How do you tell how mineralized your soil is?

[BamaBill]

With the talk of heavily mineralized soil in the detecting forums got me to wondering. How do you check to see just how mineralized your soil is? Are there any on-line sources that can give you an idea of how mineralized different areas are? Seems to me it would be useful if you're travelling somewhere to do some detecting and don't know what you're in for.

 

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[Sandman]

This is the main reason many buy a detector with a manual ground balance as it doesn't matter where you are, the detector can be balanced to handle the minerals. True they cost more, but so does a car with a better engine or radio. They all drive us from here to there, but some do it better.

 

[Tom_in_CA]

I believe you can do it this way: Crumble up a handful of the dirt, so that it's finely ground. Then take a magnet and wiggle it in the handful of dirt. The amount of specks or dust that stick to the magnet will tell you how mineralized the soil is. Of course, that won't give you a very good comparison to other soils, but at least it will show you that the soil isn't mineral free

I saw an illistration once, where a fellow took a plastic ziplock baggie of some sand from a beach gully washout, that was known for being very mineralized. Only a pulse machine would work in this black-sand portion of the beach. Anyhow, he took a large heavy magnet, and illistrated how mineralized the sand was, by showing that the magnet actually held on to the outside of the bag, while holding the bag in the air :P

There is also a function on a couple of Whites machines, like the XLT for instance, where you can hold the coil still on the ground, and it would read the mineral content of the ground, and give a # on a scale. I was never too sure what the application of that was.... as I never saw any purpose to use it.

 

[BamaBill]

Sandman, reason I asked is because I've read several people complain that in heavier mineralized soil the Tejon is reduced to the average depth of other detectors, even with it ground balanced. I know you can't believe everything you read on the Net, but I'm still sorting things out. Unfortunately, I don't have a Tesoro dealer near me where I can just go and find out the truth for myself. I just wish there were more Alabama MD'ers on here that could help me out, since this does seem to really depend on what area of the country you're detecting in. Unless you're telling me that with GB you can get the same performance from specific machines, regardless of location. Seems that the depth numbers I've read in places on the same machines are all over the map.

 

[99thpercentile]

This is a good question but it needs to be more carefully worded since there are several issues at play here. There are three physical properties that control the effectiveness of your metal detector: magnetic susceptibility, magnetic viscosity and electrical conductivity. My understanding of what most people on this forum are referring to when they say mineralized soil is some combination of high magnetic susceptibility and high magnetic viscosity. Another issue at play with sensors that ground balance is the spatial distribution of soil properties. It is entirely possible that the spatial variation of soil properties is on the same scale as the size of your targets. This is an issue we run into when looking for unexploded ordnance (UXO) or landmines. All metal detectors with ground balancing make some assumptions about a uniform half space, which means constant soil properties. So you can see there are a number of issues here.

As to how do you determine how mineralized a soil is, you can measure the magnetic susceptibility of the soil. There are a number of ways to do this in the laboratory or in the field. To determine magnetic viscosity, the magnetic susceptibility is measured at a number of frequencies and the change versus frequency is essentially the magnetic viscosity. I have listed some of the measurement systems below.

Bartington MS2 system (Field coils: D, F, H; Lab coils; B, C), whole system ~ $10K
ZH Instruments SM-30 field sensor ~$1500 (there are several other sensors in this size and price range)
ZH Instruments SM-100 lab sensor ~$9K

This is the subject of my PhD dissertation when applied to landmine detection.


Ryan

 

[Sandman]

Like the Geico Caveman, "WWWhat?"

 

[diggerfororo]

Without getting to technical, The easiest way is with a manual GB machine. I coin hunt with a Fisher CZ6 (one of the first prototypes)with manual GB. I ground balance my machine at every site I hunt. The GB nob has 10 settings and most soil in the midwest will Balance between 3 and 6. With 1 being the lowest and 10 the highest . If your soil is neutral than you will have a low setting and if it is highly mineralized you will have a high setting.

If you have a machine with auto GB it will be hard to tell except when you detect over pockets of high mineral and you will start getting false readings at normal sweep speeds. If you slow down and reduce your sensativity it should go away. Hunting in highly mineralized areas will effect your depth capabilities to a great extent.

Les

 

[EasyMoney]

With my cz-70, the closer I have to set the Ground balance toward 1 the more magnetite and hematite (iron) it has in the soil. The more i need to set it toward 10 there is usually more salt.

In my soil here in Oregon the thing works around a 1 to a 2 1/2, but in some "sweeter" less mineralized soil it will read more toward a 4. Rarely have I seen it work well around a 5 on the Fisher GB scale.

I know someone who lives in Ohio and his cz-70 has to be set between a 4 and a 5 most of the time.

 

[thompy]

hook up with someone with a T-2 or f 75 they could give you a reading off their FEo2 meter

 

[hollowpointred]

Like the Geico Caveman, "WWWhat?"

HAHAHAHA! .....can you put that in laymans terms 99thpercentile!

 

[ivan salis]

in simple non PHD (Piled High and Deep) type terms -- a dectector works by making a electric signal area under the detector -- as it is moved along it goes over metal objects -- the electric feild "reacts" to the metal -- the machine beeps --on cheap mechines thats it all you get is a beep ---on higher dollar type machines the machine can often sort out the type of metal it "thinks" it is based upon the type of signal the metal object is "returning" to the machine in the electrical feild and how deep it "thinks" it is by the strength of the signal ---differant metals being made of differant stuff react differantly sending differant signals back -- this is how the metal ID and depth feature works on most detectors-- "notch" or cancel works by say ignore certain types or range of signals -- commonly most folks tell the machines to ignore the iron range signals to get rid of nails or scrap iron-- often the ground itself has minerals like iron in it -- so the machine in a area where theres lots of "iron" naturally in the soil --- would see a solid sheet of iron --- to fix the problem requires that you be able to manually balance the detector so that it doesn't see the naturally occuring "iron" -- by adjusting the machine to ignore the local high level mineral content thus blinding it to the high iron levels in the soil --often cheaper machines have preset or have limited automatic type ground balancing abilitys fine in most places (say 90%) but that render then almost useless in high mineral areas --* for cheaper machines often the beach with its mineralized saltwater wet sand area is a nightmare -- the machine "goes nuts" beeping all the dang all the time --- for some all is not lost --true it will only work rather shallowly but by using low power / sen (just barely turned on) and the disc (at max) the machine often times can still be used although it will not run as deep-- thats it is simple 8th grade "billy bob speak"---Ivan

 

[99thpercentile]

Here was the original question, "How do you check to see just how mineralized your soil is? Are there any on-line sources that can give you an idea of how mineralized different areas are? Seems to me it would be useful if you're traveling somewhere to do some detecting and don't know what you're in for."

There are two physical properties that affect what you call the mineralization of the soil, magnetic susceptibility and magnetic viscosity. Magnetic susceptibility is the easiest to understand. It is the ratio of magnetization to applied field.

kappa = M / H
kappa = volume magnetic susceptibility (dimensionless, no units)
M = magnetization
H = applied field

Think of it this way, if you have two materials with different magnetic susceptibilities exposed to the same applied field. The material with the higher susceptibility would end up with a higher magnetization. All materials have a susceptibility, water for example is diamagnetic and has a very small negative susceptibility. Magnetite the most importation mineral in magnetic soils has susceptibility in the thousands. Read the PDF from the link below to understand in more detail.

Here is a quote from the following document. "The answer to this question can be as simple or difficult as you like! Let us start simply. Magnetic susceptibility, as we have seen, is basically a measure of how ‘magnetisable’ a material is."

www.bartington.com/media/1f7a0815/Om0409 J_Dearing_Handbook_iss7.pdf

The more difficult issue is magnetic viscosity. This is the most relevant to metal detectors since it is a function of changing magnetic fields, not static magnetic fields. The most common way to measure magnetic viscosity is to measure the magnetic susceptibility of a material at multiple frequencies. The amount of change is proportional to the magnetic viscosity. High magnetic viscosities cause metal detectors to behave poorly. Here is an analogy: magnetic viscosity is like a delay mechanism in the soil. Your metal detector is generating a time varying magnetic field, in the air their is no secondary field generated. If you did an air test with a metal target the secondary field would be generated by the metal object and return to the sensor almost instantly. If you repeated this test with the metal target buried in some sand from Home Depot the response would also be almost instantaneous. But if you buried the metal target in a highly mineralized soil then the secondary field will be slightly delayed. This causes the response from the soil and the response from the target to be almost the same.

I hope this is more in laymens' terms. If not, let me know and I'll try again.

 

[HMS Beagle]

I understand whats being said here, and I've had the same question. I'm not positive about it but, if its the magnetic properties. How does salt affect it. I always thought "ground mineralization" meant just that, ie: phosphorus, potassium, calcium, magnesium, sulfur etc. And if thats the case would'nt Ph paper be sufficent to indicate general "mineral" level?
Beagle

 

[ivan salis]

certian minerals* due what their made of --- are conductive (basically it reacts when exposed to the metal detectors electric feild) thus they cause problems --- most of the local farm bureau's will be able to tell you all about their local "soil" conditions.

* iron mainly

 

[EasyMoney]

Phosphorous, sulfer, and calcium are not good conductors of electricity. Neither are they capable of carrying a magnetic field of anything more than a nano half-second. None of the above are metalic in composition. If they were able to be bonded with a metalic substance they would have properties that would enable them to carry an electrical current, even if it were only 1/1000th of a watt. But they are not, and they do not, and if the electrons in each atom are not greatly attracted to the nucleous they will be highly unstable in nature and will not hold a charge long, electrically or magnetically. It would all burn off in a split second, much like the way a static charge quickly leaves a baloon when you rub it on something and stick it to a window, etc.

"Minerals" in a soil are considered by metal detecting buffs (and especially electrical and electronics engineers and technicians) to be those that are capable of carrying either a magnetic force, or an electrical one, or both. Hence, soils that have substances such as Fe (iron), or magnetite, or hematite, gold, magnesium, mangenese, etc, for example, ALL carry both electrical current if induced, and/or a capacity to carry a magnetic field, hence, a "mineralized" soil. Tinfoil is a combination of two metals together, an alloy. Gold is almost as good a carrier as silver for electricity, thus the reason why the silver scale is higher up than a gold one on an analog metal detector. Gold and silver make very poor to none as a magnetic carrier. Iron and iron ores do though and some rocks are exactly that, iron "ores", but not specifically iron.

If your soil was high-calcium and the calcium was conductive magnetically or electrically then a whole bucketful of old teeth recently dug out of the local cemetary would give a very good and loud response because they would be made almost entirely of calcium. Fortunately they are not and it does not,otherwise people may be mining calcium out of the cemetaries already.

If you want to know how many "minerals" you have in a soil, then run a magnet through it and see how many "iron filings" you find in it. These iron filings are the "minerals" in "mineralized soil" that people refer to.

Salt (sodium) is a mineral too, but not in the sense of a TH'ing person. They are merely types of "salt", or sodium, and there are many of them too, and yes, they really are minerals but don't carry electrical charges or magnetic charges.