# centrifugue X jig



## RIQSON (Feb 10, 2017)

Hi All

I call from Brasil , I am partner of one 18"cutter head dredge in Colombia ,
somebody can help-me understand for what purpose is more appropriate a CENTRIFUGUE and what purpose a JIG ?
we , in the dredge use sluicebox with carpets, after 20 hours we shake the carpets to get one concentrate about150/200 klg) - its more better use a centrifugue or a jig to reduce and perhaps to do direct smelting??

thanks
Luiz


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## Deano (Feb 10, 2017)

Assuming that you are running the cutter head in double double cut mode at bottom then you will have feed material containing high levels of heavy minerals.

Double cut mode means that you pump and dump all of the material above 1 metre up from bedrock.

Double double cut mode means that when you have cleared all of the material above the 1 metre level you treat all of the remaining material down to bedrock in the next passes and then come back to try and get any bedrock material which is soft enough to be excavated.

The bedrock is usually the highest grade material and considerable gold values can be lost by running it with the heavy material feeds from just above the bedrock.

You usually have a diver checking the bedrock to locate softer areas for dredging.

The feed to processing will now contain a lot of heavy, usually iron, sands.

Despite the promises of the sellers of all centrifugal equipment this type of equipment cannot treat poorly classified (say < 10mm screen) heavy rich material, it chokes on the heavies and if set to clear the heavies it will lose fine gold.

The more classification you do the better they will perform but they will all have the problem with the heavy material at the bottom sizing.

A jig will take the same sized feed as above and get out a concentrate with most of the gold down to 75 microns in the con.

Losses of finer gold start at this sizing, most operators will run poorly sized and inconsistently mixed feeds so that you get slugs of feed mixed with times of just water, this tends to make a mess of finer recoveries.

Your sluice will get most of the gold > 100 microns if set up and run properly, if run as per the TV dramas you will be lucky to get any gold below 300 microns.

Those are the main methods of primary recovery.

If you have cons from any of the above above primary recovery systems then you need to clean them up for smelting.

The one thing that the TV series does get right is that the best way to clean your cons up is with a small Wilfley or similar table.

Set up and run properly you will get a very clean con which, if the residual iron is removed with a magnet, can be direct smelted without using any flux.

Deano


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## RIQSON (Feb 12, 2017)

ok, many thanks for the explanation


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## cuchugold (Oct 31, 2017)

Deano said:


> Assuming that you are running the cutter head in double double cut mode at bottom then you will have feed material containing high levels of heavy minerals.
> 
> Double cut mode means that you pump and dump all of the material above 1 metre up from bedrock.
> 
> ...


Found this interesting video. I'm interested in the previous step to get the concentrates. The presenter mentions jig at the beginning.
https://www.youtube.com/watch?v=Z8W7mXZX9sY#t=552.801224
https://www.youtube.com/watch?v=Wlj4-jxJgs4

In my case, I could move the cons to an intermediate processing location, with water, electricity, etc. I have some family I trust to run the location. If I could run 1 ton per hour through a jig/concentrator, I'd be thrilled. I can recirculate the water. The placer will take a while to be processed. Milling the vein ore is still an unsolved issue.

edit to add: Deano, I found this video of a dry jig. I'd like to see your opinion about it. Very easy to build.
https://www.youtube.com/watch?v=HSL_f98PnQs


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## Deano (Oct 31, 2017)

Over the years there have been many devices designed for dry separation of gold from soil.

If you want to just separate nuggets then these will do a good job.

If you are looking for separation of fine to very fine gold then they all do a poor job.

Many hawkers of such devices will point to the fine gold being separated into the cons, what they do not show is the bulk of the fine gold going out with the tails.

The best devices I have seen operating are the ones using a pulsed air stream to treat a tightly sized feed.

Deano


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## cuchugold (Nov 22, 2017)

Hi again Deano:
I performed some tests in a dry jig and also in a standard water jig.
The tailings are showing about 4 grams per Ton in the water jig, of gold less than 75 uM. And about 6.5 grams per Ton in the dry jig, but this includes gold bigger than 75 uM.
I'd like your opinion on what is the main transport mechanism and mechanics for this gold in the tailings, i.e. some is being dragged away by the coarser material, and some by the water. I'd like to see if I can recover this gold mechanically, by washing the coarse with water or something, without cyaniding.
The placer ore is also giving a similar profile for the tailings, but a lot of bigger rocks and pebbles are screened out at 3 mm before processing, instead of a uniform feed from the milled ore screened at 1 mm screen size.
Thanks in advance.


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## Deano (Nov 22, 2017)

There are many operators of jig plants making a very good living on 1 gram/cu metre dirt.

If you have jig tails of 4 grams there are three possibilities.

1 The gold is still locked in ore particles and is fine enough that these particles do not have their specific gravity altered and thus they report to the jig tailings.

2 The gold is all very fine and flat, generally << 75 microns, and is not amenable to gravity separation.

3 The jig is being operated in a manner such that it does not recover the gold which it should recover.

My experience is that the most likely cause of losses is number 3.

Usually a mix of poor feed sizing, incorrect ragging and bad water balance along with poorly designed units themselves.

Also includes operating using clay feeds with poor clay breaking pre-jig equipment.

Most people have no idea of gold particle sizing, unless you actually pass the particles through a sieve you are just guessing.

Deano


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## cuchugold (Nov 23, 2017)

Thanks Deano. These particles of gold seem to be trapped in the silt and clay portion of the dirt. With water this dirt forms a gel like substance, that will dry and crack before settling. In air it forms a cloud of dust mist that takes hours or days to settle, or is carried away with any wind. I can see some gold with a magnifier, but will probably need a microscope. I never looked at the problem like this. There must be a lot trapped in the clay tailings of the main mine sites, washed by sluices. As you say, gravity does not affect the suspension or separation of these solids. Yet this gold rich clay portion is a relatively small % of the total solids, the quartz sand portion of the tailings is basically barren of gold.

The samples I bring back are from the richest spots. By no means I mean that the whole or average site ore is this rich in the clay portion, but I'm assuming it will have similar characteristics in % of clay, sand, etc. so don't pay attention to the amounts. Some samples of vein ore have 1 oz of gold per 10 Kg, after crushing and panning. That's almost like a big nugget, and as rare. I'm thinking that all the clay tailings from panning that I have left behind are rich too.


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## Reno Chris (Nov 23, 2017)

The standard method of dealing with gold in heavy clay is the use of some sort of trommel to wash the material and separate the gold out of the clay.


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## cuchugold (Nov 24, 2017)

Reno Chris said:


> The standard method of dealing with gold in heavy clay is the use of some sort of trommel to wash the material and separate the gold out of the clay.


Paraphrasing Deano: They show what they catch, not what gets carried away in the tailings.
These photos from a 'pure clay' mine a few dozen miles north. Probably the biggest deposit in Latin America, as exploited by gangs and the military. Estimated 34 million Oz in the ground... I worked nearby a few years ago doing 'tailings' and I wonder how much I let go in my tailings. Look at the destruction. Mercury in there too.


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## Reno Chris (Nov 26, 2017)

As with many artisanal mining efforts, they have no capital, therefore they must construct what they can with materials harvested from the land around them or purchased for almost nothing. They let the gold go in the tailings because they cannot afford the means necessary to catch it.


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## cuchugold (Nov 26, 2017)

Don't let the humble appearance of the sluices fool you. This is a big bucks operation on a gigantic area: Range Rovers, Helicopters, smuggling airstrips, millions of $ in earth moving equipment, excavators, planes, armies of child soldiers ready and willing to kill, guns, explosives, etc. Another universe.

https://twitter.com/twitter/statuses/933740177629040640


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