# Help with Ore Processing



## Aeon13 (Nov 18, 2015)

Good day to all! I am new to gold refining and other gold processing techniques. Thanks to this forum and members I have learned a lot already with just a short time. I would like to show you guys the processing of gold ores used by my uncle. They extract these ores from the mountains, grind it then leach it with cyanide. This is how they do it. They put these ground ore into the first stage (leaching) and wait for the liquid going to the second stage which contains the liquid gold. This second stage is then pumped to a container but first they will mix zinc powder prior to it.Then a filter is placed on the container to recover the powder which has gold in it . The liquid at the container is then pumped back to the first stage. They do this process for about 6-7 cycles. Then they get the filtered material for smelting.
Do you guys have any opinion on how to improve this system that they use? My uncle and his colleagues are small scale miners. It breaks my heart to see the things they do to get these ores. Specially the way they go inside the portal with just a blower used to supply oxygen inside. There has been death related to oxygen depletion while inside these portals . These portals range from 100-500 meters as of today. They also don't have any support placed in these portals. They know the risk yet they do it to live. I want to help them by maximizing the amount of gold that they may recover. This is the reason for me joining and posting here. I know that people here are kind and helpful. I read many topics already here by the way. I just did't find a complete process which looks like my uncle's set up. I will post the actual pictures once I have the time to visit them again.
Thanks in advance. More power and Godbless.


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## Deano (Nov 19, 2015)

The processing system as you have described it is a small scale version of how the large mines processed gold ore before carbon in pulp processing took over the industry.

It would probably not be warranted to try to change the processing route as a whole lot of new skills and equipment would be required.

This leaves the possibility of improving the efficiency of the existing plant.

The standard residence time of ore in a processing plant is around 24 hours.

If they are running multicycle processing it is an indication that either or both of the following is occurring.

If coarse gold is present in the ore then it will take longer to dissolve. Use a small jig or table to remove this coarse gold from the ore before leaching. 

The coarse gold can be direct smelted if cleaned up enough, or treated by intensive cyanidation in a separate small circuit.

If the ore is not milled finely enough then it takes the cyanide solution a long time to penetrate the fissures in the ore particles to access the gold. Use finer milling to speed up the leaching.

Warning

If there is gold in sulfides then you can get a phenomenon called overmilling of sulfides where the recoverable grade of gold drops when very fine milling of the ore occurs.

Do some milling tests followed by leaching tests to establish the best grind size for your material.

Some sulfide ores require an extended leach time to dissolve the gold even at the optimal grind size, if this is so with your ore then there is very little that can be done to speed up the leach cycle.

I am not even remotely likely to comment on actual mining procedures, this is a legal minefield.

My experience is that most small scale miners who have been in operation for several years have a pretty good working knowledge of the practical side of the operation.

Generally they have developed methods which suit them and their site and at best only need small tweaks to their systems.

It may appear to someone unfamiliar with mining that they are working under unsafe conditions and using outdated techniques.

Usually the operators who are actually using unsafe methods have been culled from the mining business early on in the game.


Deano


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## Aeon13 (Nov 19, 2015)

Deano said:


> The processing system as you have described it is a small scale version of how the large mines processed gold ore before carbon in pulp processing took over the industry.
> 
> It would probably not be warranted to try to change the processing route as a whole lot of new skills and equipment would be required.
> 
> ...



Thank you Deano for your reply. Then I guess there will be no more improvement that can be done with the system. I have read a process of leaching using starch. Do you know anyone who used this method? I also read about purging air into the pulp would improve leaching. If this is true, would it be practical to do it with this set up?
I will continue to read here and I'm sure I will learn many things. Thank you again!

Mohammed


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## Deano (Nov 19, 2015)

Leaching using starch is a method where the dissolved gold is collected on undissolved starch similarly to collecting the gold on activated carbon.

There are a great number of similar adsorbent systems none of which have been commercialised.

Most of them remain interesting research projects which did not advance the systems enough to become used industrially.

Air is usually introduced into the pulp by the agitation system used to keep the pulp mixed.

Extra air is generally only required when high organic or sulfide loads are part of the ore.

I would be very surprised if the operators had not carried out tests to see if this was needed.

Deano


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## Aeon13 (Nov 19, 2015)

Deano said:


> Leaching using starch is a method where the dissolved gold is collected on undissolved starch similarly to collecting the gold on activated carbon.
> 
> There are a great number of similar adsorbent systems none of which have been commercialised.
> 
> ...


Thanks again for the fast reply Deano.
I think there no tests carried out. They are not really that informed about the elements present in these ores. They just get it then process it with this setup. I was surprised myself after talking to them. They don't even know how the "Karat" measurement of gold is done and its importance. The buyers here pay them in based on the specific gravity.They for a fact don't also know these numbers as specific gravity.They just know it as a measurement for the price. 19.2 is the highest and the lower the measurement the lower the price. I learned that the specific gravity of pure gold is 19.3. I want to explain these things to them but its hard with their situation and considering that I'm much younger than them makes my opinions less significant :mrgreen: . I want to ask your opinion though. Is it right to base the gold price on the specific gravity of gold or much better using gold test kits with acids?
Thanks again!


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## Reno Chris (Nov 20, 2015)

Please give us a better description of your uncle's process or we may make suggestions that do not apply or make no sense because we have only a vague understanding of what your uncle is doing.

How small does he crush the ore? Like fine sand?
Is the ore leached in a vat or in a heap piled up on a plastic sheet?
Are chemicals like lime added to stabilize the cyanide?
Is the leach solution de-aerated before it is exposed to the zinc?
Does he pre-treat the zinc with lead Nitrate?
Does he recover only gold or is there significant silver present also?
How does he filter out the zinc to capture it and make sure none is lost?
Does he test the gold solution to know when to add more zinc?
Does he test the ore to know when it is fully leached?
Does he melt the gold and pour a bar or sell the raw zinc-gold powder to the buyer?

The success of this process is in the details of operating it. If operated improperly it can be inefficient. If operated properly it can be very efficient. 
If we do not know the details, it is tough to make useful suggestions.

Raw gold is best tested based on an assay of the raw dore bar. That is how it is done by most gold buyers/refiners in the US. Only smaller scale operators use scratch tests and touchstones with acids. The acid test kits are made for testing jewelry that is normally certain Karat purity like 14K or 18K. Assays give a more exact result. Many buyers that purchase gold at remote mine sites pay only a small percentage of the spot gold price. I don't know that this applies to your uncle, but it is common.


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## Aeon13 (Nov 20, 2015)

Reno Chris said:


> Please give us a better description of your uncle's process or we may make suggestions that do not apply or make no sense because we have only a vague understanding of what your uncle is doing.
> 
> How small does he crush the ore? Like fine sand?
> Is the ore leached in a vat or in a heap piled up on a plastic sheet?
> ...




Thanks for the reply sir Reno. I apologize for giving such vague information. I am new to this thing and is continuously learning from you guys. Yes I know how these buyers are most of the times abusing small scale miners like my uncle and his colleagues. This is one reason I want to learn this field and help them make the most out of it. Besides, they do the hard and dangerous work. I think assay testing is not accessible here in our place. The buyers pay them based on the specific gravity of the end product. 

About your questions.

*How small does he crush the ore? Like fine sand?*-_ the size is like sand (not fine)_
*Is the ore leached in a vat or in a heap piled up on a plastic sheet?*_ they use heap leaching_
*Are chemicals like lime added to stabilize the cyanide?* _yes they add lime_
*Is the leach solution de-aerated before it is exposed to the zinc?* _He does not do this. How is this process done?_
*Does he pre-treat the zinc with lead Nitrate?*_ no, He just add the zinc dust._
*Does he recover only gold or is there significant silver present also?*_ silver is also present and he is able to recover also._
*How does he filter out the zinc to capture it and make sure none is lost?* _This I have to verify. I was not able to see the filtering inside the container. What would you prefer for him to use in this stage?_
*Does he test the gold solution to know when to add more zinc?* _No, I guess he based this on his experience and these are things that I want to help them. Maybe he is not doing it efficiently. _
*Does he test the ore to know when it is fully leached?*_ This is also not done. But he repeats the cycle six times to ensure that all gold is recovered. In what way can we test the ore?I want to help him by making a stannous chloride solution for the pregnant solution. _
*Does he melt the gold and pour a bar or sell the raw zinc-gold powder to the buyer?* _He melts the gold using coal. This process makes the end product a bit dirty. I watched guys melt gold using OXYACETYLENE and the result is much better._

I cannot express enough my gratitude with the help you are giving me. Please know that your not only helping me but also the small scale miners that I will be sharing what will I learn from your knowledge. These miners are humble, caring and hardworking people. In behalf of them. Thank you very much.


Mohammed


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## Reno Chris (Nov 20, 2015)

Mohammed:
I can give you many thoughts and suggestions as I have set up an run an operation like this in the USA (Nevada). I have written mining magazine articles on how to do this. 
Before I give you my thoughts and suggestions, I have a few more questions based on your last answers. 

How does he put the ore onto the heap pad? (what equipment does he use?)
How deep is the ore piled onto the pad? 
When he believes the gold is leached out, does he push the old ore off the heap leach pad and add more on; or is he able to build the pad further and keep adding more ore on top?
Does he have enough space to enlarge the pad?
How long does he put the cyanide leach waters on the pad? 
In the 6 or 7 times, does he put all the cyanide liquid on, wait a couple days as it drains out, and then after processing to collect the gold out of the liquid, then re-apply the liquid? 
How long does one "leaching cycle" take?
How does he apply the cyanide solution to the heap? Sprinklers? Drip lines? Some other way?
What sort of pump does he use?
How much silver is present? More silver than gold by weight or only a little silver, mostly gold. Is the final bar gold colored or silver?
Is there any visible gold that can be panned out of the ore before it is processed on the heap pad?
Is there any pyrite or sulfide minerals in the ores put on the pad?

If you will provide me these further details, I promise to give you an extensive answer with many possible suggestions to improve his process.


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## kurtak (Nov 21, 2015)

This looks like it could become another one of those meat & potatoes threads filled with lots of good info - maybe even end up in the library 8) 

Mohammed - you have come to the right place to ask questions & learn & you have two of the best helping you so far (Deano & Chris) when it comes to the mining & processing of ore

There are others here that are "world class" in their knowledge of PM (Precious Metal) recovery & refining that can help with improving your families operation including but not limited to things such as doing actual assays, melting/smelting & alternate methods of processing &/or recovery 

I look forward to seeing this thread progress

Kurt


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## Aeon13 (Nov 21, 2015)

Reno Chris said:


> Mohammed:
> I can give you many thoughts and suggestions as I have set up an run an operation like this in the USA (Nevada). I have written mining magazine articles on how to do this.
> Before I give you my thoughts and suggestions, I have a few more questions based on your last answers.
> 
> ...



Wow! Its an honor sir Reno Chris. I really came at the right place this time. And to have information from such a professional in the mining field. I am grateful.

About your questions, I have to go back there at mines and ask again for me to have accurate answers. I will also take pictures of the system employed. By this, I hope I can show you the exact process being done.

Thank you so much sir Reno Chris and every one here in the forum. I will post here as soon as I get the information. 

Mohammed


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## Aeon13 (Nov 21, 2015)

kurtak said:


> This looks like it could become another one of those meat & potatoes threads filled with lots of good info - maybe even end up in the library 8)
> 
> Mohammed - you have come to the right place to ask questions & learn & you have two of the best helping you so far (Deano & Chris) when it comes to the mining & processing of ore
> 
> ...



Hi Kurt! Yeah I really came at the right place. You guys here in the forum are really very helpful. I learned so much already with just less than 10 posts that I made(But a lot to read here). This thread was made for the sole purpose to help these miners in our place. I saw their situation and how they get ores and its is really a very hard and risky job. That's why I want to help them improve and maximize their profit.Also, everyone having the same concern will benefit reading these thread because such "world class" individuals are contributing with priceless knowledge that they have. I am humbled by people of great experience and knowledge that share these with inexperienced people that they don't even know personally. I am grateful (I am always repeating these words because I can't really express how grateful I am,please forgive me if it annoys some).

Thanks for the reply Kurt.

Mohammed


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## Reno Chris (Nov 21, 2015)

"world class" may be a bit much, but I am competent and experienced to help with getting the best recovery that is possible in a practical way for a small scale operation. I'll keep an eye on this thread for future answers.


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## Reno Chris (Nov 22, 2015)

Heap leaching was developed as a low cost technique for extracting gold and silver from lean and low grade ores. Heap leaching is very inexpensive on a cost per ton basis. Most mines will put anything that grades .01 oz/ton or better on the heap. All the heap consists of is a large area covered with a heavy duty, thick plastic sheet, graded to drain to a central point. Gold bearing rock is stacked in a big heap on the sheet up to 50 or even 100 feet deep and then sprinkled with a weak solution of cyanide. Millions of ounces of gold are recovered annually from this type of operation all over the world. It is very common in my home state of Nevada. The cyanide solution dissolves gold and silver and the liquid drains down to a central point where it is pumped through a recovery plant and the gold and silver are extracted. Additional cyanide is added to the solution as necessary, and it is then recycled and put back onto the heap to dissolve more precious metals. Heap leaching is not really rocket science. Basically all you are doing is irrigating piles of rock.

_*How does he put the ore onto the heap pad? (what equipment does he use?)*_
One of the common problems in constructing a heap to be leached is that when materials are put onto the pad they tend to form channels. The coarse material forms a shell around the outside and the liquid will flow through these channels and miss the interior part. I have attached an image to show the concept of what this channel segregation looks like. The more fine material like clay which is present in the ore, the greater the tendency is for this channeling. This means that solution will flow through certain channels within the heap, avoiding other areas, so that these isolated spots do not receive sufficient solution and therefore the gold and silver within them is not recovered. If there are dry spots within the heap when it is removed after leaching is completed, those dry spots did not get processed and the gold within them still remains in the ore.

*How long does he put the cyanide leach waters on the pad? *
The gold and silver take a long time to be removed by the heap leach process. The majority will come out within a few weeks, but smaller amounts will continue to come out for months and even years. It is normal for heap leach operations in Nevada, USA and to spend years processing the material on the heaps. For small operator there is a point of limited return when you are not getting enough out of the pile to make it worth your time, but your uncle may not be leaching his rock long enough to get the gold that is possible out of the rock. When I was running a small scale heap leach operation, we would leach the ore for about six weeks to two months before we pushed it off and loaded new material on.

*How does he apply the cyanide solution to the heap? Sprinklers? Drip lines? Some other way?*
Once the heap is built, the solution has to be applied to the heap in the most efficient manner. Early heaps commonly used various types of sprinklers to apply the solution. In time it was realized that there were problems with losses created by the over spray from sprinklers or splashing. Sprinkler heads also sometimes fouled with the solutions when they dry. In constructing the facility, only plastic or black iron pipe can be used for handling cyanide solutions, as zinc, copper and brass are all dissolved by the cyanide solution. The best method of applying the solution to the heap is by using plastic agricultural drip irrigation lines. Perforated plastic irrigation line is inexpensive, easy to lay out and offers few problems even after continued use. It also can be laid out to cover the sides of the heap pile better as often the sides do not get the full amount of solution needed to leach them. Multiple lines of perforated plastic line are laid out on top of the heap and manifolded to a pump and piping system.

*Is there any visible gold that can be panned out of the ore before it is processed on the heap pad?*
Cyanide will dissolve gold particles either large or small, but it takes a long, long time to dissolve large pieces. A piece of gold the size of a coin might take several hundred years to dissolve. In general, particles large enough to be recovered by panning or other gravity based methods should not go on the heap as they take too long to dissolve. It is very common that systems are constructed to process gold ores which have both a gravity circuit to capture the coarser gold particles, and a cyanide circuit to capture the fine dust sized particles and those too small to see without strong magnification.


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## Finn from Ecuador (Nov 22, 2015)

Deano said:


> If there is gold in sulfides then you can get a phenomenon called overmilling of sulfides where the recoverable grade of gold drops when very fine milling of the ore occurs



May i ask what would you describe as "very fine milling"? Would 100% -150 mesh for example be very fine?

This is so good thread, i mean that this kind of practical approach would be hard to find from literature.

Salud

Finn


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## Deano (Nov 22, 2015)

Overmilling of sulfides is totally dependent on the ore sample. different mines will have different milling levels at which this phenomenon occurs.

The effect is related to the level of interferent species present in the ore, the more interferent present the coarser the grind at which overmilling occurs.

Generally the effect occurs with milling below 75 micron or 200 mesh.

I have seen it at 100 microns and I have seen one very clean ore where it was totally absent.

This is why I use the term "generally" in answers.

Deano


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## Aeon13 (Nov 23, 2015)

hello I'm back guys. 
Sir Reno Chris I was able to go down to the mines and ask your questions as well as take some pictures. I am a little hesitant about my answer if the process is using vat or heap leaching because I think I have a little understanding of the difference of the two. Please forgive me for this. I have attached the actual picture of the pad. About your questions.

*Does he pre-treat the zinc with lead Nitrate? *Yes he adds lead to the zinc dust.(I verified this and he said he is adding lead but did not use it while I was watching him last time)
*How does he filter out the zinc to capture it and make sure none is lost?* He filters the zinc with gold powder using satin fabric. 4 layers of satin is placed. I will put some pictures of this. 
*How does he put the ore onto the heap pad? (what equipment does he use?) *They just put the ore manually. By the way they mix the ore with lime like mixing cement with sand before they put the mixture on the pad.
*How deep is the ore piled onto the pad?* About 3.3 feet. Just small space to full 
*When he believes the gold is leached out, does he push the old ore off the heap leach pad and add more on; or is he able to build the pad further and keep adding more ore on top?* They remove the old ore and replace it. I helped them "pull out" the old ore while I was there. not easy, my hand got some calluses now :mrgreen: )
*Does he have enough space to enlarge the pad?* Yes he has enough space to enlarge
*How long does he put the cyanide leach waters on the pad?* 5 days before draining cycle.
*In the 6 or 7 times, does he put all the cyanide liquid on, wait a couple days as it drains out, and then after processing to collect the gold out of the liquid, then re-apply the liquid?* This is the complete process. After putting cyanide he will wait 5 days without draining. After 5 days he drains it. After draining, the solution from the blue tank will go back in the leach pad. This will take 5 hours again to drain. This cycle of draining is done 6-7 times.
*How long does one "leaching cycle" take?* It takes 5 days plus 30 hours of the draining cycle.
*How does he apply the cyanide solution to the heap? Sprinklers? Drip lines? Some other way?* This is done just by putting the cyanide solution into the pad in just one point.
*What sort of pump does he use?* I placed a picture of the pump
*How much silver is present? More silver than gold by weight or only a little silver, mostly gold. Is the final bar gold colored or silver?* He told me that there is more silver than gold. The final bar is colored gold.
*Is there any visible gold that can be panned out of the ore before it is processed on the heap pad?* He did saw this but it is very rare.
*Is there any pyrite or sulfide minerals in the ores put on the pad?* They don’t put pyrite. I saw some pyrites outside the portal. They remove this and don't mix it with the ore. As for the sulfide, we both don’t know physical appearance of this.


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## Aeon13 (Nov 23, 2015)

This is the process done with the pregnant solution


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## Aeon13 (Nov 23, 2015)

This is the pump used.


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## Aeon13 (Nov 23, 2015)

This is the actual leaching pad. The original level of the pad is the one with the lighter color of ore. My uncle is the one wearing black shirt.


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## Aeon13 (Nov 23, 2015)

This is where the satin is placed. 4 layers each will be placed.


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## Aeon13 (Nov 23, 2015)

This is where the pregnant solution from the leach pad go.


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## Aeon13 (Nov 23, 2015)

These are some pictures of the mine.


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## Aeon13 (Nov 23, 2015)

picture of the cyanide used and the bamboo bridge which is the only way from the processing to the portal and vice versa.


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## Aeon13 (Nov 23, 2015)

With all these details and pictures I hope I have given you guys the actual place in which my uncle is mining. Sir Reno Chris, I hope I have given you the answers you are asking. Please tell me if there are more and I will be very willing to go back there and ask or have some pictures. Please help me help them. 

A very big THANK YOU to this forum,forum members and specially to sir Reno Chris. 


Mohammed


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## Anonymous (Nov 23, 2015)

kurtak said:


> This looks like it could become another one of those meat & potatoes threads filled with lots of good info - maybe even end up in the library 8)
> 
> 
> Kurt



Kurt

If Dean is involved it will be. The man is a "mine" of useful information and techniques. I like him a lot.

Jon


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## kurtak (Nov 24, 2015)

spaceships said:


> kurtak said:
> 
> 
> > This looks like it could become another one of those meat & potatoes threads filled with lots of good info - maybe even end up in the library 8)
> ...



Agreed --- but lets not forget Chris - he is a "mine" full of info as well - I read everything written by BOTH of them :mrgreen: 

As I see it there is a lot that can come out of this thread besides just the question about the leaching part of the process 

I hope & look forward to reading MORE in this thread :!: 

Kurt


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## Reno Chris (Nov 25, 2015)

Well, this is why I asked questions - So I don't take the time to write down advice which does not even apply. A heap leach is a process where the ore is piled on top of a plastic sheet, the cyanide applied to the the surface and the gold and silver are dissolved as it percolates down through and the gold bearing liquid collected once it drains through the pile. That's not really what your uncle is doing. Vat leaching is done in some sort of container and this is what your uncle is doing. 
One thing I want to point out is that the reaction of cyanide to dissolve gold is one which requires oxygen from the air. If you add cyanide and gold and have no air, the gold will not dissolve even if you wait 100 years. The oxygen is required. In a standard commercial vat leach, the mix of the ore and cyanide (called a slurry) is mixed by mechanical stirring and air bubbled through it. When your uncle fills his container, once the air in the cyanide solution is consumed, all solution of the gold stops. There is little point in his waiting 5 days between cycles. He would be better off to wait only one or two days in his filling and draining cycle. Most of the dissolving probably takes place while he is draining the container and refilling it. 
I would recommend getting a gold pan and panning the ore regularly. A test with a pan is cheap and easily and will tell of you have coarser gold particles. I would even test the treated ore tailings to be sure there is not a problem with missed gold. Its an easy safeguard to prevent wasting gold. Many types of gold deposits have some coarser, visible gold that the cyanide captures poorly. Also, just because you tested it once and there was no coarser gold, that does not mean that in another part of the same deposit mined at a later time there could not be some coarser gold. 
You never said if he has only one container to process ore, but he might consider building a second. This would allow him to dig out one while leaching the other, making the process more efficient. 
Hard to say how well the satin filter would work. If it were me doing that, I would add diatomaceous earth into the bags to aid in the filtration.
If he does not use the lead to treat the zinc, there is a good chance he is missing gold. Oxygen of the air coats the zinc dust with zinc oxide, which prevents the gold in the cyanide solution from reacting with the zinc, so the gold just flows on through and the zinc stays as zinc. The lead makes for an electrolitic reaction to allow the gold and zinc to react. Commercially in the US and developed countries, the cyanide solution with the gold is treated with a vacuum to remove oxygen from the solution before it is reacted with the zinc. So the lead is necessary. I am sure the people who trained him told him to use the lead.


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## Deano (Nov 25, 2015)

Further to what Reno Chris advises there are some things which can be done to improve the processing.

There are two simple and cheap ways to recover gold from a vat leach, adsorption onto carbon or zincing.
The operators have chosen zincing which is probably a sensible choice as they do not have to learn carbon stripping or ashing.

If you are using carbon as an adsorbent you do not care all that much about getting high gold tenor in the leach liquor as the carbon will get all of the gold provided the leach liquor is run through the carbon column slowly enough.
However if you are zincing then you want to have as high a gold tenor in the leach liquor as possible so that you get the best possible return on the zinc.

This generally involves cycling the leach solution through the material in the vat to get higher gold tenor in the liquor.
The photos show the use of rock filled filter fabric lined drains for the leach liquor, they do not show whether these drains feed into a sump for liquor recirculation or not.

Generally in a vat leach you place your drains at a maximum of 1.5 metres apart, for a small vat as shown in the photos you would have the drains around 1 metre apart.
Use local creek gravel undersize screened at around 12mm (1/2") to form a better bed between and over the drains, aim for about 300mm (1 foot) cover over the drains.
The usual practice is to use 50 to 75mm (2 to 3") slotted black agricultural drain hose with the filter fabric rather than the rock drains.

The drains can either lead to an internal sump inside the vat or can lead through the vat wall to an external sump.
Most operators favour the internal sump as it eliminates the opportunity for possible liquor loss from a leak in an external sump.
A small electric or diesel powered diaphragm pump is used to recirculate the liquor from the sump to the top of the vat, it doesn't matter if this type of pump runs dry, it is also self priming.
If run as an internal sump you make an access shaft with the old cyanide drums for your pump hosing and access.

Generally you do not want the depth of ore to be much greater than 2 metres (6') to allow a reasonable percolation rate through the bed.
The cyanide solution volume is such that it covers the ore bed by around 100mm (4") when the bed is saturated.

In small scale operations such as shown you aerate the return solution by plunging the return stream into the liquor covering the bed or by running the return liquor down a riffle bed so that the liquor is aerated at each riffle stage.
There are no prizes for having the aeration system look good, it is just there to get air into the liquor.

All operations at this scale recycle the cyanide liquor after zincing.
This means that any gold missed through poor zincing is not lost but remains in the liquor for the next cycle.
This is not to be taken as approval for shoddy practices but means that if the processing is not optimal you will not suffer great losses even if the process is slightly flawed.
Note that the leaching rate is much slower for high gold tenor solutions than for barren solutions, much better to get your zincing right.

Usually at the end of the leaching cycle the vat is drained of the cyanide liquor and a water rinse is put through.
The water from this rinse is saved in a separate empty vat and used as make up water for evaporation etc losses in the main leach solution.

Deano


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## Aeon13 (Nov 25, 2015)

Reno Chris said:


> Well, this is why I asked questions - So I don't take the time to write down advice which does not even apply. A heap leach is a process where the ore is piled on top of a plastic sheet, the cyanide applied to the the surface and the gold and silver are dissolved as it percolates down through and the gold bearing liquid collected once it drains through the pile. That's not really what your uncle is doing. Vat leaching is done in some sort of container and this is what your uncle is doing.
> One thing I want to point out is that the reaction of cyanide to dissolve gold is one which requires oxygen from the air. If you add cyanide and gold and have no air, the gold will not dissolve even if you wait 100 years. The oxygen is required. In a standard commercial vat leach, the mix of the ore and cyanide (called a slurry) is mixed by mechanical stirring and air bubbled through it. When your uncle fills his container, once the air in the cyanide solution is consumed, all solution of the gold stops. There is little point in his waiting 5 days between cycles. He would be better off to wait only one or two days in his filling and draining cycle. Most of the dissolving probably takes place while he is draining the container and refilling it.
> I would recommend getting a gold pan and panning the ore regularly. A test with a pan is cheap and easily and will tell of you have coarser gold particles. I would even test the treated ore tailings to be sure there is not a problem with missed gold. Its an easy safeguard to prevent wasting gold. Many types of gold deposits have some coarser, visible gold that the cyanide captures poorly. Also, just because you tested it once and there was no coarser gold, that does not mean that in another part of the same deposit mined at a later time there could not be some coarser gold.
> You never said if he has only one container to process ore, but he might consider building a second. This would allow him to dig out one while leaching the other, making the process more efficient.
> ...



Thanks for the reply sir Reno Chris. I would then recommend him to only have two days before starting the draining and refilling cycle. Would you recommend then for him to pump air into the leach? He has a pan and is also using it to sample the ore. 

There is another process in which he uses the used ore again. In the process of milling, the liquid that was used is recovered and they are able to collect some really fine ore (like mud). They dry this and its consistency is like powder. Is it necessary to dry this mud like ore? They told me that drying and mixing of old ore is needed for the cyanide to reach every part of the mixture. Is there a better way to do this? After drying, they mix it with the used ore and dump it again on the leach pad. But this time only 3 days instead of 5 days is the duration before the draining and refilling cycle. They use a 5:8 ratio of the powder like ore to the used ore. 

I will also recommend for him to make another pad. He has only one pad now.

The adding of diatomaceous earth is a new idea. How is this added? Just put it inside the bags? How will the recovery of gold differ with diatomaceous earth mixed with it? 

All these ideas and recommendations that you are giving me are very useful. I make sure that it will be used and applied. 

Thank you so much again sir Reno Chris!

Mohammed


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## FrugalRefiner (Nov 25, 2015)

Mohammed, you're getting some excellent advice. I'll add my one bit. Wear gloves! Have everyone else wear them as well. 

Dave


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## Aeon13 (Nov 25, 2015)

Deano said:


> Further to what Reno Chris advises there are some things which can be done to improve the processing.
> 
> There are two simple and cheap ways to recover gold from a vat leach, adsorption onto carbon or zincing.
> The operators have chosen zincing which is probably a sensible choice as they do not have to learn carbon stripping or ashing.
> ...



Thanks sir Deano for this informative reply.

So much information is given that I have to ask question and is really good for me and others reading this thread to learn.

Is carbon stripping a better way in this process. Because if this is better, I will try my best to learn and teach it to them.

Also the term "gold tenor" is new to me. 

The drained liquor as I have shown in the diagram will go to an external sump which will be treated with zinc and undergo filtration and recirculated back to the leach.

I will check the size of the gravel used and will recommend the size you stated.

Forgive me sir but I was not able to imagine this statement "aim for about 300mm (1 foot) cover over the drains.".

Compared to rock drains is the slotted drain hose better?

I must say that the conversion to foot and inches that you are inserting inside the parenthesis is really helpful for my visualization.

Thank you so much sir Deano!


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## Aeon13 (Nov 25, 2015)

FrugalRefiner said:


> Mohammed, you're getting some excellent advice. I'll add my one bit. Wear gloves! Have everyone else wear them as well.
> 
> Dave



Hi sir Dave! You are right. To get these information from such expert individuals including you is priceless. I am happy to learn from you guys because I will be able to share these knowledge to the humble small scale miners here. As I have said you guys are the ones helping them. I'm just a bridge but I am also able to learn so much.


I will tell them to wear gloves because as of the moment they are not using such.

I have an interest in gold refining also. Read Hoke's book already. I will be asking you questions in the future if it is ok with you.

Thank you for the advice sir FrugalRefiner!

Mohammed


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## Deano (Nov 26, 2015)

Carbon stripping is really only learnt from hands on experience, how to build and operate a strip plant is not something I could teach you by email.
Stick with the zincing.

Gold tenor is the concentration of the gold in the leach liquor. The higher the tenor the more gold is in a unit volume of liquor.

Normally you would run the leach vat in recirculating mode for a time sufficient to get the bulk of the gold into the liquor.

I would do this by running the vat and sampling the liquor at the same time each day for say 7 days. The liquor is recirculated from the drain sump back to the top of the vat continuously during this time, hence the diaphragm pump.
During this time no zincing occurs, you are just interested in the level of gold in the leach liquor.
Best to use a clean plastic bottle for the samples.

After 7 days have the gold in solution levels read at a lab, the levels should be such that they can be reliably read by direct aspiration on AAS.

What you should find is that the gold tenor rises quickly for the first few days and then rises slowly after that.
The rate of increase depends on the quantity of gold available for leaching, the flow rate of the liquor through the vat material and the cyanide level in the liquor.
You should be able to see from the assays exactly where the rate of gold tenor increase slows right down.
Note that once the rate of gold leaching slows right down it will maintain that rate for possibly several months.

That slowing right down time is the point at which you zinc out your gold, this gives you the fastest recovery of the bulk of the gold in the ore.

You will, however, still have a vat where leaching is still occurring and will continue to occur for months as long as the pumping cycle and cyanide levels are maintained.

Generally there will be gold losses from leakages and re-adsorption in the vat.
This is the stage where it is sensible to adsorb the gold from the liquor onto carbon to minimise these losses.
If you do this you should have a liquor sample analysed weekly to see when the gold leaching rate is so low that it is no longer viable to continue the vat.

At this stage the vat is drained and left to dry for 3 to 6 months.
It is then refilled with cyanide solution and the cycle restarted.
The gold tenor from this second leaching stage is generally low enough that carbon is used as an adsorbent.

This second cycle is continued until the liquor assays say to stop again.
You now again drain and allow the ore to dry again.
These cycles of leaching followed by draining and drying and then leaching again are continued until there is not enough gold coming out to be viable.
This is the stage where you finally empty the ore from the vat.

You have to actually run the vat through a full cycle which may take many months in order to find out how long the total cycle takes. Each ore is different and milling changes alone will substantially affect the cycle time.
This is why I am not giving actual times per cycle, for a specific ore you can only find out by doing the cycles.

I don't know if they are still available but there used to be test strips for cyanide solution which colour changed according to the gold tenor.
These are an option to lab instrumental analyses of the liquors.

The carbon can be either stripped and reused or ashed and the ash residue contacted with cyanide solution to give a high gold tenor solution suitable for zincing.
Judging from the photos the ashing is the best procedure.

The obvious reaction to the above is; oh dear my vat will be tied up for possibly a year leaching just one load of ore.
Once again, judging from the photos, I would want to get as much gold as possible from your ore, it does not look like a lot of fun doing the mining part.

The usual method of operation is to have a series of vats which can be anywhere in the sequence from ready to start leaching to finished leaching and about to dig out the ore and refill the vat with fresh ore.
This way you will still be getting the bulk of the gold quickly but will be slowly getting the rest of the gold as a background exercise.

Most vat leaches have an internal sump to avoid the losses which will inevitably occur with an external sump.
You usually have a separate vat or vats which act as liquor storage vats for the leach liquors waiting zincing or for liquors going from a low recovery vat which is being dried and the liquors need to be stored short term before being put into the next vat full of ore.

The term "aim for about 300mm (1 foot) cover over the drains" means to have the drains on the bottom of the vat and to shovel the sized creek fine gravel right across the bottom of the vat until you have a layer which covers the drains by 300 mm or 1 foot.
This layer will maximise the flow of liquor through the vat as the whole floor of the vat is receiving the liquor through the gravel rather than just the small flow only through the edge of the drains themselves.
The drains all lead into a pre dug and lined sump for pumping from.

Most operators use slotted drain hose because they use internal pumping sumps and it is less work when setting up the base of the vat to just lay out fabric wrapped hose rather than make up and place heavy rock drains.
Slotted drain hose is cheap and lasts for many years as will the filter fabric providing that it is kept away from sunlight.

Deano


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## Aeon13 (Nov 27, 2015)

Thanks for the reply sir Deano.



> I don't know if they are still available but there used to be test strips for cyanide solution which colour changed according to the gold tenor.


- I will try to find this strip if it is still available because laboratory sampling and testing here is of low possibility.



> I would want to get as much gold as possible from your ore, it does not look like a lot of fun doing the mining part.


- You are so right about the mining part sir. Hard labor and the risk is inevitable for them.



> The term "aim for about 300mm (1 foot) cover over the drains" means to have the drains on the bottom of the vat and to shovel the sized creek fine gravel right across the bottom of the vat until you have a layer which covers the drains by 300 mm or 1 foot.


- I added some drawings on the previous one that I posted and added what I understood from thise statement. They are colored red. This is to ensure that I am understanding you exactly sir Deano because these points are of great help and I want to apply them.

Again, I want to thank you sir Deano for the priceless knowledge that you shared to me and to this thread. I am sure that these will help both the miners here in our place as well as anyone in the forum who has same concerns.


Mohammed


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## Reno Chris (Nov 27, 2015)

> *There is another process in which he uses the used ore again. In the process of milling, the liquid that was used is recovered and they are able to collect some really fine ore (like mud). They dry this and its consistency is like powder. Is it necessary to dry this mud like ore? They told me that drying and mixing of old ore is needed for the cyanide to reach every part of the mixture. *


Can you explain this again? After the ore is treated is it then crushed again? I am not sure of what you mean and there may be a translation problem. 

When your uncle fills the container with the cyanide liquid, does he cover over all the ore and then just leave it for some days, or does he continue to pump liquid out of and back into the container? If he just fills it and lets it sit, once the oxygen in the water is used up, no more gold will dissolve even if you wait for years. Oxygen is critical for the cyanide to dissolve the gold. 

The importance of the gold concentration in the liquid has to do with the capture of the gold onto the zinc. I had mentioned that oxygen can block the gold from being captured by the zinc and in some systems, the gold bearing solution is treated by vacuum to remove the oxygen from the liquid. If the gold tenor or concentration is high enough, the oxygen in the liquid is not a problem. If the gold concentration is low, then the oxygen is much more likely to be a problem. The easy answer for your uncle is to use the lead nitrate to pre-treat the zinc before he uses it. Since he has no AA analysis, he cannot know what the gold concentration is (Atomic adsorption is how large mines monitor the gold concentration in the solution), he needs to use the Lead nitrate as he was taught to do. Not using it may well allow gold to be missed. I've not heard of the test strips Deano mentioned (not that they are not available, just that I have no experience with them) - the easy answer however is the pre-treatment with the lead as it resolves the problem. 

Be sure he keeps trash out of the ore put into the container. Junk wood pieces can themselves adsorb gold out of the cyanide solution and hold it so that he will never recover it. 

Carbon is an easier process to capture the gold from the solution, but much harder to remove the gold from the carbon economically (you can burn the carbon and flux the ash, but that is expensive). Big mines use carbon and have facilities to strip the carbon and then recycle it to capture more gold. The decision to use carbon or zinc for big mines is based on how much silver the ore contains. High silver ores get the zinc treatment. 

Deano brought up another good point - does your uncle wash the ore with clean water at the end of the last cycle before he removes the ore and disposes of it? The treated ore will hold gold bearing solution in the moisture it contains. Big mines will always wash the ore with clean water both in heap leach and vat leach types of systems.


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## Aeon13 (Nov 27, 2015)

Thanks for your reply sir Reno Chris.

I apologize if this statement of mine is unclear. I will try to explain it further.


> There is another process in which he uses the used ore again. In the process of milling, the liquid that was used is recovered and they are able to collect some really fine ore (like mud). They dry this and its consistency is like powder. Is it necessary to dry this mud like ore? They told me that drying and mixing of old ore is needed for the cyanide to reach every part of the mixture.


- At the beginning, They mill the ore. This process crushes it and this is the main ore (just my term which is the sand like and not so fine ore). But the milling process also uses water, for this they collect the water which is colored gray. This gray water contains fine ore. They dry this by exposing it to sunlight. I attached the picture of this fine ore in my previous posts. The consistency is like that of fine powder. This fine ore is of lower concentration of gold but they recover it anyway. The statement " he uses the used ore again" takes place on the start of the recovering of gold with the fine ore (ore recovered from the water which is product of the milling). The used ore (the main ore, not fine) refers to the one that was leached and removed from the leach pad. They put this used ore in one place. For the fine ore,They dry it and after drying, they mix it with the used ore (like mixing cement and sand) with the ratio of 5 sacks of fine ore to 8 sacks used ore (They told me mixing is done for the cyanide to reach every part of the fine ore). Leaching the mixture takes less days than that of pure ore leaching.So they have two types of leaching that is done. First is the leaching of the pure ore. Then the leaching of the fine ore and used ore mixture.



> When your uncle fills the container with the cyanide liquid, does he cover over all the ore and then just leave it for some days, or does he continue to pump liquid out of and back into the container? If he just fills it and lets it sit, once the oxygen in the water is used up, no more gold will dissolve even if you wait for years. Oxygen is critical for the cyanide to dissolve the gold.


 The answer is yes sir Reno Chris. He lets it sit for days not pumping the liquid back and into the container. What would you recommend for this part of the process? I told him to lessen the days for the sitting.



> Deano brought up another good point - does your uncle wash the ore with clean water at the end of the last cycle before he removes the ore and disposes of it? The treated ore will hold gold bearing solution in the moisture it contains. Big mines will always wash the ore with clean water both in heap leach and vat leach types of systems.


 - I have not asked yet this. But as I have stated in the process above, they put the used ore aside and then mix it with the fine ore for the leaching. Maybe this will also fully remove any gold left in the used ore"?



> Be sure he keeps trash out of the ore put into the container. Junk wood pieces can themselves adsorb gold out of the cyanide solution and hold it so that he will never recover it.


 I would recommend and emphasize this point to him sir Reno Chris.



> The adding of diatomaceous earth is a new idea. How is this added? Just put it inside the bags? How will the recovery of gold differ with diatomaceous earth mixed with it?


- I am interested in this one if you have any idea sir Reno Chris.

Thank you again sir Reno Chris for your patience to understand my statements. I know language barrier is sometimes getting in the way. Thanks again.

Mohammed


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## Deano (Nov 27, 2015)

The idea of the gravel is to provide a graded bed to stop the ore fines from clogging the filter fabric. It is every thing from 12mm (1/2") to the fine sand fraction, not just the coarse fraction.

You should have the filter fabric wrapped drain pipe first placed on the floor of the vat with the outlet of the drain feeding your pumping sump.

If you have a plastic liner in the vat you then put a 50mm (2") layer of sand measured up from the floor of the vat. This stops the layer of river gravel from putting holes in the plastic liner.

The coarsest gravel, the 12mm or 1/2" fraction is placed at the bottom of the vat with the finer sizes of gravel placed above it.

The pumping shaft is put in position before the ore is added to the vat, the bottom of the pumping shaft sits on some large flat stones to stop it puncturing the liner.

It is greatly preferred to use a plastic liner rather than a clay liner, the clay is almost guaranteed to leak sooner or later.

Remember that a leak is not just an environmental problem, you will be losing gold as well.

The plastic liners can be joined by welding or by glueing, most operators weld but a carefully done glue job will suffice.

When the vat is being emptied you only excavate to 0.3 metres (1") from the walls to minimise the chances of damaging the liner.

When filling the vat you do everything possible to prevent compaction of the ore in the vat, no walking on it. If you have to walk on the surface do so on boards to minimise compaction.

Some operators will put a coarse plastic mesh layer at the top of the river gravel layer to act as a marker when emptying the vat.

I would recommend such in your case to stop you shovelling out the fine fraction of the river gravel. This fine fraction plays an important role in holding up the fine fraction of the ore during leaching.

Unless your vat is dug in solid clay or a waterproofing agent has been used to treat the canvas layer you show as the outer layer of the vat you will have leakage from the vat.

Note that waterproofing agents generally do not have a long life in alkaline cyanide conditions.

Deano


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## Deano (Nov 27, 2015)

See if this works for a crude cross section of a vat.

Deano


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## Aeon13 (Nov 28, 2015)

Thanks for your reply sir Deano.

Thank you for the drawing that you made. I appreciate it very much because it is much easier to understand things with the aid of a visual aid. Drawing such diagrams also is not easy as it looks.

I understood your explanation sir and I will share this information to the miners.

I downloaded the Microsoft PowerPoint.app.zip but was not able to find what you are trying to send maybe.

Thank you so much sir Deano!


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## cuchugold (Oct 31, 2017)

Deano said:


> If coarse gold is present in the ore then it will take longer to dissolve. Use a small jig or table to remove this coarse gold from the ore before leaching.
> Deano


Hello again Deano. Would you kindly post what you currently consider state-of-the-art processes, and equipment, for gravity concentration of coarser size gold, prior to any leaching process?. In particular, the advantages of a jig, over a sluice or rocker. Thanks in advance.


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## Deano (Oct 31, 2017)

If you are going to leach the tailings from a gravity process then what method you use to remove this coarse gold from the ore stream before the leach step is dependent on the size of the gold particles and the level of these particles in the feed.

You have three scenarios.

Firstly there is no coarse gold in which case all of the feed is leached with no gravity circuit.

Secondly there is only very coarse and very fine gold in which case you would be able to remove all of the coarse gold with a simple sluice prior to leaching the sluice tailings.

Thirdly there is coarse, medium and fine gold present in the ore. The coarse gold is removed by a sluice, the fine gold will be leached, the medium gold is that which may require a third processing step. When I say medium gold I am talking about 75 to 300 micron sized particles, these are the ones which are getting too large to leach but which are also getting too small to recover in a sluice.

The first thing to establish is how much gold is present in the medium size range, if there is a substantial amount then it may be worthwhile to put in a circuit to recover it. 

If there is not a lot of medium gold then you let it go to the leach system and accept that there will be some smallish losses from incomplete leaching, you have to be pragmatic about this.

If you have a lot of medium sized gold then you have two options depending on what volume of material per hour you are treating.

For smallish operations, say 1 to 10 tons per hour, you would usually use a jig to extract the medium gold.

For larger operations you would use a Gemini table.

There are many centrifugal concentrators on the market which do a good job but they also do a good job of emptying your wallet. Not recommended for small operations.

The cons from a jig or Gemini table will need to be either leached in a dedicated circuit or cleaned up on a Wilfley table, the table tails are sent to the leach circuit.

Deano


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## cuchugold (Nov 1, 2017)

Deano said:


> If you are going to leach the tailings from a gravity process then what method you use to remove this coarse gold from the ore stream before the leach step is dependent on the size of the gold particles and the level of these particles in the feed.
> 
> You have three scenarios.
> 
> ...


Thanks a lot Deano. The samples I have are not very consistent, sometimes there are plenty of nuggets, sometimes only finer dust. I never even considered the 'medium size'. I have to look in more detail. Thank you for that too. Would a jig recover the coarse and medium together, before any leaching is necessary?. What jig would you recommend for a 1 ton per hour operation?.

edit to add: Another question for Deano: Is this a good plan: Feed the placer ore, as is, into a jig, then sieve the tailings at 200 mesh (75 microns), discard the coarser, and accumulate the finer into a pit for future leaching. The concentrates from the jig also sieved and fed to a table for cleanup. Tailings from table to leaching pit (or dedicated strong leach small tank?). Alternatively, I could put a sieve stack (vibrating along with the jig motion), on top of the jig, to catch coarser nuggets, etc. With different size iron shot in the 2 or 3 sieve stacks, some sorting and milling will happen at the same time. Simpler that way, perhaps.


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## Deano (Nov 1, 2017)

The reason you run a sluice in the feed line of a jig is to not have to keep sorting through all the jig ragging looking for any nuggets.

Generally a jig will handle about 1 ton per hour of ore for each square foot of jig area. If your gold is trending to the minus 100 micron size then the jig feed rate is dropped to around 1/2 ton per hour or less.

The jig tails are panned to see what feed rate is appropriate for your gold size. If you see fine gold in the pan you slow down the feed rate.

The feed to the jig must be screened, usually a 3mm screen is used.

The coarser the screen used the greater the losses of fine gold on the jig.

Screening the jig tails at 75 microns sounds simple, in practice it will involve a large amount of hand sieving.

My preference would be to carry out some leaching tests on say the 1 to 3 mm fraction of the jig tails and see if there are enough values to be worth leaching, similarly for the minus 1mm jig tails.

The results of these tests will tell you whether the entire jig tail should be leached or just the minus 1mm fraction or maybe none of the jig tail.

You are trying to get a smooth feed entry on to the jig, the last thing you want is to have some further equipment making this difficult to do. Any milling done will be minimal and not worth the expense of doing.

All jig cons are cleaned up on a table ready for smelting, the table tails usually report to the leach circuit.

Deano


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## cuchugold (Nov 1, 2017)

Deano: It all makes sense. I truly appreciate your counsel. Now it is time to get to work, stop thinking, kill all the engineers, and start shoveling dirt for me.

I'll report next year what happened, or sooner if I get any questions. I see a plan coming together, even leaving a Vat leaching on-site while I'm away. At 5 meters depth (~bedrock), there is no shortage of water at all.

If you could suggest a model or type of jig to use, that perhaps I could manufacture, that'll be a bonus.

Cheers.


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## Platdigger (Nov 2, 2017)

I hope you guys don't mind my putting this here, and I know it probably won't help a guy much clean over in Ireland, but, I just happen to have such a jig as is being talked about in this thread.
I believe it is good for about ten ton per hour. I was not able to use it were I wanted to. So there it sits.
Again, I hope this is not an interruption to this thread. Good thread by the way. 
As all the threads are were we are so lucky as to have Deano post in.
The gold I intended to use it on is pretty small, probably 80 to 100 mesh. May not have been the right piece of equipment for the job anyway. 
And only a few grams per ton.


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## cuchugold (Nov 2, 2017)

Only my ancestors and one passport are from Ireland. Never been there!. Good luck selling the equipment. Adieu.


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## cuchugold (Nov 5, 2017)

Platdigger said:


> I hope you guys don't mind my putting this here, and I know it probably won't help a guy much clean over in Ireland, but, I just happen to have such a jig as is being talked about in this thread.
> I believe it is good for about ten ton per hour. I was not able to use it were I wanted to. So there it sits.
> Again, I hope this is not an interruption to this thread. Good thread by the way.
> As all the threads are were we are so lucky as to have Deano post in.
> ...


Can you post some photos of the jig?. Electric or gas?. Dual or single?. It must be very big for 10 T/hr. What's the weight?. Where is the equipment located and the asking price?. I think it's too big for my purposes.


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## Platdigger (Nov 5, 2017)

Well first off it is in Wa State. Just went up there to get some pics and the phone went dead.
It is dual.
It is electric. Looks like probably a 5 horse. My plan was to switch it to gas.
It must weigh around 1000 to 1200#. Just a guess.
I have the measurements of the screens some were.
Could all ways go back in the next few days and get any dimensions you might want.
Asking price? Make me an offer, I just might take it.
By the way, this thing take a lot of water to run it. Not sure how big of a pump it would take.


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## cuchugold (Nov 6, 2017)

Thanks Plat. It's too big for me.


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