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GeneralMetal detectors in mineral hunting?
22nd Apr 2014 20:59 UTCHenri Koskinen Expert
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
22nd Apr 2014 22:26 UTCMichael Wood
23rd Apr 2014 00:12 UTCAlfredo Petrov Manager
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
23rd Apr 2014 09:11 UTCStefan Oertel
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
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
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
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
Ilkka
23rd Apr 2014 16:33 UTCBeth Schaefer
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
25th Apr 2014 16:03 UTCPaul Brandes 🌟 Manager
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
Henri
5th Sep 2014 10:27 UTCEugene Ruhinguka
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
5th Sep 2014 16:38 UTCDoug Daniels
5th Sep 2014 20:19 UTCAlfredo Petrov Manager
12th Sep 2014 13:26 UTCDavid Gunning
12th Sep 2014 17:28 UTCUwe Ludwig
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
12th Sep 2014 21:47 UTCRoger Curry
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
Good hunting!
Jim Urbaniak
13th Sep 2014 08:56 UTCUwe Ludwig
Rgds
Uwe Ludwig
"
14th Sep 2014 22:35 UTCToby Billing
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
25th Dec 2014 19:56 UTCRyan Allen
26th Dec 2014 02:45 UTCHoward Heitner
26th Dec 2014 05:19 UTCD Mike Reinke
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
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