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An opportune harvest of Gold in Serra do Caldeirão claims, Brazil - (25)
  
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Jordi Fabre
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PostPosted: Jul 07, 2016 12:02    Post subject: An opportune harvest of Gold in Serra do Caldeirão claims, Brazil - (25)  

Great adition made by Mr. Roger Warin!

To see it click on this link or in the image:

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PostPosted: Aug 29, 2017 05:42    Post subject: Re: An opportune harvest of Gold in Serra do Caldeirão claims, Brazil - (25)  

I recently received a beautiful sample of the characteristic hopper crystals of gold from this locality with request to analyze the composition.

According to the study on the geology and metallogeny of gold deposits in Pontes e Lacerda by Geraldes et al. (International Geology Review, 1997. DOI 10.1080/00206819709465282) we expect pure gold for this type of samples (one deposit reported Au-Ag alloy or electrum).

Indeed, the analysis showed very pure gold, with 98.5 to 99.5% Au in the analyzed sample. I performed EDS analyses. The determination of the exact composition would require a technique that could compromise the integrity of the sample, and it is not necessary for the needs of a mineral collection.

Obviously, this does not mean that all samples are composed by pure gold. Depending on the deposit (there are about 23 gold deposits in the Pontes e Lacerda region) there are variable amounts of other noble metals, silver and copper. But in this case, this seems to be a very pure sample.



oro serra noseque.jpg
 Mineral: Gold
 Locality:
Serra do Caldeirão claims, Pontes e Lacerda, Alto Guaporé District, Mato Grosso, Brazil
 Dimensions: FOV 0.8 cm
 Description:
 Viewed:  835 Time(s)

oro serra noseque.jpg



jf24 4.jpg
 Mineral: Gold
 Locality:
Serra do Caldeirão claims, Pontes e Lacerda, Alto Guaporé District, Mato Grosso, Brazil
 Description:
SEM image of a hopper crystal of gold.
 Viewed:  844 Time(s)

jf24 4.jpg



jf24.jpg
 Mineral: Gold
 Locality:
Serra do Caldeirão claims, Pontes e Lacerda, Alto Guaporé District, Mato Grosso, Brazil
 Description:
Another gold crystal showed by SEM
 Viewed:  836 Time(s)

jf24.jpg



Spectrum jf24.jpg
 Description:
EDS analysis of the gold crystals showed in the previous images
 Viewed:  835 Time(s)

Spectrum jf24.jpg



oro serra noseque2.jpg
 Mineral: Gold
 Locality:
Serra do Caldeirão claims, Pontes e Lacerda, Alto Guaporé District, Mato Grosso, Brazil
 Dimensions: FOV 0.5 cm
 Description:
 Viewed:  845 Time(s)

oro serra noseque2.jpg



jf24 3.jpg
 Mineral: Gold
 Locality:
Serra do Caldeirão claims, Pontes e Lacerda, Alto Guaporé District, Mato Grosso, Brazil
 Description:
Interesting features on the surface of gold crystals. I cannot say of these minute crystals and spherules, composed by pure gold, are syngenetic with the crystals or a posterior deposition (by bacterial activity for example).
 Viewed:  834 Time(s)

jf24 3.jpg


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