Can some one assay a small pyrites sample ?

[Goldfreak]

Have some pyrites that is of interest that I found in South Australia mainly in chunky cubic form (see picture below) from under ground. This may not contain any gold. Also have anouther sample from north qld that I know has some gold value. Just wondering if any one does small assays of pyrites at a reasonable cost or if its worth getting the gear and doing myself ?

 

[XLOOX]

Depends what you think is a reasonable cost - a few hundred bucks per sample ?

Doesnt sound reasonable? well if you want to do it yourself then you could grind it to powder in your dolly pot, heat it in a carbon crucible with a butane flame until all the sulfur is gone, cool, grind it again, dissolve out the iron with brick acid, filter ,dissolve out the silica with Alubrite, filter, wash with water, dry, then put back in the crucible with flux and heat to 1300C until you have a prill, which will be so small that you cant find it to weigh it and your scales wont go that low anyway.....

No way that DIY fire assay by a 1st timer who is not a analytic chemist will deliver any result worth anything so suggest that as first step you see what commercial lab prices are but the sample size you show though will be too low for most labs to take.

https://www.northaustralianlaboratories.com/serviceshttps://www.alsglobal.com/en/geochemistry

 

[Hawkear]

Have some pyrites that is of interest that I found in South Australia mainly in chunky cubic form (see picture below) from under ground. This may not contain any gold. Also have anouther sample from north qld that I know has some gold valueView attachment 9788. Just wondering if any one does small assays of pyrites at a reasonable cost or if its worth getting the gear and doing myself ?

Can the SA museum help with that?
I had occasion to ring the Victorian museum about something similar and they were very eager to help people like us.
They were happy to assist with mineral identification questions in return for information about the locality of the find as it helps them build up a mineral library of the state. You are not obliged to disclose "secret locations" but disclosure of a general locality should be a reasonable expectation.
I would be surprised if they wouldn't also have an XRF machine that can do an assay quite quickly to determine if the pyrite is auriferous.
One thing they said was that the specimen must be delivered in person as they do not encourage sending potentially dangerous substances by post.
Another was that due to other tasks they could not guarantee when they would have the time to complete the identification.
So perhaps give the SA museum a ring.

 

[grubstake]

I would be surprised if they wouldn't also have an XRF machine that can do an assay quite quickly to determine if the pyrite is auriferous.

Would that even work? My understanding from Kalgoorlie experience is that gold in pyrites is in the form of nano-size particles inside pyrite crystals. Hence the use of roasting to break down the pyrite crystals so that the gold can then be recovered chemically.

 

[mbasko]

Would that even work? My understanding from Kalgoorlie experience is that gold in pyrites is in the form of nano-size particles inside pyrite crystals. Hence the use of roasting to break down the pyrite crystals so that the gold can then be recovered chemically.

Yes & No.
Depends on the grade of the sample.
I'd assume lab based fire assay would still be the better of the two.

Olympus Industrial Resources:

XRF Analyzer for the Detection of Gold​

It is common knowledge that handheld XRF analyzers do not support direct low level measurement of Au in geological samples (e.g., low ppm and ppb). The lab-based fire assay technique is commonly recognized as the method of choice for Au analysis. Au L-level X-ray lines are located in a very crowded area of the X-ray fluorescence energy spectrum. In this part of the spectrum, interference from other elements (e.g., As, Zn, W, and Se) can yield a false-positive Au determination.

Direct measurement of Au by XRF can be achieved in specific cases such as high-grade (> 5 ppm) quartz vein environments (relatively interference free) or within refined Au products (where Au is present in very high concentrations).

 

[Hawkear]

Would that even work? My understanding from Kalgoorlie experience is that gold in pyrites is in the form of nano-size particles inside pyrite crystals. Hence the use of roasting to break down the pyrite crystals so that the gold can then be recovered chemically.

Shouldn't make any difference as XRF is a process that works at the atomic level and would be independent of particle size.
In fact larger particle size could be a problem if irregularly spaced and sampling measurements would need to be done over multiple sites to ensure that irregularly spaced particles are accurately represented in an overall average.
XRF machines are manufactured to various levels of accuracy and speciality for the elements to be detected. Laboratory based XRF machines such as used by institutions such as universities, museums etc. can have much higher accuracy levels than the smaller and less expensive handheld XRFs.

 

[XLOOX]

Arsenic(As) is extremely closely associated with iron pyrites often at a level 10,000x the gold level & if it is present that will overwhelm the gold signal for XRF. No harm in trying though but wont know for sure if the reading is a false positive or not until do a fire assay.

Also it is all a bit moot as Goldfreak wont be looking to start a mine based on 2 sugarcube sized samples , I think he is just curious as to what his nice specimens contain.

 

[Goldfreak]

Thanks for the info. I will make enquiries at the Adelaide museum. I have more of the material from SA in that picture but still only about 500g. No idea how much they would need ? The stuff I have from Queensland are sulphide heavies from supposedly ( according to trove and other research ) rich ore and is almost all still hidden in a house in Cairns that has since been sold. Not sure how I can get that back with out coming across to the new owners as a weirdo or dealer wanting to retrieve a big bag of something lol. Thanks to everyone for sharing their thoughts.

 

[Nap.in.Cbr]

I would suggest using a lab such as ALS, SGS, or OSLS. The minimum sample size is ~35-50g depending on what you want. Assay costs are pretty reasonable in my opinion. We use all 3 labs at work. (I'm a geologist for a mining company) My favourite is ALS. Attached is their fee schedule.

 

[XLOOX]

So total cost would be something like
BAT01 Admin $42.90 per batch
+ for each sample:
LOG22 $1.75
DRY21 $1.30
CRU32 $4.05
PUL31 $7.85
Au-AA25 $22.45
or (Au-GRA21 $33.75) depending on grade

so looks like $43 per batch + $40 per sample. thats really great and I am amazed ALS will do that price for a one off customer with. asmall number of samples. !

 

[Goldfreak]

So total cost would be something like
BAT01 Admin $42.90 per batch
+ for each sample:
LOG22 $1.75
DRY21 $1.30
CRU32 $4.05
PUL31 $7.85
Au-AA25 $22.45
or (Au-GRA21 $33.75) depending on grade

so looks like $43 per batch + $40 per sample. thats really great and I am amazed ALS will do that price for a one off customer with. asmall number of samples. !

Sounds like a great deal

 

[Nap.in.Cbr]

So total cost would be something like
BAT01 Admin $42.90 per batch
+ for each sample:
LOG22 $1.75
DRY21 $1.30
CRU32 $4.05
PUL31 $7.85
Au-AA25 $22.45
or (Au-GRA21 $33.75) depending on grade

so looks like $43 per batch + $40 per sample. thats really great and I am amazed ALS will do that price for a one off customer with. asmall number of samples. !

Yeah they're great. That is just for gold. If you want mor elements it's additional cost.
The biggest issue for us is that there's a large backlog due to strong demand. So be prepared to wait 6ish weeks atm (at their Orange lab)

 

[Goldfreak]

Putting together anouther sample. Harder to find than I thought though because the gravel from the drill rig was pumped onto an area a few years ago which is now over grown with grass. Kids like the crystals ( one looks like a diamond but unlikely ) and interestigly the pyrites hasnt oxidised on the surface in that time.