Ghost Nugget

[AU_Solitude]

What am I missing? This nugget weighs just short of half a gram. SDC 2300 barely whispers on it at 1", GB Pro at 100 gain and threshold hum barely pick it up at about the same distance (1"-1.5" off the coil.) As is common knowledge, these detectors will (and have) picked up gold small enough to not really be considered a nugget (see bits in vial.)

What is causing this nugget to be invisible? It is somewhat porous but not to the extent it should affect detection. What are your thoughts?

 

[Lunk]

I will venture a guess and say that perhaps the gold is alloyed with some other mineral(s) that give the nugget as a whole extremely weak coductivity? It's definitely a head-scratcher. Is there a physicist in the room?

[Steve Herschbach]

Lunk got it while I was typing!

Try this. Set the Gold Bug Pro up again and manually adjust the ground balance all the way one way. Test the nugget. Now run the ground balance all the way in the other direction, and test again. Any difference?

I once was shown a nugget of similar size that was flat out invisible to a Gold Bug 2! I would refuse to believe it if I had not seen it with my own eyes.

Pure silver is very conductive. Pure gold is not as conductive as silver, but still quite good. Here is the weird part. Adding silver to gold does not make it more conductive, but causes the conductivity to drop dramatically. I have a chart somewhere I will try and find tomorrow that shows this. The gist of it is however is that gold/silver alloys can be a lot harder to detect than pure silver or pure gold, and that nugget looks to have a high silver content. The shape is not helping either. So the main culprit here is no doubt low conductivity. The fact you have a hard time detecting it proves just that.

There may be more however. Gold signals on the low end overlap not just with ferrous targets but actual ground signals, and if so can be eliminated by the ground balance system. Any ground balancing system will as a side effect produce invisible nuggets or hard to detect nuggets. You can't change the ground balance on the SDC 2300 so now you know the basis for our little experiment with the Gold Bug Pro. Can't wait to hear the results.

[Lunk]

Sorry Steve, didn't mean to usurp your response...my bad!?

[AU_Solitude]

Thanks Steve, your explanation definitely makes sense.

So running the ground balance between 60-75 seems to make for a much cleaner signal - I might gain 1/2", so just short of 2" still but definitely a difference.

When I bring the ground balance below around 20 it doesn't even make a peep rubbing it against the coil. 75+ things seem to start to progressively deteriorate with a very scratchy signal. 

So weird.  

 

 

[Steve Herschbach]

Cool, glad to see the experiment produced expected results.

Since detectors only see magnetic effects or conductivity if you set the magnetics aside a metal detector is a type of conductivity meter. Any item a detector can't see by definition has conductivity lower than the detector can sense.

Or that would be the case for a good old fashioned pure non-ground balance detector. The ground balance system is just a type of discrimination circuit and sometimes good items get tossed with the bad. These are the items that fall into the dreaded "hole".

It is why air tests on videos can be faked by misadjusting the ground balance system. The problem is the ground balance setting that gives the best air test may also produce lots of ground signals - in fact you can pretty much count on it.

However, you just learned a detecting secret for extreme low mineral ground. Ground grab and tracking systems have nothing to grab, and factory presets can be too conservative. Being able to manually adjust the ground balance and knowing which way to push it can give extra performance in extreme low mineral / no mineral ground.

Old fashioned pure TR detectors are valued for beach hunting in pure coral type beach sands for this very reason - no hole for weak gold targets to fall into.

The SDC does have a system based on the Fine Gold settings on the GPX 5000 and it is remarkable for the ground it can ignore. There is always a price to pay however and the SDC does miss certain types of gold because of this. All ground balancing detectors do to some degree and in general the more impervious normal detectors are to ground effects the bigger the likely holes are. The GPZ 7000 exploits this known weakness as much as is currently possible.