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Certain metals detectable by ground scan?
4

Certain metals detectable by ground scan?

Certain metals detectable by ground scan?

(OP)
Hi all. I don't get by here much but I wanted to ask a question that I've been curious about, since my father inlaw has decided to move to Alaska to mine for gold. I'm no metallurgist, I am but a lowly engineering student that is still seeking my associates degree. But it does seem to me, with my limited knowledge of such things, that one should be able to at least tell what type of metal is under the ground (or laying on your shop floor) with a scan of some type.

For example, doesn't every metal give off a certain, measurable magnetic field? If so, wouldn't some instruments or scanners be able to pick that up, and then be able to tell you what type of metal was there? I was wondering, because the method he's using to try to get some of the gold seems... archaic at best. Simply letting water flow through a sieving machine, and collecting the particles. Well of course anyone who thinks about it, would realize that there are probably much larger sized chunks of gold, at various depths beneath the bottom of the river/stream that he is mining in. And the water is only 1 foot deep (or less) in some places.

Of course the trick is locating the larger chunks, as the river/stream is miles and miles long. Where do you dig? How deep? Is there some way to pick up the weak magnetic field that gold has? Or am I barking up the wrong tree here? I haven't gotten far in my engineering studies, but I remember hearing somewhere that all metals have a magnetic field which surrounds them, but of course this will vary from metal to metal. Thus, gold would have its own, and once you calibrated your equipment or had sensitive enough equipment, you may be able to tune it to detect only gold.

Is this possible? If not, how far off base am I?

RE: Certain metals detectable by ground scan?

But it does seem to me, with my limited knowledge of such things, that one should be able to at least tell what type of metal is under the ground (or laying on your shop floor) with a scan of some type.

>> No.

For example, doesn't every metal give off a certain, measurable magnetic field? If so, wouldn't some instruments or scanners be able to pick that up, and then be able to tell you what type of metal was there?

>> No. Where did you get that piece of erroneous information?

Is this possible? If not, how far off base am I?

>> No. You are pretty far off base. Even if you knew nothing about the physics, do you really think that you're the only one that's ever asked this question? IF such methods existed, don't you think that every accessible location would have already been mined out and that your father would be completely wasting his time?


TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

RE: Certain metals detectable by ground scan?

Large deposits can be found in the same way that submarines can be detected. You use the earths magnetic field and a very sensitive magnetometer and you look for distortions in the field. The problem with doing this in rock is that every kind of rock offers some distortion, so figuring out which ones are important is the issue. It really comes down to signal-to-noise, and there is no system that can clearly identify 'how much' of 'what' in a natural mixed setting.

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P.E. Metallurgy, Plymouth Tube

RE: Certain metals detectable by ground scan?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Certain metals detectable by ground scan?

(OP)
Whoops, accidentally gave the wrong guy a "Great post!". That was meant for Edstainless.

Regardless, thanks ed for the helpful reply. Not so much to the other two. Must not actually be engineers.

Anyway Ed, it sounds like you're on the same line of thought I'm headed down. I wonder if the noise you speak of, could be filtered out in some form or fashion. They do have ground penetrating radar that yields some different colors on screen for different densities.

RE: Certain metals detectable by ground scan?

bennylava;
The other two are indeed engineers and valuable contributors to ET. I was the one that gave the purple star to ornerynorsk because of his wit.

RE: Certain metals detectable by ground scan?

I imagine sifting for gold is like fishing. It's not necessarily about finding the most gold possible.

RE: Certain metals detectable by ground scan?

Metal detectors can differentiate non-ferrous and ferrous metals fairly well. A colleague does a lot of mining/prospecting, and they use one to find small nuggets hidden in cracks/crevices.

RE: Certain metals detectable by ground scan?

bennylava, I did pass along the star to EdStainless. Don't write off IRstuff, either, he is extremely knowledgeable, as evidenced by his many posts on subjects far, far above my level.
Research "proton magnetometer". However, to be entirely practical, you may find yourself with a pan doing "stream surveys" after all. Some of the best minds on the planet have been on the case for the easy track to gold for centuries, and no magic solution has appeared.
Thanks metengr!

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Certain metals detectable by ground scan?

Metal detectors work by setting their own fields up, not just using the earths field.
The benefit is that you get much better signals, but you can only 'see' a few inches.
Mining companies have truck mounted units that can penetrate a few feet.
The best method is still simply being able to identify minerals and follow the deposits.

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P.E. Metallurgy, Plymouth Tube

RE: Certain metals detectable by ground scan?

Magnetometers can only detect innate magnetism, which is typically limited to iron-bearing soils and minerals, but unless they're extruded in place, the magnetic domains will tend to be randomly oriented. Gold is not a ferromagnetic metal and has no innate magnetism. Were it surrounded by magnetized ferromagnetic minerals, you might possibly detect a drop in magnetism, but, typically, gold veins are relatively small.

Most other methods described above can detect differences in the materials, but not what specific materials they are, so you'd have to dig, which is expensive, compared to the potential return. In fact, even a GPR would likely have a poor ROI. Gold miners of the 1849 variety, when gold was more commonplace, seldom found even gold to pay for the services and goods they consume while they were mining for gold. Interestingly, most of them didn't actually "mine," they "panned" for the gold.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

RE: Certain metals detectable by ground scan?

Do a little Youtube searching and you'll find lots of clowns running around with metal detectors looking for nuggets- in rock traps near streams, in road drains...

Others just placer mine whole areas, like the deposits in the road drains and the rock traps. The density difference between gold and other minerals is so large that it doesn't take much- just a big pump and a properly designed flume, and of course a shovel and having no care about flooding a stream with sediments. We tend to try not to do the latter when building stuff, so why it should be OK to disturb and re-entrain the sediments along the sides or bottoms of streams is beyond me.

RE: Certain metals detectable by ground scan?

Molten Metal ,
I think you will find that a great many states now have laws in place to deter people from carrying out the activity you describe. I believe Alaska is one of the few states that allows it, as long as you do not mess up the salmon spawning grounds.
B.E.

You are judged not by what you know, but by what you can do.

RE: Certain metals detectable by ground scan?

On your original post: In case you are interested, there is a good way to identify the type of metal laying on your shop floor - a portable X-ray diffraction (XRD) unit, which can identify elements and relative quantities (Niton XRD analyzers are common). As I read through this thread, I wondered how it would do on a piece of unpolished rock in detecting if gold is present...

RE: Certain metals detectable by ground scan?

I don't know the current magnetic technology, but 50 years ago it was believed that ferromagnetism was the result of unbalanced electron spin. Some years later, a non-metallurgist friend said that Aluminum (non-ferromagnetic metal)

Design for RELIABILITY, manufacturability, and maintainability

RE: Certain metals detectable by ground scan?

Ooops - I hit the wrong key and left a truncated post

I don't know the current magnetic technology, but 50 years ago it was believed that ferromagnetism was the result of unbalance electron spin. Some years later, a non-metallurgist friend said that Aluminum (non-ferromagnetic metal)will become magnetic in a moving electrical field. I accepted this at the time because I know electric current produces a magnetic field but I don't understand how that works with a non-ferromagnetic metal.

Is it true that...
Aluminum (non-ferromagnetic metal)will become magnetic in a moving electrical field??

If so, what is the mechanism?

Design for RELIABILITY, manufacturability, and maintainability

RE: Certain metals detectable by ground scan?

Any electrically conductive material will generate Eddy Currents when moved in a magnetic field.
The result of these eddy currents is that they have a magnetic field associated with them (like all current flow does).

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: Certain metals detectable by ground scan?

Thanks Ed. I knew that but had forgotten. It is why they insulate layers of sheet steel in motor rotors to interrupt eddy currents

Design for RELIABILITY, manufacturability, and maintainability

RE: Certain metals detectable by ground scan?

re: XRD, see: http://www.olympus-ims.com/en/xrf-xrd/mobile-bench... Only 15mg required, i.e., sample chamber is TINY, and sample must be small enough to fit the chamber

alternative systems require access to a thin sample: http://www.icdd.com/resources/axa/vol52/v52_23.pdf
http://www.eng.uc.edu/~beaucag/Classes/Analysis/Ch...

In either case, bulk testing of large quantities or areas is not feasible, and the depth of penetration of x-rays limits its ability to probe; for hydrocarbons, which have low absorptivity, optimum thicknesses are on the order of millimeters, which means that for metals and rocks, the thickness limit is even thinner.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

RE: Certain metals detectable by ground scan?

I wrote the wrong thing in my question - what I meant to ask about was feasibility of identification of gold using handheld X-ray fluorescens (XRF). XRD would not really make sense.

RE: Certain metals detectable by ground scan?

Modern hand held XRF units (using micro tubes) can be tuned to give very good resolution and discrimination of elements, but there is still very little penetration.

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P.E. Metallurgy, Plymouth Tube

RE: Certain metals detectable by ground scan?

Grinding the surface is necessary for alloy identification. With an ore sample, I wonder if that really is necessary since all you are trying to do is see if gold shows up on the oxidized surface - it might be a fast means of identifying candidate rocks.

RE: Certain metals detectable by ground scan?

surface irregularity may impact analysis accuracy, but not simple detection.
People frequently use XRF on compacted powder samples.

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P.E. Metallurgy, Plymouth Tube

RE: Certain metals detectable by ground scan?

I expect gold in a rock to be nonhomogeneous in a mixture with other elements. All you can analyze with portable XRF is the surface, but you can hit the rock on several spots on the surface to see if gold is present. Then you could break the rock up is any is detected.

RE: Certain metals detectable by ground scan?

You'd only pick up surface specs, and even then, it would be over a small area, with no guarantee of anything more within the body of the rock. I think this would be a good alternate punishment for Sisyphus, not unlike kissing frogs looking for a princess. This process would be absurdly slow, compared to modern power panning, which uses dredging equipment to dump massive amounts of silt into the panning process. And, the panning process already has gold separated from the rock by millions of years of erosion. I've got a coworker that has occasionally done that sort of thing, and after a full day's of panning, he's got enough gold to maybe buy dinner.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

RE: Certain metals detectable by ground scan?

Remember, the people who got rich in the gold rush sold shovels and other support items and services. Very few miners/panners made anything to speak of. So maybe the original poster and/or his dad, should go into the portable XRF business (of course, that is pretty well dominated by several large corporate competitors with big R&D budgets, so, good luck).

I think you would have more luck using a metal detector on the beach or anywhere frequented by tourists than you would in a river somewhere in Alaska where people have rarely or never been. In the former, you might find manufactured goods or coins that contain little if any gold, but are valuable. At least you would get a lot of hits to keep your interest. In the latter, you have to deal with your batteries performing poorly in cold, wet conditions, and any metal you detect, even if it is gold, still has to be found.

The point of panning in a river is that the gold is in the sediment in particulate format. Finding it with any kind of scanner doesn't help you separate it from the water.

RE: Certain metals detectable by ground scan?

(OP)
Don't see any quote button so

Ed wrote "Any electrically conductive material will generate Eddy Currents when moved in a magnetic field.
The result of these eddy currents is that they have a magnetic field associated with them (like all current flow does)."


Gold is quite conductive. And don't they have to build special underground facilities to test certain equipment, when they need to get away from electromagnetic interference from say... radio stations and such? I remember that BMW has such a facility underground somewhere, so they can have a "dead zone" to test in. Well, if gold is highly conductive, and these EMF's will penetrate into the earth, and you can cause eddy currents, then couldn't you run and EMF into the ground, and have other equipment that was tuned to look for the eddy currents? Wouldn't those currents somehow be detectable from the surface?

FYI it wasn't me that is doing the mining. I just thought it was interesting because my father inlaw decided to go do alaska and start doing it.

RE: Certain metals detectable by ground scan?

(OP)
I'd like to bump this thread, for my last question in my last post.

RE: Certain metals detectable by ground scan?

It's not a bad thought. That's exactly how metal detectors work, there is a bit of a flaw though. Going to drop a few discussion points and leave the conclusion as an exercise for the reader...

  • If you're prospecting for gold, it's likely you'll be finding dust, flakes and maybe some small nuggets, not massive veins
  • The largest wavelength that can induce an eddy current in a piece of metal is limited by the physical dimensions of the piece of metal
  • Higher frequencies (shorter wavelength) radio waves do not penetrate the ground nearly as well as lower frequency radio waves

Nathan Brink

RE: Certain metals detectable by ground scan?

None of this discussion has really added much beyond IRstuff's first post. Countless people have worked on trying to detect or find gold deposits for centuries, using existing technologies. One day a new technology may be invented that may work but it will not be be invented by someone who has not yet learned and understood existing technologies.

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