yes - gold on the surface and certainly gets concentrated/dispersed via weather/waterflow. There's likely LOADS more gold (and other siderophile metals) deep within the earth's core. What we find on the surface is what was deposited in the crust by asteroids - then broken-up, weathered, and concentrated somewhere else. $\endgroup$
    – john3103
    Feb 26, 2016 at 20:58
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    $\begingroup$ Sure, but my point is that without the action of liquid (and often superheated) water, there doesn't seem to be ways for a lot of those metals to get concentrated into ore bodies. $\endgroup$
    – jamesqf
    Feb 27, 2016 at 7:13

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