Processing Black Sands

[SchoolOfHardRocks]

I've heard that prospector's "would be surprised, & never discard black sands again if they knew how much gold is in it"...Well, with my 2nd season coming to a close I think I have stock piled enough to think about processing it.

I have about 2 gallons of black sands and am wondering, what's the most efficient way to process it? I've heard about the crushing method & the heat & freeze method...but what is the best way? Are there other ways??

My plan is to document this process from beginning to end on this thread once I have determined which processing method will work best for me..who knows someone else may benefit from seeing my trial and error with black sands. Plus it will keep me busy while I'm patiently waiting for spring

 

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[rockbar]

That's not much volume, so you might just fab up or purchase a small mortar and pestle and mill some by hand and see if that liberates any free-milling gold from the sands. If you find that crushing yields gold that will be large enough to capture with gravity concentration, then careful panning or sluicing (clean-up) may recover it. This would be one of the easiest and least expensive ways to treat your sands.
Another method is to use a rock tumbler and some steel ball bearings as a mini ball mill to crush the sands. This method also allows you to try to amalgamate the fine gold in the tumbler. I doubt many would recommend you try amalgamating with such a small volume… wouldn't be worth the risk of dealing with a toxic substance.
If, on the other hand, you find that no manner of crushing liberates any worthwhile amount of free gold, then you may send some in for an assay just to satisfy your curiosity. However, if it's not free-milling, I wouldn't bother unless you had a few tons of it to send to a processing facility.
Just my 2cents and hope this is helpful.

 

[johnedoe]

You might look this over.
http://www.treasurenet.com/forums/p...-solution-fine-gold-recovery.html#post4460925

Here is the PDF for the method..... This works better than a ball mill.
http://www.geology.gov.yk.ca/pdf/141114_Nov1014_Grinding_for_Gold_Presentation.pdf

 

[arizau]

First, a question...Did you classify the material you originally panned/processed into various size fractions (for example, plus and minus 30, 50 and 100)? If you did not then that could be a productive first step. Carefully re-panning the now like sized material separately, in small quantities (about a tablespoon at a time) could yield gold that you missed the first time around.
.
Second...Should you choose to do any grinding or crushing then make sure you classify the ground material (see above) before you try panning again. It is so much easier to pan/recover gold from like sized material as then, it is up to 4 times heavier than any of the other material that it is mixed in with. If gold was still not apparent after grinding a representative test amount then that is where I personally would stop messing with the material since at that point I would consider it not worth my time. However, I would still save future cons and do the same test on them just in case.

These may be procedures that you already know but are instructive for those who do not know them.

Good luck.

 

[rockbar]

johnedoe,
That's an excellent study the Clarkson boys did. Sounds like the rod mill is the way to go. Great info on sluice box design.

 

[goldenIrishman]

Well first off you have to decide when enough is enough. You can rework the sands till the cows come home and still have a bit of gold left in them. Here is how I do mine. It's fairly quick, very easy and leaves very little gold in the sands.

1. Process materials in sluice as usual.
2. Classify black sands by size and pan individual sizes down to get the visible gold out of them.
3. Grind the sands down to as fine as you can get them. I use a rock tumbler for this and end up with -100 mesh very quickly. Grinding weights are only 3 pounds per batch but as soon as you finish one you can reload the tumbler barrel and get it going on the next batch while you start panning down the one you just removed.
4. Pan the materials down a teaspoon at a time or use a miller table to process them. Miller table is faster but panning is more fun in my book.
5. After the gold has been recovered, soak it in white vinegar to remove the grime left from the tumbling stage.

Getting all of the gold out is pretty much impossible no matter what you do. You can beat yourself to death trying to get it all. This is why you have to decide when to call it quits.

 

[johnedoe]

johnedoe,
That's an excellent study the Clarkson boys did. Sounds like the rod mill is the way to go. Great info on sluice box design.

Thank you ... glad I can help a little.
You may also find this thread of some use....... http://www.treasurenet.com/forums/sluicing/455210-how-build-operate-sluice-box.html#post4446082

 

[SchoolOfHardRocks]

Thank you all for the valuable information. Looks like I have missed some crucial steps & all of this crushing talk should wait until i properly classify and pan everything first....at my current panning rate that shoud be enough to get me through the winter lol.

Once I have done that properly i will proceed to crushing....Thanks again!!

 

[johnedoe]

Thank you all for the valuable information. Looks like I have missed some crucial steps & all of this crushing talk should wait until i properly classify and pan everything first....at my current panning rate that shoud be enough to get me through the winter lol.

Once I have done that properly i will proceed to crushing....Thanks again!!

For your panning knowledge you might want to watch this series of short video's on panning, Once you get a handle on the concepts you can then take some short cuts that will help speed things up a little more......Enjoy.
http://www.treasurenet.com/forums/panning-gold/459664-art-gold-panning.html

And if this is not enough studying for you there is this too....
You get through these you should be able to capture just about any gold your gonna find......
http://www.treasurenet.com/forums/panning-gold/455285-how-build-operate-miller-table.html

Have fun.....

 

[CApicker]

Good luck HardRocks! I have always wondered what would come out of that Black Sand... I never classify past about 1/4 inch and I run all my black sand out of my Blue Bowl with very fine Gold in it I'm sure. I like the stuff that's big enough to see anyway... will look forward to seeing what you do.

 

[goldenIrishman]

Good luck HardRocks! I have always wondered what would come out of that Black Sand... I never classify past about 1/4 inch and I run all my black sand out of my Blue Bowl with very fine Gold in it I'm sure. I like the stuff that's big enough to see anyway... will look forward to seeing what you do.

One thing I've learned over the years is that there are some very simple ways to get that micro gold without having to bust your backside to do it. I knew I was missing some of the fine stuff and a couple of weeks ago I came across a little microscope at the local swap meet for $25. Turns out it was the best investment in furthering my gold education I have made this year. By examining the tailings I was able to see just what I'd been missing for years! I looked at everything from non magnetic black sands to magnetics and even those pesky heavy blonde and garnet (redhead?) sands that love to hang around in the pan. EVERYTHING had some gold in it!

In the case of the magnetic black sands, I was able to see how some of the gold had a coating on it that allowed the magnet to pull it out of the pan. The blonde sands showed me small pieces of gold still stuck in the matrix rocks. So I wanted to be able to get this gold and I didn't want to have to resort to leaching or using Aqua Regina to get it. Even though I had used a Mercury amalgamation in the past, I wanted to get away from that as well. I had a dual drum rock tumbler that I used to use for amalgamation and decided to turn it into a small batch crusher. I loaded up about 3/4 of a cup of the -50/+70 mesh non-magnetic black sands into one of the drums along with a half dozen old deep well sockets and some water to keep it in a slurry. I let it tumble for about 24 hours and when I pulled them out of the barrel they went right through a 100 mesh classifier like it wasn't even there. I panned it down and took a small sample of the stuff that walked up the pan when I did the tapping on the pan thing. I put the sample under the scope and sure enough it was almost all gold. It was dirty looking so I put it in a small vial with white vinegar in it for a couple of hours and then looked at it again. Much better looking now as the pictures below show. By crushing the sands I was even able to skip the "Shake & Bake" step but I'm still thinking of giving it a try after the crushing just to see what happens with the stuff left in the pan after cleaning the rest of the gold out.

The way I look at it, you can either do this kind of processing at the end of every run or you can save up the black sands and spend the off season cleaning them out when you can't get out to get new materials. After all... No matter how small it is, even the small stuff adds up to gold in the poke!

 

[johnedoe]

Nice work goldenIrishman........
What magnification were you using?

 

[KevinInColorado]

Very nice work. Thanks for sharing enough details for me to try this out too. When you talk about deep well sockets do you mean the sort you'd remove a spark plug with?

Also, did you stop it before 24 hours to see how it was doing? I mean did you really need the full 24 hours to get this result?

 

[goldenIrishman]

Nice work goldenIrishman........
What magnification were you using?

Thanks JD. That was at 100X on the microscope but I have to zoom in with the phone camera to get a full frame. I would estimate that between the scope and the camera it's about 160X magnification. The camera on my phone isn't all that great for this but it's all I've got until I can swing a USB microscope. The microscope will also do 450X and 1000X but the depth of focus makes it impossible to get enough in focus to make it worth using.

 

[johnedoe]

I may have to try some of this on our beach sands...... I didn't think there would be anything really hiding since they are already subjected to a lot of action from the surf and materials they are mixed with...

Also looking at these photomicrographs led me to think that there would be no use in it.....
cleangold photomicrographs

But these are also after clean up to some degree..... I am going to have to look at more of the cons themselves.

 

[goldenIrishman]

Very nice work. Thanks for sharing enough details for me to try this out too. When you talk about deep well sockets do you mean the sort you'd remove a spark plug with?

Also, did you stop it before 24 hours to see how it was doing? I mean did you really need the full 24 hours to get this result?

Thanks Kev. Spark plug sockets or something even longer will work. I'm considering picking up a 3ft length of 1" cold rolled bar stock and cutting it into lengths that will just fit inside the drum. That way they'll have more weight to them and won't have the opening in the middle that seems to trap sand inside them. My tumbler is limited to a total of 3lbs per barrel. That's the total for sand, rods and water combined. I let it run without checking it as I didn't expect it to work so well. I'm also going to try adding a drop or two of dish soap to the next batch to see if things come out cleaner.

I may have to try some of this on our beach sands...... I didn't think there would be anything really hiding since they are already subjected to a lot of action from the surf and materials they are mixed with...

Also looking at these photomicrographs led me to think that there would be no use in it.....
cleangold photomicrographs

But these are also after clean up to some degree..... I am going to have to look at more of the cons themselves.

Well I thought that I'd gotten everything out of the sands as well. A quick check under the microscope showed me just how wrong that line of thinking was. I know that you can find gold on a lot of the beaches from Santa Barbra, CA north. Considering that the current runs north to south, I'd be checking on the south side of any rivers or streams that flow into the ocean. The crushing action knocks off the coating that is on a lot of the micro gold so you can actually see it for what it is. I'm also going to try doing the "Shake & Bake" on the sands after crushing to see if it turns up even more gold.
====================================================================================================

I think I'm going to do another batch but this time I'm going to weigh the amount of sand I put in the drum before I run it. Then once I have recovered the gold weigh it up as well. Since my scale is good down to 1/100 of a gram I should be able to get a good idea of the percentage of gold I've been missing in the past. Experimenting like this is fun for me and if it helps me to improve my take or figure out an easier way to do the recovery then so much the better! Ahhh The joys of being a science geek!

 

[johnedoe]

looks like your getting there.
This page of the PDF pretty well gives you all the parameters for the rod mill.


I will definitely be looking more closely at the beach sands to see if there are any additional hidden surprises....

 

[goldenIrishman]

Well I've got some limits I have to work with here.
1. Set speed on the tumbler
2. Max weight of 3 Lbs in each barrel

The varied rod diameter (1", 3/4" and 1/2") is easy enough to do but 40% of volume is going to put me way over weight for the tumbler system I've got. Once I get a shop area put together I can make up a tumbler with a much higher weight limit.

I'm also thinking that it might be a good idea to get some of the smaller diameter classifiers with meshes under 100. Since this first batch went through the screen like it wasn't even there, finer mesh screens will allow me to classify to like sizes so the specific gravity effect still works. I'd imagine that having -100 mixed in with -150 or -200 materials would cause problems.

I did two batches so far. The first I did dry and the second was wet. The second batch came out MUCH better so water seems to be a must have in the mix.

 

[johnedoe]

The water cons ratio is 1 to 1.... But your on the right track.

 

[goldenIrishman]

The water cons ratio is 1 to 1.... But your on the right track.

By Weight or volume?