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Why Is Gold A Low Conductor And Silver A High Conductor When

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The smooth flow of electrons in a metal is the key to high conductivity. In bulk metals the electron shells of individual atoms morph into electron bands. The outer sp bands in copper, silver and gold all conduct well, but can be effected by the next inner d band that can cause scattering (i.e. lower conductivity). “This is least important in silver where the 4d-electrons are about 4 eV away from the Fermi-level (which is also why silver is colorless). But the 3dbands in copper and the 5dbands in gold are closer to the Fermi level (absorption in the blue) and they cause more scattering with the sp electrons.” Silver wins.

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The answer you are looking for is both simple and complex.  I will try to explain the simple part.  First, whether a target is a high or a low conductor is determined by the GB control and just where it is set.  If the GB is set so the ground signal is nulled, then any detected object that generates a low tone has a longer time constant than the ground signal.

This results in the GB signal channel being greater than the metal response channel.  Thus, the summed signals results in a negative response, and this results in a low tone.  

In the case of gold nuggets this means the nugget has to be pure enough, the right size and density and often the right shape or right surface characteristics.  Over the years, much of the  gold I found came from Rich Hill AZ.  Fortunately, this gold is quite pure (92% or so).  As such, gold larger than a quarter OZ was large enough to generate a low tone.  All gold smaller would create a high tone,.  Early US gold coins follow this pattern, meaning a $5 US gold coin would or could fall in the GB hole and be almost not detected.  All lower valued gold coins would be a high tone or a low conductor.

As the purity of gold is reduced, the conductivity of the gold diminishes, thus, much if not most is detected as low conductors.  A good example is the gold we found about 5 miles from Rich Hill where all the gold found registered as low conductors even up to the 1 oz nugget found.  At this site almost a pound of gold was found with many of the nuggets greater than 1/4 oz and all tested with the TDI registered as low conductors.

Reg

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Finding the amount of reduction of the conductivity of gold as it is alloyed has turned out to be quite difficult.  Fortunately, I did find some shocking information on the old PI forum that does help.  Here is that info.

Eric
Here are some numbers for copper-gold and silver-gold alloys.
The first column is the % of gold in the alloy.
The second column is the conductivity relative to copper of the copper-gold alloy.
The third column is the conductivity relative to copper of the silver-gold alloy.
% au cu ag
100 .75 .75
90 .14 .23
80 ??? .17
70 .11 .14
60 .12 .14
50 .14 .15
40 .17 .17
30 .22 .21
20 .30 ???
10 .47 .44
0 1.0 1.05
Lead shot is usually alloyed with antimony, so its conductivity is less than pure lead.
Robert

(The above info was posted by  the late Robert Hoolko).

Hi Beachcomber,
Alloying even a few percent of other metals causes the conductivity of gold to drop dramatically. Even if the other metal is a good conductor, like silver. I haven't seen any published values for the different alloys either. I have a conductivity meter which gives a reading as a percentage of that of annealed copper. A 9K ring gives a reading of 18%. Unfortunately the object has to have a surface area of about a square centimeter, otherwise you do not get enough signal to read. This is a very wide ring, so it can be done. No other rings I have work. Great for coins though, a nickel reads 5.3%
Eric.

 

As an example from the chart we see that gold can go from a reading of 77 at pure gold to 16 when alloyed with silver such that the gold is only 75%. The 16 reading would place that same gold closer to the conductivity of lead, while the pure reading is much closer to copper.

This last post refers to a website where standardize gold alloys were listed by a company, deringerney, in 2010.

Hope this info helps.

Reg

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Thanks everyone for your informative replies---I think the takeaway from all this is Dig Everything when gold hunting.

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Thanks Reg, this helps explain why gold has such a wide response on my CTX 3030 screen. 

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FWIW, it seems that silver production was down last year as high-producing lodes are increasingly hard to come by. 

The argument has been made that there will be VERY little relatively easily mineable silver left on the planet in a few decades. 

It's also claimed that at any given time there may actually be more above-ground useable non-bullion gold on Earth than silver because most gold is kept "intact" i.e. not used in manufacturing but instead kept as jewelry or bullion; OTOH, most non-bullion silver is used-up in manufacturing. The silver bullion market is incredibly small compared to gold.

Remember a few years ago when waste companies would offer free "recycling" of old computer motherboards? They were doing that to salvage the tiny amounts of gold those motherboards contained. Since silver is only about 1/80th the price of gold on an ounce-to-ounce basis at this time it's just not worth it from a financial standpoint to salvage all the silver deposited in landfills across the nation. If silver rises to a few hundred dollars per ounce, as some speculate it eventually will, it might be a good idea at that point to invest in companies specializing in the recovery and recycling of silver used-up in manufacturing. Some financial experts say that the "normal" ratio between gold and silver in terms of price should be more along the lines of 1:15 than the present 1:80. Time will tell. If it does, look for metal detector companies to begin marketing machines specializing in finding silver.

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