# Iridium ore or XRF error



## tomrod (Dec 8, 2016)

I have an ore sample that reads 6 percent gold, 37 percent silver and 39 percent iridium with a Bruker XRF. I see a lot of silver but the the iridium content seems incredibly high. Is there a good place to get this tested?


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## Lou (Dec 8, 2016)

It's in error.


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## goldandsilver123 (Dec 9, 2016)

Lou said:


> It's in error.



We get a lot of people coming to us thinking that their material is high in precious metals because they made a XRF analysis.

Do you know why the XRF is so off? I know that without the precious metals software, handheld Thermo sees gold as tungsten. Is it a software "problem" or does it need something like more photon energy? 

They do not believe that the analysis is wrong, so we just say we're not interested..


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## anachronism (Dec 9, 2016)

We use XRF a lot. Lou's points are extremely valid because from experience you have to ensure that the conditions are right to give you a correct reading. for example there are a lot of items that only read "true" if you keep a 100 percent copper base behind it to remove a lot of the spurious readings. Otherwise it is easy to get all excited over nothing.


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## nickvc (Dec 10, 2016)

The key to using an xrf gun or xrf analysis well is to understand its limitations and plenty of practice on known materials which the xrf can and does get wrong, having said this they are a fantastic tool if used correctly.


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## Lou (Dec 10, 2016)

I'm probably a broken record like usual but analytically speaking....context context context. It's all what's in the sample and how it's prepared. 

As for XRF, it can be any number of things:

1. The instrument isn't calibrated or warmed up properly,
2. The analyte of interest is much less in concentration (o not present to detection limit) relative to a matrix or bulk contaminant that has a similar spot in the fluorescence spectrum. Most handhelds use algorithms designed for standard materials (i.e. Karat or regular old copper alloys) and operate in modes. If the energy-dispersive instrument is in the precious metals analyzing mode, it can attribute W as Au or Ta (or Se) as Pt.





On their wavelength dispersive freezer-sized instruments, a well known smelter uses copper disks samples from heats (while taking a shot sample for fire assay) that have been milled flat so that an irregular surface doesn't goof up the results.


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