View Full Version : Why won't this work... geology question.
01-07-2000, 11:33 AM
I am turning to the TM to find out why this cockamamie idea won't work.
Here is what this idea is loosely based on. In one of my Earth Science courses in college, we studied mineral formation.. In the course of this, we studied how minerals came out of a melt. If I remember correctly (which is in serious doubt) factors such as speed of cooling, presence of H20, pressure, etc. were largely responsible for the formation of ore bodies.
Why then, can we not tap into a source of magma (such as an active volcano or the Mid-Atlantic ridge) put in a few ceramic pipes that would artificially recreate the necessary conditions, and produce a thick chunk of gold? I am envisioning some sort of hollow ceramic shaft, magma flows up into it and into side arms where cooling, pressure, etc. can be controlled.
Is it because it is too expensive? Well, this is a reason why it is not done, not a reason why it can't be done. In time, if the marginal price of gold extraction rose enough, it would become economically feasible. With tighter environmental prohibitions against gold mining and the finite nature of gold stocks, this might happen within a hundred to two hundred years.
Is it because we don't have access to a melt with the right properties? If I remember right, exposed Hawaiian magma is mostly basalt with out a lot of … of something (I can't remember what at the moment) that keeps it quite fluid. So not all magma sources are going to have the right constituent elements. Is this true for all sources of accessible magma? Is the Mid-Atlantic ridge even accessible?
Is it because magma is too damned hot? Sure, we can work with molten steel, but is molten rock so hot that any ceramic materials we have today are incapable of containing it or doing anything with it?
Are there basic engineering problems that would prevent this from working? How would we pump the melt up into the shaft? Would an artesian well-like location work?
Am I missing something simple? This is the most likely reason this would not work. Am I missing some critical element of the picture, such as time? If the melt needed to cool for a period of decades before a significant concentration of the desired element built up, that would make this a silly idea. It would not, however, mean that it could not work. It would just mean it is not a feasible idea.
So I am turning this over to the TM - why won't this work? Have I basically answered my own question? If so, which one(s) is(are) the reason(s) it won't work?
Once in a while you can get shown the light
in the strangest of places
if you look at it right…
01-07-2000, 11:39 AM
Main Entry: cock·a·ma·my
Variant(s): or cock·a·ma·mie /"kä-k&-'mA-mE/
Etymology: perhaps alteration of decalcomania
: RIDICULOUS, INCREDIBLE <of all the cockamamy excuses I ever heard -- Leo Rosten>
01-07-2000, 01:20 PM
Am I missing something simple?
It sounds like you expect that if you have magma you can cool it in different ways to get anything you want - lead, gold, Boeing 747's, etc. It doesn't work that way.
Barring nuclear reactions, chemical elements (http://www.webelements.com) do not change over time. So, whatever is in your magma is what you can get when you cool it. If your magma happens to be 10% gold, great! If your magma happens to be 0% gold, then you lose.
If you were talking about some substance that needs to be smelted, like iron, all you are doing is saving the step of heating up the ore by piping in already hot ore - you still have to smelt it.
01-07-2000, 01:26 PM
Somebody tell me how that captal D became a smiley face. I didn't do it. Alchemy?
01-07-2000, 01:35 PM
But, Mr.John you did put a colon right in front of it without a space. ( : D = :D )
01-07-2000, 01:39 PM
Hey Rhythmdvl, clear something up for me. Are you thinking that, in a fluid, all the various compounds separate out based on their density? That's what I thought you meant, but douglips doesn't seem to think so.
Let me rephrase what I think Rhythm said, so that he can shoot it down if I'm all wet. If you figure that ordinarily, minerals mix together a little bit like creamy Italian dressing - they have different densities but, since they are solids, they don't separate. They are "emulsified" by their solid shapes, just as oil and vinegar are emulsified by egg whites.
Turn the stuff to liquid, and they "emulsification" leaves, you've got just plain oil and vinegar now. The liquid gold would sink to the bottom, and the lighter stuff (tin? mica? orthoclase feldspar? cotton balls?) would float to the surface. Then we'd just sink the patented Rhythmdvl Ceramic Tube down to the level of the molten gold, passing all the molten mica and twinkie wrappers, and suck it up. The gold wouldn't need to be super-abundant in percentage terms, since the original mass you're dealing with is tremendous, and gold is practically worth its weight in gold.
Is that right?
I think the main problem with this might be that it's really far down before you get to actual liquid metal. Relatively shallow ores will flow plasticly, like wet clay. In fact, it is the "solid but able to flow under heat and pressure" nature that makes the mantle such an interesting place - huge convection cells of dense, hot, mushy rock move around with a teensy layer of light, hard crust on the top. So if we make it to the mantle, we're still left with creamy Italian. You'll find gold not in a homogenous layer, but in "marbelized" veins and pockets.
We really can't build mind shafts very deep if you consider the size of the earth. Pressures at those depths would crush would ever wasn't melted by the temperature. Certainly, liquid rock does get closer to the surface near volcanoes, as you've mentioned. But that is a vastly smaller mass than you'd need to get a lot of gold, unless you got really lucky.
So I guess the mining companies figure they'll trust their luck with (relatively!) shallow gold mines.
Waaa! Everybody ignores me 'cept the Republicans!
01-07-2000, 01:43 PM
Ooops. Meant to say, "... pressures at those depths would crush whatever the temperature didn't melt".
01-07-2000, 02:58 PM
A current and very likely theory on ore body creation is that the valuable metals and metallic minerals (along with quartz and a few other minerals) are disolved in extremely hot, high pressure water. The water transports them through the magma body depending on pressure and zones of weakness. Where the minerals come out of solution, either at a black smoker on the seafloor or injected into relatively cooler rock still at depth, there you will find the mineral deposits. If you could tap into one of these hydrothermal needles in a magmatic body haystack, your project could work.
01-07-2000, 03:20 PM
It sounds like you expect that if you have magma you can cool it in different ways to
get anything you want - lead, gold, Boeing 747's, etc. It doesn't work that way.
Barring nuclear reactions, chemical elements do not change over time. So, whatever is
in your magma is what you can get when you cool it. If your magma happens to be
10% gold, great! If your magma happens to be 0% gold, then you lose.
Sure, I totally agree. Well, except for the bit about 747s. A DC10 maybe, but not a 747 :) Anyway, I mentioned in the OP that a problem might be accessing a melt with the right properties. Plunk a RCT (thanks Boris!) into a Hawaiian volcano and you might end up with lots of basalt. But the mantle, being relatively well mixed, contains a bit of everything. Getting to that melt, well, that is a different story.
Hey Rhythmdvl, clear something up for me. Are you thinking that, in a fluid, all the
various compounds separate out based on their density?
Well, the process is a bit complicated. Here is a disgustingly gross oversimplification of it. The various elements are floating around in the well-mixed melt. When it moves up into a fissure in the crust, cooling takes place. If it cools slow enough and at the right temperature (I think that some of these 'right' temperatures are achieved/maintained by the melt flowing into a horizontal fissure.) elements will begin to solidify out of the melt. There is a certain temperature/pressure that is somewhat specific to each element (this is named after the guy who noticed it first. Can't remember, will keep looking). At the critical temperature, the element will begin to come out of the melt, and coalesce to form an ore body.
In other words, elements have different melting points. Gold will melt at a different temperature than copper. Imagine a bit of magma containing both. At the current temperature, both will remain in solution. A bit lower than one's melting point but above the other's, and only one will separate out of the melt. Cool it in stages, and the various elements separate out individually. Cool it slow enough and you can get some nice crystals.
I went back to double check somethings from the classes' page, but am not sure I would be able to get the formatting right if I cut-n-pasted it right here. Not a lot there (they are basically lecture notes) but you can see some for yourself at http://rainbow.ldeo.columbia.edu/ees/lithosphere/lec8.html look especially at number six, Aqueous fluids in magma.
All this talk of pipes makes me glad it is Friday at four o'clock. Mmm… pipeweed.
Once in a while you can get shown the light
in the strangest of places
if you look at it right…
01-07-2000, 05:16 PM
The guy you're thinking about, Rhythmdvl, is Normal L. Bowen. The sequence he first described is called "Bowens Reaction Series" and the process that produces this series is called Fractional Crystallization (FC). It is the single most important process that contributes to the evolution and diversification of magma systems (although many would argue with me in favor of partial melting--FC in reverse, or assimilation as a more important process).
Simply, it works like this: Magmas are complex chemical mixtures consisting of a number of different components, mostly O, Si, Al, Fe, Ca, Na, K, Mg, with a highly variable amount of volatiles (CO2, S, H2O) and the remainder consisting of minor elements (P, Mn, Ti) and, lastly, trace elements (all the rest, including gold). The amounts of each is, of course, highly variable depending on what rock melted to form the magma and the conditions under which melting took place.
No matter what the exact composition of the magma is, as soon as it starts to ascend (because liquids are less dense than rock), it starts to cool and the process of FC begins. (Actually, this is not strictly true because, in the rare case that the magma is loaded with a sulfurous phase then liquid immiscibility would be a dominant process and the magma would separate like Boris B's Italian dressing. This isn't very common at all, but when it does happen, then Platinum-Group elements follow the sulfur phase and concentrate there. But we're interested in Au, not Pt, so I digress...)
Magmas do not cool homogenously, like pure water does, because it is not a pure, homogenous substance, like pure water is. Thus, instead of "freezing" (ie, crystallizing) at once, it "freezes" in parts. Minerals with the highest melting points "freeze" first... minerals with slightly lower melting points next... etc., etc., ad nauseum. Of course, *exactly* what crystallizes and when is wholly a function of the composition of the magma. But, since--at least in terms of major elements--magmas are broadly similar, we see pretty much the same pattern in all magmatic systems: minerals rich in Mg, Fe, and Ca first; minerals rich in K and Na last.
(Trust me! This has something to do with gold!)
As the Mg, Fe, Ca-rich minerals ("mafic minerals") form, they create solids which are more dense than the surrounding magma. Thus, they start trying to sink--or at least aren't as able to ascend. The magma thus loses these components and becomes richer in everything else. Remember: magmas also have trace elements--these aren't abundant enough to form their own mineral phases; instead, they incorporate themselves in "regular" minerals that they fit into (similar size, charge, EN, etc.). So trace elements like Ni and Cr are included in minerals containing Fe; elements like Sr are included in minerals containing Ca, etc.
Some trace elements have properties that exclude them from *every* common mineral phase because they are too large, have too high a valence, or whatever. These "incompatible" trace elements include (among others) gold and silver. So, as a magma is slowly crystallizing and leaving minerals behind, it is enriching itself in incompatible trace elements. That's why highly evolved magmas (rocks) like rhyolites and granites are associated with Au-Ag deposits and primitive magmas (rocks) like basalts are not. Tapping into Hawaii wouldn't work for many, many reasons--but mostly because Hawaii is basaltic.
Okay... once we've concentrated the Au-Ag in the magma, we've got to get it out and concentrate it some more, since it's still not all that concentrated. This is done at higher levels in the crust where the magma interacts with groundwater. If the water is just right--high temperature, low pH, and oodles of Cl ions--then Au and Ag will dissolve into this hydrous phase (acidic, high-T, high-Cl waters "mobilize" these metals). The pathways for these metal-bearing waters are frequently narrow fractures (if not, you get disseminated, aka "no-seeum", aka Carlin-style deposits). As soon as the water's properties change (via cooling, mixing with other waters, etc.), then ALL the gold and silver and whatever else (quartz) precipitates out and--BOOM! Vein gold! Vein gold eventually weathers and you get placer deposits, or stream gold.
Woah! It's after 5... gotta go drink and keep talking about igneous processes (I'm so popular at the bar!)
Hope this helps... assuming anyone's still awake.
Your Trace Element Geochemist,
John (Pantellerite--a damn fine felsic rock in its own right).
01-07-2000, 05:36 PM
Thanks, Pantellerite. I forgot all about the Bowen reaction series. You've brought back memories of Geology 1 (that's right, it wasn't Geology 101, it was Geology 1. Just to make sure your knew you were in Rocks for Jocks). "Hmm, what's this?"
"Taste it to see if it's halite!"
"Tastes kind of salty."
"No, it's not salty enough. That's just salt from the hands of the hundreds of freshman who have touched it. Hey, look at this flat crystalline face. I've never seen a rock cleaved like that!"
"No, that's not a crystalline face. That's where the specimen was cut off of the original rock with a saw."
"Rats. Okay, it's flecked with large black crystals."
"No, those are small black crystals."
"They look big to me."
"Oh. I guess we don't know what it is then."
That which does not kill me just makes me really irritable
WAG: Too expensive is the ususal reason why something like this isn't done.
There's gold in sea water, something like 1 grain per cubic meter. It can be extracted, but it's just not worth it. And I think this extraction method would be used before your magma method.
I think the price of gold would have to go way up for them to try either.
Let the Truth of Love be lighted/ Let the Love of Truth shine clear. Sensibility/ Armed with sense and liberty
With the Heart and Mind united in a single/ Perfect/ Sphere. - Rush
01-08-2000, 12:17 AM
I'm not clear where the gold comes from. I doubt the typical magma would have lots of gold just waiting to be pumped out.
It is too clear, and so it is hard to see.
01-08-2000, 12:19 AM
Function: noun Date: 1864
1:the art or process of transferring pictures and designs from specially prepared paper (as to glass)2 :DECAL
De calculations that AWB made show dat we would definatly suffer from sticker shock at de new price of gold. Man, I do NOT wanta be there when that gold well blows.
"Pardon me while I have a strange interlude."-Marx
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