FMF - Friends of Minerals Forum, discussion and message board

[Lucca]

A colleague and I engaged in EDS (energy-dispersive X-ray spectrometery) testing gold ore in jewelry. In one test we found in order of abundance: Ag, Te. then S. To our best knowledge the provenance of the ore is that it derives from either California or Arizona. There was no Cu.

My question is: What mineral is it likely to be? the gold was found in a dark to black matrix.

I thank you for any assistance. Mineralogy is not my field.

Henry

[Bob Carnein]

Hessite is silver telluride (with a 1:1 Ag:S atomic ratio). The sulfur may be present in another mineral; because of its large ionic radius, the Te ion doesn't substitute for sulfur, making it unlikely that the mineral is a silver sulfide (e.g. acanthite) with Te replacing S. It's also possible that the sample contains acanthite with native tellurium.

[Peter Lemkin]

Calaverite is a rather rare gold telluride with the formula AuTe2. But there are five others. In the USA, as far as I know two of these were 'common' only in Cripple Creek, Colorado. Also found in Kalgoorlie, Australia and Ontario. There is a good technical article on processing of such ores:
https://www.911metallurgist.com/blog/wp-content/uploads/2016/09/Recovering-Gold-from-Telluride-Ore.pdf
(link normalized by FMF)

I would think this gold was from a gold telluride or some telluride was used to process the ore. At about half the price of Gold, Tellurium is too expensive to toss into the 'pot' without a reason.

[Peter Lemkin]

An aside: While I have no gold tellurides in my collection ;-(, I once had the privilege to examine in my hands some fantastic specimens of calavarite xx from Telluride, CO! Sadly, they are not on display anywhere - but stored away for some future ? museum display in San Miguel Co., CO. These were really spectacular crystals!, although large quantities were not found in Telluride well crystallized and large - or perhaps were, and (as so often during the 1800 mining era) tossed into the ore cars along with the common 'ugly' ores.