Non-Chemical Nautural gold melt left beads in borax

[Steve582615]

I spent yesterday melting some natural gold that I had dollied out of gold speciments from my last prospecting trip in Western Australia. I've done this before and I have also melted quite a bit of silver to make cast rings. I normally use benzomatic torch with MAPP and a quartz crucible in a small furnace made from lightweight aluminium silicate firebrick. But this time I ran into a few issues.
the first is that gold balls fomed in the borax glass and I had diffiuclty pouring into graphite mold. (Not hot enough?) The second is that I seemed to have silver balls form as part of the melt. Quite white metal compared to the gold. My question is can silver separate out from gold while being melted? I've never seen that before.
I retrieved the balls out of the borax glaze by crushing the crucible and picking/panning the gold for a remelt.
My self analysiis suggest less borax and more heat.
the borax glass/slag was very dark. There was some impurities in the mix going in as it is raw crushed gold.

 

[Yggdrasil]

If you have a thickish layer of Borax in your dish, quite a lot of prills can be hiding there and reemerge when it is liquefied again.
I guess that is where your silverish metal came from, if you use the same dish that is.
So far I have never heard about separeting Gold and Silver by smelting.

Clean Gold don't need Borax, maybe placer Gold needs it I don't know.

 

[Justincase]

Before I started to work on scrap materials my main training was in the collection of samples for various interests.
What the two activities have in common is "Locard's Exchange Principle"
"with contact between two items, there will be an exchange."
You may be able to limit that exchange or the test you are using to detect an exchange may be too crude to quantify such slight contamination.
But there will always be cross-contamination to some degree.
I simply used the same crucible for clean gold until it starts to show cracks, that way whatever was left from your last melt will go into your next.
Once cracked melting dish will always need to be collected together and eventually crushed for recovery.
It is relatively easy to purify gold by smelting as most other elements that will be alloyed can be oxidized or at a more industrial scale purged with chlorine while melted.
But I can not think of a way to remove gold from silver as it is less reactive.

 

[Steve582615]

If you have a thickish layer of Borax in your dish, quite a lot of prills can be hiding there and reemerge when it is liquefied again.
I guess that is where your silverish metal came from, if you use the same dish that is.
So far I have never heard about separeting Gold and Silver by smelting.

Clean Gold don't need Borax, maybe placer Gold needs it I don't know.

thanks for the observationon the borax. In this case I used a new small crucible. I did about 6 pours from it and the result was progressively worse. I think I overdid the borax. next time much less borax. But there was also fine crushed ironstone in the material for melting.

 

[4metals]

What type of Borax do you use? All Borax isn’t the same. When you heat up the Borax you use does it foam up and expand?

 

[AustAuScrap]

Hi,
On my last West Australia metal detecting trip I got lucky enough to get enough to sell some surplus. I sold to Perth Mint at a place they had near the Perth Airport. There was lots of paper work but after all the bullsh** it got time to weigh in, -hand over. One of the Mint guys said that West Australia gold had a lot more Silver in it naturally than say gold from South Australia , or Victoria. he also mentioned they would test South Australian gold for polonium which made it a no buy for their mint,
Is it possible that this high level of naturally found silver content was the root cause of the problem Steve had as opposed to the borax?

 

[Steve582615]

What type of Borax do you use? All Borax isn’t the same. When you heat up the Borax you use does it foam up and expand?

yes it does foam up a bit but then subsides and goes to syrup.

 

[4metals]

That is because you are using a hydrated borax. For assays and melting an anhydrous borax is better as it doesn’t foam up.
Using fluorspar in your flux will thin it enough so it doesn’t hold any beads. Usually 2 parts anhydrous borax to 1 part soda ash and 1/4 part fluorspar gives a nice fluid flux that is not inclined to hold beads of metal.