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 Post subject: Placer mining
PostPosted: Wed Apr 01, 2015 10:19 pm 
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Joined: Wed Jan 14, 2015 3:52 pm
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Location: N Dakota
Placer mining of sapphires seems a bit different than the gold mining I have done in the past. I have seen a few different metheods and machines used that just make me shake my head. The specific gravity of sapphire runs 3.5 - 4 vs gold at 18 has me confused on effective recovery methods.
Where I have plans of hunting the stones are usually screened with 1/4" and 1/8" mesh. Most stones running less than 10mm. Most only half that size. A mini wash plant or trammel and classifier screens reduce overburden to minimum. So now how to separate from there. A sluice will work but with how much other unwanted material? A jig has similar issues, and requires power. Would a spiral separator / concentrator be effective? If classified to say a 1 or 2mm tolerance it should run uniformly enough.
Not to say the tried and true shake and flip isn't fun, but if a more efficient way is out there I'm all for it

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 Post subject: Re: Placer mining
PostPosted: Wed Apr 01, 2015 11:08 pm 
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Joined: Sat Jul 14, 2012 5:11 pm
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Dan, your idea of riffles, etc for sapphires, just won't work.
The heavier gravels just clog up the thing, and sapphires rumble over the top.
We use a "pulsator", and this is the most efficient recovery system.
Basically a large box, it has a stainless mesh screen close to the top, with riffles fitted over this.
It fills with water, then a plunger on the side, causes the water level to rise and fall on the pulse of the plunger. As the sapphire rich wash flows over the screen, the heavy materials get immediately dumped behind the riffles.
I'll dig out a photo, and post it tonight.
Barry.


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 Post subject: Re: Placer mining
PostPosted: Sun Apr 05, 2015 4:15 pm 
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Location: N Dakota
I repaired my gold screw this morning, a new motor and battery, and away we go. So the first thing I did was run a test. Pulled a small bag of 2mm sapphires and ran them through the screw to set the angle. Then I ran them with 3 parts gravel to 1 part sapphire. Only missed a doz into the tailings. Found them to be flat discs. Next I ran the gravels and sapphires with a bit of jet dry as a wetting agent. That worked better in fact I recovered 4 more 1mm stones out of the gravel. So I know it works, however closer screening of gravels would work better. I found the gravels contain cinnabar and some geodesic materials that travel up the screw as well. The larger size materials push the sapphires out, by closer screening the recovery will be better. The next trial I will re-run the gravels I still have in a bucket from the initial find and see what results come out of it. I thought I recovered everything down to 2mm. I expect to find smaller stones but its always fun to see how much you miss after you are sure you got all of it.

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 Post subject: Re: Placer mining
PostPosted: Sun Apr 05, 2015 11:24 pm 
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Joined: Wed Jan 14, 2015 3:52 pm
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Location: N Dakota
so the gravel was run again, and I did quite well with my initial screening. 5 gal pail produced nearly a doz sapphires that I had missed. Garnets about the size of buckshot turned up, a doz lead shot BBs, and to my surprise a clear pink to red 6mm sapphire. That one was neat because it walked up the screw by itself, no other rocks at all. But like I said before the screening needs to be better classified. The gold screw isnt meant to run 1/4' material, its more for fine materials. I think if I screened in 2mm steps in mesh size it will perform equal to my eyesight anyway. But I will check out a pulsator and see if I cant make one for a couple hundred $$. Just upgraded my sluice to a totally recirculated system for less than a hundred $$. Now is the time for upgrades and repairs. I wont be able to get into the high country for almost 2 months yet.

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 Post subject: Re: Placer mining
PostPosted: Mon Feb 01, 2016 5:01 pm 
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Joined: Wed Jan 14, 2015 3:52 pm
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Location: N Dakota
It's been a year since my last post here. Never made it anywhere last year. But I did accomplish a few things. First, I built a pulse jig. It is a much better recovery tool for gems than a sluice box. I did get to run gravels but only because I had them shipped in. Do what you have to.
Recently I found a online download of all the forms and regulations for filing minerals claim in Montana. On Federal BLM lands at least. Previously found similar info for national forest lands. I believe I now have all the claims information in 1 place. To go along with that is a PLSS and PLOT mapping system that has active claim locations. So now I can verify the areas I had planned to prospect are either claimed or open before I head out. It's not a 100% but it is a good reference to start with.
It looks as though my thought process of where to look for sapphires base on geodata was spot on. Those areas are busy with active claims. But similar areas nearby seem overlooked even though historical documents have proof of mineable materials. Gives a guy hope anyway. So now that I am armed with better information I can spread out my search area and find more prospectable areas in the region. always got to have a back up plan

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 Post subject: Re: Placer mining
PostPosted: Tue Feb 02, 2016 7:21 pm 
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Joined: Wed Sep 02, 2015 10:52 pm
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Location: Central Queensland, Australia
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It looks as though my thought process of where to look for sapphires base on geodata was spot on. Those areas are busy with active claims. But similar areas nearby seem overlooked even though historical documents have proof of mineable materials. Gives a guy hope anyway. So now that I am armed with better information I can spread out my search area and find more prospectable areas in the region. always got to have a back up plan




Hope is what guys like us thrive on :) That big find is always out there......

As you say, with the information available to us these days through the www, we can be better informed as to where to concentrate our search efforts.


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