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GPX 6000 Halo Effect On Small Nuggets


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I have several times observed disapearance of fast timing gold after disturbance. Either you treck it out (wish the 6k had a manual GB option like the 7k), or the timing constants change in relation to the ground mineralization as the small nugget gets moved and change position in the soil. This happens less likely with the SDC due to MPF.

GC

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I don't know how much the so-called "hole effect" can manifest itself in detection with a PI detector ... which often occurs in more demanding mineralized terrains ...

1. dig a hole not too deep ,, put a target in it ..- the target will be detected.

2. Then deepen this hole .... to such an extent ... that the targets in the hole will no longer be detectable.

3 .. Finally, cover the target in a deep hole ... with soil and and the deep target.. will be detectable again ...!!!

... to avoid such an effect ... the soil is gradually dug in the plane into a "flat hole" in the size of at least the width of the coil ....

Another advantage of digging a flat hole is that after the subsequent detection of a flat hole, you can find other targets that are stored even deeper.

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I'm in the doubting camp regarding halos. The well known weakness of PI detectors is detecting exactly what people describe the "halo effect" as being - detecting finely disseminated particles. And chemical leaching into soils is about as finely dissemenated as it gets, it's on the molecular particle size level. That reason alone makes me doubt it exists. But there are other reasons too.

The only copper mineral I've reliably found to give a "real" target response at any kind of depth beyond say 2 or 3 inches so far has been chalcocite, and only when in massive form, not diffuse.

The "halo effect" is often brought up in terms of edge of detection (or beyond) targets - that is to say - targets which wouldn't normally be thought to be detectable at the depth they were found. Yet, these diffuse sorts of oxides and sulfides when on ore chunks are almost always (in my experience) limited to close to surface effects on a detector and drop to zero very quickly at any kind of depth. And they are much more concentrated on the ore than they would be in a soil halo. So I'm confused how exactly they are presenting as target enhancers all the way down to the edge of detection in much more diffuse forms.

Alkali and other salts are diffuse, and can definitely sound like conductive targets. But they are generally massively distributed and go from the surface down to depth, and when damp are basically one giant conductor. Whereas the halo around a nugget is very localized, and must contain much, much less conductive material than the nugget itself in most normal cases. 

I don't see any measurable or repeatable evidence for the halo effect IMO, but I do see a clear, measurable, repeatable effect that target geometry and orientation has on edge of detection targets. And even on targets at any depth. I think this is the most logical explanation personally since we all agree it exists and can be measured. But I'm always open to learning something new, I'd love to see someone show some kind of evidence that the halo effect exists. Leaching can be sped up in situ, so it's testable.

Actually come to think of it, it's testable even without speeding up leaching. copper and silver oxides and sulfides must be present in fairly large quantities to be detectable on a metal detector. These quantities would show up as massive Ag/Cu soil abnormalities on an assay. So a person could pretty easily send some soil samples in from target with the "halo" effect, and some without, and compare.

 

 

 

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13 hours ago, Jonathan Porter said:

Halo effect is VERY probable and acknowledged by metal detector developers who I associate with, when a nugget has been in-situ for a very long time any oxidisable metals such as silver and copper can weather out into the surrounding soils over time. This halo then presents to the detector a much larger target than the actual original seed nugget and goes a long way to explaining why a nugget can be sensed at far greater depths that an in air test can achieve.

Having worked in the mining industry for over 35 years and working with several metallurgists and geologists (incl 2 professors), they all told me that it isn't likely at all. The tiny amount of locked up copper and silver within nuggets doesnt display in any amount worthy of note in the surrounding soil even with XRF. I think its an old wives tale lol. But you are spot on with the ground chemistry statement, its far more tricky and specific than we realize. This will have a far greater impact on signal quality, especially when disturbed. A great many clays contain various aluminium minerals such as diaspore that unknowingly react to and reflect EM fields. Sodium is also a problem as anyone detecting salt lakes or flats will understand. That we can use metal detectors to find such small gold at all is a modern miracle!

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I have often dug rusty pieces of steel and knew it was steel well before I actually got to the target because of the rust staining spread out in a ‘Halo’ around the target. Remove the halo, place the actual target back at the original depth and orientation in the same hole and no target anymore. Another example is of a number of coins buried by an associate in a test bed in mineralised soils over 30 years ago and how gradually over time all those targets became discernible by detectors when originally they were well past the edge of detection. 

Yes it is theory and not fully understood but there is plentyof anecdotal evidence to suggest that Halo’s exist 😇, exactly how that works I’m not sure but ground definitely has a chemistry that can alter over time. One example is supergene gold in laterites (most gold wash layers are a form of laterisation where ground water moves through the soils on into the bedrock till it hits the water table, by then a lot of minerals are in solution (especially iron) only to be percolated back up into the wash layer), studies have shown pieces of gold formed in laterite can have a trail or halo of micro gold migrating in towards the seed nugget which has grown over time, I have found a few of these over the years especially around Sandstone in West Australia.

If it also a common thing to follow a reef from the surface from rich specimens laying over the stump of the reef that when found produce reasonably good grades of gold (but not big like the surface gold was) then have it turn into a massive enrichment right on the water table only to dissipate away into sulphides or low grade ore as you go deeper. I’m pretty certain most nugget patches are old water table gold enrichments that have weathered out into the environment with the nuggety gold coming from adjacent iron rich country rock in close proximity to the gold bearing reefs. This would go a long way to explaining why the nuggets often tend to be in the upper gravel layers and do not continue to depth even though the wash layer is still going down (particularly obvious phenomenon in flatter country where gold has weathered from colluvial/elluvial deposits like we have here in Australia).

Once again just my 2cents, I am enjoying this discussion.

JP

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As Steve mentioned, I have dug in areas in Northern NV. that a detected signal would sound worth digging and when a mound of dirt came out of the whole, the excavated pile would sound off on the detector just as well as the hole it came from. Almost always in reddish and moist soil. Always a disappointment when you know you have dug for nothing. I would rather find junk than nothing.  

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I think we all agree minerals can leach into the adjacent soils. But I think there is a problem drawing correlaries between hot ground being detectable, and nugget halos being detectable. 

The source of the clays and alkalis we can detect are derived from massive occurences - great freshwater lakes (NNV), or massive weathering of ore bodies or iron-rich sediments which contained undetectable (with a PI) levels of salts, Fe, etc. We aren't detecting leached halos when we detect a big clay ball or an alkali pocket, it's important distinction. These macro-scale occurences are concentrated down into things like veneers of salt impregnated soils or iron+salt bearing clay pockets as the water evaporates or the ore bodies erode. It's the opposite of leaching on a nugget. They are concentrated down to the scale of feet instead of miles.

The source of the halos we are talking about detecting are coming from nuggets on the scale of matchheads - and only derived from the very thin surface layer of these matchheads at that, since the oxidation only occurs on the surface of the nugget.

Concentration and scale are key here to the mystery, I believe. I couldn't have detected these NNV soils if the lake hadn't evaporated and concentrated a massive volume of diffuse salts into a thin veneer. Also my PI's usually never hear the massive ore bodies (like swarms of quartz hosted gold/copper/Fe minerals) from which the hot ground I detect is derived from, I can only hear the ground itself because a massive ore body has eroded and concentrated Fe oxides into a thinner layer or pockets of alluvium. I can hear hot rocks though - like magnetites, serpentines, basalts, etc. But again, the Fe in these has been concentrated relative to the rocks/minerals around them due to various geologic processes involving input of energy.

To make a similar comparison you would need something like a massive patch of gold nuggets which has somehow leached all their surface Ag/Cu into the halo of one single nugget in the patch. If that was occurring, I could see the argument (there are actually theories of nuggets forming from diffuse fine gold particles like this, due to bacteria). There is really no concentrating force acting on a buried desert nugget halo though. And ones in active water courses are being moved and the halo constantly dispersed. So after the surface Ag/Cu leaches from the nugget, the halo should only get more diffuse over time, this is entropy. There has to be energy applied (like the sun evaporating the surface of a lake, for example) to make it work in reverse. But that's the opposite of what people state, where apparantly the halo effect gets more detectable over time. That's another reason I don't see it being real.

 

 

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