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  • Chemical Action around Metal in the Soil

    During my coinhunting experiences, I have observed a phenomenon, which I think takes place around all metals in the soil, not just single coins.


    What I’ve observed is this: I’ve observed this only on older coins, which might come from a depth (in the soil) of 5 or more inches. (I’m speaking now of a metal detector that does not indicate target depth.) The initial signal that I hear is clear and sharp, and would initially suggest a target that is either bigger than a Dime or Penny, or possibly a target that is only 2 to 3 inches in depth. Upon digging the initial plug, the target is not found, and when checking the hole, the signal seems weaker, but still in the center of the hole. Then, upon carefully stirring the dirt in the bottom of the hole, an older coin is found (perhaps a rather thin Silver dime). At the depth where the coin originally resided (assuming it didn’t fall down from the side of the first cut), the detector reading is much weaker than the original one, now that the surrounding soil has been disturbed. I have observed this phenomenon on many occasions.


    To me this suggests that there is some type of “chemical action”, which takes place around a long-time buried coin (or any metal) when placed in the soil. This action seems to be a “leaching” out of the metal, into the surrounding soil, such that the soil itself takes on the appearance of the metal. It is my belief that the original signal from a metal detector appears to be “bigger” because of this “leaching” out of the metal into the soil. Of course once the soil is disturbed, the field or halo is disturbed and it no longer provides the same intensity of signal because now, all that is left is the mass of the coin itself.


    I’m fairly certain that this same phenomenon occurs on larger masses of buried metals as well. A few years back, Dr. Manuel Ortiz called this “field” F.E.R.F. I believe this was his term, which stood for Free Electron Radiation Field. Probably other researchers have observed the same phenomenon, and termed it something else, but it had the same derivation. I’m sure that when people bury “test targets”, and say that they must “age” for awhile –it is this “field” that is being generated over time.


    I’m familiar with, and have studied, the general corrosion processes, which take place in the soil around refined (Iron and Steel) metals and the Less Noble metals.


    My questions are in regards to the More Noble Metals, when they are situated in the soil. Metal such as Gold, Silver and even Copper. I’d like to find a logical, perhaps chemical or electrochemical explanation for what happens around Noble Metals in the soil. What processes are involved? Are they electrical in nature, or chemical, or perhaps electrochemical? Is it a migration of ions, or electrons (or neither or both)? Is radiation from the Sun involved? Do other Less Noble Metals in the same vicinity play a part in the process? What part does soil conductivity and soil moisture play in this action?


    If anyone knows of any sources of information, I would appreciate any info or recommendations of book references (or the like) that I might find in a university library.

  • #2
    Re: Chemical Action around Metal in the Soil

    hi


    can not say as to documentation on this...


    there are very few compounds/complexes with the


    noble metals..with gold the cyanide and also a


    gold chloride (chloroauric acid-HAuCl4) and


    also aqua-regia...do these or can these occur


    in nature--hydrogen from water,chlorine from


    salt---must be correct conditions---temp/presure/


    ph/etc...this probably adds not to that you


    know though...perhaps though you not consider


    the organic mechanism...the yucca plant can


    pull the silicon from soil---that why the leaves


    are as such...there is also---truely----bacteria


    that eat gold---again no reference--just some


    words heard/seen/read etc. through life..


    reg-rick

    Comment


    • #3
      Re: Chemical Action around Metal in the Soil

      Hi Sam and Rick,


      This effect has always been a puzzle as it is hard to understand how such a tenuous addition of metal ions into the soil could enhance detector performance. Maybe, there is an alternative explanation. One effect that is observable with a PI detector is that coins, rings and other metal objects often give detection ranges greater than would be expected when buried in a wet beach. The explanation that I favour for this effect is that because a wet beach is conductive, the transmitter pulse from the search coil must induce a current ring in the beach itself. This pulsed current in the beach must in turn induce eddy currents in an included metal object. These secondary currents would add to those induced directly from the coil. The net result is to make the transmitter coil appear nearer to the object than it really is, thereby giving more range and a broader signal. This explanation is backed up by a geophysical paper that I have at the office that deals with the effect of conductive objects in a weakly conductive media when excited by a pulsed magnetic field. When I next go in, I will try and locate the title and post it for those that want to do further research.


      What occurs with a pulsed field must also occur with sinusoidal fields as generated by IB type detectors and one presumes that frequency plays an important part, with higher frequencies showing the effect more. Generally speaking, sinewave detectors do not work well on a wet beach because the response to the medium conductivity is too great. However, on inland soils which are less conductive, the generated current in the ground may still be sufficient to give the enhancing effect. Also, this fits in with the phenomena that as the object is dug, the signal often diminishes. This would be due to the fact that the path of the current ring in the ground is broken up and interrupted by the digging process. Also, objects that are recently buried would still be surrounded by disturbed soil and time would be necessary to allow the soil to compact and stabilise so that current paths could be established. If this explanation is correct then objects buried in dry sand would not have any enhancement as there would be no conductivity.


      Eric.

      Comment


      • #4
        Re: Chemical Action around Metal in the Soil

        hi eric-


        next in study is control---make a test bed,perhaps


        inside a greenhouse,(the origonal post suggests


        light also a factor---if the limited transmition


        of wavelengths is acceptable because of glass/plastic)


        in order to establish some general cause/effects..


        starting with wet/dry etc...the nobel metals leach/


        ion effects must be far less than metals with higher


        reactivity as zinc,copper etc.----myself in the lessons of life---in the study of vaccume---a paper


        read on entraped water in metal at high temperature-


        (red hot)--biologic entities that eat gold---and


        many other such odd things (that can be qualified or


        quantified)---led me to conclude---a man can study


        sand for a lifetime and learn nothing about sand---


        the semiconductor....myself to study this,any more


        fat to the fire, will cause an overflow---still


        have to finish build the detector...still at bench-


        no field work for me--and winter coming on--software


        to write........................................


        regards-rick

        Comment


        • #5
          Title of paper.

          Approximate calculations of the transient electromagnetic response from buried conductors in a conductive half space. Mc Neil, Edwards and Levy. Geophysics, Vol.49 No.7 (July 1984, p918-924).

          Comment


          • #6
            Re: Chemical Action around Metal in the Soil

            Thanks, Eric. You propose an interesting reason for the observed reaction that I had not considered.


            I can't say that I've ever observed the subject phenomenon in extremely dry or sandy soil, but perhaps someone else has.


            All of my experience with this phenomenon has been seen in the rich top soils of Iowa. The soil can range from very dry to fairly moist. Conductivity levels would range accordingly, but probably never gets as conductive as beach sands, and never as dry as desert conditions.


            One characteristic we do have, however, is fairly high iron and mineral concentrations, in a lot of areas. Some areas are so mineralized, as to make them almost impossible to hunt in, without a really good "ground balance" circuit. Even then, I suspect the overall depth of penetration is reduced significantly.


            If I understand you correctly, you don't really subscribe to the theory that Noble metals, in the soil, can "leach" out into the surrounding area over time, thus creating what would appear to be a slightly larger target area. Or, is it that you just have never found any substantial evidence to support this theory?


            I appreciate your comments, and if you could find that geophysical paper, I would like to know the title.

            Comment


            • #7
              Re: Chemical Action around Metal in the Soil

              hi again-


              had to go earlyer--another thoughts--water (pure)


              is an insulator--therefor ions are involved---even


              in central us far from ocean there is salt in the


              air...which by way makes it to ground...not sure


              on positive/negative ions but could it be that


              simple attraction/repultion mechanism in vicinity


              of metal is involved ? causing an aglomeration of


              ions near/away from metal--produce this "halo" effect.


              the ionic conduction must be sluggish at best in


              the matrix of soil/sand--more loss of energy as heat..


              maybe when things here slow down--me study---make


              ring of tubing (hula hoop) fill with salt water


              add to dry ground look for wider pulse/rhase change


              etc...would be interesting study..


              regards-rick

              Comment


              • #8
                Re: Chemical Action around Metal in the Soil

                Hi Sam and Rick,


                What actually takes place in a soil when subjected to an electromagnetic field is likely a sum of different effects resulting from its conductive and magnetic properties. The geophysical literature describes various phenomena relating to the detection of conductive orebodies and as it is only a matter of scale, similar effects must also occur in the detection of small metal objects at shallow depth. Orebodies often have “halos” which enhance the signal; induced polarisation can also distort the decay curve with pulsed fields. Magnetic minerals can bend or deflect the field from the coil so that detection ranges are sometimes reduced, other times enhanced. Much of my hobby detector R and D has been related to beach and underwater detection where the enhancement effect of eddy currents in the medium seems to me the to be the best explanation. Particularly so, as the effects discussed have been observed with gold coins and rings which do not leach or oxidise in the same way as other metals. In England we occasionally find Roman gold coins which have been buried for nearly 2000 years and they are just as bright and with the design as detailed as the day they were lost.


                Controlled experiments in the ground are incredibly difficult to do as it is almost impossible to change only one parameter at a time. I have tried burying coins in a plastic sleeve to insulate them from the surrounding ground, removing and replacing just a core of soil to give minimum disturbance but the results have never been really conclusive.


                Eric.

                Comment


                • #9
                  Re: Chemical Action around Metal in the Soil

                  >Hi Sam and Rick,


                  >What actually takes place in a soil when subjected to an electromagnetic field is likely a sum of different effects resulting from its conductive and magnetic properties. The geophysical literature describes various phenomena relating to the detection of conductive orebodies and as it is only a matter of scale, similar effects must also occur in the detection of small metal objects at shallow depth. Orebodies often have “halos” which enhance the signal; induced polarisation can also distort the decay curve with pulsed fields....


                  So, what physical mechanism would you suppose is responsible for these halos? Could this be subtle ion drift, which grows ever stronger the longer the surrounding soil is undisturbed?


                  I've always wondered about this possibility: What about the electrochemical actions that might result in the soil (the electrolyte) between dissimilar metals. In particular, metals at great distance from each other in the Table of Electromotive Series Potentials. As an example, say we have a Gold bar buried in somewhat moist soil (a suitable electrolyte). Could it enter into some electrochemical action with nearby (a few feet) steel or iron, such as a steel fence post? Further, would this action between two dissimilar metals be sufficient to cause some or all of this "halo" effect, due to the buildup of ions (of one polarity or another) in the surrounding soil?


                  I have experimented with these dissimilar actions at some length, but as I believe you mentioned, found it quite difficult to establish any repeatable or concrete evidence to support my theory.


                  Just some food for thought....


                  I appreciate your insight and info.

                  Comment


                  • #10
                    Re: Chemical Action around Metal in the Soil

                    >Hi Sam and Rick,


                    >What actually takes place in a soil when subjected to an electromagnetic field is likely a sum of different effects resulting from its conductive and magnetic properties. The geophysical literature describes various phenomena relating to the detection of conductive orebodies and as it is only a matter of scale, similar effects must also occur in the detection of small metal objects at shallow depth. Orebodies often have “halos” which enhance the signal; induced polarisation can also distort the decay curve with pulsed fields. Magnetic minerals can bend or deflect the field from the coil so that detection ranges are sometimes reduced, other times enhanced. Much of my hobby detector R and D has been related to beach and underwater detection where the enhancement effect of eddy currents in the medium seems to me the to be the best explanation. Particularly so, as the effects discussed have been observed with gold coins and rings which do not leach or oxidise in the same way as other metals. In England we occasionally find Roman gold coins which have been buried for nearly 2000 years and they are just as bright and with the design as detailed as the day they were lost.


                    >Controlled experiments in the ground are incredibly difficult to do as it is almost impossible to change only one parameter at a time. I have tried burying coins in a plastic sleeve to insulate them from the surrounding ground, removing and replacing just a core of soil to give minimum disturbance but the results have never been really conclusive.


                    >Eric.


                    REPLY by Dell:


                    Eric, I've followed your web pages since you began and in my humble opinion you provide the most usable information of the effects of electronics interaction with Earth science than any other on the internet. My friend Jack Goodier contacted you and was also impressed with your sincerity, and willingness to help with the abundant knowledge of your experience.


                    I hope Sam & Carl benefit from your wisdom as much as I have in my own endeavors.


                    Dell, "on the trail to Treasure"

                    Comment


                    • #11
                      Re: Chemical Action around Metal in the Soil

                      hi again--


                      so then if this is because of a sum of effects,


                      to change only one parameter might yield to the


                      conclution of uncertain...interesting would be


                      to study..again not me now--but one more thing-


                      sometimes to know all (most-almost all) of the


                      particulars can to some take the "joy" out of


                      the endever...for me 30 years ago start to fix


                      tv--was very exciting--now ho-hum...a way to


                      make a buck---but with md there probably will


                      be at least some surprise unde the coil---


                      can't hardly contain to get this done to also


                      first hand "see" this effect...


                      regards-rick

                      Comment


                      • #12
                        Re: Chemical Action around Metal in the Soil

                        >So, what physical mechanism would you suppose is responsible for these halos? Could this be subtle ion drift, which grows ever stronger the longer the surrounding soil is undisturbed?


                        >I've always wondered about this possibility: What about the electrochemical actions that might result in the soil (the electrolyte) between dissimilar metals. In particular, metals at great distance from each other in the Table of Electromotive Series Potentials. As an example, say we have a Gold bar buried in somewhat moist soil (a suitable electrolyte). Could it enter into some electrochemical action with nearby (a few feet) steel or iron, such as a steel fence post? Further, would this action between two dissimilar metals be sufficient to cause some or all of this "halo" effect, due to the buildup of ions (of one polarity or another) in the surrounding soil?


                        Like you, I had thought about ion migration causing halo effects. But after talking to a couple of electrochemists, I don't think that can happen with gold. It is an incredibly stable element and only in very rare conditions can you make it react with anything. And those conditions just don't happen in soil no matter what the moisture or mineral content might be. Silver and copper are definitely a possibility for ion migration, though.


                        I had not thought about Eric's explanation, but it does make sense. As you know, I like to come up with ways to experimentally test theories, so here are some thoughts on this. Dig some large holes, say 24" diameter 12" deep. Placing a single silver quarter at the same depth in each hole, cover them in different ways: loose soil, hard packed soil (use a compactor), soil that is heavily salted (conductive), soil with mineralization (iron oxide), added moisture, etc. Use builder's sand if your native soil is already mineralized. An alternative to digging holes is to use large containers, like 5 gallon sheetrock/paint buckets that are scattered all over new construction sites.


                        With maybe a half-dozen holes and various combinations you should be able to get a good feel for how the surrounding soil affects depth. If Eric's idea is correct I think the hard packed moist-salty soil should improve depth. I would also like to see the difference between an IB-phase machine and a PI detector, but I do not (yet) have a PI. If there is no improvement then that certainly leaves open the possibility of long-term ion migration which is difficult to test for.


                        Any thoughts? Know a good source for powdered iron oxide (besides my pickup)?


                        - Carl

                        Comment


                        • #13
                          Re: Chemical Action around Metal in the Soil

                          Hi Sam, Rick, Carl and all,


                          From my experience with beach conductivity tests it would be better to have a larger hole, or container, than 24 x 12in. The reason is this:- the magnetic field from even a 10in search coil extends several feet both into the ground and laterally. How far you can detect a car both on axis and sideways is a good indication. As the transmitter switches off, in the case of a PI, a current will flow in the conductive soil which will attempt to maintain the field as it was at the instant before switch off over the whole volume of soil that is excited. The current rapidly dissipates itself due to the resistivity of the soil, diffusing inwards and downwards as it does so. It is this collapsing secondary current over the excited soil volume which modifies the object response.


                          With the more conductive seawater, even a five gallon container of the stuff is undetectable, while a detector on the wet beach, or worse still in the water itself, gives a large signal, depending on the pulse delay. Once, in the early days of madness, we added salt to a swimming pool to bring it up to the composition of seawater. Result, no signal.


                          To stand a chance of getting any useful result with various soils you would probably need to have a hole, or container, at least three feet diameter and three feet deep. The diameter is probably more important, as most soils do not extend to three feet before there is a discontinuity to the subsoil or bedrock.


                          It gets even more complicated if you wish to add magnetic minerals. The mineral Magnetite will distort the field from the coil without, of itself, giving any signal, while Maghemite will distort the field and give a signal. Magnetic soils usually contain both minerals in varying proportions. (for a detailed study of magnetic soil minerals look up articles by E. Le Borne in Ann. Geophysique 1955 and 1960). Add to this the ground conductivity which tends to be layered and you have the makings of a PhD research project.


                          Eric

                          Comment


                          • #14
                            Re: Chemical Action around Metal in the Soil

                            >From my experience with beach conductivity tests it would be better to have a larger hole, or container, than 24 x 12in. The reason is this:- the magnetic field from even a 10in search coil extends several feet both into the ground and laterally. How far you can detect a car both on axis and sideways is a good indication.


                            My thought on this is that the "far-field" should have a rapidly diminishing influence on this "double-induction" effect. If a current ring is being produced, I would think that it would be strongest directly under the coil where the flux density is not only highest, but the flux is fairly perpendicular. You may be right, so it adds another parameter that can be looked at.


                            I started dwelling on this a little more - I can see the possibility of double-induction with PI detectors because they are time-duplexed. That is, the transmit pulse induces the soil current ring which then gives a boost to the target eddy current during the receive mode.


                            But will this also happen with IB detectors which are continuous-time? I would think that any induced soil current ring has to take away from the induced target eddy current which decreases detection depth. In other words, with IB the soil is stealing energy. With PI the soil steals energy during the transmit cycle which should also reduce the target eddy current, but unlike IB it returns its energy during the much more sensitive receive mode. I don't know, I may be WAY OFF on this one!


                            >It gets even more complicated if you wish to add magnetic minerals. The mineral Magnetite will distort the field from the coil without, of itself, giving any signal, while Maghemite will distort the field and give a signal. Magnetic soils usually contain both minerals in varying proportions. (for a detailed study of magnetic soil minerals look up articles by E. Le Borne in Ann. Geophysique 1955 and 1960). Add to this the ground conductivity which tends to be layered and you have the makings of a PhD research project.


                            Yes, it does get complicated very rapidly, which is why I think you have to try and limit the variables as much as possible. Like using builder's sand or some other inert "soil" that you can mix to a specific and repeatable level of mineralization or whatever. This is why I consider product test reports to be worthless - they are conducted over grossly inconsistent soils.


                            Thanks for providing references. I hope to get around to some of this testing in the future and will start by looking up those articles.


                            - Carl

                            Comment


                            • #15
                              Re: Chemical Action around Metal in the Soil

                              Yes, thank you all for your ideas and insight.


                              As with most things of this nature, there always seem to be more questions than answers, and lots of considerations to think about.


                              When time permits, I want to try a few of the experiments that were outlined above. I'll let you know what sort of results I get.

                              Comment

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