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[Jordi Fabre]

Great adition made by Mr. Roger Warin!

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

[Cesar M. Salvan]

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.