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GeneralMetal detectors in mineral hunting?

22nd Apr 2014 20:59 UTCHenri Koskinen Expert

I have never heard of anyone using metal detectors as a tool in rockhounding and searching Mindat does not yield much info about metal detectors either.

Does anyone have experience with metal detectors? What kind of minerals could metal detectors be used to spot?

If I buy one and test it in a calcite quarry where nice fluorite is found together with marcasite/pyrite would it be of any help? What about cassiterite, columbite, silver, copper etc.?

Henri

22nd Apr 2014 21:32 UTCDavid Von Bargen Manager

Metal detectors are used extensively in looking for native copper in the Upper Peninsula of Michigan. It is also useful when looking for native silver or gold nuggets, I would also think that it could be used for iron meteorites. You are basically only able to find metallic minerals with a detector.

22nd Apr 2014 22:26 UTCMichael Wood

I seem to remember, while I was messing about with minerals as a kid, that certain metal sulphides (pyrite or chalcopyrite spring to mind) conduct electricity. Would a metallic mineral, (such as chalcopyrite) if it were capable of conducting electricity to some extent, be picked up by a metal detector?

23rd Apr 2014 00:12 UTCAlfredo Petrov Manager

I once checked every thumbnail-size crystal in my collection to see which ones would cause a metal detector to react, with some interesting results.

Minerals with non-metallic luster do not of course usually conduct electricity and so elicit no reaction from a metal detector, with a very few exceptions. Cassiterite is an exception. I hear blue diamonds are also an exception, only blue ones. (Anyone have a TN blue diamond they'd donate for testing? :-D )

Minerals with metallic luster give very variable responses. Native metals and semimetals all give strong reactions, and graphite too (which causes lots of problems for gold hunters in some types of rock). The sulphides are quite variable: some always react (galena, covellite, pyrrhotite....), which causes trouble for gold hunters. Some almost never react, like marcasite, sphalerite, and the many species of sulphosalts. (A metal detector can be a good tool for distinguishing massive sulphosalts from massive sulphides; the bonding in sulphosalts makes them much less conductive.) A few oxides are conductive (eg: magnetite), but not many.

Unfortunately some of the most common metallic-looking minerals (like pyrite, chalcopyrite, hematite...) give inconsistent responses, being sometimes noticeably conductive and sometimes not, perhaps depending on impurities present, or on their physical integrity (eg: a large perfect pyrite crystal is likely to react, whereas a massive pyrite concretion will not).

Some models of detectors can discriminate between magnetic conductors (iron, magnetite....) and nonmagnetic ones (gold nuggets, aluminum cigarette box paper...). But any claims made for detectors that can allegedly distinguish between gold, silver, copper, aluminium, etc. should be taken with a grain of salt.

23rd Apr 2014 01:41 UTCReiner Mielke Expert

The biggest problem with metal detectors is garbage such as blasting caps, pull tabs, nails, rusty wet iron, aluminum etc. Other than that they can be useful if something of interest is associated with something conductive and you do not mind digging up a lot of trash. Metal detectors can discriminate between different metals sometimes but not always because there are so many variables involved. Of course some machines are better than others at it, but generally the more expensive the machine the better it will be. Metal detectors are also designed to be better at detecting certain metals in certain ground conditions so no one machine is best at everything.

23rd Apr 2014 09:11 UTCStefan Oertel

I am using wall scanners for ore mineral detection for several years. They are light weight and a great tool to run over mine walls to see where the ore body starts. It also is a great help in deciding which rock to hammer or take home for cutting. Meanwhile I have several generations of Bosch scanners at home....

While conductivity was mentioned before, the scanner and metal detectors also detect magnetic materials (magnetite, pyrrhotite...). Here is a short but nice description of and a rare view into an opened Bosch scanner:
How it works: Wall Scanners

And my one in action in northern Italy on some pyrrhotite ore body:
http://www.uranglasuren.com/ores/Technique_1/files/dmf.jpg

Cheers,

Stefan

PS No, I am not affiliated with Bosch, I just like them.

PS2 Don't rely to much on them, you might miss some stuff....

23rd Apr 2014 10:09 UTCHenri Koskinen Expert

Thanks for all the comments.

I found some data on electrical properties and resistivities of minerals

http://crack.seismo.unr.edu/ftp/pub/louie/class/492/data/2011/GPH492_ALL_FILES_2011/AppliedGeophysics_Telford/AppliedGPH_ElectricalPropertiesOfRocksAndMinerals.pdf

Newer and better models of metal detectors (costing 500 dollars or so) are claimed to be quite sensitive and should be able to discriminate between various sources of beeps,but that's according to the ADDs.

Henri

23rd Apr 2014 10:26 UTCChristian Auer 🌟 Expert

Funny that I wanted to start a thead about metal detecting today.

Reason is that I`m a proud owner of a XP Deus, bought just recently.

Last weekend I tested it on a historic mining area. To my biggest surprise I din`t only find old coins (1800-1812) but als some very interesting galena-pyrrhotite boulders. That`s all I can say till now.

Maybe we can compare a bit technical datas like used frequency, ...?

23rd Apr 2014 12:51 UTCHenri Koskinen Expert

Hello Christian

I don't have a detector but have been thinking about buying one. There is a Garret AT PRO/GOLD version that costs about 600 euros and a cheaper one called ACE 250 (260 euros) that are said to have good price/quality. XP Deus is a bit more expensive I believe, depending on the exact version.

I tried to find discussion in the NET about using detectors for mineral hunting, but there seems to be very little data to be found, apart from gold/copper prospecting. Your positive comment about finding pyrrhotite/galena is about the best info (along with other comments in this thread) I have seen so far.

Pyrrhotite should be a good conductor and galena is sometimes a good conductor, that's what I have read anyway. I would be very interested to read here if you make additional observations. If I decide to buy a detector I will post my observations also in this thread.

Henri

23rd Apr 2014 14:43 UTCIlkka Mikkola

The big nodules of metallic antimony at Seinäjoki, Finland were found with metal detectors

Ilkka

23rd Apr 2014 16:33 UTCBeth Schaefer

Ooh - a physics question!

Metal detectors can detect ferromagnetic materials or diamagnetic materials. They do this through Faraday's law of induction. A changing magnetic field is produced by the metal detector; when this is passed over a ferro or diamagnetic material a current starts to flow in the material. This current created in the specimen creates its own magnetic field, which is then picked up by the receiver coil of the metal detector. The key word is changing magnetic field - you won't pick up a current unless the original magnetic field is changing. An oscillator produces current in the field coil which produces the initial changing magnetic field. The current induced in the sample produces its own changing magnetic field, which then induces a voltage (current) in the pickup coil.

Ferromagnetic materials will create magnetic fields in the same direction as the original magnetic fields, diamagnetic materials will produce magnetic fields in the opposite direction to the original field. The degree of response depends on the type of material (i.e. its magnetic susceptibility). Ferromagnetic materials have positive susceptibilities, diamagnetic materials have negative susceptibilities. The resistance of the material also will affect how the current flows in the material.

Just because a mineral has metal atoms in it doesn't necessarily mean it will react to a metal detector. And a gold bar from a bank will react differently than a natrually formed gold nugget in the ground, because of the difference in conductivity - the natural gold sample will have pits (voids) that will inhibit flow of current, while a gold bar in Fort Knox has no such issues.

If you like more technical information, I found a very good site that talks about how metals detectors can be set to ignore ferrous materials, and discriminate amoungst the non-ferrous metals (for instance, to ignore the aluminum soda can tabs). This site also has an exhaustive discussion about the effect of soils on metal detecting.

http://www.minelab.com/__files/f/11043

Here is a good paper from The Physic Teacher about Faraday's law and its application to metal detectors (from Colorado School of Mines)

http://inside.mines.edu/~jamcneil/TPT_MetalDetector.pdf

23rd Apr 2014 18:12 UTCJohn Truax

It takes practice to become excellent at metal detecting, but people are clever and some become surprisingly good at deciphering the beeps, and reading the displays. In Michigan a digging friend uses them to distinguish between copper filled nodules and copper included agate nodules, each give a slightly different reading. Using a detector we are able to know there were copper included agates inside of the boulders were were moving and that was very useful.

25th Apr 2014 16:03 UTCPaul Brandes 🌟 Manager

In addition to John's post above, many of the Michigan copper-agate hunters don't use the full sized detectors. Rather, they will use "pinpoint" detectors that have a very small probe at the end to determine if a nodule has copper in it or not. I personally use a White's Spectrum detector that has served me well for over 20 years now. In addition to finding many superb copper and silver specimens, I have also found some gold nuggets in Colorado (although a dedicated gold detector will be much better at finding gold).

Below is one of many Keweenaw specimens I have found over the years using a metal detector:

25th Apr 2014 19:08 UTCHenri Koskinen Expert

Thanks Paul and others who have contributed to this thread. I feel now compelled to buy a detector. I think it will be fun to play with a detector and I believe that there is real chance of finding something interesting.

Henri

5th Sep 2014 10:27 UTCEugene Ruhinguka

Dear all,

Can you tell me if there is a machine or metal detector that can detect detect deep underground cassiterite ore. if yes from where can I get it or what is its cost?

Thank you.

Eugene

5th Sep 2014 15:22 UTCReiner Mielke Expert

If cassiterite is not conductive ( you can test it with an ohmmeter) then an EM based machine cannot detect it. However even if it is conductive then you will not be able to detect it more than a metre away. If it is a large piece maybe further, it all depends on the size or conductivity ( may small pieces all linked together can act as if it where a single large piece).

5th Sep 2014 16:38 UTCDoug Daniels

There are geophysical instruments that may be useful in such a situation, using either electromagnetic induction or resistivity. However, you would need a fairly large body of cassiterite (or whatever), and it would be best to model the inferred deposit to see if the methods would work. And, the instruments (and associated software to interpret the data) are fairly expensive, running into the tens of thousands of dollars. You can also rent the instruments, but you would still need to know how to use them and how to interpret the data (so, hire someone who knows how to do it).

5th Sep 2014 20:19 UTCAlfredo Petrov Manager

The conductivity of cassiterite is quite variable. Black iron-rich varieties have the best conductivity. Eugene is probably looking for cassiterite of pegmatite origin, and the conductivity of that is lower, so I foresee little success using a metal detector.

12th Sep 2014 13:26 UTCDavid Gunning

A few years ago, while hoping to long-shot validate a double meteorite occurrence at Round Pond, on the Maine coast, I purchased a metal detector, a Tesoro, Campadre. The detector worked fine, beeping to beat the band. As it turned-out, however, much of the bedrock in that area is slightly magnetically prone, and so, as you might well imagine, I went home with plenty of beeping samples of purely terrestrial origins. Incidentally, it appears that the reported double meteorite strike may have been something of meteoric fantasy and/or fiction.

12th Sep 2014 17:28 UTCUwe Ludwig

According to my experience there are two sides of using a metal detector for mineral collecting.

Between 1990 and abt. 2010 some mining dumps in my region have been recultivated. Because of the relatively much silver minerals in the dump material we all had metal detectors to scanning the fresh cut dump sites. Yes, the one side - besides a lot of metal pieces as nails, wire, old tools we found silver specimens, too. However, at the other side - we became nearly blind for the other minerals on the dump surface because we were concentrated only for the peep-sounds.

I think metal detectors are a must for meteor hunters and collectors for battle artefacts etc. For collecting minerals it is not binding necessary to have one.

Rgds

Uwe Ludwig

12th Sep 2014 20:29 UTCStephen Moreton Expert

For reasons I do not understand, the dendritic native silver from the Alva silver mine, Scotland, gives only very feeble responses on my detector, if at all. This in spite of some pieces being very rich (see pics here on mindat of dendrites up to 3 cm long). The only silver I have ever detected there had Queen Victoria's head on it! I did find one pea-size bit of rammelsbergite, which gave a strong signal.

12th Sep 2014 21:47 UTCRoger Curry

Hi Stephen.

The way detectors work is by inducing a current in anything metallic. If you were mad, and rolled up a dendrite into a tight ball, then the current would be able to circulate within the ball and become "detectable". But with the dendrite, the current can only circulate in tiny volumes - the diameter of the individual wire crystals.

I think...!

Regards,

Rog

12th Sep 2014 22:26 UTCJames Urbaniak

My experience as a rockhound with metal detecting in some manner relates to Uwe's comments; however so that I don't become blinded to other mineral opportunities, I often use my detector to identify a good prospecting site. I understand too it can be an invaluable tool in searching for meteorites at the beach and in the desert. I've not had success hunting for meteorites but I only have a few short hours in and plan on giving it more chances, since meteorites are few and far between. I have learned the 'temperment' of my detector over the years though and have been able to tune into what it can and can't do. One of the earliest problems I had, as I was learning to use it, was that I found I wasn't digging deep enough for my hits and that I shouldn't give up just because I'm 15cm into the ground.

Good hunting!

Jim Urbaniak

13th Sep 2014 08:56 UTCUwe Ludwig

I think the reason whether a signal is strong or weak in any cases depends on the detectors signal methode. There are two methodes: the "move" detecting an the "no move" detecting. In the first case the signal comes only if the detector head is moved over the subject and in the second case the signal comes also if the head is remaining above the subject. I think the move-detectors are cheaper as the no-move-detectors.

Rgds

Uwe Ludwig

"

14th Sep 2014 22:35 UTCToby Billing

Metal detectors are in very wide usage in Australia for gold hunting. I use one (Minelab GPX4000, a pulse induction type detector) for nugget hunting and also when I'm digging a gold bearing reef I'll detect the quartz with a small coil and pick out the specimens for trimming.

The type of detector I use is very difficult to use on hardrock mine dumps as it is so sensitive it will pick up the tiniest bit of a detonator shard and flakes off picks and drills etc. and there is a LOT of that stuff in mullock.

They can be a great tool and a mate of mine has used a discriminating VLF type detector on heaps to find silver and copper specimens, you do need the right detector for the job you are doing with it and to know how to use that type and model detector well. An experienced operator can find gold where many others have not or have missed many bits.

25th Dec 2014 16:33 UTCcharles gittings

It seams to me a combination of detecting old mine dumps along with a screening the waste rock would work, say with a vibratory set up with water,go through the hole dump,it shouldn't take long to know if it's going to work or not

25th Dec 2014 19:56 UTCRyan Allen

I use a whites mxt and find it difficult. Not much for gold ever found in this area. I usually have to crank the iron discrimination right up or i end up digging bits of logging metal. I still find it amazing at what VDI reading different rocks give. The most rusty metallic looking stuff i can visually find usually wont even give an iron hit. Then there is this drab looking light brown material that appears like a granite that sends the machine for a loop every time. Some of the almandine matrix i find gives off a particular tone but its not strong enough to give VDI. Pyrite ive found with the detector is usually in nodes and gives off avery strong VDI reading almost identical to a gold nugget. Using a detector is great to comb over places ive already done visual inspections in case i have missed something. I very rarely use the detector on recon days as its awkward in dense underbrush and to be truthful even on virgin ground if its highly mineralized you could spend days digging nothing. I know i have :) Lets not forget about the time i spent hours picking fish hook tips out of calcite rhombs thinking i was onto something big. Ended up being a favorite high water trolling area for fisherman. Modern day fish hooks give a wide variety of VDI readings. Biggest asset to using a detector is patience

26th Dec 2014 02:45 UTCHoward Heitner

Metal detectors have been used to look for placer gold deposits in streams that are known to have gold. They are not detecting the gold, but rather the magnetite that settles out in the same places on the stream bed.

26th Dec 2014 05:19 UTCD Mike Reinke

Ryan,

really?! That wasn't ancient calcite then, was it? Certainly not precambrian...<!> Where was the calcite forming? You wouldn't by any chance have a picture? I particularly like the "thinking I was on to something big." Been there with minerals! The elation is at least as high as reality is low.

Mike

26th Dec 2014 06:05 UTCRyan Allen

http://i864.photobucket.com/albums/ab209/billycap4u/The%20Lake/20140504_183401_5_bestshot.jpg

http://i864.photobucket.com/albums/ab209/billycap4u/The%20Lake/20140504_183419_2_bestshot.jpg

Not sure of its age...

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