Certain metals detectable by ground scan? 4

[bennylava]

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?

 

[IRstuff]

Most will do both XRD and XRF, the issue, again, is that x-ray penetration is not that robust, so any field samples need to be ground up.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529

 

[EdStainless]

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.

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

 

[mrfailure]

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.

 

[IRstuff]

Irregular surface topology likely results in irregular answers.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529

 

[EdStainless]

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

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

 

[IRstuff]

I was referring to the surface irregularities of a typical, unweathered rock. Even then, it would, at best, pickup only surface materials.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529

 

[rconner]

FYI

https://www.yahoo.com/news/prospector-finds-huge-gold-nugget-031848166.html

;>)
All have a good weekend!

 

[mrfailure]

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.

 

[IRstuff]

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 forum1529

 

[Coctyle]

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.

 

[bennylava]

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.

 

[bennylava]

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

 

[NBrink]

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...

[ul]
[li]If you're prospecting for gold, it's likely you'll be finding dust, flakes and maybe some small nuggets, not massive veins[/li]
[li]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[/li]
[li]Higher frequencies (shorter wavelength) radio waves do not penetrate the ground nearly as well as lower frequency radio waves[/li]
[/ul]


Nathan Brink

 

[Compositepro]

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.