Jump to content

Best Way To Recover Diamonds And Sapphires In Dry Gravel?


Recommended Posts

I'm planning on doing some gemstone prospecting here soon. I know I can more or less dry pan for diamonds and sapphires, but I'd like to move a bit more dirt, like 1/4 yard test holes in washes, 4-5 test holes a day.

I need something light and portable (ATV packable). Lacking any other ideas, I'm just going to use my drywasher.

Is there anything better than that?

  • Like 1
Link to comment
Share on other sites


Using a dry washer my grandfather would always have a bucket of water to classify small amounts of what he thought was a gem. The water helped in that aspect of the process if there was to much dirt on the gems.

I am sure that there is someone else who would know more about that than me, I was still to young when I went with him looking for gems.

Gold was what I really helped him with and learned about sluices and some dry washers.

Good luck.

Link to comment
Share on other sites

That's a tough one. Dry panning for gold when the density contrast is 19 to 2.6 is one thing but when it's 4 to 2.6 that's something else. When I was doing diamond exploration back in the day we used hand jigs. Not much more than a 1/2 mm classifying screen that you move (jig) an inch up and down in a bucket of water, say, twice a second. Yeah, it takes practice but the guys who did it day after day got really good! We were looking for garnet and ilmenite diamond indicators though. The attached gives you the idea. It's not rocket-science. You do need to classify the material first (+1mm -5mm?) and a minimal amount of water. Maybe classify it, bag it and haul it to somewhere with water? It's hard work so the dry washer sounds worth trying. Spike a sample with a couple of sapphires first and see if you lose them! Also, like gold, diamonds will be on bedrock. You can throw away everything except the last inch. Let me know how it goes.

 

  • Like 1
Link to comment
Share on other sites

Interesting, never considered a hand jig like that. I'm going to have to think on that concept a bit and see if there is some more portable, mechanized way I could build something like that. In my mind it seems like the jigging is just fluidizing the gravel, so I should be able to accomplish that with dry gravel too as long as I can fluidize the gravel - like with air/vibration. Which I guess is basically what a drywasher does.

I'll give the drywasher a try for lack of anything better right now, if it's catching the garnets then it should catch diamonds and sapphires too I guess. The issue for me is total lack of water, I'd have to haul it around with me on my ATV, so for exploration working dry methods seems required.

If I do find a place worth working, I have 2 duplex jigs that I bought years ago to refurbish and stopped halfway through due to lack of any real place to use them. These suckers are 600lbs each though, not something to move around a lot. 

image.png.3f5fa025bc88ac2650219cc850071ee9.png

  • Like 1
Link to comment
Share on other sites

In my head what I'm thinking to create a mechanized, dry version of that hand jigging concept is something like a big vibrating 2ftx3ftx6" deep tray with air at the bottom (like an air hockey table). No riffles, just a tray set flat and level and maybe some small recesses ("nugget traps"), with a grizzly on top to shovel onto/classify.

Let it run for 15 or 20 seconds then run a flat bar across to take the top half of the gravel off, then shovel into again and repeat the process. Similar to a drywasher I guess... But seems to me the closer in SG the gems are to the average SG of the gravel, the flatter you'd need to run, so running completely flat seems best and get rid of the riffles entirely? I guess you could call it a "dry jig" - not quite jig and not quite drywasher.

Basically fluidized and always just removing the top cut of gravel out of the tray, leaving the bottom cut to continually concentrate. Light sands might just naturally overflow off the sides too, as new gravels enter the tray, not sure. Maybe try out one of these new battery powered leaf blowers to make it more portable. Hmm, sounds like a winter welding project. :smile:

Link to comment
Share on other sites

To my surprise Google had quite a lot on dry jigs.

Take a look at this YouTube and be sure to read all the comments, 'Fraid there's some not so good news in there. But it sounds like the guy has already been down the road you are contemplating. My gut feel is that it's a stretch but give your dry blower a shot first.

 

Link to comment
Share on other sites

Interesting. He keeps saying it works great with gems, but then has a comment in the description saying it doesn't work. Why?

I can't help but feel the author of that video might be a forum member? He's probably exploring some of the same areas I am anyways and that avatar seems familiar like I've seen it posted here, he also runs a TDI SL so I'm guessing he reads this forum at least. 

Granular convection is a problem with size sorting, so I guess a solution might be to classify strategically such that the average size of the gems is close to the smallest size particle in the gravel mixture. "Overclassify" I guess, which is sort of the opposite of what you'd do with a wet jig.

I'm guessing he's already tried that though. I'll have to dig through some more of his videos when I get time tonight.

Edit: @Jim in Idaho I thought I recognized the avatar. Care to answer some questions on gemstone recovery and jigs? :smile:

Link to comment
Share on other sites

Here is a very crude drawing to illustrate the idea of using granular convection (aka 'brazil nut effect') as a benefit, instead of a hinderence. This is what I'm wondering if Jim experimented with.

The idea being this: let's say your gems are on average no smaller than 20 mesh. And on average no larger than 1/4". You'd set your bottom screen to be 25 mesh and your top screen to be 3/8"-1/2". The vibrator on the jig should automate the screening process too.

So, now the granular convection "problem" may actual help. Because the gems will among the smallest gravel sizes and thus will not convect up to the top with the larger pieces. The larger pieces should act to keep the smaller gems buried and in the jig. As long as the gems are always smaller in size than the average gravel pebble, granular convection should actually increase the efficiency rather than decrease the jig efficiency. At least in my head that seems like worth experimenting with. I think the key would be proper screen selection for any given environment/targets.

Further, there is also the standard jigging concentration effect going on top of that too. Seems like it should work? The undersize could be bucketed and run at home in a sluice if losses are a concern, the oversize should be able to just be eyeballed.

image.png.ddd38ecff96dedfcdd2006c9e26352ea.png

  • Like 1
Link to comment
Share on other sites

I've done a large amount of experimentation on dry gem recovery. Mostly because of my prospecting in Wyoming. I've made several mechanical units to accomplish that before deciding you can't defeat "granular convection". It may be possible to use it, however. I have not looked into that. I am currently working on a dry sluice for gold, however, that works really well. I recently went to Wyoming, and tried it on one of the WPA club claims, and found considerable amount of flour gold with it. Unfortunately, I have already said more than I should regarding that sluice. Since I'm going to apply for a patent, the less said at this point, the better.

 Back on the gem recovery, dry. There is no way, using gravity, to recover gems dry. Can't be done....with one exception, which is moot anyway because no gems have high enough density to make it work. My experiments suggest that granular convection stops operating with a density ratio around 4:1. Since most soils are about 2.5, the gems would need to be at least 10, and I know of no gems that are that dense. The same applies to trying to separate heavy metals from black sand (another failure of mine....LOL). Operating dry is a whole 'nother world from working in water.

Interesting, though, and the rewards of finding solutions, would  be great.

Jasong, I would consider it an honor to meet up with you someday...I think we'd hit it off.

Jim

  • Like 2
Link to comment
Share on other sites

18 hours ago, jasong said:

Here is a very crude drawing to illustrate the idea of using granular convection (aka 'brazil nut effect') as a benefit, instead of a hinderence. This is what I'm wondering if Jim experimented with.

The idea being this: let's say your gems are on average no smaller than 20 mesh. And on average no larger than 1/4". You'd set your bottom screen to be 25 mesh and your top screen to be 3/8"-1/2". The vibrator on the jig should automate the screening process too.

So, now the granular convection "problem" may actual help. Because the gems will among the smallest gravel sizes and thus will not convect up to the top with the larger pieces. The larger pieces should act to keep the smaller gems buried and in the jig. As long as the gems are always smaller in size than the average gravel pebble, granular convection should actually increase the efficiency rather than decrease the jig efficiency. At least in my head that seems like worth experimenting with. I think the key would be proper screen selection for any given environment/targets.

Further, there is also the standard jigging concentration effect going on top of that too. Seems like it should work? The undersize could be bucketed and run at home in a sluice if losses are a concern, the oversize should be able to just be eyeballed.

image.png.ddd38ecff96dedfcdd2006c9e26352ea.png

Trouble with this, Jasong, is all you'll build is a classifier. You'll just collect all the gravel sized between the oversize screen and the undersize screen. But, I don't want to discourage your thinking. Keep at it, the answer may be out there, though some very bright people in the packaging industry, have been trying to solve this for decades, with few results. Here's another thing to throw your way....the shape of the container has a large bearing on GC, and can actually make GC work in reverse, in some instances.

Jim

  • Like 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...