# Gold in limestone



## happyprince

Hi everybody,
I have had a limestone rock tested and there is gold in it.I wonder if you could help me about this matter? Does Aqua Regia method work with gold ores with/in limestone? What is the best method of recovering/refining gold in limestones?If Aqua Regia method Works,what is the best method to precipitate the gold ? I plan to dissolve limestone with nitric acid and then to do the Aqua Regia process...Another question,can mercury process work also with this type of ore?
Thanks in advance...


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## solar_plasma

I am only curious, how much gold is in that limestone material? Are there other metals in it beside gold and calcium? Your idea about HNO3 sounds a bit expensive to me (and you would need 2 mole HNO3 per mole of CaCO3), but I want to wait and read, what the experts will answer.


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## happyprince

As far as tests show,there is around 1% (one percent) gold in it...Actually I cannot totally understand the chemical formulas you write here because I have no knowledge of chemistry... I just want to learn if there is a practical way , Aqua Regia maybe, to get the gold out of the ore.I will crush the stone before Nitric Acid,then apply Aqua Regia method... I also will be thankfull if anyone can tell me what is the best method to precipitate gold in Aqua Regia.Of course if that method Works with that ore... Thanks for your reply...


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## happyprince

By the way there is very little amount of titanium,cobalt ,chrome and iron in it.


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## butcher

Acids are expensive, and limestone would neutralize the acid, this would use up a lot of acid creating a lot of waste to deal with, if the gold can be separated mechanical you would be $$$ ahead.

Even if you choose to leach with acids you should concentrate on pretreatments, and concentrating the ore as much as possible beforehand, to get a high metal to limestone ratio. 

Just because ore has gold does not always make the ore valuable, even if the ore was rich if it cost you more money than you could make from it, the ore would not be worth processing, there are many gold mines in the area where I live, they still have a lot of gold in them, these mines shut down not because they ran out of gold but because the cost of labor or cost of getting the gold out was not any longer profitable, when labor was hard to find during the wars, or when the price of labor or equipment went up, miners will become loggers if the logging companies would pay more for their labor... you will need to determine how much gold the ore contains, not just in a couple of choice rocks, but over the whole mining area, if you get an assay of a rich looking rock you pick up it may not represent the rest of the mine, and you could be spending much money to mine a virtually worthless mine not figuring it out until you have lost your pants in the process, mining is something normally better done by big company's with deep pockets, it can cost a lot of money to get set up, and it can cost a lot of money to process and keep the process going, it can be very easy to get in over your head with hopes and dreams of riches, that may not be there, this is why company's will spend a lot of money and time on research even before they decide to develop a mine, you also need to spend some time and money on a lot of research before you can decide, after you know how much gold per ton, you will need to research the best ways to process the ore, I imagine there is more to the ore chemistry than just gold and limestone, what form is the gold in can it be concentrated or separated without chemicals, would chemical leaching be better than concentrating and smelting, how much will it cost for the equipment and manpower needed to be able to make at least a little profit, would it be better to concentrate and sell the ore, what about transporting the ore, do you have rights and claims to the mine and other legal issues in order, what about the environmental impacts and permits of operation...

It not as easy as just dissolving away the limestone in dilute sulfuric acid and getting rich on gold, much study, preparation, testing, getting legal issues in order, and even experimentation will need to be done even before you will see any gold.

Caution about roasting or putting an ore in acids, you really need to have a good knowledge of what the ore contains, you could be trying to leach the ore and not realize your standing there breathing arsenic fumes, or hydrogen sulfide gases, you cannot always count on your sense of smell to warn you of the dangers.



I only have done some hobby experiments with ore, and have no experience as a professional miner so this is mostly just my opinion.


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## solar_plasma

That's just what I thought. If it only was CaCO3 (limestone) and gold...would be easy to answer, how this could be made profitable (though not by nitric, unless you get it for free). But I learned that things aren't always what they seem to be. I will follow this with great interest.

Until then, find Palladium's links in his signatur and read.

And this onemight interest you: http://ia700400.us.archive.org/35/items/metallurgyofgold00roserich/metallurgyofgold00roserich.pdf


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## happyprince

Thanks a lot for your reply and precious time spent for it.I really appreciate that.
How about mercury processing then? Can mercury work in this kind of material? Thanks a lot...


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## solar_plasma

> How about mercury processing then? Can mercury work in this kind of material? Thanks a lot...



NO, forget mercury!  Too poisonous to us normal humans. Bad idea!


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## shaftsinkerawc

Tell us more about your ore. Is it free milling? Have you crushed any yet? What type of assay was done to confirm the 1%? Have you got any pictures & have you looked at it under magnification?


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## happyprince

Actually it is in powder form now. It belongs to a friend of mine and he is sure there is gold in it.(He tested it with lead method and a device the name of which I cannot remember now...)... I can supply photos on Monday or Tuesday because he will give me sample material then... I just want to learn how to recover gold before I get it...Thanks...


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## Harold_V

happyprince said:


> As far as tests show,there is around 1% (one percent) gold in it...


Nonsense! That's 291 ounces/ton. Are you aware that one ounce per ton is considered high grade ore? Are you equally aware that many of the major operations are processing ores that bear as little as .10 ounce per ton? If you are, doesn't it give you cause to wonder why you have such a rich deposit?

Before you start knitting little booties, might be a good idea to see if she's really pregnant. I expect your "assay" (for lack of a better description) is useless.

By the way, how was that 1% determined? And---why was it displayed as a percentage instead of ounces per ton? Makes no sense. (Not to me!)

For the record----it would be VERY unusual that you could process an ore with acids and achieve a reasonable recovery. 

Before you'd be able to make a decision about how to process, you'd be best served to have a fire assay performed on your "ore". I expect you're not going to like what you learn, however, so how to process will be to move on and get over your dream, as it most likely is just that, a dream. 

Be advised that you can assay almost anything and detect the presence of gold. It's very widespread--but not often found in commercial quantity. Remember, the ocean itself contains gold. 

Harold


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## NobleMetalWorks

I was going to say something, but Harold, you have said it all!

I think some inexpensive XRF scanners do not give results under 1%, but give all results that can be scanned. I believe this is because under a certain percentage, it becomes more difficult to give an accurate reading, so it just simply gives a 1%. If you had your ore scanned by XRF, not only was this the wrong was to assay your ore, but it very well could be that the XRF scanner was the very type I am talking about. So while your ore may contain extremely small quantities of Au, it's most likely not recoverable, just like Harold has stated.

In the last few months, I have had two people claim they have ore that is made up of 1% Au. Both scanned by a guy running around with a cheap Chinese made XRF scanner, who is charging people to drive out to their claim, and scan their ore for them. I live close to Placer County California, so you can just imagine. Instead of arguing, I just simply tell them I don't process ore. You cannot argue with these people, you cannot tell them they are wrong, you just have to pass them along to the next person. Some people will forever believe there is recoverable Au where there just simply isn't, and no amount of reason, or proof, will ever change their mind.

Scott


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## Geo

personally, i have never heard of gold bearing limestone. limestone is a metamorphic rock that is formed on the bottom of seas and oceans due to the build up of shells from sea life. the gold would have had to have been deposited before the ocean existed. im not saying it didnt happen, just that i have never heard of it. there would be a clear zone of separation between the original bedrock and the limestone layer. i cant see how the gold would be in the limestone at all. the same applies to sandstone. i have seen gold deposits under sandstone but not in sandstone.


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## solar_plasma

In the film I mentioned some time ago (I still haven't found the english original version), they said, also hot springs may transport gold to the surface and concentrate it...though I don't know if the material around hot springs can be limestone...at least some kind of CaCO3 containing minerals.


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## steyr223

Aliens :shock:


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## g_axelsson

butcher said:


> It not as easy as just dissolving away the limestone in dilute sulfuric acid and getting rich on gold...


Sulphuric acid isn't recommended for treatment of lime stone. CaCO3 + H2SO4 => CaSO4 + H2O + CO2

CaSO4 is the formula for gypsum and isn't soluble in water, you would create a mess. I would recommend HCl for dissolving limestone. It gives CaCl2 that is water soluble. (I'm doing it all the time when I prepare mineral specimens of crystals in limestone.)



happyprince said:


> As far as tests show,there is around 1% (one percent) gold in it...


I agree with Harold and others, 1% is a rediculous high number, it sounds like a badly calibrated XRF reading.
Concentrate a sample (for example 100g) by dissolving the lime stone in hydrochloric acid and rerun the analyse on the concentrate made up of undissolvable minerals. Let's say that the concentrate is reduced to 1/6th in weight then the new analyse should give 6 times as high reading. If it doesn't then there is a severe problem with your analyse.
I also recommend that you send a sample for fire assay, if the ore is as rich then you can afford it easily and if it shows no values you would save a lot of money not chasing something that isn't there.



Geo said:


> personally, i have never heard of gold bearing limestone.


There are some examples of gold in calcite / limestone even if it isn't common.
I didn't find the reference I was looking for but in the Getchell mine I think gold was found in a sulphide impregnated lime stone breccia.
_"Nearly every mineral of the ore is host for at least some of the gold pyrite marcasite and the carbonaceous matrix of the gumbo are the most important gold bearers but gold also occurs sparsely in realgar arsenopyrite and coarse quartz."_
The example I was looking for was a classical occurence in Great Britain where a calcite outcrop were impregnated with so much gold that the calcite didn't fracture as it normally does. I've seen fantastic samples where the calcite has been etched to show the fine crystals of gold.
Oh... here it is, enjoy! :mrgreen: http://www.johnbetts-fineminerals.com/jhbnyc/mineralmuseum/picshow.php?id=34321






Göran


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## Geo

thanks Göran, nice example. it would have to be some sort of geothermal venting sending the gold up through the limestone to create the deposit. still, very uncommon.


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## solar_plasma

In nature CaCO3 is getting dissolved by CO2 and water or better H2CO3 and forms dissolvable Ca(HCO3)2, at the air it will give CO2 back and form CaCO3 again. The same method is used in coral reef tanks in the limestone reactor. Can anybody tell, if this effect also is used in pm mining industry? I could only google the fact that for example calcite is mined for gold, I did not find anything about the methods. In big style this method, using CO2 and water under pressure and maybe reusing the CO2, would seem economic and ecological to me, - with large amounts of pure CaCO3 whiting as main product and some gold as a byproduct. Only curious...


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## g_axelsson

That would be a too slow process to be economical. I have seen three processes used in mines, all start with with crushing and milling the ore. Then either gravimetric methods are used (coarse gold), cyanide leaching (microscopic gold) or flotation (when the gold is associated with sulphides).
Sometimes more than one method is used, for example the Björkdal gold mine uses gravimetric extraction of coarse gold and froth flotation of the tailings.

Göran


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## solar_plasma

I wasn't aware of there are so many gold mines in Sweden. Since much stone material was transported over here from Sweden under the glacial periods, I wonder,if some of your swedish gold rocks might lie in my garden now, or at least at our coasts....I think at future beach tours I will look twice, when I find suspect rocks! :lol:

As a kid I found a big rock on Bornholm with yellow metallic traces in it, ...should have tested it :mrgreen: just couldn't take it with me, it was at least some meters big.


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## frontiermetals2020

Geo said:


> personally, i have never heard of gold bearing limestone. limestone is a metamorphic rock that is formed on the bottom of seas and oceans due to the build up of shells from sea life. the gold would have had to have been deposited before the ocean existed. im not saying it didnt happen, just that i have never heard of it. there would be a clear zone of separation between the original bedrock and the limestone layer. i cant see how the gold would be in the limestone at all. the same applies to sandstone. i have seen gold deposits under sandstone but not in sandstone.


Gold can and does occur in limestone. Cripple Creek is one such area as volcanic intrusions pushed up through limestone and depositing gold throughout. Also the Shafter silver mines in West Texas. Limestone beds with replacement deposits of silver and gold bearing ores. Marble, being metamorphed limestone often has metals running through it. Gold is where you find it, as they say.


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## DarkspARCS

Nevada has some prime examples of this as well...


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## kdaddy

If you roast the limestone in a hot bonfire and then drop it in a bucket of water it will dissolve into powder. Then you can pan to concentrate the PM's if any are present.


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## Oberon702

Just commenting on someone else’s post. Limestone is a sedimentary rock....not metamorphic. It’s made of dead organic matter and so it’s loaded with carbon. Sometimes hot acidic hydrothermal fluids deep underground will fill cracks in the ground caused by earthquakes, faults shifting, etc.. sometimes this acidic fluid can hit a layer of limestone and the limestone will neutralize or lower the acidity of the fluid so that it’s dissolved minerals will drop out of solution or precipitate and will absorb in to the surrounding Limestone. It is not called Limestone at that point. I believe they call it Dolomitized Limestone, Dolomite or Dolostone. Basically it means the Limestone is impregnated with magnesium as a result of the hydrothermal solution altering the Limestone. Any gold in the Dolostone is going to be microscopic. You can’t just jump into gold extraction and start handling dangerous chemicals. You need to research research research! Know your geology! Understand the chemistry and set of circumstances that have to happen for gold to be brought to the surface. Have humility. Be safe. Use proper PPE. Any be prepared to fail over and over again and not find any gold because it’s going to happen. I am a beginner prospector myself in Las Vegas who didn’t know anything about mining geology 9 months ago. But I watch a lot of YouTube videos, you might like Jeff Williams gold videos, USGS reports are wonderful! And understanding the terminology you come across is a necessity.


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## Jram026

Hi,
I've come across large hills in my region that are of flattop in nature, the kind related to hot springs. Opposite to these ancient hot springs is a very large mass of limestone. The limestone is cracked visibly from satellite imagery. 
I want to put to you that hydro fluids (gold bearing) flowed through the limestone at the time that these hot springs were in full swing. 
My question: does anyone have drawings or pictures of how exactly this type of system works in detail? 
For instance, there are signs of heavy iron oxide leeching out (rusty streams). Historically, Fine gold retrieved by the old timers. Gravity surveys show vent shape like analomies like there were jet engines powering into the atmosphere. Close to one of the anaomlies the Geo Chem showed RareEarthMinerals at incredibly highlevels. I cant find much detail on specifically hot springs.


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## fishaholic5

I believe there has been some work done on mineral deposition by hot springs in New Zealand and there has been a lot of research on carbonate hosted hydrothermal gold deposits in the US and other countries


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## butcher

Hydrothermal fluids
https://www.google.com/search?bih=705&biw=1024&hl=en-GB&sxsrf=ALeKk02vwU2mXETh1-OacbpTIh1VJprBLw%3A1585225610292&ei=ip98Xsi7Ec34-gT6tLmwDg&q=hydrothermal+vents+temperature&oq=gold+thermal+vent+calcium&gs_l=psy-ab.1.2.0i71l8.0.0..28115...0.1..0.0.0.......0......gws-wiz.N9EKQMWczUI

Black smokers.
https://www.ncl.ac.uk/media/wwwnclacuk/teacherstoolkit/emilijakopustaite/Teachers%20notes_hydrothermal%20vents%20background%20information.pdf

Hot springs calcium carbonate
https://www.google.com/search?q=hot+springs+mineral+deposits&source=lmns&bih=705&biw=1024&hl=en-GB&ved=2ahUKEwjD__CAlbjoAhUEhZ4KHUvfBk0Q_AUoAHoECAEQAA


Geothermal deposits
https://www.google.com/search?q=geothermal+deposits&source=lmns&bih=705&biw=1024&hl=en-GB&ved=2ahUKEwi_1Z_qlbjoAhVrkp4KHccnBRwQ_AUoAHoECAEQAA

Epithermal
https://www.google.com/search?q=epithermal+gold+deposits&source=lmns&bih=705&biw=1024&hl=en-GB&ved=2ahUKEwj-trKVnLjoAhU8wJcIHbpsBEUQ_AUoAHoECAEQAA

Mesothermal
https://www.google.com/search?biw=1024&bih=705&sxsrf=ALeKk03Rtegmc_XKXl9iFZYprm35tPam0Q%3A1585228432986&ei=kKp8XvTkO92u0PEP47u3-Ac&q=mesothermal+gold+gold+deposits&oq=mesothermal+gold+gold+deposits&gs_l=psy-ab.3...26034.35619..36289...0.1..0.774.3321.5j6j3j2j6-1......0....1..gws-wiz.......0i71j0i67j0i7i30j0i8i7i30j0i7i5i30j0i333j0i13j0i13i30j0i13i5i30j0j0i30j0i5i30j0i8i13i30.uWurvIbV8A4&ved=0ahUKEwj07IqNnLjoAhVdFzQIHePdDX8Q4dUDCAs&uact=5


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## DarkspARCS

Oberon702 said:


> Just commenting on someone else’s post. Limestone is a sedimentary rock....not metamorphic. It’s made of dead organic matter and so it’s loaded with carbon. Sometimes hot acidic hydrothermal fluids deep underground will fill cracks in the ground caused by earthquakes, faults shifting, etc.. sometimes this acidic fluid can hit a layer of limestone and the limestone will neutralize or lower the acidity of the fluid so that it’s dissolved minerals will drop out of solution or precipitate and will absorb in to the surrounding Limestone. It is not called Limestone at that point. I believe they call it Dolomitized Limestone, Dolomite or Dolostone. Basically it means the Limestone is impregnated with magnesium as a result of the hydrothermal solution altering the Limestone. Any gold in the Dolostone is going to be microscopic. You can’t just jump into gold extraction and start handling dangerous chemicals. You need to research research research! Know your geology! Understand the chemistry and set of circumstances that have to happen for gold to be brought to the surface. Have humility. Be safe. Use proper PPE. Any be prepared to fail over and over again and not find any gold because it’s going to happen. I am a beginner prospector myself in Las Vegas who didn’t know anything about mining geology 9 months ago. But I watch a lot of YouTube videos, you might like Jeff Williams gold videos, USGS reports are wonderful! And understanding the terminology you come across is a necessity.



I wanted to add to this excellent explanation on the gold forming process with some geological explanations as well as observations Ive made here locally...

As a prospector in the State of Nevada (one of the worlds major gold producers) I have reviewed several mining districts where volcanic intrusions either from prehistoric arc subduction zones or techtonic upheaval has broken through sea beds that existed for hundreds of thousands if not millions of years which means three forms of carbonaceous rock: limestone/ sandstone, dolomite/ quartzite, and marble/ monzanite (depending on the depth the sedimentary layering) ...

One of the best locations you can actually review just how deep the ocean floor sediments became is the Grand Canyon, where miles of carbonaceous sedimentary rock is revealed at depth.

When you think about that you begin to understand just how violent the forces that cracked open miles of sedimentary rock had to have been, so that when the magmas flowed it now became a jumble of the three states rock exists within, sedimentary, metamorphic, with igneous intrusions criscrossed all throughout it.

These sea beds are comprised of carbon, the very substance used to extract precious metals suspended in the cyanide solutions used to leach complex ores (of which Nevada has pleanty of lol). So with that in mind these sedimentary rocks will litterally absorb the gold in those magmas just the same as activated charcoal does. Its the salts (carbon/ sodium/ phosphorus/ potassium/ chloride) embeded within these limestones that neutralize the acidity of these magmas ( selenic/ silicic/ sulfuric) and thus lowering the Ph of the solutions and enabling the carbons to literally capture the gold particles like a sponge does water.

The divide between the limestone walls and the intrusive magmas is know as a Contact Zone... These contact zones are where you want to look for rich gold ore because the dolomites literally grabbed the gold with such attraction that these areas will be literally oozing with gold/ silver/ pgm coagulation... Like precious metal streams (thus the technical term streamers)

So yes... Limestones hardened into dolomite or marble from techtonic forces caused by volcanism are a well known source here in Nevada for gold and silver.


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