CANADIAN GOLD PROSPECTING FORUM - Gold Prospecting Forums

Gold Prospecting Forums - General => Hard Rock Mining => Topic started by: bama on July 06, 2009, 09:58:45 AM

Title: a simple test for gold in pryrite
Post by: bama on July 06, 2009, 09:58:45 AM
Hey folks,
In a nugget patch I've been working there is vein of green stone(chorite shist). It really sounds off my metal detector. I think it is loaded with pryrite. Is there a simple test for gold I can do? Also around this vein is decomposed bedrock that has a lot of black sand, not much gold. Could this sand contain gold that isn't
visible to the eye? Any suggestions that don't involve costly assays?

bama
Title: Re: a simple test for gold in pryrite
Post by: krueger95 on July 10, 2009, 11:01:40 AM
Hello-
I'm new here-- so please forgive me for sticking my nose in here.
I too am very interested in a simple test for gold or silver in pyrites. We have chalcopyrite and some rusty red material in quartz and then some silphides. Was told that they recovered gold and silver from this ore 60 years ago but no one is available to tell me more.
So---- I'm looking for a simple "bench top" test for gold and silver.
Thanks.
Stan
Title: Re: a simple test for gold in pryrite
Post by: ClickTheYellowChick on July 10, 2009, 12:45:23 PM
Welcome aboard, Montana Krueger!  <-wave->

Great first question!  If there is something "bench top simple" out there, I'm sure this group's members will know about it.

I personally have seen pyrites and gold on the surface of the same rock.  Wish I had one in my specimen collection, but alas, it belonged to someone else.

Again, Welcome!  ;D

Kind regards

Title: Re: a simple test for gold in pryrite
Post by: GollyMrScience on July 10, 2009, 06:29:15 PM
I have pics of gold in pyrite through a microscope that only starts to show gold within the striations of the pyrite at 150 power. Some does not show up till you get to electron microscope so that stuff can get REAL tiny.
There are some basic tests that can be done but they are generally pretty course and will only give you results if larger amounts of gold.
Are you looking for a field test to just confirm that gold is there?
Title: Re: a simple test for gold in pryrite
Post by: krueger95 on July 10, 2009, 07:06:24 PM
It would be very nice to find a field test for gold &/or silver in pyrites and sulfides.
Any suggestions ?
Thanks for your assistance.
Stan
Title: Re: a simple test for gold in pryrite
Post by: gpg on July 19, 2009, 08:40:13 AM
THis was posted by Geowizard on the Alaska Gold Forum.

For iron pyrite (sulfide), here's the test:

(In a ventilated area... using a small sample)

Crush and roast the sample at high heat.

When iron sulfide is roasted, the sulfur vaporizes and results in iron.

The iron will pick up with a magnet.
Title: Re: a simple test for gold in pryrite
Post by: PlacerPal on July 19, 2009, 12:40:18 PM
Interesting information from Bob Redberg about gold and iron pyrite.

"The reason most prospectors know a lot about the appearance and habits of iron pyrite is twofold:
1) To keep from being fooled.
2) Because of the known association between pyrite and gold. Pyrite is found in, or asociated with,
more than 70% of the world's gold deposits."

Topics:

The Mysterious Process That Traps Gold in Pyrite

Nature's Method of Releasing Gold from Pyrite

The Commercial Process for Recovering Gold From Pyrite

And much, more more.

Interesting Things About Gold  (http://www.bobbredberg.com/geo/goldbits.html)

 :)
Title: Re: a simple test for gold in pryrite
Post by: GollyMrScience on July 19, 2009, 05:41:23 PM
Well I would probably want to add some details to some of what is written.
The Carlin Gold IS visible and ranges in size from flour to microscopic. Under an electron microscope the gold can be seen as blebs in the pyrite and even as coatings in the striations of crystal sulphides. This is common with many sulphide sourced gold.
He states that gold is found in the form of iron pyrite but gold is found in the form of gold and pyrite as pyrite its just that they are sometimes in very close association.
One confusing aspect is that gold found in host rock containing sulphides can have free gold, gold in association with sulphides, and gold right in the sulphides. For a panner finding gold from that kind of ore they are panning the "nuggets" and will never see the ultra fines.
It would be unfair to characterize the iron pyrite as the host when in fact many of the sulphides can be found in association. Often as a mixed bag of sulphides as during formation the sulfur was complexing with different metals. Arsenic, Iron, Copper etc and any and all of them could be associated with gold.
The idea of roasting has merit and has worked to some degree in the past though it was not so good until chloriation and cyanide came into wider use. Some mills did roast to break down the sulphides before stamp milling and mercury plates and the process did increase gold recovery but the mercury systems just could not get at a lot of the gold and even after roasting the ores were often a pain as they caused contamination of the mercury and both gold and mercury losses.
Title: Re: a simple test for gold in pryrite
Post by: Gotrek on July 21, 2009, 11:46:06 AM
As a simple rough field test you could carry some Stannous Chloride with you, place a drop on the rock let it wok for a bit and transfer the drop to a dry tissue.  The color purple in stain would indicate the presence of gold.

You can make a Stannous Chloride solution by adding Tin to hydrochloric (muriatic) acid and dissolving it over heat.

the solution can easily be carried in a small vial along with a droper, tissue and "Q-Tips"  Store it in a dry dark container and it should last for a few days.  But it does not keep for extended periods.  The good new is you can renew it by adding more tin to the mix.Delos Toole Free Articles (http://www.delostooleauthor.com/gold_platinum.html)

EDIT: sorry I'm not clear enough in my post.  You would first have to place a drop of Aqua regia or acid/peroxide on the sands/stone to sample to dissolve the gold (if present) then test with the stannous chloride solution.  Sorry about that.  Let me know if it's still unclear. 

May not be the most efficient way but quick and easy to carry.
Title: Re: a simple test for gold in pryrite
Post by: ClickTheYellowChick on July 21, 2009, 12:09:29 PM
As a simple rough field test you could carry some Stannous Chloride with you, place a drop on the rock let it wok for a bit and transfer the drop to a dry tissue.  The color purple in stain would indicate the presence of gold.

You can make a Stannous Chloride solution by adding Tin to hydrochloric (muriatic) acid and dissolving it over heat.

the solution can easily be carried in a small vial along with a droper, tissue and "Q-Tips"  Store it in a dry dark container and it should last for a few days.  But it does not keep for extended periods.  The good new is you can renew it by adding more tin to the mix.
Delos Toole Free Articles (http://www.delostooleauthor.com/gold_platinum.html)

Hi, GoTrek,

That Delos Toole set of articles is a neat set of resources you shared in your link.  Good Job! <-yes_>

Suggesting a stannous chloride field test for presence of gold in a sample, will NOT meet with the desired outcome, especially on a pyrite, the topic of this thread.  May I elaborate?

You are correct in your edit: Gold has to already be in dissolved, aka be in ionic form, within an acidic solution, before the Stannous Chloride protocol will work as you described.  

And if it is a sulfide you are working at trying to digest in order to test, such as pyrite is, even attempting to digest the gold trapped in the sulfide in the first place with A/R is going to present a hindering challenge before even trying to use the Stannous Chloride test.  Trying to digest gold in the presence of a sulfide is something like a Catch 22 experience.  Any gold digestion will quickly be involved in a circular-type reaction, rendering it difficult for stannous chloride to achieve a "positive identification" chemically using acid dissolved tin.

While always being prepared with a portable kit containing gold testing acids, I'm not sure I'd carry such a field kit of acids, but that's just me.

Kind regards,
Megan
Title: Re: a simple test for gold in pryrite
Post by: GollyMrScience on July 21, 2009, 12:39:04 PM
As Chick suggests you will need to get that gold into solution.
Hard to get out of doing a complete work up of grinding the sample to liberate gold,adding acid chemistry (aqua regia), filtering and then testing the solution.
It sounds way harder than it is and once you are set up for it its no big deal. The sulphides need to be handled too which is why roasting is often done first.
I have seen a couple of kits available for testing with pre made chemistry but its not that hard to make up your own.
The stannous chloride will tell you that there is gold but other than the reaction intensity there is really no way to easly get a quantitative assay.
At one point in my life I was carting around a bush assay lab capable of doing basic assays with a torch and a microscope to check bead size. I even went so far as to put together a small single dish scorifying oven. Down and dirty assays in the evenings in camp. Lots of work and eventually I just quit all the hassles and took lots of samples and either took them back to my own lab or sent them off for commercial assay.
Sample anything that does not jump up and run away. Take careful notes and take it back someplace comfy like to work on. In the bush its better to cover the ground and take the samples and not slow down for nuthin'!
Title: Re: a simple test for gold in pryrite
Post by: ClickTheYellowChick on July 21, 2009, 01:44:16 PM
Golly,

I LOVE your closing summary line o'thought...."sample anything that doesn't jump up and run away."  

EXCELLENT way to put it!   <-yes_>

That goes for pyrites, non-pyrites, quartz, granite, basalt, and about a bazillion other occurrences!

Megan
Title: Re: a simple test for gold in pryrite
Post by: PlacerPal on July 22, 2009, 12:16:46 AM
Hi Gotrek,

Well, here we go again. The Mavericks are playing in the background. ;D

A Stannous Chloride (SnCl2) field test for presence of gold in a sample, CERTAINLY could meet with the desired outcome!

Prospectors, Geologists, GeoChemists, Chemists, Lab Techs, etc. have used the test for..... well what seems like forever for me. 

One can buy a gold test kit today that can do the test very well and it is not affected by "sulphides". I know because I have
the chemicals on the shelf in my lab within 6 ft of me, I use them and I have beakers containing the test solutions waiting
for precipitation of the gold. I used the stannous chloride to test the solutions for gold which is already evident by the yellow
colour and I use the stannous chloride to test the solutions after gold precipitation to check and make sure all the gold has
been precipitated.

I could put a relatively non-toxic gold test kit together in about 5 minutes. But then I would have to write the Operators
Manual suitable to cover all types of test samples. That would take time stolen from my present effort writing instrument
installation, operating and maintenance manuals - instruments we manufacture to do chemical analysis. Maybe I will do it
when I get a "round tuit"  ;)

Getting back to the Delos Toole article and method for gold testing, the method probably worked just fine for Toole and may
others who were testing possible gold ore samples. Toole referred to testing ore concentrates, which "used to mean" to anyone
familiar with the mining industry, to be the crushed and milled ore samples ready for the leaching plant or the smelter, not
the chunky bits of rock with waste. Toole should have been more clear and specified a crushed, milled and well mixed ore sample -
the concentrate.

Toole did not carry Aqua Regia into the field which is good. He mixed small amounts hydrochloric and nitric acids to make
Aqua Regia (AR) along with the ore sample in a test tube out in the field. Then he boiled the acid/ore mixture for 5 - 8 minutes
over a lamp flame which would have driven off any sulphides as SO2 and any other gases such as the toxic NO and NO2 leaving
the leached auric gold chloride AuHCl3 in solution. Now Toole has the gold in solution and he has driven off the sulphides. We are
 ready to test the leachate for gold.


The tin chloride (stannous chloride - SnCl2) test is an excellent test for gold. Just blot some of the leachate solution onto an
absorbent material like a filter paper, a tissue, some toweling or better the thick absorbent paper fibre paint clean-up "rag" that
comes in a roll. Then add a drop of the tin chloride to the blotted area. A light pink colour - minor gold, darker pink - more gold,
heavy pink/purple colour - major gold.

The Delos Toole gold test method probably was never intended to be used to test iron pyrites which was known as Fools Gold
and usually quickly discarded. The method was intended to be used to test gold-platinum-palladium ore samples. However the
method could be revised to test pyrites for gold. The pyrites crystal samples would have to crushed and milled to a fine powder.
The powdered sample roasted to drive off the sulphides reducing the sample to iron, gold and any other precious metals if present
and then leached and tested. Caution roasting as the pyrite may contain arsenic and the arsenic sulphide fumes are major toxic g
ases at very low ppm!

Tin Chloride is dead simple to make by anyone. The Source in Canada, called Radio Shack in the USA, as well as other electronics
suppliers sell a tin solder that is 99% tin. Simply dissolve a length of the tin solder in HCl (Muriatic Acid), put the solution in a
brown glass bottle with an eye-dropper combination cap. Add a few inches of the tin solder to the solution to compensate for
deterioration and then off to the field to do gold testing with the tin chloride! Oh yes, take along the sample crusher, the leachate,
the glass test tubes, blotting paper and a mini butane torch for a heat source. If testing iron pyrite, take along a roaster too - a
stainless steel tablespoon with a wood handle to hold the pyrite/gold sample in the flame until the sample turns black and stops
smoking!

Testing and iron pyrite crystal sample for surface gold "may" have merit. I would certainly like to try it myself. If I come across
a sample of iron pyrite I will try it and report back. Hmmm.... I used to live on the CDN shield, greenstone belt and iron pyrite
as well as chalcopyrite was everywhere. Everyone had huge pyrite crystal samples at home and at school. Maybe time to call in
some pay back time debts. Besides maybe the old fart classmates and neighbours would like to advance prospecting science.
A good winter project!

The Delos Toole gold test method in the referenced link was written in 2000. Much has changed since them especially for the
procurement of chemicals. HCl (Muriatic Acid) is easy to get at the local hardware, but Nitric Acid is on the "banned list" and
impossible to get unless one has a business, is a University, Research Institute, the  gov, etc. and then documents and permits are
needed. The Delos Toole method should be completely rewritten to update it, include alternative and better less toxic leachate,
better sample preparation and a section dealing with pyrites and chalcopyrite samples. Maybe if I get a "round tuit" I will rewrite
the test if someone else does not do it!

 :)
Title: Re: a simple test for gold in pryrite
Post by: GollyMrScience on July 22, 2009, 02:02:49 PM
As you can see - more than one way to skin a cat.
Pals post does raise an important  point that you needs to be remembered. Different people use different terms for the same thing and it is important to make sure you are talking about what you THINK you are talking about.
Case in point:
Pal said "Getting back to the Delos Toole article and method for gold testing, the method probably worked just fine for Toole and may
others who were testing possible gold ore samples. Toole referred to testing ore concentrates, which "used to mean" to anyone
familiar with the mining industry, to be the crushed and milled ore samples ready for the leaching plant or the smelter, not
the chunky bits of rock with waste. Toole should have been more clear and specified a crushed, milled and well mixed ore sample -
the concentrate."

Very good point as people who work in the industry use terms like "processed sample"and "concentrate sample" etc to mean different things.
A processed sample might mean concentrated by physical or chemical means or it could mean just run though a grinder.

Some call it a treated sample if chemistry is used and concentrate if physical. Or you can have a multi step processed sample with concentration and treatment.
Whatever the terms applied it is important that you be able to translate whatever result you get back to the original sample for a realistic evaluation of mineral content. It is also very important to know what the heck the other guy means as he describes what he did to the ore and you the same for him.
Title: Re: a simple test for gold in pryrite
Post by: Yukon Digger on July 22, 2009, 10:07:30 PM
I've sometimes had good luck crushing the sample, putting it over a fire/coals in an old pan for a 1/2 hr or so then cool it, recrush it fine and pan it out.  A 6 inch chunck of 4" dia steel pipe with a plate welded on the base and a 3/4 " steel rod for a crusher is fine. Those old Canadian Shield prospectors had pans at camp but never for placer. Glad I got to work with some of them when I was cutting my teeth.

I'd forgotten about the SnCl2 thing. This is  a great site for learning new stuff and for jogging the old memory banks.
Title: Re: a simple test for gold in pryrite
Post by: PlacerPal on July 22, 2009, 11:02:12 PM
I've sometimes had good luck crushing the sample, putting it over a fire/coals in an old pan for a 1/2 hr or so then cool it, recrush it fine and pan it out.  A 6 inch chunck of 4" dia steel pipe with a plate welded on the base and a 3/4 " steel rod for a crusher is fine. Those old Canadian Shield prospectors had pans at camp but never for placer. Glad I got to work with some of them when I was cutting my teeth.

I'd forgotten about the SnCl2 thing. This is  a great site for learning new stuff and for jogging the old memory banks.

Yeah,the pans were used to make Bannock.
Bannock was the staff of life for a prospector!

A prospector's grubstake had these main ingredients.
Flour, salt, baking powder, lard.

Here is an original recipe we used:

    *  6 Cups of flour
    * 1 Cup of lard - bacon or bear fat
    * 3 Tablespoons of baking powder
    * 1 Tablespoon of salt
    * 3 Cups of water

Knead well and slowly cook over a low campfire in the pan, turning over once.

Then we met the Cree who enhanced the recipe:

    *  6 Cups of flour
    * 1 Cup of lard, bacon or bear fat
    * 3 Tablespoons of baking powder
    * 1 Tablespoon of salt
    * 2 Cups of blueberries, cranberries, raspberries, strawberries, whatever was in season
      or in the winter currants or raisins (Possibly an enhancement from making Pemmican)
    * 3 Cups of water

Hmmm.... I wonder if somewhere there still are Bannock baking and tastings contests?

 :)
Title: Re: a simple test for gold in pryrite
Post by: GollyMrScience on July 23, 2009, 10:37:24 AM
Ahmen on Bannock!!!!  {-applause-}

Love the stuff. For something so basic and easy it is so versatile. Everything from dessert bannock to basic bread to a kind of dumpling.
I have even had bannock with pemmican rolled in it like a pop over.
Make it with or without baking powder - use grease from lard, bacon or bear or use oil - add berries or dried fruit - mix the dough in a pot -pan -or right in the bag of flour.
Bake it on a peeled and fire treated stick, fry it, dutch oven it, bake it in a pan or flat rock tilted towards the fire, drop it in stews and soups like drop dumplings, deep fry it, bake it like ash cakes.
Use whilte flour, whole wheat, cat tail flour -both pollen and root, you name it.
I make it in the bush and I make it at home.
We should start a bannock thread.  <-good_>  <-yahoo_>
Now I'm hungry.
As for the bannock contests I know they still have them at the mountain man black powder get togethers. Ah the smell of brimstone, bacon and bannock in the morning mmm mmm mmmmmmmmmm!



Title: Re: a simple test for gold in pryrite
Post by: ClickTheYellowChick on July 23, 2009, 10:52:50 AM
Grab a couple handsful of worker drones, squeeze 'em vigorously atop bread before popping into mouth. 

YUMMY honey glaze!

YC
Title: Re: a simple test for gold in pryrite
Post by: PlacerPal on July 25, 2009, 10:48:40 PM
It would be very nice to find a field test for gold &/or silver in pyrites and sulfides.
Any suggestions ?
Thanks for your assistance.
Stan

Okay, here you go. I love this stuff!

Two apparent types of iron pyrite samples were leached with a simple leachate and
the leachate tested with tin chloride (stannous chloride or SnCl2)

The first iron pyrite sample was porous and consisted of many small crystals. Source unknown

The second iron pyrite sample appeared to be one solid crystal typical of the CDN shield.
Again source unknown. Got both samples at the local rockhound shop.

The samples were not crushed and leached whole as found. Leach time 1 hour at 60 Deg C
Crushing the samples made no difference in the test results.
The tin chloride was a freshly prepared solution from pure tin.

The porous iron pyrite sample tested some some gold and a trace of silver.

The solid crystal iron pyrite sample tested no gold and no silver.

To better show how silver can show up in this test, I included and image of
testing done on black sand concentrates.

Please see the images below for visual results.

Conclusion is the tin chloride test for gold (and silver) is still a good field test.
However, the tests are probably better done "at home". Its "kitchen chemistry".  ;D

Title: Re: a simple test for gold in pryrite
Post by: batholith on August 27, 2009, 06:03:04 AM
Wonderful info, Thanks all.

Just wondering if someone could suggest a leachate other than Aqua regia. I am not too comfortable with that (call me chicken!). I've read about some iodine based leachates but haven't been able to find any specifics. Essentially, the problem with the leachate is what has kept me from trying the SnCl test.

Regards,
Batholith
Title: Re: a simple test for gold in pryrite
Post by: batholith on August 30, 2009, 03:24:43 AM
A further thought, might using an Iodine based leachate interfere with the SnCl test being that it is a Halide?
Title: Re: a simple test for gold in pryrite
Post by: PlacerPal on September 18, 2009, 10:10:23 PM
Wonderful info, Thanks all.

Just wondering if someone could suggest a leachate other than Aqua regia. I am not too comfortable with that (call me chicken!). I've read about some iodine based leachates but haven't been able to find any specifics. Essentially, the problem with the leachate is what has kept me from trying the SnCl test.

Regards,
Batholith

What about hydrochloric acid and bleach? I've got a batch of cons soaking in this now. will let you know how it goes.

pretty sure this would also work with the sncl test once the free chlorine is evaporated or neautralised with sodium thiosulfate? i'm no expert on this stuff

Seems like you are using the Halox bleach method. That's a tough leach to manage as you need to keep the
ORP very high at about 900 mv. ORP goes too low (400) and no leaching.

The tin chloride (SnCl2) test will only react with the gold chloride. If you can get the gold leached to gold chloride,
then the tin chloride test will work fine.

Please let us know how the leaching and tin chloride testing goes.
Thanks.

 :)