electrical resistance of gold nuggets

[Paul]

Hello,

I heard that a typical gold nugget has the electrical resistance near lead, which is about 1/10 of pure gold. Does any know if that's true or a close estimate?

much thanks,
Paul

[chemelec]

Hello,

I heard that a typical gold nugget has the electrical resistance near lead, which is about 1/10 of pure gold. Does any know if that's true or a close estimate?

much thanks,
Paul

Pure Gold is a pretty good conductor but a Nugget is Not pure gold.

However The Conductivity of nuggets will Vary Consideraby, all the way from good to almost nothing, depending on What other Metals or Minerals are present. There is no Definate Answer to this.

[Unregistered]

Yes, but there is a scientific answer based on statistics showing the distribution spread, average, etc. That's a little more technical than I need, but an idea would be nice. I'm not sure the variance is quite as severe as you suggest. It might be true that some nuggets would be 1/1000th of pure gold, but I'm thinking that is a rarity along with nuggets that are 99% electrical conductivity of pure gold.

This might be a question that only insiders at say Minelab, Garrett, Tesoro could provide, but perhaps they're not willing to speak. :-(

Paul

[Elie]

This might be a question that only insiders at say Minelab, Garrett, Tesoro could provide...
Paul

Why is that?

[Carl-NC]

Take a variety of nuggets, and check them with a detector that gives a numerical phase readout, like a DFX or Explorer.

- Carl

[Reg]

Hi Paul,

I am not sure the actual reason for your question, but hopefully this will help. Gold is a good conductor but it has nowhere near the conductance of silver or copper.

If you were to take different nuggets and compare their readout on a TID machine, they would read rather low when compared to similar sized copper or silver items. The readings would be more along the lines of some brass items and a little higher than similar size lead objects. Unfortunately, brass items can vary tremendously, so there is no easy or convenient means of finding a target to simulate a gold item. As an example, a 1/4 oz nugget could read anywhere between a nickel and maybe a pull tab. Generally, smaller nuggets will read less, with many reading well down in the tinfoil range.

Now, lead is a good conductor when compared to some items such as water, but it is also a poor conductor when compared to silver and copper. It is much more like gold but still less conductive than gold on a general scale.

Many people recommend a person use an item made of lead as a test target when testing a detector to determine its abilities to detect gold simply because lead is much more available for most people and its detection ability is more along the lines of gold, than is silver or copper. If the detector can detect a piece of lead, then most likely a similar size piece of gold will be detected also.

I hope this helps.

Reg

[Paul]

Cool! I think you're correct about the variance of brass. So lead is close enough.

I'm just trying to get an estimate on the RL time constants for various size nuggets for calculation purposes. I estimate that a 1" diameter nugget has roughly 20 nH and 320 micro ohms and nearly 1/2 pf and resonates at nearly 2GHz. So at 0.55 max time constant takes 50 micro seconds.

Paul

[J_Player]

The resistivity of some PURE metals is listed below:
Gold ....... 2.44 μΩ-cm
Copper ... 1.724 μΩ-cm (annealed)
Copper ... 1.771 μΩ-cm (hard-drawn)
Silver ..... 1.62 μΩ-cm
Lead .... 20.5 μΩ-cm

You will note that copper shows a different value when annealed than when work-hardened. Also, alloying these metals will usually create more resistance. Adding 0.5% Arsenic to copper lowers the conductivity to 40% of the value for pure copper. Take note: if your nugget measures in the range of lead, then it has over 8 time more resistance than pure gold.

Because there are so many trace metals in a nugget, it is impossible to predict a range of conductivity for a "average" nugget. In addition to variances caused by the alloy, and work-hardening, the resistivity will also vary depending on how the nugget originally cooled, and formed metal grains. By annealing a gold nugget, you will change the grain boundaries and more than likely change the resistivity.

Here is a link to a table of resistivity of some common industrial metals used by Eddy Current Technology, Inc: http://www.eddy-current.com/condres.htm
Here is another link that shows some more detailed information about the properties of gold, silver and copper: http://www.du.edu/~jcalvert/phys/copper.htm

[Paul]

Because there are so many trace metals in a nugget, it is impossible to predict a range of conductivity for a "average" nugget.

Actually it's not the predictability of "a" nugget that's of interest. Rather you can scientifically arrive at an accurate average taken from many samples. Also you get the distribution spread. From what I'm hearing the distribution spread is not that broad and the average resistivity seems close to lead.

Of course it goes without saying that you can find nuggets that might be 1000 time less conductive than even lead or perhaps some that are near pure gold.

Thanks for the info btw.

Paul

[Reg]

Hi Paul,

Eric Foster conducted some tests on Gold quite some time back and found the ability to detect gold mixed with silver using a PI detector varied dramatically as the ratio of the two metals changed.

What I have found is more from experience. The ability to detect gold nuggets can vary dramatically from the gold characteristics as well as the secondary metal content.

The surface characteristics or shapes can make a real difference. As an example, I have a couple of what I call invisible nuggets that have a total surface area about equal to a person's small fingernail. Now, a typical solid nugget of this size will or can be detected maybe as deep as 8" or so.

However, these nuggets, because of their actual surface characteristics are impossible for most PI's to detect even when rubbed across the coil. I found I had to reduce the delay to about 7 usec or so before I could get a nice reliable signal.

These nuggets are strange enough that many VLF's have difficulty with them. The VLF's designed for gold hunting will work the best but even them will have a tough time detecting such nuggets more than a couple to 4 inches in depth, max.

Now, I didn't find these nuggets. They were sent to me to see if a PI could detect them or what it would take in terms of changes for a PI to be able to detect such nuggets. Also, I was told that this particular gold has a nature such that even larger nuggets, up to a 1/4 oz or so are extremely hard to detect by most detectors.

The reality is, there is no nice convenient perfect subsitute metal one can use to simulate gold, since gold itself can vary so much.

As such, I have found that lead works fine as a test target if a person just wants to know how well their detector will do. Generally, a detector will actually detect gold a little better than the lead, but the differences will not be that great.

So, for the average person, a simple testing of lead will answer how well or how small of gold they can detect. I have used this subsitute for years and it has worked fine for me.

Reg

[Unregistered]

The surface characteristics or shapes can make a real difference. As an example, I have a couple of what I call invisible nuggets that have a total surface area about equal to a person's small fingernail. Now, a typical solid nugget of this size will or can be detected maybe as deep as 8" or so.

I agree that shape would make a big difference. Therefore trying to determine resistivity of natural nuggets by means of a detector is not accurate.

The reality is, there is no nice convenient perfect subsitute metal one can use to simulate gold, since gold itself can vary so much.

Actually the quest is to find the average nugget that you want to fine-tune your detector to. To do so you would need to find a good average.

However, these nuggets, because of their actual surface characteristics are impossible for most PI's to detect even when rubbed across the coil. I found I had to reduce the delay to about 7 usec or so before I could get a nice reliable signal.

What delay times do you normally use? Can you post pictures of these nuggets?


Paul

[Reg]

Hi Paul,

I am using a delay time of about 7 usec or so, but this depends upon the coil size. On larger coils, the delay required goes up to maybe 10 usec or so.

As for pics of the nuggets, I need to transfer some from my old computer. Many of the nuggets I found were given away. Unfortunately, I don't get to hunt as much as others do since I do live about 500 miles away from where I prefer to hunt.

Thanks for asking for pics. I have or had several pics on my website but I just noticed my old website isn't functioning. I probably wouldn't have noticed this for some time if you hadn't asked. It seems that my attempt at renewing my site didn't complete last month as I had thought. Hopefully, I can get this straightened out quickly and get the site up and running again in a day or so.

When I do, I will need to update my site but that will take a while since I really haven't done much with it for a couple of years and all the info is on my old computer. Anyway, that site is (when working):

www.nuggethunter.com

Reg

[Reg]

Hi Paul,

I have attached a pic of the signal out of the SD 2100. This pic was taken by using an external coil of wire located about 6" from the ML coil. The external coil had a dummy load across it so it would display properly on the scope.

The display shows ML's different pulse lengths. The short dip in voltage across the bottom is the actual pulse on signal.

Hope this helps.

[Unregistered]

Thanks for asking for pics. I have or had several pics on my website but I just noticed my old website isn't functioning. I probably wouldn't have noticed this for some time if you hadn't asked. It seems that my attempt at renewing my site didn't complete last month as I had thought. Hopefully, I can get this straightened out quickly and get the site up and running again in a day or so.

When I do, I will need to update my site but that will take a while since I really haven't done much with it for a couple of years and all the info is on my old computer. Anyway, that site is (when working):

www.nuggethunter.com

I found your site at archive.org
http://web.archive.org/web/200402112....com/photo.htm

I see two pictures of nuggets. Nice finds btw. Are any of those the silent nuggets?

Paul

[Paul]

Great scope pic. I'll comment on it in the other thread:

http://thunting.com/geotech/forums/s...1832#post41832

Paul