Why is gold is found in seams?

Beeker

Might seem a silly question, but it is something I have often wondered about.
The Big Bang created Hydrogen and Helium, heavier elements including gold, were created in the insides of stars and returned to space during supernova explosions where they recombined into latter generations of stars and planets, like the Earth. When the Earth formed 4.5 billion years ago, {give or take a week:D} gold and the other elements would have coalesced together to form the early planet.
So how did gold, or any of the other minerals end up in seams and not distributed evenly throughout the planet?

Capt'n Midnight

many minerals can be concentrated due to the action of water

heavy metals are rare because most of them fell to the centre of the planet

all the gold ever mined would make a cube about 20.5m on a side which is tiny compared to the volumes of coal, limestone and oil that we've taken out of the ground


the really weird one is the banded iron formations which account for most of the iron ore we use today, formed when the iron dissolved in sea water precipitated out when blue-green algae released oxygen over billions of years

Beeker

Capt'n Midnight wrote: »

many minerals can be concentrated due to the action of water

heavy metals are rare because most of them fell to the centre of the planet

all the gold ever mined would make a cube about 20.5m on a side which is tiny compared to the volumes of coal, limestone and oil that we've taken out of the ground


the really weird one is the banded iron formations which account for most of the iron ore we use today, formed when the iron dissolved in sea water precipitated out when blue-green algae released oxygen over billions of years

Thanks for you answer, I suppose I was just wondering how atoms of gold "found" other atoms of gold and came together as it were.

mikhail

It's an interesting question. I don't know the answer, but the first thing which comes to mind is that you're assuming that it comes out of a supernova as a nebula of gold atoms. Perhaps that's not the case. Capt'n Midnight's mention of chemical processes sounds promising too.

gerryk

Beeker wrote: »

Thanks for you answer, I suppose I was just wondering how atoms of gold "found" other atoms of gold and came together as it were.

Purely a theory, but perhaps in the same way as chromatography or staged filtration work.

Ronanc1

Just watched the second episode of "the birth of britain" with Tony Robinson on channel 4, it was dedicated to gold and answered alot of the questions in this thread which i myself wondered about when i read it.

glenbrook

Good question.

I suspect it has to do with the same reason rocks get sorted on a beach or fat hardens on the surface of cooling gravy. Gold is a very dense substance, and in a fluid (water, molten rock) it will naturally sink towards the bottom. Gold also has a melting point around 1000C which is lower than most of the rocks that it is found in. Therefore it will stay molten longer, as the rock cools, becoming more concentrated in the process.

The other thing is that gold rarely chemically combines with other elements. Hence it doesn't tarnish and is valuable. For this reason it does not dissolve in water or acid and is not usually carried away in solution like other minerals. This process can also concentrate the ore.

Alluvial deposits are caused by water erosion of gold bearing rocks. Gold is concentrated in this way because the gold particles tend to sink to the bottom of the stream, a fact exploited by gold panners.

Capt'n Midnight

To nit pick a little, Gold does dissolve in water.


Of course it's not very soluble but during the early part of the 20th century the Germans spent quite a bit of money trying to do this , and a ship and all. In fairness the government really could have done with a get rich quick scheme and the bloke involved had actually figured out how to make fertilizer* out of thin air. http://en.wikipedia.org/wiki/Fritz_Haber


*and explosives and he was involved in poison gas

(a history of bombing by Sven Lindqvist is scary book , he mentions a British civil servant who calculates the optimum size of shrapnel so that the pieces don't pass all the way through a person's body, because that would be wasting kinetic energy, when instead you could have more smaller pieces that would expend all their energy in a person , the stuff you read about the guys on the Manhattan project are similar they solve the technical problem and then consider the victims )

If you've heard of the Nitrogen cycle, then you may be suprised to know that Humans are now fixing more than nature

Pablo_

Just finished a book which talked about that, but sketchy on it.... It has to do with its unreactiveness, and its inability to be dissolved. It 'flowed' into crevaces in sediment as tiny grains carried in water, something about the sedmentary rocks eroding and .....:cool: ......

better get that book - Popular science book called "The Ingredients", really easy approach to elements and the whole table of elements. Full chapter on gold. Interesting how they are using plants in australia to 'fix' gold, turning out to be as good as old fashioned mining!

NotCarrotRidge

glenbrook wrote: »

Good question.

I suspect it has to do with the same reason rocks get sorted on a beach or fat hardens on the surface of cooling gravy. Gold is a very dense substance, and in a fluid (water, molten rock) it will naturally sink towards the bottom. Gold also has a melting point around 1000C which is lower than most of the rocks that it is found in. Therefore it will stay molten longer, as the rock cools, becoming more concentrated in the process.

The other thing is that gold rarely chemically combines with other elements. Hence it doesn't tarnish and is valuable. For this reason it does not dissolve in water or acid and is not usually carried away in solution like other minerals. This process can also concentrate the ore.

Alluvial deposits are caused by water erosion of gold bearing rocks. Gold is concentrated in this way because the gold particles tend to sink to the bottom of the stream, a fact exploited by gold panners.

That's pretty much it. Most other elements will have formed crystals, leaving gold in the remnant fluids. Those fluids solidify in whatever cracks they find (or make for themselves).

Ronanc1

For this reason it does not dissolve in water or acid

And to double knit-pick gold can be dissolved in acid, Not one found naturally occuring but there is one. Aqua regia a mixture of Hydrochloric Acid and Nitric Acid can dissolve gold it was used in the Bohr institute to dissolve nobel prize medals when the nazis invaded, it works because of the chlorine which is capable of chemically effecting gold iirc.

Capt'n Midnight

Ronanc1 wrote: »

And to double knit-pick gold can be dissolved in acid, Not one found naturally occuring but there is one.

Actually gold can be dissolved in water, it's just that it isn't very soluble

http://goldfever.com/gold_sea.htm