My question is, why is earth’s gold in veins? Why aren’t the gold particles just mixed in randomly with all of the other materials that originally formed the earth?
I don’t know the full answer, but two pieces of it: For one thing, gold is very dense, nearly the densest chemical substance in the Universe (“chemical substance” as opposed to the material of white dwarfs or neutron stars). When the proto-Earth was still molten, the various materials tended to separate out by weight. This naturally put most of the Earth’s gold in the core; it’s only occasionally that volcanic activity brings some to the surface.
Also, unlike most metals, gold is extremely unreactive. Most metals are found in the form of oxide ores: It’s only copper, silver, and gold, plus a few even less common than gold, that are found in their pure form.
Most volcanoes are very shallow, with all melted rocks coming from lower parts of the crust itself (or maybe the upper mantle) coming nowhere near the core. Possibly all the gold found on the surface today came from asteroid strikes.
The question of gold in veins can be asked about pretty much any element or mineral found only in specific locations, and the answer is: it’s complicated.
I had no idea that gold was mostly made by merging neutron stars.
In fighting my own ignorance, I came across this neat periodic table of elements, color-coded by origin (SVG link).
What I have always understood was the supernovas both produced the heavier-than-iron elements as well as dispersed them into space for later planet formation.
Would neutron star collisions be nearly as effective at this as supernovas?
To expand on this: Since “nova” refers to the appearance of a new visible star, from an observational perspective any transient light source falls into the category. However, I think an astrophysicist would not usually include mergers into the category “supernova”, at least not without qualification. “Kilonova” has been coined for these massive mergers.
But much rarer. That would imply if the sun formed from a nebula where such a collision never took place, the amount of gold on the planet would be very meager.
Oversimplifying it (and I’m no geologist/mineralogist myself) it is chemistry and physics. We get veins of gold for similar reasons that we get frost on windows and pillars of salt in the Dead Sea. Gold exists in a location and condition that allows it to be dissolved, then moves to a new location without the same conditions and precipitates out. The same goes for the quartz it is associated with. Gold veins are essentially especially blingy geodes.
For what it is worth this article popped up on my linkedin feed regarding how gold gets to certain deposits from the magma.
Its not a hugely non geologist friendly article and a summary appears to be …
“Thus, the generation of Au deposits in the crust may result from the conjunction in time and space of three essential factors: an upper mantle or lower crustal source region particularly enriched in Au, a transient remobilisation event and favourable lithospheric-scale plumbing structures.”
Whatever that may mean, but the article has some graphics that may help. The article does indicate this is a competing theory to others that are out there.
With a neutron star collision, pretty much all processes are going on at once. They’re not all going at the same rate, though, so in the end once everything cools down, you’ll have a mix of elements in various proportions.
Free neutrons will naturally decay into a proton, electron, and an electron anitneutrino. Gravity forces the neutrons to remain stable in a neutron star. Disrupt that and lots of energy (the scientific term is “oodles”) is available to break down neutrons and build up just about anything.
From neutrons decaying into protons, electrons, and various other debris once a chunk of the neutron star too small to remain neutronium is chipped off the star.
