Fine Gold Recovery from Dredging operation

[buckyboy]

I am seeking suggestions for recovering fine gold using a dredge. This dredge is not in a river bed, but on private property in the Motherlode outside of Jamestown. We have ground with shallow bedrock and the gold is definitely there and am getting color during clean up. However I am certain we are blowing a lot through the 3 inch keene combo. The prop owner is convinced faster is better, but from what I have read and what I am seeing slower is better and am still trying to put together recovery that will get everything possible.

We fill the dredging hole with water on first day and run it through Keene 3 inch as mentioned above and running the motor wide open. Second day, we take the sluice box out of the trommel and place it to catch discharge of 3 inch Keene. The second sluice is 18 inches wide with a very big mesh (pic tomorrow) and riffles and is 8 feet long. Pleasantly surprised with this approach as the material spread out very nicely. lots of black sand. At the end of large sluice I set up a settling pond with some material (think of it as coffee filter slightly thicker) 5 feet wide and 7 feet long and ran the water coming out of large sluice over it to see what we were missing. The water would "pond up" over the filter material and leech into another small water collection area. So we start up and do a good run of a lot of material and shut down. Lots of black sand in primary sluice (3 inch keene combo) and lots in big sluice. Bad thing lots of black sand in filtered settling pond which tells me we are not catching as much as we should in the primary sluices.

The material is rug in the Keene combo. The rug in the big sluice is something like, well, a bunch of plastic linguine that was used as a floor mat in a tire store. No kidding, still had the logo on it. So I will say without any reservations that I will eventually get this situation to work, but am hoping that someone will get me going down the right road for this situation as I am relying on trial and error. Again, more pics on Wed or Thur.

Thanks for your support!

 

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[HuntFish]

buckyboy... search "popandson" or "popandson sluice" He’s written a couple papers on the subject of fine gold recovery (100-200 mesh/200-325 mesh).

 

[strickman]

running wide open will lose fines,i do better when i slow down-it seems to give the gold more time to settle out.it also -depends on what type of material you are in---clay,sand,hardpack,cleaning crevices etc... i know my self personally,every time i get into-a lot of sand,it's easy running-and it's easy to overload your box.especially if you are rippin' and runnin'.last summer i hit a spot with good recent flood gold that was in the loose sand,i know now that i lost a lot due to overloading my box.sometimes if i hit a lot of loose i will let it run clear-water for a while to let the riffles do thier majick.you can't get it all but it will help.angle ,pitch,speed,material,all affect recovery.and each different combination may work better in certain conditions.some places you can run faster-some you have to really s-l-o-w down.just keep checking tailings,to see.

 

[Hoser John]

1st off you are NOT running a dredge-you are running one of the worst recovery machines ever made. You simply need a over/under REAL dredge to scalp them micron small gold,put it below under pressure for fines retention,and away from the bigger stuff. Then all the rest is strickly overkill. Lousy highbankers aireate the mix and make a frothing air filled mess. This is ABSOLUTELY the opposite of the nice smooth spread out flow from a flarejet into a o/u box-your in my old stomping grounds and man alive gold abounds-tons a au 2 u 2 -John

 

[jimmygoat]

Buckyboy, No matter what recovery method you use, you can pan the tails and see if you're losing any gold. Jimmygoat

 

[Tarkus]

Bucky: If your handy with metal and welding you may want to build a trommel, not that complicated and will classify large amounts of material quickly. I'm in process of building a couple of them now to incorporate into what once were my dredges. If you know the size material you want to work at different locations just change out the screen size to fit your material needs.

Good luck

 

[patches63]

well, until recently, i had a 3inch keene combo myself.was great on pickers,the fine gold retention was pretty dismal.especially when using miners moss.stock riffles too close together was a big part of problem.moss and tight riffles=more water/slope.if in an area where fines only,and flakes an flour are the norm,try high profile expanded metal over carpet only.you wont lose pickers/nugs that way either.this is especially effective when chopping up decomposed bedrock, slate,shale etc.bedrock material can be long,jagged pieces which pack into those stock riffles tightly.joel farmer of usprospector supply,coined a term,pattern interuption.differing sizes/ shapes/spacing of riffles, used in series.say you started at top of sluice,under the hopper.first foot or so,your smallest profile expanded metal over astroturf.then a foot of larger metal over deep ribbed carpet.then a foot or more of high profile expanded over moss,perhaps even a raised 1/4 inch screen say 1/4 to 3/8 of an inch above this section only.so that all rocks larger than that would go over the top,only fines would cross the moss or carpet of that section.that would also slow the flow going into the nextpart of sluice.since pattern interruption is our goal,lets try 1/2 inch square woven metal over the deepest carpet we have.remember that we slowed the flow with the over/under in the previous section,thus we can lower the profile below that.since we eliminated all, or most of the riffles,the box is running very clean,less water and slope.boil outs caused by tight riffles eliminated.the changes of carpet,heights/profiles of the metal,the over/under section etc.stock riffle frame unbolts easily.harbor freight sells those large orange spring clamps for holding down the sections in box.local scrap yards,metal area at landfills youll find what you need.or fabricating shop trash piles.if you visit golddredger.com search archives.about a year ago,two young bucks had a thread,sample,sample,sample.lots of great pics and info there.maybe the best highbanking thread ever.good luck!

 

[Tarkus]

Sorry Bucky: I had spaced your first post about using a trommel with a dredge output, a little tired.
My post may still apply if you insert shaker were trommel is,. how much material do you think to process in one pass (in yards).

 

[buckyboy]

Thanks to the new posts, Tarkus don't know how much we can move with the undulating bedrock. Perty sure backhoe bucket is 24 inch would be nice to have a one footer too. I have said this before but will take vid and post it. Tired here too thermostat went out on way to pick up classifier material in Columbia, shaved 3 hours off of day and raining tonight and tomorrow we need it.

On a related question if anyone can answer as I played with some fines tonight in the pan. The question is on super super fine micron gold would it not take that very fine gold a bit longer to settle in a sluice or for that matter in an empty five? I panned some material that went through some 100 mesh and man I had to be gentle, but that last swirls had a nice glistening gold twinkling so barely visible but there for sure. Is there some type of threshold of what size of gold can be recovered with what we have been discussing above?

Thanks again everyone!

 

[jimmygoat]

Hi Buckyboy. One of the keys to recovering fine gold is classification. Find out what size your gold is and classiffy accordingly. Also getting rid of the magnetite is a big help. You can get some great info from the American society for applied technology. They are no longer active ,but you can buy info. Also I'm sure John Hoser has a tip or two. Jimmygoat P.S. use shampoo when panning or running fines, calgon with clay(1 tablespoon per 1/3 barrel of clay) and let soak overnight then run. Goodluck

 

[Tarkus]

Funny I was playing with some fines tonight also, flakes so light I'd pan them down, swirl the sand away and watch as the yellow stuff caught a little air and started to float. had a few with some mercury coating it, did the same thing. I'm gonna add some jet dry next time to cut the water surface tension, easier to keep it in the pan?

This is the majority of the Au where I'm working and desperately trying to figure out and configure equipment to retain it. Any suggestions! was told a "Knudsen bowl" would concentrate and collect down to micron efficiently can't seem to find much data on them

 

[Enlitnd1]

Centrifugal concentrating devices such as knudsen bowls are the ultimate solution for fine gold retention. Normal gangue material has a specific gravity of around 2.5 and gold, of course, near 20. The differential between the two being the controlling factor. The differential determines the difference in the settling rate. If, through centrifugal force, the specific gravity of both gangue and mineral are trebled, the differential is also trebled.
Classifying your feed material size down to 3/16" will cause the bowl to work well and not blind off the riffles. There are other similar bowls on the market but I don't know how they compare in price.
Another slightly less effective approach is to use a Pan American pulsator jig, also known as a finishing jig. These simple devices, when operated properly, have known retention rates in excess of 90% down to 300 mesh and because the heavy mineral content is positively retained, it is not susceptible to loss as with a riffle system where heavy mineral particles can eventually migrate into the tailings discharge.
For a more authoritative treatment of these subjects refer to Taggert's Handbook of Mineral Dressing. Widely considered to be the Bible on these and related subjects, Taggert was written in the 1930's and is the most comprehensive and scholarly work available on these and related topics.

Bill in Ariz.

 

[Tarkus]

Thank You Bill

 

[jog]

You might try installing a classifier screen at the head of the box. This will let the small gold get trapped under the screen where the bigger rocks can't push the fines down out of the sluice.

 

[nuggetshooter323]

You could try putting some ribbed rubber matting under the carpet for the full length of the sluice box.