The "Halo Effect" on metal targets

[nuggethunting]

Hello All,

Here is an interesting article on the Halo Effect. I'm not a huge fan of solid gold nuggets giving a halo, or at least a halo that does much, but for iron targets no question.

The Halo Effect – by Kevin Hoagland

Any object that is buried in the ground that will deteriorate or rust such as iron, or tarnish like silver can create a positive signal by a detector. Relic detectorists experience this more than most detectorists in finding iron signals that have oxidized into the soil causing a very small iron target to appear to have much more mass. As the metal begins to decay, it leaches into the surrounding soil and given proper soil conditions can produce a good target signal. Once this oxidation layer is broken, it may disappear causing the detectorist to believe that the target was a false signal.



This is mentioned for the fact that gold in nature is not pure. The most common metals associated with gold will rust or tarnish. Once you begin to dig the target and break the oxidation ring, the target may disappear. If this happens do not abandon the dig until you are convinced that there is no target. In many cases you will be able to see a difference in the soil coloration. In the case of iron targets, the ground around the target may be a dark red or black due to the oxidizing action. Be especially careful of this in areas where gold is known to be found in iron ores.

[Ridge Runner]

Rob

For over the forty years I've been swinging a detector I find true in your post. In some soil the clad coins all the silver will be gone. On most true silver coins back when you had silver they would come out of the ground like new are as they went in. If you can open the ground where the coin lays without disturbing it you can see what gives you the halo effect some time. It's all about the soil the coin is in. On the coast if you can find any clad coin that still has silver it hasn't been there long.

Chuck Anders

[DOC]

Rob,

I think it depends on the gold nugget. Up in Gold Basin you rarely dig a nugget that is not iron stained. Now since the advent of the newer GPX / SDC2300 / GPZ machines I have not seen a discernible difference between the target sounds of nugget in the ground and when you get them in the pile of dirt. Other that the fact that they get louder when you have them out of the hole.

However, I do distinctly remember using the SD2200d and having a really nice target in the ground, and then pulling it out of the hole into the pile of dirt and having a heck of a time locating it. And even when you had it in the scoop it wasn't quite the strength of the target sound that you heard when it was in the ground. In all of these instances the nugget was small and iron stained.

So I always assumed that the oxidation from the staining had to have created a small halo around the nugget.

I do not subscribe to the theory that gold itself creates a halo, gold's inability to oxidize is one of the unique properties of gold. But when you have a nugget that has a lot of iron ion the cracks and crevices, that may make a difference.

Doc

[adam]

On many, many occasions , I have seen this " halo" effect from hot rocks as well. Don`t recall ever having one with gold, but like already said, I suppose a high Iron content would cause it. Silver would too , and that is common in gold nuggets as well as Iron.

[oldies1955]

I get a halo effect around saguaro roots!
Tom H.

[Mike Furness]

Tom ... oldies 1955 ... same here ... I have dug around a few only to remember that I was apparently chasing a higher concentration of minerals. You only do it a couple times before light dawns in the ole chrome dome ... then it forgets for awhile and you do it again! it's a target signal right ... so you have to dig it ... until you realize the target is making you dig all around the circumference of the cactus! Isn't chasing targets fun!?

Mike F

[DOC]

Barrel Cactus and Joshua Trees do the same thing.

I always have to warn new customers of that lest they dig up a protected plant chasing a ghost target.

Doc

[oldies1955]

Well....glad im not alone!
Tom H.

[AZNuggetBob]

I have had this halo effect on many nuggets, usually larger nuggets on flatter ground. I agree with Adam I think its caused by a nugget sitting in one spot for a long time and the silver and or copper leaches out into the surrounding soil creating a metal rich aura around the nugget. you'll often find that when the hole is exposed to air for a few days or you disturb it, by mixing it digging, the aura or halo just disappears. have you ever noticed that when you just rinse a new found nugget it has a better surface color and when you clean it physically the color is dull? you've just cleaned the purer higher K gold surface off the nugget from leaching lessor metals off the surface while it was in the ground.

AzNuggetBob

[nuggethunting]

Hey Guys,

This is always a great discussion, but I have my thoughts also. Ok some agree that the impurities such as copper, silver and other base metals weather out into the soil if the gold nuggets sits in one place for a long time.

Other mentioned gold nuggets with a lot of iron on them will also cause a "Halo."

There is no questions that the "Halo Effect," which cause a single object to sound louder or be seen as a larger target happens with Iron. This normally includes cans, wire, nails, metal straps and other iron rubbish we pick up in the goldfields all the time. The reaction between water, oxygen and the metal causes rust. Over time the object will rust, and disperse into the soil around the original object, making it seen bigger in size and signal strength. At some point in time, the metal object can rust away completely leaving just rust or iron oxides from the original iron object.

I have found many targets like this, most were cans and such, thinner types of iron metal that completely were gone. Once you start to dig them, it's nothing but a bunch of rusted soil. Once you disturb the soil enough, the target response will null or completely disappear.

I'm a 100% believer on the "Halo Effect" of iron objects!!

That being said, tossing out gold with iron included, I'm not a 100% believer. From experience with gold nuggets, using scanners to see the gold vs. other metals, the other metal percentages were so minimal I'm not a huge believe you could product a big Halo, or a Halo that is like Iron. Also, only the outside of the gold nugget would be penetrated, so whatever impurities that would be on the outside of the gold nugget would oxide away. I think this is such a minimal percentage I'm not a huge believer of gold giving off much of a Halo.

Also, various signal responses on gold nuggets in my opinion are not "Halo Effects." Gold nuggets have so many sizes, shapes, densities and such, all this will effect the response you get on your detector. Just cause you get a strange signal response (non typical High-Low or Low High) in my opinion don't mean that's a Halo.

It's a great discuss if anything. These are just my opinions from many years of digging trash & gold nuggets across the Southwest.

[Grubstake1]

I thought the {HALO} effect was when the gold Angels showed you where to dig! :P Grubstake

[AZNuggetBob]

Rob I think its just a matter of simple oxidation leaching out of the nuggets into the surrounding soil. iron,silver,copper, etc. I found nuggets out at Vulture you could drag across the bar with a magnet and had no obvious iron on the outside. AzNuggetBob

[nuggethunting]

Hello AzNuggetBob,

I agree with you, but the point I was trying to get across is the percentage of the nugget "rusting" or "oxidizing" away. For example, you have a somewhat solid nugget that is gram in weight. The weight of impurities for the most part couldn't be more than 10% or less of the total weight of the nugget. Most nuggets in Arizona for example that are fairly solid are in the range of .850 - .940 fine. Most of the stuff I find is in the low 90's in gold purity. The remainder 10% is impurities and some of them might not oxide like silver.

That being said, you have a gram sized nugget that over time only has 10% impurities of the total weight, but for the most part the surface of the nugget will only be effected. Realistically, the nugget would never oxide to the core of the nugget. The outer (rind of the nugget) 10-15% of a solid gold nugget would be effected by oxidation (weather from acids, water & oxygen).

If this is all true, then only like 10-15% of the 10% impurities would oxidize away leaving very little if anything for a Halo Effect.

Over time, a iron object can leach away leaving 0% of the original metal, but 100% rust absorbed into the soils surrounding the piece.

I'm basing these finding on more solid pieces of gold, not pieces that contain a lot of iron.

P.S. On another note, hope you're getting out to do a bit of beeping Bob.

[AZNuggetBob]

I see what your saying Rob and I agree that not all nuggets contain a lot of metals that will oxidize., and not all nuggets leave a halo. when a metal oxidizes it spreads out into the soil ten fold with rain water etc. or more than its original size and this is why it only leaves a halo effect rather than a solid hit. and yes I still get out now and then, when its not flooding.
AzNuggetBob

[nuggethunting]

Hey AzNuggetBob,

The Halo Effect is an interesting subject. Many years ago this topic was brought up on the forums, could have been here. I found an article written by a chemist that explained the breakdown of metal. It was pretty interested, talked about oxidation of Silver, Copper and other metal and how fast the break down. Even talked about how Gold is "Noble," but man made chemicals could dissolve it.

Sounds like Wickenburg got hit hard with rain. I'm sure some of the gullies got flushed out.

[Alchemist]

Hi,

Interesting thread,.

I agree with the idea that impurities are leached out over time, this has been proved by many nuggets having a pure gold outer skin covering. Some semiconductors such as diodes are made from doping silicon with metal oxides much like those that would leach from a gold nugget. Local earth fields may cause these oxides and salts to form into dendritic strings stretching out from the nugget in all directions, these could conduct eddy currents around the nugget giving the illusion of a larger target.

The problem with this is, I've noticed halos with gold of very pure genesis, i.e. they started out from the host rock at over 96% so where has the impurities come from?

There's another possibility to consider. As the surrounding rock is breaking down pyrites and other host material are also oxidizing and releasing minute particles of gold into the ground water and environs. Some of these particles dissolve if the water has the right combinations of salts. A couple of scientific papers I've read have shown how these minute particles are "drawn" towards larger masses of metal and finally accrete to it. There's been instances of railroad spikes and pick heads being found in old mine shaft sumps that have a very fine covering of pure gold, even sticks of miocene age have been found with a gold precipitated covering.

The point is; the halo may also work in reverse. As gold particles in the ground water are drawn to the nugget mass they may form into dendritic "wires" slowly moving towards the nugget and finally being joined to it and cemented by reprecipitated gold from the ground water. The field of nano technology, especially nano-wires may one day shed light on this. The nuggets own field in response to the earth's and focusing due to local ore bodies, would form the dendritic wires along the nuggets lines of force.

HH

Kev.

[AZNuggetBob]

I agree Kev
Years ago I was running a loader removing the tailings from the end of a trommel wash plant. as I was loading out the oversize I looked into the end of the trommel and spotted what turned to be a bright gold plated horse shoe going round and round stuck in the trommel screen. I shut down the plant pulled it out of the screen. puzzled me for years. wish I had a photo. plant/claim owner kept it. anyway there where a few spots on it that had flaked off (I assume)from tumbling with rocks in the trommel. thick rust under the heavy gold plating. at first I thought maybe some how it became covered with mercury in the creek and then amalgamated the gold from the creek over time. but it didn't make sense as mercury doesn't like to stick to oxidized iron surfaces. your theory may explain how it became gold plated. but I still believe blobs of mercury in creek beds and even cinnabar deposits can form gold nuggets by hydrothermal amalgamation.
Btw in the last lab I was working in we successfully did several tests/experiments on growing gold and silver crystals using a combination of chemicals and electrolysis from high and low temp salt solutions. the horse shoe didnt have any crystals as I recall just a very nice gold plating.
AzNuggetBob