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Why Won't My Detector Find A Bottle Full Of Small Nuggets? Or A Gold Chain?


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This subject comes up so often it is time to get it into its own thread so I can just link to it in the future.

It is best to think of metal detectors made for prospecting as "nugget detectors" as that is the truth of the matter. Nuggets have some size to them.

Metal detectors are electromagnetic devices, and as such can detect items that are conductive and non-magnetic, like gold, or non-conductive but magnetic, like magnetite. Or both, like metallic iron.

When dealing with gold you are dealing only with conductivity. The more conductive the mass, the easier it is to detect. In general what this means is bigger is better. Any detector has a limit to how small an item it can detect.

Here is the kicker. Multiple undetectable targets do not add up to create a detectable target. I do not know how many times I've seen or been told of people throwing a vial of small gold on the ground and running a detector over it and declaring the detector will not find gold because it does not pick up the vial of gold. Or people thinking the detector has a problem.

Let us say that on a scale of 0 - 10 zero represents an undetectable piece of gold, and 10 one that really beeps. 0 + 0 + 0 + 0 + 0 still equals zero. So lots of tiny gold is just as undetectable as a single piece of tiny gold. You need a single conductive mass.

Fine gold usually has a coating, and putting a bunch of fine gold in a vial still results in little or no signal. If the gold is super clean and packed tightly you will get a weak signal. Melt it all together, and now it goes beep.

Another way to look at it is take some fine gold and pour it in a pile. Get a multimeter and test your little pile of gold for conductivity. It is hard to get much current if any through a loose pile of gold.

So bottom line is you might have 5 ounces of fine gold right under your feet, and you will walk right over it with your metal detector. Rich gold ore where the gold is finely dispersed in the rock will be hard to detect or undetectable. Wiry or spongy masses of gold are hard to detect.

Jewelry hunters run into this when trying to detect lost necklaces. A fine chain is very hard to detect as each link is undetectable and the connection between the links is poor enough the signals does not add up to much. Often all you can detect is the clasp. Rings even display this issue if the weld breaks. A complete ring really gives a great signal. Break the ring, it will be very hard to detect.

Now once an item is detectable, it does add up. 10 + 10 = 20 so two large nuggets in the same spot are easier to detect than each by itself. If each link in the gold chain can be detected, then it will add up into a more detectable target. A fun trick with target id detectors is to tape 5 nickels together and run them under the coil. They will read as 25 cents!

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Great response!

I like how you described how nuggets bedding down in the same spot will produce a stronger signal.

Last summer, I hit two spots with the Gold Bug Pro where I got a very broad signal in packed dirt, shallow on bedrock. I had never experienced this before, and I didn't know what to make of it. I almost thought it was some kind of ground mineralization effect or something, but as I'd been finding nuggets consistently in that area, I dug all of the dirt anyway.

In the process of scraping and gathering, I uncovered a crevice that ran about ten inches deep, cleaned it out as well, and threw everything in the gold pan. The signal in the ground was gone, but now there was a strong signal in the pan!

I panned down the dirt a bit and quickly saw the flash of gold. I spread the dirt out with the water and it was full of small nuggets, any of which, individually, the detector easily saw. There was also a 4 gram nugget keeping them company that I eyeballed as I cleaned out the crevice. As all of those nuggets had bedded down in that pocket/crevice together, that was what produced the broad signal in the dirt, but when they were concentrated in the smaller area of the pan, the signal was stronger.

Thanks, as you may have solved a bit of a mystery for me. 

That was a fun day, and unbelievably, I repeated it a couple of weeks later on another section of bedrock! I doubt it will ever happen again as it's never happened before. I mean, I've hit concentrations of small nuggets before, but they rang individually as I swept the coil over them because they were more spread out in their patch's area. They did not give out the broad signal I received on the nuggets that were much closer together. 

All the best,

Lanny

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