How to test pyrite for gold? How long to roast? Pyrite Weathering Process?

[tonofsteel]

I found this and crushed/panned it. The flakes floated around like mica or pyrite. From what I know I would have to say it is mica flecks in the sample.

I have heard of the different treatments for refractory ore like:
- Aqua Regia + Stannous Cloride
- Milling/flotation and leaching with Cynaide
- Crush then Roast ore in pan with salt and throw ore into cold water then mill after

Is it possible to test the gold content by using a torch to heat the sample and then crush and pan? Or does it need to be roasted in a pan for hours and then thrown into water?

If the torch burns off sulfur then shouldn't there be a noticeable change to the flakes in the sample?


Reading about pyrites it sounds like they should weather out over time. The sample above was found in a wet area and I left it in water for quite some time since I forgot about it. The rusty stuff looks to me to be weathered but the shiny stuff does not look weathered at all. If there was copper wouldn't it be turning green or rainbow colors. If iron the shiny flakes should be rusting.

Are there any tricks to quickly get a bit of a better idea/confidence that it is worth going all lab on this? I don't want to contaminate any cooking heat sources with any nasties that might come off of a sample and don't want to go and buy one if this line of inquiry is a total waste of time.


If there is gold in pyrite would it behave any differently in the pan? I would think it would still easily wash around but maybe a tiny bit lazier than pure pyrite? Also pyrite with gold in it would shatter/flake like pure pyrite since gold is within it and not an alloy?

I come across heavy pyrite in samples but have dismissed it so far except for one sample sent in for assay. Just wondering if there is a quick way to get even a bit more confidence to pack out a sample rather than pass it over.

 

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[tonofsteel]

Can use a mini torch to blast the surface and any pyrites will burn away. (Outside + upwind, gloves, safety glasses etc) Have to heat until the particles on the rock get red hot. If they do not burn away then not pyrite.

No, I am not planning on processing any ore. Just out of curiosity looking for a way to test if there is gold in the sulfides that is relatively easy/quick and does not involve lots of dangerous substances or bulk heating of potentially harmful ore.

Tried it on a sample (not the one above) and some sulfides burnt out but there is a golden color metallic looking substance that will not burn even when red hot. It is not gold though. Looking through microscope I see a couple of spots that might be gold.

Seeing how the sulfide spatters when it burns I wonder if there was embedded gold if it would be left there or shoot out in the spatter.

Going to further test by crushing a small sample and then torching in a steel dish/bowl of some sort and then pan.




Have seen it a few times but could never find an answer, what does a change in color from yellow to red mean?
The below pictures are of a different sample but notice weird things when trying to torch a rock.







The last pic is of a different sample that started like the first pic, all yellow. After a burn it now shows the red and gold colored particles. Not gold though, had an assay with the material.



This is what real gold looks like through this cheap crappy microscope (for reference)

 

[KevinInColorado]

Looks like oxides of iron after you burned off the sulphur

 

[tonofsteel]

Thanks for the tip! Makes sense, I will go with that as the most likely explanation.

From another post:

If, after following RTRs advice, you get nothing, please realize that much of the gold bearing ore processed by mines today has no visible gold. That is why professional miners utilize assays.

Time for coffee.

I keep hearing and learning about non visible gold but as far as I can tell this means gold that is inside the structure of a pyrite grain/crystal. Is this correct or are there other ways gold is invisible?

I know the two default methods to evaluate ore are to crush and pan to check for free mill gold and to send away for assay to find total gold content (including the non visible)

But I also see all these crazy ducks out there doing alternative stuff to extract gold. It sounds like these methods are frowned upon? A certain amount of the frowning is due to safety issues as roasting/heating ore that has arsenic or other very bad for you compounds can cause for some serious concerns.

The part that is confusing is that while the ore contains non visible gold it can become visible gold with various treatments. So when I hear about roasting pyrites and quenching them to shatter the structure and release the gold or to smelt the pyrites down using different flux/collectors/methods does this mean they are going after this invisible gold? Or was this free mill gold?

Reading into it some more the weathering of pyrite overall is:
Pyrite + Oxygen + Water => Ferric Hydroxide (yellowboy) + Sulfuric Acid

Which would lead me to believe that if there is invisible gold in the pyrites it would be released upon weathering.

As far as I can tell if I want to test for invisible gold I would need to collect the pyrite using a miller or shaker table set up appropriately and then either roast/quench/classify/pan or oxidize/reduce in a furnace with the right fluxes and crucibles with a collector metal if necessary.

 

[tonofsteel]

From another thread while researching:

ALL pyrite has some level of gold in it. The problem is how to get it out and is it economical feasible to do so? Iron pyrite is hell on nitric acid, tends to use up the nitric rather quickly when trying to dissolve the host rock.

Interesting, I have some samples that are chock full of pyrite. Pyrite will be lighter than gold but heavier than pure pyrite, which is key in setting up the table for separation. Any free mill gold will come out on top and then there should be a band of pyrite/sulfides down somewhere depending on what is in the sulfide. Might be best to run for gold first then fine tune to pull the pyrites out.

 

[arizau]

Thanks for the tip! Makes sense, I will go with that as the most likely explanation.

From another post:


I keep hearing and learning about non visible gold but as far as I can tell this means gold that is inside the structure of a pyrite grain/crystal. Is this correct or are there other ways gold is invisible?

I know the two default methods to evaluate ore are to crush and pan to check for free mill gold and to send away for assay to find total gold content (including the non visible)

But I also see all these crazy ducks out there doing alternative stuff to extract gold. It sounds like these methods are frowned upon? A certain amount of the frowning is due to safety issues as roasting/heating ore that has arsenic or other very bad for you compounds can cause for some serious concerns.

The part that is confusing is that while the ore contains non visible gold it can become visible gold with various treatments. So when I hear about roasting pyrites and quenching them to shatter the structure and release the gold or to smelt the pyrites down using different flux/collectors/methods does this mean they are going after this invisible gold? Or was this free mill gold?

Reading into it some more the weathering of pyrite overall is:
Pyrite + Oxygen + Water => Ferric Hydroxide (yellowboy) + Sulfuric Acid

Which would lead me to believe that if there is invisible gold in the pyrites it would be released upon weathering.

As far as I can tell if I want to test for invisible gold I would need to collect the pyrite using a miller or shaker table set up appropriately and then either roast/quench/classify/pan or oxidize/reduce in a furnace with the right fluxes and crucibles with a collector metal if necessary.

Some gold is not associated with pyrites, just microscopic as in Carlin-type gold and those deposits are some of the richest in the world. https://en.wikipedia.org/wiki/Carlin–type_gold_deposit https://en.wikipedia.org/wiki/Carlin–type_gold_deposit
Another link that kind of explains gold associated with pyrite. Rcovery of gold in pyritic ores