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PI sensitivity

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Digger Bob brought this to my attention.

I have read about it on other forums.

PI machines will detect gold nuggets very deep but when you dig them up, the signal becomes a lot weaker.

Has anybody ever witnessed this? That is supposedly the reason PI machines will not air test very well. Is it the halo around the nugget before it is disturbed?


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Hi Jim,

Yes It is very true. I have dug 1 gram nuggets at like 14" with a 16"NF coil, but once they were out of the hole I could only hear them around 10"

There is a definite halo around them that gives them a more pronounced signal.

I have also found this to be true with tiny iron shavings. I have dug small metal shavings at great depths, but as soon as you disturb the halo around them, and get them out of the hole the signal strength diminishes dramatically.

Hope this helps.


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Gold does not put out a halo, but when you breakup the conductivity of the ground, then it either won't detector the same target if you put it back in the hole or will have very weak signal, specially if larger. Minelab talks about this in one of there earlier manuals, I believe on th SD2100, have not seen recent manuals. Don

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I've pondered this phenomenon for some time. I think a definitive answer depends first on focussing more clearly on just what a "halo" is, ie, what are we talking about? A halo of a gold nugget itself or the halo of something else that often is associated with a nugget?

In a somewhat parallel analogy, some nuggets I find seem to be magnetic, ie, they actually jump to a magnet and stick to it. But we know in our heads that gold is not magnetic. Instead, some gold nuggets contain magnetically attractive material -- perhaps in little seams found on the nugget or in its crevices or perhaps in a core deposit or fold of the nugget.

At the beach we encounter extremely powerful halos and can actually "see" them (for example, the rusty colored sand surrounding a decomposing bottle cap). Once we alter the source of the halo (by digging and disturbing the matrix of stained sand), the signal no longer seems as strong when measured by sweeping our coil from the same elevation above the rusty bottle cap as when first heard (prior to disturbing the sand).

So is something similar occurring when we encounter gold nugget halos? In other words, is the halo of a gold nugget really the halo of some other material that is associated with (or combined with) the nugget?

I suppose that one way to test this issue would be to plant a 24 karat test piece to see if a halo develops over time. Natural nuggets typically are not pure gold. Thus, we never would be sure by burying a natural nugget whether a halo thus created was from the gold or the foreign material.

Interesting question Jim. Thanks for raising it.

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Well I am no geologist but most nuggets have a weaker signal strength out of the hole than before being dug up. I have proven this to myself multiple times.

Perhaps the nugget itself is not producing a halo, but maybe the minerals in the ground around the nugget are affected somehow.

Gator- I tried to understand your theory, but I just didn't get it. :Huh_anim]:

I have dug nuggets out of a hole, then put them right back into the same hole, at the same depth and swung my detector over them at the same ground level, and could not even hear a whisper.

I hunt mostly open flat ground in N-Nevada, and I swing 16" and 20" NF round monos. Most of the nuggets I find are deep and quiet.

And I guarantee small Iron shavings create halo's, because you can often see the visible halo around them in the surrounding soils.

Reno Chris would probably have the right answer for us.


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Gus, the best way I guess to further explain it, is just from what you did, when the earth is compacted and hasn't been disturbed the signal has a pathway, when it is dug you break up the pathway with gaps, air pockets etc that doesn't allow the signal the same path and capiblity to find its way to the target(if refilled)\, Air signal isn't as go, if hole is open will not read target. The compacted earth actual helps the signal penetrate magnitically. Don

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Hi All

No it's not true :angry-smiley-010: !! Gold does not create an aura even the minor amounts of alloyed silver or copper leaching is not enough to create a true aura unless it's electrum type gold :confused0013: . High deep concentrations of mineralization may enhance the depth abilties on a PI :hmmmmmm: . Iron, lead, copper are a tottaly different story and with iron sometimes you can hear just the remnent rust aura of what was a piece of metal that is completely rusted away :grrr01: . Once the aura is distubed the target vanishes or starts to disapear :twocents: . Happy Huntin John B.

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Since many here have noticed a cause and effect and the explanation is a halo effect does not mean that it comes from the target alone

Some such as Eric Foster and others have mentioned that the TX signal is absorbed by the ground around the target as well as the target , so it seems likely that something or mineralized outside the leaching of the target might be the cause, causing the RX signal to appear stronger before digging. The more the ground is compacted by time, it would seem that density might come into play along with the target, but the target is sort of a focus to that extraneous signal thru the target. Since that is what we're looking for, we notice it more.

There is another thing that happens that I read about . air gap resistance

There were fires last yr in So Calif and the high power lines started to arc from one to another even though there was , What 20 ft between them. The air resistance was calculated for clean air but the particles of smoke from the fires decreased the resistance and they arced. I don't know if this is correct about the compacted vs "fluffed up ground " vs air, but there is something , I'm just trying to guess what it is. Just remember I have never found a nugget with a detector nor have I played one on TV :innocent0009: Wyndham

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