soil content

[William1221]

If I approach a field that I have never hunted How would I know which coil to use with out knowing the mineral content. What criteria do I use to help me determine my coil selection? How do you determine mineral content in the soil?

 

[Aarong81]

You can choose your coil based on your preferred hunting style, such as CW relic hunting or coin shooting, before knowing the conditions of the field. Then the only factors that may make you want to change coils would be trash content, hotrocks, ect. Mineralization could change your preferred coil but it would have to be unusually harsh. There is a common misnomer among detectorists that the GND# determines the 'amount' of the mineralization. In fact, the GND# only determines the % of the ratio of magnetic stuff in the soil versus the amount of electrically conductive stuff in the soil. To illustrate I will quote Jeff Foster.....
"A fifty-pound bucket of soil that contains 10 pounds of magnetic mineralization stuff and 1 pound of electrically conductive stuff would be very bad ground. The same bucket with 0.1 ounce of magnetic stuff and 0.01 ounce of electrically conductive stuff would not be bad ground. Both buckets of soil would have the same VDI number. Both buckets would have magnetic stuff in a 10:1 ratio to the electrically conductive stuff."
Since both tests would have the same GND vdi #, it cannot determine how 'good' or 'bad' the mineralization is. As long as you can Ground balance and maintain stable operation you should be able to use any coil you choose. In some areas the mineralization may cause problems with one coil but in another area it does not, but BOTH areas could have the same GND vdi#. As long as the 'ratio' of minerals is the same, the amounts of each could be very different and result in the same GND vdi.
Why is there a GND vdi at all? Because the detector needs to be able to balance to the ratio of the minerals in the ground, magnetic vs electrically conductive. There may be less confusion in this area if only Whites didn't put the GND vdi info on the screen at all. Everyone understands why it is good to ground balance but often misunderstand the GND vdi. When you GB, the detector just grabs the info from the GND vdi, it has no idea as to "how much" mineral, iron, salt, electrically conductive stuff there is in the ground, just the ratio. But there are clues that can help you tell the 'amount' of minerals besides just knowing the ratio or GND# such as how stable the detector is or if an empty hole produces a signal. EMI interference is often mistaken for harsh soil as well and it is not something you can just change a setting to get rid of it. Smaller coils are less effected by EMI interference....as well as harsh soil mineralization. Just bring a smaller coil as a backup to a new hunting area and you will always be prepared for either case.
Full quote....
"(1) Mineralized soil is soil that contains stuff to which a metal detectors search coil reacts, which is not a buried target.
(2) There are two distinct types of mineralization stuff that is magnetic and stuff that is electrically conductive.
(3) Soil most often contains a mix of magnetic stuff and electrically conductive stuff.
(4) The more mineralization stuff there is in the soil, the more mineralized the soil is. Soil with a lot of mineralization stuff in it is often called bad ground.
(5) Mineralization stuff that is just magnetic always produces a VDI number near -95 (GND 84).
(6) Mineralization stuff that is just electrically conductive always produces a VDI number near 0 (GND 4).
(7) The grounds VDI number, for the MXT, the GND number would range between about 84 and 4) based on the relative mix of how much magnetic stuff versus electrically conductive stuff there is in the soil.
( Soil that has a mix of magnetic stuff and electrically conductive stuff in roughly equal proportions would have a VDI number (D.C. Phase) reading roughly halfway between -95 and 0 (around -47).
(9) The more magnetic stuff versus electrically conductive stuff there is in the ground, the closer the VDI reading will be to -95. The more electrically conductive stuff versus magnetic stuff there is in the soil, the closer the VDI reading will be to 0.
(10) The grounds VDI number only gives an indication of the ratio of magnetic stuff in the soil versus the amount of electrically conductive stuff in the soil. It does not indicate how much mineralization stuff is in the soil.
(11) A fifty-pound bucket of soil that contains 10 pounds of magnetic mineralization stuff and 1 pound of electrically conductive stuff would be very bad ground. The same bucket with 0.1 ounce of magnetic stuff and 0.01 ounce of electrically conductive stuff would not be bad ground. Both buckets of soil would have the same VDI number. Both buckets would have magnetic stuff in a 10:1 ratio to the electrically conductive stuff.
(12) The grounds VDI number does not indicate how bad the ground is. It does not indicate how much mineralization stuff is in the ground. It only indicates the relative amount of magnetic versus electrically"
SOURCE

 

[Larry (IL)]

To the best of my knowledge your ratio of magnetic to conductive mineralization is impossible.

Since all metals are electrically conductive, if you have 10 pounds of magnetic minerals, (metals) you must also have AT LEAST 10 pounds of electrically conductive stuff.

I think something is missing from Jeff Fosters quote.

 

[Aarong81]

I know that hot rocks come in two varieties, both magnetic and both are electrically conductive. They are also both on opposite ends of the VDI spectrum. If you have equal amounts of both and GB to that you would have a GND of around -47(mid range).
I'm not sure why he would have suggested that anything is not electrically conductive because everything has an electrical conductivity value unless it is an insulator with no electrolyte on/in it such as DIRT, SALT, impure WATER, ect. In other words, everything in the ground should conduct electricity to some extent.
I think it would make more sense if he used ferrous and non-ferrous minerals for his explanation. The fact that the established GND# is only a value determining the ratio of two elements competing with each other seems to makes sense unless it is actually a measurement of only ONE element which could then be MEASURED.