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Meteorites and precious metals

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#1 Ira

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Posted 02 December 2012 - 11:17 AM

Why are there no meteorites that contain precious metals like gold, silver or platinum, at least in trace amounts?

/Ira

#2 peter scherff

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Posted 02 December 2012 - 01:26 PM

Hi Ira,

All the precious metals are found in meteorites. According to Masson, Elemental Abundances in Meteorites:
Silver occurs at levels from .031 to .57 parts per million.
Gold occurs at levels from .094 to 8.7 parts per million.
Platinum occurs at levels from .044 to 29.3 parts per million.

Peter

#3 sealevel

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Posted 02 December 2012 - 06:37 PM

Why are there no meteorites that contain precious metals like gold, silver or platinum, at least in trace amounts?

/Ira



Hi Ira,
http://www.wired.co....precious-metals

http://www.scienceda...10907132044.htm

http://news.discover...als-110907.html


Davio R.

#4 Ira

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Posted 02 December 2012 - 08:01 PM

Davio,
Thanks for the pointers to those articles. I remember reading them a while ago but had lost track of them. They are talking about ancient bombardments of the earth. Did meteorites back then have a greater abundance of precious metals than those of today? It would seem to require a heap of bombardment to really deliver any significant amounts of precious metals if the abundances were the same as the ones Peter cites above.

So, do all meteorites have the abundances of precious metals cited above or just certain types? I've never seen any meteorites touted as containing any precious metals at all. You'd think sellers would play that feature up, even if the amount isn't enough to make you rich.

/Ira

#5 peter scherff

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Posted 02 December 2012 - 08:58 PM

Hi Ira,

As a general rule, the abundance is lowest in achondrites increasing in chondrites then more in stone irons and finally the highest in irons.

I am trying to imagine a process by which there were meteorites with higher concentrations of precious metals in the past, but I can't think of any. Earth seems well made to concentrate precious metals.

Peter

#6 PGW Steve

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Posted 03 December 2012 - 11:26 AM

Would there be any relation to the frequency of precious metal occurance to melting point? Perhaps most of the good stuff burns up.

#7 peter scherff

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Posted 03 December 2012 - 04:03 PM

Hi,

When meteorites travel thru our atmosphere only a small portion of the outside of the rock heats up. For all practical purposes the interior of any meteorite has not been heated.

Peter

#8 sealevel

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Posted 04 December 2012 - 06:37 AM

Davio,
Thanks for the pointers to those articles. I remember reading them a while ago but had lost track of them. They are talking about ancient bombardments of the earth. Did meteorites back then have a greater abundance of precious metals than those of today? It would seem to require a heap of bombardment to really deliver any significant amounts of precious metals if the abundances were the same as the ones Peter cites above.

So, do all meteorites have the abundances of precious metals cited above or just certain types? I've never seen any meteorites touted as containing any precious metals at all. You'd think sellers would play that feature up, even if the amount isn't enough to make you rich.

/Ira


Hi Ira,
Peter is pretty much on the "money".

Using Peter's (Masson, et al.) "average" numbers for Gold, 4.397 parts per million (ppm), and obviously realizing the specific gravity of a meteorite is significantly higher than triple distilled water, we can calculate the following:

facts: 1 cm3 of H2O = 1 milliliter = 1 gram; 1g = 1,000mg; 1ppm = 1mg/l; 1,000g = ~2.2 lbs.

4.397 mg/l (parts per million) of Gold =
4.397 mg of Gold per ~2.2 lbs. of meteorite =
4,397.00 mg of Gold per ~2,200 lbs. of meteorite =
4.397.00 grams of Gold per ~2,200 lbs. of meteorite =
30 grams of Gold per ~15,010.234 lbs. of meteorite
_____________________________________________
That's 1 ounce of Gold per ~6.82 tons of meteorites (Hoba, in tact, = 60 metric tonnes)

That, to me, can add up to be a lot of Gold considering the monstrous planetary scale of things and a ~couple billion years of super meteoric earthly impacts. Now, factor in the density difference between water (on which these calculations were based) and meteorites and you may have an even greater amount of Gold, much of which has yet to be discovered.

Factoid: The total amount of mined gold from ancient times to the present is calculated at 158,000 metric tonnes.


Davio R.


Note: Here is my tiny 4.08 gram Hoba specimen. I don't think I'll be getting Gold rich anytime soon...

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#9 Ira

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Posted 04 December 2012 - 05:53 PM

So, shouldn't the moon and other terrestrial planets have lots of gold on them? Has anyone done an analysis of precious metals on them?

/Ira

#10 peter scherff

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Posted 04 December 2012 - 07:29 PM

Hi Ira,
Precious metals are siderophile; they like to hang out with iron. Earth has more iron than we would expect for a planet of its size. It also has more precious metals than we would expect. Our moon has less iron and precious metals than would be expected. Mars has average iron and precious metals abundances. If you want to find a precious metals in “high” abundances go to a type M asteroid. These asteroids are analogous to nickel iron meteorites. There you should find precious metals in the 35 parts per million range.
Peter

#11 Ira

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Posted 04 December 2012 - 07:40 PM

Peter, I can see how the composition of a planet would determine where the precious metals are found on it, but how would that change how much there is? Wouldn't the moon and earth be subject to the exact same kind of meteoritic bombardment, since they are essentially in the same place?

/Ira

#12 peter scherff

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Posted 04 December 2012 - 07:49 PM

Hi Ira,

The Earth & Moon are a special case. The Moon was created by a large impact with the Earth. The impact left the Earth with a large core and the Moon in turn was formed mainly of the lighter crust material.

Peter

#13 Ira

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Posted 04 December 2012 - 07:59 PM

But if precious metals were brought to earth by subsequent bombardments, then the earth and moon should have been bombarded in the same way, resulting in similar ratios of precious metals. No?

/Ira

#14 peter scherff

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Posted 04 December 2012 - 08:19 PM

Hi Ira,

The Earth is made from "meteorites", from the earliest stages of accretion to the most recent fall. We think that the meteorites that fall today are much the same as the ones that fell over 4 billion years ago. I doubt that late bombardment would change the abundance of precious metals to any appreciable extent.

Peter

#15 Glassthrower

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Posted 05 December 2012 - 12:16 AM

Iron meteorites are more rare than gold or platinum by several orders of magnitude.

Therefore, I would submit that all iron meteorites are "precious metals"..... ;)

#16 sealevel

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Posted 05 December 2012 - 07:10 AM

But if precious metals were brought to earth by subsequent bombardments, then the earth and moon should have been bombarded in the same way, resulting in similar ratios of precious metals. No?

/Ira



Hi Ira,
Let's assume your premise is correct, as I do. Then yes, the moon has precious metals at a ratio "somewhat" directly proportionate to its size, mass and volume, compared to Earth. The Moon is approximately 1/4 Earth's diameter, 1/50 Earth's volume, and 1/80 Earth's mass. As a matter of fact, Lunar Gold (no silver) was discovered in Apollo samples at nanograms per gram. Other precious metals, such as Silver, were discovered after the Apollo missions. Also, the Apollo Lunar sample isotopic abundance ratio of Gold to Iridium was found to be the same as in Earth meteorites.

http://www.pbs.org/n...e-is-water.html

Davio R.

#17 sealevel

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Posted 07 December 2012 - 08:02 AM

Hi Ira,

As a general rule, the abundance is lowest in achondrites increasing in chondrites then more in stone irons and finally the highest in irons.

I am trying to imagine a process by which there were meteorites with higher concentrations of precious metals in the past, but I can't think of any. Earth seems well made to concentrate precious metals.

Peter


I'm purchasing a Patos de Minas (Complex), IAB-complex, meteorite specimen. I found the research data on IAB-complex iron meteorites interesting. The link immediately below is an Au/ IAB-complex study in micrograms/gram of Au.

http://www.lpi.usra....01/pdf/2085.pdf



Here you go, Ira, more Gold stuff...

http://www.meteorite...ted_append3.htm

http://news.bbc.co.u...ture/401227.stm

http://www.minsocam....19/AM19_370.pdf

Davio R.


74.7 gram Patos de Minas (Complex) or syn; (Patos II) - Iron, IAB-complex

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