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GeneralCopper-Zinc-alloy

26th Mar 2015 09:07 UTCChristian Auer 🌟 Expert

A classic species meanwhile are those very common specimen, normally labeled with gold from the slag deposit of Gertraudi near Brixlegg http://www.mindat.org/loc-57140.html.

As I know they were collected around 1970-75 from a deposit that is not really old.

A friend of mine gave me already some time ago the tip that most (all?) of them are no gold but Cu-Zn-alloys which would make also sense as nobody throws away gold. He told me that all specimen he checked weren`t ductile as gold!

I have several of them also at home and got one more just recently which I analysed now by SEM-EDS. Plz see http://www.mindat.org/photo-674092.html

The average result is Cu 6,8 Zn 3,0 nothing else!

So I changed all of my pics here on mindat to alloy http://www.mindat.org/gallery.php?loc=57140&min=40557, one pic from another mindater is still copper, 3 as gold http://www.mindat.org/gallery.php?loc=57140&min=1720. I doubt all 3 gold as they look very similiar to the alloy.

Has someone else more experience on it?

26th Mar 2015 11:11 UTCPavel Kartashov Manager

I am suppose, that analyzing of normal polished microprobe preparates will produced slightly different, more proper results close to phase Cu₂Zn.

But you shouldn't to hurry up to write down this phase as tongxinite. You should to understand, that this is 100% manmade phase - as all high-temperature metallic, intermetallic, oxides, sulphides and silicates are, which were formed during solidification/cooling of slag's melt. All them aren't minerals sensu stricto.

I had purchased recently nice copper-nickel "nugget" of composition ~Cu₂Ni from smelter. This alloy covered by black masses of CuO and spinelide of composition CuNi₂O₄. But it never would come in my mind to name these phases minerals.

26th Mar 2015 11:40 UTCChristian Auer 🌟 Expert

I am fully on your side Pavel and wouldn`t write anything else than Cu-Zn-alloy on the boxes.

The reason why I even mentioned it here was to show they aren`t gold.

Still 3 pics out there on mindat labelled as gold ...

26th Mar 2015 17:10 UTCRob Woodside 🌟 Manager

Thanks, Messages sent.

26th Mar 2015 20:49 UTCRalph S Bottrill 🌟 Manager

α-Brass?

One of your photos still says gold in the description

26th Mar 2015 21:33 UTCChristian Auer 🌟 Expert

Ralph I can`t find it.

The closest phase would be Cu2Zn as Pavel suggested. Brass is Cu3Zn.

27th Mar 2015 11:06 UTCRalph S Bottrill 🌟 Manager

Chris

http://www.mindat.org/photo-531290.html says "Gold size 4 mm; Chris Auer photo and collection (ex J.Metzger coll., found in 1970)".

The composition is between the two and I would bet you have a range of Cu-Zn alloys present.

27th Mar 2015 12:43 UTCChristian Auer 🌟 Expert

Thanks Ralph, I wasn`t aware that I wrote it also into the description!

27th Mar 2015 15:15 UTCJoachim Esche 🌟 Expert

Servus Chris,

thanks for the information. I have downgraded my gold to Cu-Zn-alloy and I will also inform Andi Steinberger, from whom I got this specimen.

Joachim

27th Mar 2015 22:45 UTCGiovanni Scapin

Christian,Ralph and Rob, thank for the signal and information, i have update my photos , correct fron Gold in Cu-Zn alloy.

Regards. Giovanni

28th Sep 2016 07:19 UTCChristian Auer 🌟 Expert

Here is another analysed one: http://www.mindat.org/photo-775893.html

Its about 1:1 in atom % so quite different to others, well its artificial.

http://www.mindat.org/photo-118094.html shows copper although I guess there is also some part of zinc in it.

http://www.mindat.org/photo-351634.html shows an alloy labeled as gold. A complaint is pending since 1,5 years and its still visible??

28th Sep 2016 12:39 UTCReiner Mielke Expert

Interesting "gold" that might explain the "gold nuggets" I used to find in the jig concentrate recovered from the Hoyle Pond gold mine ore that came from the Kidd Creek Cu-Zn smelter site in Timmins. I had to use nitric acid to distinguish them from gold. I knew there was some contamination from the smelter after I found a 40kg copper "nugget" in the ore pile one day!

28th Sep 2016 14:45 UTCFred E. Davis

A brass alloy with Cu:Zn ~= 75%:25% is also known as "Prince's metal" or "Prince Rupert's metal" since it imitates the color of gold.

https://en.wikipedia.org/wiki/Brass

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