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Where does gold REALLY come from?

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#1 Ira

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Posted 17 July 2013 - 06:16 PM

We've had discussions on the origin of gold on earth here before. Taking it back to the stellar realm, I thought all elements heavier than iron were made in supernova explosions. Now, here comes a scientific paper that says that gold is made in the collision of two neutron stars. But the findings seem rather speculative based on the evidence presented. And of course, gold could come from both supernovas and colliding neutron stars. Still, I'd like the reaction of the scientist sceptics here on what seems to me to be a speculative stretch by the authors of this finding.

http://www.universet...olliding-stars/

/Ira

#2 llanitedave

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Posted 17 July 2013 - 08:49 PM

Interesting piece. Although it wants to be able to explain all the gold through neutron star collisions, it doesn't make any effort to deny the ability of supernovae to manufacture gold.

Time for some dueling theories!

#3 Rick Woods

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Posted 17 July 2013 - 10:40 PM

Transmuted lead?

#4 ColoHank

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Posted 17 July 2013 - 11:10 PM

Alchemy. Mix eye of newt...

#5 llanitedave

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Posted 18 July 2013 - 12:53 AM

Straw.

#6 Ira

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Posted 18 July 2013 - 06:31 AM

Wouldn't the collision of two neutron stars be an exceedingly rare event? And why would it produce gold at all? What happens to two neutron stars that collide with each other? And how about colliding black holes. What do they make?

/Ira

#7 Otto Piechowski

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Posted 18 July 2013 - 06:44 AM

Where does gold come from?

I live in Kentucky and I KNOW where gold comes from. Fort Knox.

Otto

#8 Pess

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Posted 18 July 2013 - 11:36 AM

You are all wrong.

My Girlfriend has firsthand knowledge that Gold comes from rich Boyfriends....

Pesse (She says you can close the thread now, we are done here) Mist

#9 Otto Piechowski

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Posted 18 July 2013 - 01:13 PM

They stole it from Fort Knox. James Bond said so.

#10 Rick Woods

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Posted 18 July 2013 - 02:10 PM

From the Lost Dutchman Mine.

#11 derangedhermit

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Posted 18 July 2013 - 10:32 PM

The press release is all about gold, but the referenced submitted paper does not even contain the word. (According to a skimming to find the discussion, and then a search of the pdf.)

#12 PhilCo126

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Posted 19 July 2013 - 07:53 AM

Atomic number 79, least chemical reactive... from the Vredefort crater :graduate:

#13 Qwickdraw

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Posted 19 July 2013 - 08:26 AM

I read that article also and find it counter intuitive at least from my limited knowledge. Seeing as the Earth is ~4 billion years old and considering any gold distributed from such an explosion would be dissipated over a huge area it just seems very unlikely that the early Earth disk could have collected enough gold to account for what we have today.

#14 star drop

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Posted 19 July 2013 - 08:44 AM

Speculative conclusions perhaps. I wonder if they saw spectral evidence of super heavy elements (atomic number > 120) and did not realize it?

#15 Pess

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Posted 19 July 2013 - 10:31 AM

I always figured Gold and other heavy elements were born in some steller furnace.

What boggles my mind, and I have never really read a good explanation, is how do 'veins' of gold develop in planets?

I mean, gold mines exist because all the gold atoms are ino ne place. How did that happen?

I know diamonds are found together because they are made by local forces. But gold came from somewhere and lumped itself into veins. Same with Silver or copper veins.

If this question has been answered, I'd love to hear it.

#16 caheaton

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Posted 19 July 2013 - 10:49 AM

Ore veins are the result of hydrothermal vents carrying mineral laden water. The ore crystallizes out of the hot water leaving behind veins of minerals.

#17 star drop

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Posted 19 July 2013 - 11:06 AM

Is the gold in the veins in the Earth's crust from relatively recent asteroid accretion or does it up well from deep magma? One would expect that a dense element such as gold to have long ago sunk into the Earth's core barring some unknown high temperature/high pressure repulsion from iron or other core constituents.

#18 Ravenous

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Posted 19 July 2013 - 11:13 AM

Most of the heavy (or rather dense) stuff in the Earth is though to have sunk to the core during the iron catastrophe - a long time ago.

The continents are mostly made of the light stuff that floated - but there are small amounts of heavy metals still mixed with them. Not everything got totally mixed, so luckily we're left with a little of these useful heavy things.

Maybe fresh supplies of heavy metals come to the surface in volcanic activity... but that's just a guess. We'd need an expert to help us with that...

#19 llanitedave

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Posted 19 July 2013 - 11:20 AM

Most volcanics come from remelted rocks of the crust or upper mantle, so there'll be little or no actual material from the deep Earth coming up.

I'm partial to the idea that a lot of our crustal heavy elements have been brought in by asteroids. One thing I've always had on my curiosity list, but never looked into so far, is a catalog of the elemental composition of the lunar soil. I'm sure there's a lot of asteroid debris mixed in with it, and I'd expect a bit higher concentration of gold and platinum that average in our own crust, since the lunar material has not been recycled downward.

#20 Pess

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Posted 19 July 2013 - 11:43 AM

Ore veins are the result of hydrothermal vents carrying mineral laden water. The ore crystallizes out of the hot water leaving behind veins of minerals.


I get that but why veins of 'pure' metal?

Why a vein of copper here, a vein of silver over there?

Pesse (And where is the nearest undiscovered vein of gold?) Mist

#21 Jay_Bird

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Posted 19 July 2013 - 12:08 PM

That's not a question with a good short answer nor is it my earth science area of work since college, but I won't let that stop me:

'Veins' may form from the last portions of a magma (molten rock) mass to solidify or crystallize deep underground. These last fractions can be concentrated in volatile (water = link to 'hydrothermal veins') and in more aloof elements like nobel metals. The presence of volatiles helps make the vein fluids more mobile at a given temperature. This is one classic scenario for quartz+gold or quartz & other metals, some elements wind up in the veins because they resisted (for want of a better expression) crystallizing as long as possible.

There are plenty of other ways to concentrate typically scarce elements. In a large magma body, there can be fractional crystallization that 'rains' minerals with some elements to accumulate as a layer, because they are heavier or because they are first to crystallize and left behind as fluid portions are squeezed away; I think some USA Chromium deposits formed like this. Or, contact metamorphism can mobilize elements from the non-igneous 'host rock' and concentrate then in a zone or rind around the igneous intrusion, or in veins radiating out from the intrusion.

Sometimes there is second natural step in concentrating metals - the ore body may be further enriched by weathering that removes much of the rock mass and leaves more concentrated deposits of the less reactive elements in place.

Mantle hot spot plumes might(?)be an exception to lack of upward transport of heavier (iron-like) elements up to the crust from the deeper mantle. Maybe that's the other source besides asteroid/meteorite replenishment of heavy elements to the crust.

#22 llanitedave

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Posted 19 July 2013 - 12:18 PM

Ore veins are the result of hydrothermal vents carrying mineral laden water. The ore crystallizes out of the hot water leaving behind veins of minerals.


I get that but why veins of 'pure' metal?

Why a vein of copper here, a vein of silver over there?

Pesse (And where is the nearest undiscovered vein of gold?) Mist


Pure metal veins are very rare. It's a function of the chemistry and temperature of the water, and the concentration of the metal. Gold doesn't combine easily with a lot of other elements, so it's more likely to be metallic (although even in an ore body, we're more likely to see parts per million concentrations of submicroscopic particles), but silver and copper are much more likely to be found as sulfides, oxides, carbonates, or any of a number of other combinations.

#23 llanitedave

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Posted 19 July 2013 - 12:20 PM

Jay's answer was better.

#24 Widespread

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Posted 19 July 2013 - 02:17 PM

I haven't read the article, but they were talking about this on the radio on my way from lunch.

The astronomer (with help from the program host) made it sound like a certainty that only stuff like lead and some radioisotopes are made by SNs, whereas the "good stuff" like gold and platinum are made by neutron star collisions.

I, too, wondered how he could be so confident.

One cool datum mentioned was that the collision in question produced a weight of gold equal to that of Earth's moon.

Er, something just occurred to me. When two neutron stars collide to form gold, where do the protons come from?

Best,
David

#25 llanitedave

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Posted 20 July 2013 - 11:23 AM

There's a process called Beta Decay that according to the link, occurs generally in "neutron-rich nuclei". I don't see how you can get more neutron rich than a neutron star.






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