Further things which may be of interest to members

[Deano]

The fluffing step is carried out after the pit has been drained for a week or two.

The excavator does not actually go into the pit, it always stays on top of the ore.

The cyanide level is correspondingly low, you have to work hard at even smelling its presence.

Keep in mind that OHS regulations must be adhered to, no one wants their project closed down through bad work practices.

In my years of vat leaching I have never even heard of anyone suffering accidental cyanide poisoning.

You respect cyanide but you do not fear it, you base your work practices around that approach.

Deano

 

[Deano]

An unexpected source of base and precious metals is often found in copper slag.

The early copper miners appeared to have two flaws in their smelting.

The first was that they did not know the best practices to follow when they smelted.

The second was that that they took the attitude of "there is plenty of rich ore available, if we do not get all of the metal recovered from the smelt it does not really matter, there is plenty more available".

This means that many of the early slags contain high levels of copper prills, most starting at 1% with some going up to 5% and more by weight.

Depending on the ore used, many of these prills had high gold levels up to 200 ppm.

The gold equalled the copper in value.

The cheapest way to recover these prills is by milling and gravity separation.

Generally it is not worth trying to mill to finer than all passing a 2mm screen.

Milling is done by sequenced jaw crushers with the final size obtained by choke feeding the last crusher.

Most of the prills are spherical but will still separate into a heavy concentrate on a well operated table.

Best table recovery is achieved if the milled slag is sized at 2mm and 0.5mm, these fractions are tabled separately.

Any prills left in the slag are not worth the cost of finer milling needed for liberation.

Ball or rod milling alters the prill shape and lowers the gravity recovery levels as well as costing more.

A general idea of what is available in a slag can be gotten by hand pulverising and then panning.

Deano

 

[4metals]

Ball or rod milling alters the prill shape and lowers the gravity recovery levels as well as costing more.

This is a descrete fact that can save someone starting out a lot of time and money, both on equipment and in time. It makes sense that a flattened bead would behave differently on the table, but to have first hand experience having doccumented that fact..... Well it is valuable!

Deano, you Aussie's are OK! Thank you.

 

[Deano]

While I was aqua regia digesting some ashed carbon I became curious as to exactly how much gold was co-precipitated with both the silver and lead present in the leach.

Both the silver and lead were, as expected, present as chlorides in solution in the aqua regia.

As the de-noxed aqua regia was allowed to cool down the silver and lead chlorides precipitated out of the solution and formed a layer on the bottom of the beaker.

There was enough of a density difference between the lead and silver chlorides that with extreme care a separation could be done on a super panner.

1 gram samples of each chloride were dissolved in separate fresh aqua regia solutions and the resulting warm solutions were analysed for silver, lead and gold.

The silver:gold ratio was 1:200, the lead gold ratio was also 1:200.

The gravity separation was surprisingly good in that the cross contamination between the lead and silver fractions was also in the ratio area of 1:200.

I suspect that there were also co-precipitation effects between the silver and lead chlorides.

A new artificial 1:1 blended sample of the gravity separated chlorides was treated to a dissolution of the silver chloride in sodium thiosulfate, this indicated the silver to gold ratio was around 220:1.

The lead chloride residue from the thiosulfate leach was analysed and showed a lead:gold ratio of 180:1.

It appeared that some of the gold released by the sodium thiosulfate dissolution of the silver chloride was adsorbed onto the lead chloride complexes.

A hot water contact between separate metal chloride samples revealed that both lead and silver chlorides desorbed gold complexes in the ratio of 10:1 metal:gold when related to the minor dissolution effects of the metal chlorides.

In other words there was a flush of gold from the hot water contact in a quantity in excess of that expected from a dissolution of the chlorides.

Aqua regia dissolution of the residue from the hot water flush gave a metal chloride:gold chloride ratio of 300:1 for both silver and lead.

This appears to indicate that the gold and silver and lead chlorides will co-precipitate from a chloride solution but the greatest mode of attachment is by adsorption of the other still dissolved chloride complexes onto the precipitated chloride complexes.


Deano



This indicates that the metal chloride mix

 

[Deano]

Let me start by saying that I am not interested in getting into the old argument about whether fire assay in ores reveals all of the gold values.

It has been my experience that in many ores where the fire assay values are zero it is possible to recover ultra fine gold by gravity means.

This is done by hammer milling ore samples and panning a < 100 micron screen undersize.

The best pan for such an exercise is a blue non-riffled pan, the gold is so fine that the agitation from a riffle will cause most values to be lost.

The pan concentrates can be fire or aqua regis assayed and will show values which were not revealed in an assay of the head ore.

A common constituent of such ores is iron in most of its forms.

The above is the reason for many small old workings on areas in shed zones from iron rich formations.

The original prospectors did all of their sampling by milling and panning, usually they were testing quartz stringers in the hope that they would thicken and contain high gold levels.

Modern sample testing does not reveal gold values which the original prospectors were following.

There are many examples of old workings where hundreds of shallow pits were dug but no major excavations occurred.

Most people assume that the old prospectors were either stupid or that they got all of the available gold.

The fact is that neither occurred, the grades were not high enough to be viable but they were present. No body digs holes for fun, these people depended on finding enough gold to live on. They found enough values to encourage them to look further but not enough values to actually mine.

Many such areas respond to metal detecting for small nuggets, most of the eroded values are found only in shed zones where the water flow is so slow that these values can be deposited, these zones can be a long way from the original source ore.


Deano

 

[4metals]

It has been my experience that in many ores where the fire assay values are zero it is possible to recover ultra fine gold by gravity means.

While I do not doubt this statement based on your life experience with the mining industry, and I do not in any way wish to cast doubt on what you have said. But there was a former member named Dr Poe who claimed that colloidal gold was everywhere and while it couldn't be assayed by conventional means, he could recover it. You, sir are by no means a Dr Poe, and if you say it is quantifiable, I believe it.

The pan concentrates can be fire or aqua regis assayed and will show values which were not revealed in an assay of the head ore.

The problem I have with a statement like this is not that gold which escapes detection by classical fire assay techniques is actually in some ores, it is that members who believe to have ore which is valuable will have yet another excuse not to bother with a fire assay. Your lab, Deano, enables you to crush and sieve the material, perform a classic fire assay, and pan and assay any suspect on your AA. Most assay labs wouldn't go that extreme once a classic fire assay, fluxed properly for the ore composition of the sample, results in a non detectable answer.

It does beg the question however, what range of PPM's gold concentration have you detected by this method? I can understand it being detectable and not being economically recoverable on a large scale. Are you talking about levels of Gold which can be profitably extracted?

 

[Deano]

The head grades of the ores which respond only to gravity separation of gold from the milled ores vary from 0.5 to 3 ppm with the majority in the bottom end of the range.

It is very much dependent on the ore tested, generally ores from a single formation carry similar grades for separate samples but similar looking ores from a separate formation may have wildly different values.

I have not seen a highly profitable ore body of this type, most would fit in the marginal at best category.

It has to be kept in mind that the ore has to be mined, milled and then gravity processed before the concentrates are treated as a separate parcel, even with economies of scale there are no cheap processing steps involved.

An indication of the difficulty of gravity processing this type of material is given by my inability to recover this type of gold from creek bed formations which would usually be regarded as guaranteed gold traps, this gold is only found in very low flow speed situations.

Very few people have the panning skills to recover this gold, the top size of the gold particles is around 5 microns with the bulk being much lower.

I wrote about this ore type because of an argument some prospectors were having about large areas of obvious prospect holes in places where gold mining was not existing either now or in the past.

Many of these areas have been extensively rock chip sampled by mining companies and the gold grades were elevated in the low ppb range but not to such a level that it was thought to be worth further testing.

The sheer amount of effort involved in the digging and testing of these sample holes was such that it was impossible to believe that it had been done without the encouragement of seeing gold in the samples.

In many of these areas there were many hundreds of these prospect holes in a few acres, this represented months of work.

Most of these holes were dug in the mid to late 1800s so the only technology available to the miners was pick and shovel followed by dolly pot and pan.

If you treat the ores in the manner of the original miners you could see gold in the pan, carry out modern sample handling and assay methods and you get nothing.

You still have to do the assays on the pan concentrates to get a head ore grade and these assays can only successfully be done on a really clean pan concentrate. It really gives me much admiration for the panning skills of the original miners.

I have always suspected that most of these early miners were hard rock tin miners from Cornwall in England, they would have been among the few people who had the panning skills to even see this gold.

Deano

 

[4metals]

Back in the day I was using a dredge in Ecuador to recover placer gold from streams. Before I traveled to Ecuador I visited Keene Engineering to purchase a dredge and have it shipped to Guayaquil so it would be there when we arrived. The salesman convinced us to select the model which was designed to also recover flour gold. Back then flour gold was a term I had never heard as I came from the secondary refining industry but I took his advice and purchased a 6" dredge which had riffles to collect "flour gold" as well as placer nuggets.

I must admit the difference between moderately successful and very successful was flour gold. When cleaning up the dredge, the fine powdery sandlike gold appeared when panning. It appeared like the finest beach sand I have ever seen except it was gold in color.

Apparently the flour gold that I recovered were mini boulders compared to the gold that Deano is talking about. When you consider the flow through the riffle, which wasn't hard enough to blow the flour gold off the dredge, it is hard to imagine just how small the particle size is on the values Deano is talking about. And I thought the dredge made to trap flour gold got the smallest of the small! Now I have to wonder if any went off the south end of that dredge.

Oh well, let it go, we still made money!

 

[cosmetal]

Back in the day I was using a dredge in Ecuador to recover placer gold from streams. Before I traveled to Ecuador I visited Keene Engineering to purchase a dredge and have it shipped to Guayaquil so it would be there when we arrived. The salesman convinced us to select the model which was designed to also recover flour gold. Back then flour gold was a term I had never heard as I came from the secondary refining industry but I took his advice and purchased a 6" dredge which had riffles to collect "flour gold" as well as placer nuggets.

I must admit the difference between moderately successful and very successful was flour gold. When cleaning up the dredge, the fine powdery sandlike gold appeared when panning. It appeared like the finest beach sand I have ever seen except it was gold in color.

Apparently the flour gold that I recovered were mini boulders compared to the gold that Deano is talking about. When you consider the flow through the riffle, which wasn't hard enough to blow the flour gold off the dredge, it is hard to imagine just how small the particle size is on the values Deano is talking about. And I thought the dredge made to trap flour gold got the smallest of the small! Now I have to wonder if any went off the south end of that dredge.

Oh well, let it go, we still made money!

I know that this can be a controversial subject, but, here it goes . . .

Back in the early ‘80’s I had the good fortune to live in Placerville, CA eight miles from Coloma, CA where the gold was found that started the 1849 gold rush.

I had four placer claims on the South Fork of the American River. My partners and I dredged these claims for years (not full time – we found good gold but not enough to support three families (gold hit $850/oz. in 1980 and fell to $599/oz. by the end of 1981).

I’ve always been interested in “micron”. “flour” or “”float” gold – however it was defined. When we cleaned out our suction dredges (panned by the river), we could see this very small gold but it didn’t seem to be worth chasing even though we produced a lot in our concentrates.

One winter came and I decided I was going to build a concentrating table to be housed in my garage where we could process these fine gold concentrates at our leisure and in comfort.

It ended up being approximately 46cm wide x 183cm long. Similar to a miller table except mine was also equipped with (here it is!) a 46cm x 46cm copper plate electroplated with silver that I would coat with mercury! Yes . . . mercury.

Before this post is condemned, please know that I am not encouraging the use of mercury. I was also raised by ex-copper miners and geologists who taught me how to handle mercury and I knew about its toxicity. My table also had a final riffle section at the very end where I had mercury traps and miner’s moss riffles.

The table consisted of controllable water flow, an upper section coated with chalk board paint, an upper miner’s moss and riffle section, the mercury coated plate, a lower miner’s moss, riffle and trap section, and the final catch basin that was suspended in a large water basin before the water was allowed to drain onto my pasture area.

Not only did the table cut out our river side panning, it caught a multitude of gold sizes - even the Deano sizes. In fact, when I started it the first time to adjust the water flow, I did not run any concentrates for a while as I fine-tuned everything. Maybe two hours or so later, I was amazed to see an extremely fine sheen of gold over all of the coated plate! It wasn't a optical illusion as I could actually move it with my gloved finger. Yes, there is colloidal gold suspended in water – at least in El Dorado County, CA there is! Fortunately, i never had any mercury escape.

Again, please do not use mercury. As Deano says, the smallest gold can be panned but it takes practice, practice, practice and patience, patience, patience! :|

 

[anachronism]

Thanks for the post cosmetal. I think it's good information, and let's face it, it's a pointless exercise to condemn talking about a method that was the used in the past just because today's standards are different.

 

[snoman701]

Thanks for the post cosmetal. I think it's good information, and let's face it, it's a pointless exercise to condemn talking about a method that was the used in the past just because today's standards are different.

I find it interesting to review history. Sometimes it's relevance isn't that far off.


Sent from my iPhone using Tapatalk

 

[4metals]

Back when I was recovering placer gold, those things were called plate amalgamators. The silver plating made the mercury more adherent than a plain copper plate which helped to prevent the mercury from breaking up into tiny balls and being lost.

We had a plate amalgamator in Ecuador as well as a mercury retort to recover the mercury. Mercury was sold in 50 pound dewars and widely used back in the early '80's.

Mercury will form an amalgam with most metals with the exception of aluminum and iron. The ability for mercury to form an amalgam with gold but not iron may be the reason it can separate the gold from iron rich black sands if they are crushed enough.

Mercury was so overused in placer mining in Ecuador back then that it was not uncommon to see small pools of mercury near the outwash of the mills. It had to take an environmental toll. We are better off today to steer clear of its use.

 

[cuchugold]

This is a great thread to read and reread.
Q for Deano: Any thoughts on the use of resin instead of carbon for the recovery of the liquor?. My experience is only using small 20 Ton vats, and found that while resin is more expensive, it is reusable and more effective.

 

[cosmetal]

Back when I was recovering placer gold, those things were called plate amalgamators. The silver plating made the mercury more adherent than a plain copper plate which helped to prevent the mercury from breaking up into tiny balls and being lost.

Mercury was so overused in placer mining in Ecuador back then that it was not uncommon to see small pools of mercury near the outwash of the mills. It had to take an environmental toll. We are better off today to steer clear of its use.

"The silver plating made the mercury more adherent than a plain copper plate which helped to prevent the mercury from breaking up into tiny balls and being lost."

Much easier . . .

"Mercury was so overused in placer mining in Ecuador back then that it was not uncommon to see small pools of mercury near the outwash of the mills. It had to take an environmental toll. We are better off today to steer clear of its use."

We would find small pools hiding in the cracks within the bedrock. They had been there so long that they were usually very pregnant with gold flakes and gold dust.

James

 

[cuchugold]

Like it or not, most of the gold from Brazil and Venezuela come from amalgamation in one fashion or another. It's just very effective enhancing gravity methods. It's very common "charged mercury", which is an amalgam of sodium, which keeps the surface very soapy and clean, facilitating capturing the gold flakes. In an operation I supervised, we retrieved more mercury from tailings processing than we used.

 

[snoman701]

Like it or not, most of the gold from Brazil and Venezuela come from amalgamation in one fashion or another. It's just very effective enhancing gravity methods. It's very common "charged mercury", which is an amalgam of sodium, which keeps the surface very soapy and clean, facilitating capturing the gold flakes. In an operation I supervised, we retrieved more mercury from tailings processing than we used.

If you were in the us, you could charge for environmental remediation!!


Sent from my iPhone using Tapatalk

 

[Deano]

Re use of resin instead of carbon for gold recovery from solution.

Resin will do a better job of adsorbing the gold complexes from cyanide solution than will carbon. It adsorbs faster and to greater completeness.

The latest resins from large producers will also strip quickly and easily.

So why are not all of the worlds gold mines using resin rather than carbon.

The initial resistance is price, resin costs multiples of carbon cost.

The second is osmotic shock in those resins still using a sulphuric/thiourea strip, the degradation rate can be fierce.

The third is inventory lockup of the gold. Resins are notorious for locking up gold which cannot be eluted, the longer these resins are used the greater the lockup level.

This means that apart from the lower adsorption levels per cycle there is an increasing amount of gold which has been processed but which cannot be recovered until the decision is taken to recover this gold by ashing the resin.

A further strike against resins is that, as with carbon, the initial and fastest adsorption occurs on the outer surface of the adsorbent particle.

The organic functionalities of the resins are subject to uv degradation and these functionalities will degrade to higher forms which are more difficult to strip and/or will degrade to forms which are less effective as adsorbents.

So with time the loading kinetics of the resins drop markedly as the surface sites are no longer active as adsorbent sites.

With carbon the greatest problems are associated with attrition of the carbon and the loss of carbon and gold values as fines.

Most of these losses occur during regeneration of the carbon and so the gold losses are minimal as the carbon has already been stripped.

Deano

 

[cuchugold]

Thanks a lot Deano!. :G

edit to add: Can you point to any links or post any knowledge regarding the recovery of gold from ores in regions with little or no water available?. I understand there are several desert/ near desert regions in Australia with plenty of good material.

 

[Deano]

There are many gold bearing areas in Australia which are in desert or semi desert conditions.

Usually the main problem is not availability of water but availability of reasonable quality water.

Often any better quality water is only available in small quantities so it is apportioned initially for drinking/ camp use and any surplus is shandied with lower grade water in an attempt to improve the plant water quality.

It is usually not viable to attempt to improve the water quality by RO etc.

Deano

 

[cuchugold]

Thank you Deano.

I'd very much appreciate your input with regards to recovery in this situation:
http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=44&p=278491#p278491