# Purple of Cassius- False Positive



## PeterM (Jan 12, 2016)

I get this hit, is it gold or a false positive, I am working on a complex gold ore, the photos provided shows me this when I add a drop of Stannous Chloride solution to my pregnant chloride solution. Oddly the hit will disappears after a while but I can make it reappear with a drop of barren AR. Possibly, I have too high of an ORP. My thoughts are the AR will momentarily pull the gold into stability but will not keep it there for long. Any thoughts guys? I need help!!!!


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## FrugalRefiner (Jan 12, 2016)

Maybe it's just my monitor, but I don't see any purple, just yellow.

Dave


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## PeterM (Jan 12, 2016)

Seriously?


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## Eamonn (Jan 12, 2016)

It dosn't look purple to me either.


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## Lino1406 (Jan 12, 2016)

Stannous chloride test is not a proof for gold


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## patnor1011 (Jan 12, 2016)

How did you treat ore prior to leaching? 
What other metals are present, what did assay found?


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## PeterM (Jan 12, 2016)

Fellas, I am dealing with a very concentrated solution keep that in mind.


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## solar_plasma (Jan 12, 2016)

Do you see any purple stain on those white spoons, when you dry them while the test is still positive?

Btw do you have an excess of oxidizer in there?

@Lino, purple stain would be pretty specific for gold, wouldn't it?


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## FrugalRefiner (Jan 12, 2016)

Since you're dealing with an ore, I've moved this topic to the Prospecting, Mining, Ore Concentrates & Geochemical section in the hopes you'll get more helpful answers.

Dave


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## goldsilverpro (Jan 12, 2016)

Doesn't look "gold purple" to me either.


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## g_axelsson (Jan 12, 2016)

Try to denox it before testing.

Though, doesn't look as positive to me. Have you tested your stannous lately? Do you get a positive if you add a bit of gold chloride to your sample?

Göran


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## jason_recliner (Jan 12, 2016)

PeterM said:


> Fellas, I am dealing with a very concentrated solution keep that in mind.


In a spoon, I would expect a typical positive stannous test of a very concentrated gold solution to be black.
You're more likely to see purple by combining a single drop of each on absorbent paper. The more consistent you can make your tests, the easier they will be to discern.


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## PeterM (Jan 12, 2016)

jason_recliner said:


> PeterM said:
> 
> 
> > Fellas, I am dealing with a very concentrated solution keep that in mind.
> ...



It this what your referring too?


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## patnor1011 (Jan 12, 2016)

How did you treat ore prior leach? Did you roast it sufficiently enough? What other metals did assay found present in that ore?


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## PeterM (Jan 12, 2016)

patnor1011 said:


> How did you treat ore prior leach? Did you roast it sufficiently enough? What other metals did assay found present in that ore?



Yes sir, a chemical pretreatment but no roast. No, it doesn't fire assay because of the Se, and Te present.


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## PeterM (Jan 12, 2016)

g_axelsson said:


> Try to denox it before testing.
> 
> Though, doesn't look as positive to me. Have you tested your stannous lately? Do you get a positive if you add a bit of gold chloride to your sample?
> 
> Göran


The Stannous Chloride is fresh, I make it often.


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## solar_plasma (Jan 13, 2016)

Drive off any chlorine first. Try again.

If nothing helps, cementing on copper powder, filtering and dissolving this cleaner probe might be a way to go. If it is still negative I doubt there is any gold in this solution. Disclaimer: I have no clue about ores.


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## Grelko (Jan 13, 2016)

PeterM said:


> because of the Se, and Te present.



What would the chances be, that the Selenium in this ore, could have become selenic acid? It'll dissolve gold also (gold III selenate), and is there a chance that this could be holding it in solution? https://en.wikipedia.org/wiki/Selenic_acid

Edit - This may be of some interest also, and added page numbers.

The Chemical News and Journal of Physical Science, Volume 86

Action of Tellurium and Selenium on Gold and Silver salts

Pages 309-311

https://books.google.com/books?id=8xlLAAAAYAAJ&pg=PA309&lpg=PA309&dq=selenium+aqua+regia+gold&source=bl&ots=5MTHGIKr2A&sig=S8O-XOlWSxC0GiN3I42awNe9KxI&hl=en&sa=X&ved=0ahUKEwiamaCTuqbKAhUGLyYKHQzGB24Q6AEILDAD#v=onepage&q=selenium%20aqua%20regia%20gold&f=false

Another edit - reworded


PeterM said:


> Fellas, I am dealing with a very concentrated solution keep that in mind.



Gold (III) Selenate
Properties - small yellow cryst; decomposes in light
solubility - i, H2O, s H2SO4, HNO3

Look at the very first post, picture 2, spoon on the right. if you zoom in, it looks like yellow crystals. Did you get rid of the extra nitric?


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## PeterM (Jan 13, 2016)

Grelko said:


> PeterM said:
> 
> 
> > because of the Se, and Te present.
> ...



Tushay Grelko, Thanks for the info. FYIP: I use Urea to expel the Nitric while the preg is hot (Red-Brown nitrus fumes occur). I'll study the links. Keep it coming!!!


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## Anonymous (Jan 13, 2016)

Those first pics where you point out that it's "a very concentrated solution." That's not overly concentrated to be honest and I mean that in the best possible way.

Just as a jokey aside- tushay is actually a french word - touché 8) 

Good luck with it.

Jon

Edit: In light if the fact you're talking about mining Peter, and I'm normally looking at tests from concentrated e-scrap my comment above needs to be put into context. 8)


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## goldsilverpro (Jan 13, 2016)

In the spoon, try diluting 1 drop with 3 or 4 drops of distilled water. Then add 1 drop of stannous chloride and see what you get. Sometimes you get better results by diluting highly concentrated samples. It takes very little gold to show up.

By the way, porcelain spot plates are cheap and better than spoons.
http://www.hometrainingtools.com/porcelain-spot-plate

Porcelain spot plates are also very handy for dissolving and testing very small quantities of metals (or ores, concentrates, etc). In the field, I used them to test for various PM brazes on stators on jet engines. I filed off some of the braze (file fairly deep) with a very small triangular file onto a clean sheet of paper. I transferred a few filings to a spot plate and added a drop of nitric and 4 drops of HCl. When dissolved, I tested (for gold/nickel braze) with a drop of stannous chloride. I used other solutions to pinpoint the Ag/Cu and Ag/Cu/Pd brazes. To speed the dissolving, you can put the spot plate on a warm hot plate or a sheet of steel that's been sitting in the summer sun. You can also heat a spot using a cigarette lighter or small torch underneath that spot. Ms. Hoke talks about the hotplate thing in her Testing book (free download). She also uses an abrasive to roughen the spots for rubbing PM objects, like on a touchstone. Reading this book will convince you of the value of spot plates.

They also work great for keeping the chunks of lead in proper order when doing fire assay cupellations - I numbered the spots 1 thru 12.

I assume these cheap spot plates (probably Chinese) will hold up to the heat and chemicals. I've always used the Coors brand but they are now $27 and up. There are dark blue ones, black ones and clear Pyrex ones that I haven't tried. I've always thought the black ones might be better for light colored things like silver chloride and DMG Pd. Coor's original black porcelain ones contained a uranium compound, I think.


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## Platdigger (Jan 13, 2016)

Well, according to the document given by Grelko, both Selenium and Tellurium will come down with sulfur dioxide. So, most likely they will come down with stanus also, giving a messed up test.
Just a thought.


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## PeterM (Jan 13, 2016)

Platdigger said:


> Well, according to the document given by Grelko, both Selenium and Tellurium will come down with sulfur dioxide. So, most likely they will come down with Stannous Chloride also, giving a messed up test.
> Just a thought.


Your probably right, however Se and Te are soluble in HNO3, which will require another digest, possibly 24 hours of the Au precips to elute the Se & Te before you anneal the gold. Otherwise it may go up in smoke.


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## goldsilverpro (Jan 13, 2016)

Have you tried my dilution suggestion?


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## Grelko (Jan 13, 2016)

I haven't processed ore, but I have a knack for finding information. This might help you or other members find out what's causing your problem.

Documented Gold Bearing Telluride/Oxide Ores http://goldrefiningforum.com/phpBB3/viewtopic.php?f=44&t=8709&p=81710&hilit=gold+selenite#p81710

Gold-Selenide Separation http://goldrefiningforum.com/phpBB3/viewtopic.php?f=44&t=7308&p=206968&hilit=gold+selenide#p206968

http://www.ptable.com/ (Dynamic periodic table) click on Se or Te, theres alot of information about each of these.

Be careful, since Se and Te can be toxic, even the smoke/fumes.

Edit - I'd try what GoldSilverPro has suggested first. He would know alot more about recovery/refining, than I would.

Also (tin with selenium) http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=49&t=19477 might explain your stannous problem.

---------------------------
New Edit - Microscopic Determination of the Ore Minerals, Issue 914 https://books.google.com/books?id=bejQAAAAMAAJ&pg=PA206&lpg=PA206&dq=selenium+stannous+chloride+gold&source=bl&ots=Jkp_TLYsGX&sig=LdEBF95uNG_M3bm90xdNGrgHij4&hl=en&sa=X&ved=0ahUKEwiPx4XezqfKAhWDPj4KHe8hAnsQ6AEIMzAF#v=onepage&q=selenium%20stannous%20chloride%20gold&f=false

Bottom of page 206 - (stannous chloride precipitates tellurium as a black powder, which obscures to a large degree, the red selenium precipitate)

This is most likely the reason for your false reading for gold.


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## Lou (Jan 22, 2016)

Tellurium and selenium are both thrown down (one as black, the other as a red powder) with sulfites or SO2 post aqua regia digest. Most often you can smell their presence (I can at least, selenium and tellurium both stink to me!).

This is why roasting, or ozone, is important to remove chalcogenides such as these.


Lou


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