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Date Posted: 18:37:55 08/14/02 Wed
Author: Steve Herschbach
Subject: Re: Nugget hunting using discrimination
In reply to: Reg 's message, "Nugget hunting using discrimination" on 00:30:01 08/14/02 Wed

Hi Reg,

I can confirm your findings.

I wanted a detector to find nuggets around lots of iron trash. I took a 5 dwt nugget and put it on the surface, and then put 4 nails around it in a box about 3 inches away.

I tried every detector on my wall (I'm a dealer) including the GMT, Gold Bug 2, Lobo in disc mode, XT18000, CZ5, XLT, DFX, and others.

The Gold Bug 2 was the only detector that simply went "beep" clean and clear in iron id mode. The other machines totally masked the nugget. The GMT was the runner-up, as there was a difference on the meter between the nail box with and without the nugget in the middle, but with the nugget the probability was still that it was iron according to the meter.

The GB2 does seem to have a unique ability to see a nugget next to a nail.

I got pretty excited about this, as I know a lake that has lots of potential for water hunting, but which is full of nails. I tried the GB2 out, but found that in the water the large amount of rust created large low conductivity halos around the iron trash, resulting in lots of false "good" readings. So for underwater use it turned out to not be the magic bullet I was hoping for.

But for dry land use the GB2 seems to have something really different in it's iron id system. It might make a very interesting machine for desert ghost towns and such for those who want to dig non-ferrous targets only.

I have found about 16 ounces of gold so far this summer detecting, and most of that was with the GB2 and 14" coil in iron id mode. Some people have a knee jerk reaction against discrimination while nugget detecting, but anyone that bench tests a GB2 in iron id mode on gold nuggets may be surprised at the depth and sensitivity.

One trick I have found is that the threshold control DOES affect the signal strength in iron id mode, even though it is a silent-search mode. Ground balance in all metal. Now switch to iron id. Turn the threshold all the way down and test, then turn all the way up and test. A large difference in target signal and depth will be apparent.

If the threshold is set at max, the machine "chirps" quite a bit, but it does not have that magic "target" sound. I run with the threshold set to max in iron id mode and simply don't hear the chirps. But go over a nugget and the clear "beep" stops me in my tracks. Much like coin hunting in a high trash area.

You can set the threshold lower for totally silent operation, but it does give up some sensitivity.

Finally, there is a bonus in that many hot rocks simply will not register in iron id mode.

I have found the GB2 is conservative in iron id mode, and will call quite a few larger iron targets gold that my GMT clearly identifies as iron. I think the risk of it ignoring gold is small. However, I did have a customer bring in a 1/2 dwt nugget that simply refused to beep in the GB2 iron id mode. No obvious sign of iron matix, etc. it just looked like a fairly solid little nugget. Something about it's alloy mix and size/shape caused the iron id to ignore it totally.

I should point out that I normally hunt areas that have nearly neutral ground mineralization (slate/shale bedrock) with little variation. So there is little ground iron to mess with the id systems, and no need for constant ground balancing. Under these near ideal conditions the iron id systems are more reliable than is likely to be the case in most more mineralized areas.

Steve Herschbach

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