Black Sand

[Ben78]

What would one do if they wanted to find out the composition of black sand they are digging?

A creek I've been digging has no mines records anywhere in its catchment for gold or other minerals. I've been getting good gold but the black sand is something else - and it is heavy! Starting to wonder what it is and if it is worth keeping.

Has anyone tried to smelt their black sand? Is there a lab you can send it to?

 

[Heatho]

I think you could just send it off for an assay to determine what's in it Ben, might cost a couple of hundred bucks though. Could be Tin, Silver or Platinum or platinum group metals or anything else for that matter. You could also look into fire assay techniques such as cupellation and get a sample bead of the metal out for XRF analysis.

It's all fairly complicated but not undoable. You can even get microwave smelting kits these days.

 

[Ben78]

Cheers Heatho, I was thinking along the lines of it possibly being tin or manganese. If either I should be able to electric arc furnace them into metal

 

[Heatho]

That would be cool to see, yeah it's all very interesting stuff, I love chemistry and metalurgy is extremely interesting too. Keen to see how you go with it. Be awesome if it were Silver. Plenty of Tin and Manganese up your way, though there are Silver deposits also.

 

[KarlS]

I had ask similar question some time ago. As I did not got satisfactory answer I come up with this procedure to recover gold or PGM from black sands.
Get empty tin from baked beans or similar. Put the tin over the pipe of similar diameter as the can and with piece of wood beat the bottom of the tin to the kind of conical shape. Fill the tin about half full with lead.
In the cast iron pot or fry pan roast your black sands over the camp fire. It will stink mostly of Sulphur, so keep away from the fumes.
Now met the lead in your tin. Add roasted black sand to the tin. Stir it well with metal rod. Any gold or PGM will sink to the bottom and much lighter iron compunds will float on molten lead surface.
Let it cool down. You will have to cut out tin metal. With cut off tip of the lead cone. That where your gold is going to be concentrated .
Pour some white vinigar in the glass container and add some hydrogen peroxide. Drop
the lump of lead you cut off in to the solution. It will turn kind of milky colour. Leave it there until the lead disolve. Your gold is going to be in the sludge on the bottom of the container.
Don't drink the solution, although it is kind of sweet(lead acetate ) it is no good for you. If you want make resulting liquid environmentally safe add some battery acid (sulphuric acid ) to it. It will precipitate lead as lead sulfate which is almost unsolvable and therefore fairly safe.
There must be a way how to get lead back from this solution, but as I done chemistry some 50 years ago I do not remember how..
As how effective this method is, well it depends on gold concentration in the black sand. I had recovered 2.8 grams of gold from 420 grams of black sand from one location. And I got no gold fron 340 grams of black sand from different location.
Karl

 

[MJB]

From the few books I have read, Black Sands usually consists mostly of Magnatite and Hematite. Magnatite is fairly magnetic but Hematite is only slightly magnetic but both can be picked up with a fairly good rare earth magnet. Finer, heavy lighter sand found in your pan seems heavier that the black sands and consists of Zircon.

Some places black sand is really fine and others the grains are much larger. I would have thought that if black sand was valuable many a prospector would have started mining and selling it years ago but most of us just call it a nuisance. The only reason I can see in keeping the stuff is for the fine precious metal values that it MAY contain once a quick clean up has already been done. Bung it in ya poverty pot and process it when you get time...it all adds up.

 

[Metamorphic]

Apart from the presence of other 'rare earth' elements, precious metals do still remain within Black Sands and micro gold, almost at the atomic level, can be en capsuled in Magnetite and other minerals.

The process of assay is rather time consuming and expensive however, and would be an option only for those with a keen interest in Chemistry, Metallurgy and other physical sciences involved in the changing of 'matter' as an experimental process alone i would think.

As for the economically viable extraction of precious metals, it would simply be a waste of time and money not to mention the dangers involved with the temperatures needed to 'fracture' the black sands, the gases released, and/or the chemicals used in the process.

It would be really cool to see this done by someone with a keen knowledge and interest in the process though.

Regards

 

[Ben78]

If you have a look at this video - https://youtu.be/7NQ-5AO-vxU at the 1:15 mark I zoom in on the country rock. It's not Breccia I'm fairly certain its Pegmatite which according to wiki -

Pegmatites are important because they often contain rare earth minerals and gemstones, such as aquamarine, tourmaline, topaz, fluorite, apatite and corundum, often along with tin and tungsten minerals, among others.

There is definitely garnet in it, as well as tourmaline and the feldspar phenocrysts are huge. Cassiterite is approx 7 times heavier than water which would make a pan full of it seem quite heavy.

 

[Heatho]

I guess this is why Mercury was so popular, it made it easy to capture the Gold you can't see, same with heap leaching and Cyanide, these 2 would have been and probably still are the the cheapest ways to do this for large operations.

Fire assay as Karl did is spot on but time consuming and maybe expensive, great for knowing what is in it though. Once you have your Gold in the Lead tip then Cupellation in a cupel/crucible is the way to separate the Lead and Gold.

I read a lot about all this a while back but have forgotten half of it. There is a yank forum totally dedicated to this stuff, can't remember the name of that either ATM, will see if I can find it again.

 

[rc62burke]

Hi All
I think this is the one Heatho is referring to. http://goldrefiningforum.com/~goldrefi/phpBB3/index.php?sid=2528067e334e34a54f31e68d25d77e54

I did a trial run on some black sand wasn't to effective in forming a button but ended up with a lots of small balls that were very silver looking.
I only used a crude heating pot & a smelting flux of, Borax, Soda ash & flour, the flour is what is needed when you think there is possible silver oxide in the black sand, for the small amount that I did & for the poor result I was surprised to see the silver balls.

cheers
Lee

 

[Heatho]

That's the 1 Lee, good find. Might gives this a go sometime soon myself just with a small amount of Black Sand, less than a kg and see what's in it. There are quite a few places where the beach sand in NSW contains Platinum group metals with Gold, most are probably NP though.