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questionable palladian gold from Icabarú

Posted by Cesar Menor-Salvan  
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Cesar Menor-Salvan December 05, 2008 01:30AM
Recently I performed the analysis of a sample of putative palladium rich gold from Icabarú (Venezuela). The morphology and shape of the sample is very close to the specimen represented in

http://www.mindat.org/photo-117876.html

The analysis (EDS) shows that the palladium present (if it is actually present in the sample) is below the detection limit. I performed a precise trace analysis and the major metal present (apart gold) is mercury. The purity of analysed gold is 99.9%

I suspect we have a fake. Anybody has got additional information or could confirm my suspects?

Thanks!!
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Uwe Kolitsch December 05, 2008 04:22PM
The uploader kindly asked me to supply the following info:

"this is how this style of crystal came to the market and was labelled as, and has been sold by
mineral dealers for the last 5 years....the analysis i was told done was at the university of reno, by friends of scottt werschky

i will ask about this"

He also objected to the use of the word "fake" at this moment.
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Tony Peterson December 05, 2008 04:48PM
It so happens that I recently purchased a small specimen of this and as soon as it arrives I will have it analyzed.

Tony
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Cesar Menor-Salvan December 05, 2008 06:28PM
Indeed, I discussed the question with the supplier of the sample. It is clear that there is not bad faith at all and appears NOT to be a fake.
But is clear that accurate analysis of more samples are necessary and clarify when we can apply the name "palladian gold". Moreover, I think is desirable more accuracy in the location. Tony, please show us your analysis when you have it..

Other question is the criteria for the "palladian gold" definition. Since it is the name of a variety and not the official name of a species, one could call "palladian gold" to a sample containing just traces of Pd.
Is possible that the EDS analysis performed to one sample by the supplier contains a quantity around 0.5-1%, and Pd peaks appears in the spectrum, and in other samples (for example the one I owe), the quantity falls to a level invisible by EDS.

So, is possible that I just had bad luck and analysed the particularly palladium poor sample in a lot of gold with low Pd levels?? In the analysis of my sample I found indeed low levels of Pd ( 0.005-0.009%). Since my gold has some palladium, is palladian gold?. But it has also Hg (0.01%). Is mercurial gold?


Cesar
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Alfredo Petrov December 05, 2008 06:33PM
This problem of collectors using element adjectives for minerals with minute traces of foreign elements is an ongoing annoyance - "auriferous pyrite", "radian barite"...
Even if it does contain 0.x% Pd, which is not so rare, better just to call it "Gold".
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Uwe Kolitsch February 06, 2009 05:53PM
The following info (supplied by R. Scott Werschky) is posted on behalf of the uploader:


>I found one SEM scan of the Pd-Au which I will bring to Tucson. I am
>having 3 more pieces run on the SEM to check, as well as sacrificing a
>couple more pieces to have wet chemistry work done which will give exact
>amounts of Au, Pd and all trace chemistry.
>I glanced over some of the comments on the blog, and will talk to Bob
>Cook. His comments are out of context, and not correct. I will however,
>retract the classification of palladium-rich in favor of
>palladium-bearing. I got the Pd-rich based on presence of Pd in 3 SEM
>scans combined with the literature stating the average Pd component in
>these is between 7 and 9%. In any case, the presence of Pd is indeed
>significant as it is exceedingly rare.
(...)
So where
>did the Pd come from? I can't imagine someone adding such a rare metal
>into the mix. If these were faked, I would expect to see others faked
>with only pure gold. We also don't see any nucleation points either.
>As to the high purity of the gold, Venezuela is famous for high-purity
>gold. When I worked for the USGS, a colleague came back from Venezuela
>with gold crystals of 99% purity in the form of stacked octahedrons in fan
>shapes. These placer mined crystals were found sitting on a silt layer
>within a gravel sequence. The only explanation is that they formed in
>situ in the sediments, precipitating out of the humic acid rich
>waters. There were no distortions to the delicate crystals from stream
>transport!


Have approved photo.



Edited 1 time(s). Last edit at 02/06/2009 05:54PM by Uwe Kolitsch.
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NH February 07, 2009 07:41AM
Well, the part about Pd being "such a rare metal" doesn't make sense as it's cheaper than gold and readily available as bullion. It would take more work (Pd has a higher melting point than Au), but would be cheaper than using pure gold. In fact, Pd is one of the main alloying components in white gold.
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Cesar Menor-Salvan February 07, 2009 11:27AM
After reading the last posts in this topic, I feel me convinced that the gold crystals from Icabaru are merely fakes.

>gold. When I worked for the USGS, a colleague came back from Venezuela
>with gold crystals of 99% purity in the form of stacked octahedrons in fan
>shapes. These placer mined crystals were found sitting on a silt layer
>within a gravel sequence. The only explanation is that they formed in
>situ in the sediments, precipitating out of the humic acid rich
>waters. There were no distortions to the delicate crystals from stream
>transport!

This is very hard to believe. Dissolved gold precipitating as big idiomorphous crystals, and unaltered in a gravel sequence? You can find some early papers (i.e. Economic Geology, 1946, 41: 47) demonstrating that this phenomenon of solution/transport of noble metals by humic acid in macroscopic quantities and natural medium is very unlikely.
Some modern works show the ability of humic acids to reduce gold ions and the possibility of the use of these organic complex polymers to fabricate gold ¡nanoparticles! (Analyst, 2007 132: 1210) .
Indeed, the ability of humic acids to form gold complexes was demonstrated, and the precipitation of gold as colloids and nanocrystals by organic complexant and bacterial activities was also demonstrated (i.e. GCA, 1996, 60:4369) and the partial dissolution of primary gold by biologic activity or humic acids was studied (i.e. Geoderma, 1989, 45:241).
Also, in fact there are phenomenons of gold mobilization and reprecipitation as crystalline grains or phenomenons of secondary enrichment due to the action of humics acids as còmplexants (i.e., J. Geochem. Exploration, 1996, 57, 115, Lithology and Min. Resources, 2000,35:538 )

I think that the most important previous finding that support the origin of authigenic crystalline gold in river placers is the work of McCready et al. (Economic Geology, 2003, 989:623). This work describes the placer gold from Neuquén river, Argentina. In this placer, the gold was found as crystalline particles formed as overgrowths on detrital gold. The purity of these particles is high for the natural gold, >98% (not 99.9%), due to the enrichment of preexistent particles by transport and precipitation by humic acids. McCready et al. reports authigenic pure gold crystals as big as 50 micrometers!!!!, far away from the centimetric size of those of Icabarú. I did not found other descriptions of gold crystals in placers related to this.

So, the questions: in the putative magic Venezuela placer, the humic acid precipitates gold...from where???? gold ions in water??? to form 1 cm crystals??,... to from 1 cm crystals of 99.9% purity???. If these phenomenon were real, the reduction of gold probably form very small particles or enrich preexistent particles in the placer.

Apart sci-fi (in the sense of application of actual scientific studies to explain fanciful amazing phenomenons), in the case of the Icabaru gold crystals I studied, the purity (99.9%), the shape and the low level impurities (Hg and Pd mainly) of the samples available in Spain, suggest that these supposed origin in placer by precipitation of hypotetical gold solutions is very unlikely. The Ockham razor readily suggest that these gold are of antropic origin :)

If these crystals were not a fake, the recent (the crystal edges are sharp) neoformation of multimilimeter or centimeter-size well developed gold crystals in river placer by humic acid transport and precipitation, for sure constitutes a revolutionary find in the geochemistry of gold, the organic geochemistry of humic acid and, taking in mind the scarcity of the phenomenon (only at the unknown and mysterious river at Icabarú, Venezuela), these gold samples should be worth much money, as a freak of nature,...:)

I think that this case of fake gold crystals is closed and out of discussion.



Edited 2 time(s). Last edit at 02/14/2009 03:21PM by Cesar Menor Salvan.
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Rob Woodside February 23, 2009 08:49PM
Palladian Gold is more brown than yellow, not easy to forget once you have seen some. The above photo doesn't appear that brown. I think it is still a mystery how gold xllizes in alluvial situations, but it does!!! The largest xls I have heard of were on an American gold coin and were in the mm size range. There already has been a celebrated case of Venusualan matte gold octos that were castings and as someone else said, "Buyer Beware!!!"
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Pavel Kartashov February 24, 2009 06:33AM
Palladian gold is more orange, rather brownish. And high-palladian gold is white with pinkish tints. See http://www.mindat.org/photo-43359.html

Gold with only traces of palladium - 0.n-0.0n % - should be named Pd-bearing gold from my point of view.

By the way, ones should note, that on EDS microprobes Pd peaks significantly overlaps with Ag ones. Silver is usual component of native gold. So if measurements were made by unskilled analytic there is high possibility to discover palladium in any gold specimen with low fineness. Some 'palladian' gold varieties with 1-2 % Pd, described by some investigators from Prepolar Ural deposits, are exactly such artifacts. Usually these works had belong to students and aspirants.

About gold crystals with Hg admixture. It is old trick - crystalline gold growing from gold amalgam. You dissolve your gold sand in mercury and than dissolve excess of mercury in strong HNO3 with cooling. As result perfect octahedrons of gold is possible to obtain. The same result may to give very slow evaporation of Hg from big volume of gold amalgam. As I know amalgamation method is widely use on South American gold mines. So the first portion of such crystals can be produced quite occasionally.

In my childhood I'd obtained two almost mm gold octahedrons from gold dissolved by mercury from 4 old gold-plated watches. If you have 100 g of gold sand and some kg of mercury, you able to begin to grow gold crystals up to 1 cm and more... :) :) ;)
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Pavel Kartashov February 24, 2009 06:59AM
By the way metallic palladium able easily be added in gold amalgam. Pd dissolve in mercury quite readily. As result we would obtain Au-Pd compounds under quite low temperatures much more lower than Pd melting point.

I had observed growth of secondary placer gold in Ethiopia. Nugget of light-yellow primary gold Au875 was overgrown by masses of new-formed dark-yellow Au999 with formation octopus-like nugget - body from primary gold and legs from new-precipitated one. On this nugget direction of solution movement was visible very well. This new-precipitated gold was quite massive - summary legs weight was may be 4-5 g or more. Unfortunately the nugget was too large and I haven't so much money to buy it immediately. When I returned to this workshop some days later, this nugget was partially used for some local jewelery production - it was presented by 3/5 of its original size. By the way on its minced surface very sharp boundary between primary and former gold was visible very well. I was so downcasted, that hadn't buy these ruines of former splendour. I was wrong of course, because this was material for good publication on modern gold formation in placers in any case.
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