XRF scope

[Laz7777]

I sell my placer fines to Sierra Gold and Coin in Grass Valley. they have an xrf scope and I usually ask for them to scan my fines for reference.
every time the analysis comes up with something different for gold content and for alloys. one time it has even registered for iridium, which in my reading isn't a possible alloy of gold.
I think that Tolumne Todd has one, my basic question is this: how can there be accuracy when you're looking at thousands of tiny particles of gold?
I have my doubts.

 

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[Tuolumne]

Yeah the spectrum analysis will look for elements that match the data base. So sometimes it may say 1% something wierd but when I bring up the spectrum it may or may not line up with the real elemental marking on the spectrum graph.

If its all from the same location, melt it into a button or better yet a pointed triangle
Then retest and you should get more reliable reading of the homoganous button or the triangle you will see heavier elements on bottom and the lighter stuff is on top.

If you have super fine gold get your flux mix down right and sometimes adding heavy copper so the gold can latch onto something may help too


Best results are over one minute exposure and you will get more accurate zap

The XRF only goes in 4microns, human hair is 100 microns.
I can put small amounts, like fly poop size and get a good readout.
Otherwise you put it in small plastic bag and take 30 10 second shots and take average reading

My unit is made for field portability so it's very fancy, some models are just for simple base metals, but mine does every heavy element besides the first two lines on periodic table.

Gold plate or gold filled can look like 100% gold or give weird Karat reading
My office everything is guilty until proven innocent
When in doubt file and retest.

Homogenous bullion or stamped jewelry is easy to tell if it's off or red flag reading.

Nuggets and placer are harder to get down unless you fire assay.
But I know from XRF then melting and sending to refiner I'm only off by 1-2% on the fine placer

A specimen or nuggets with matrix should be sold at premium and not melted
Most small placer already has many impurities knocked off so it's usually 22k or better.
Alot of it is electrum,in my area too if it's chunky
But if you had Pt or any previous metals you would know for sure and that would spur you on to get fire assay or you can use XRF for leverage to get better price if your reading is high

My XRF has built in camera with target area illuminated so I can see exactly a pinpoint in the middle of the window which is size of a dime, so it's already a small target area.
My Olympus model is a 2011 model, 4watt. What type does he have? Mine looks like a radar gun not a scope- r u sure that guy has a $20k XRF- 1% of coin shops have this so if he does it's cool, only know one other place in NorCal w Xrf like mine

 

[Laz7777]

thanks for all the info todd.
I do not know the brand of scope my buyer has. it's a rather large radar gun looking thing. the only thing I can remember about it is that it's yellow and the scanning process has a red laser line going across the target, like a bar code scanner.
typical scanning time is always just a few seconds, on the monitor I always see the phrase "gold plate not detected", then underneath the readout for the composition, with a smaller area across the top that shows trace elements.
so, basically you're saying that placer fines might not be getting an accurate reading?

 

[Tuolumne]

get him to do a longer test, I can set it for ten minutes when its in the housing and hooked up to the computer, but really try one minute blast and you will get better reading than the hand held way. The computer innovex software im running also has better read out than the hand held screen. We always keep it housed unless we are doing big silverware or big items not fitting the xrf housing unit. Just take multiple reading and take the mean, thats what I do with customers, its fair if they dont want to melt it into a button. Also it depends on how clean your material is, you could be picking up iron, Pt group metals, zircon or any heavy element in that xrf scan, so the cleaner your sample the better.

But in general your fines are higher K than course nugs so its already in your favor, just keep in mind that the read out hes giving you is +- .5%, half a percent, so with longer blast it could go up or down from there......

 

[Laz7777]

the first time I saw him use it, I had a large batch of mostly flour and it read at 96%.
from the same stretch of river, it read as low as 91.

my thought on the accuracy is the last time it showed iridium, a PMG and not found with gold and it came up with over 3% (in further reading, gold is 40x more abundant than Ir)

my fines are very clean even though I use nothing more than a pan and magnet to clean.

 

[Tuolumne]

yeah you need the computer screen that has the spectrum, I can click on the Ir and if the peaks dont match then its a false reading.

The xrf has a data base and its computer is searching for matches, 3% is alot of Ir so I would do a longer blast for sure but the spectrum graph is needed to rule out the Ir.

But remember, some of our california gold DOES have Ir especially in Placer deposits!! so I think your lucky, its more rare than gold too lol! Bring it to my office and we can test all day......

 

[Laz7777]

where would the Ir come from? in reading about it I found that it is associated with copper or nickel deposits.
copper is definitely associated with gold, but most XRF readings I've had never showed copper.
I'd always have silver, some iron (not from black sand) and some lead, especially with amalgam.
and oh, selenium with amalgams as well.

I'd love to visit, if I'm heading through your way on the way to Nevada county, I'll contact you.

 

[Tuolumne]

just google gold, iridium and california and you will have tuns of info, lots of the Pt group will be with gold in placer form...... there was a great article in one of the gold magazine imcj about it too

 

[Laz7777]

I found this:
https://www.mindat.org/loc-26699.html

which is downstream from me.
I'm wondering if I'm not getting seperation from the iridium, rather than it being alloyed with my gold. I have seen small amounts of a dull silver material, -30 mesh.
gravity seperation may not be viable, due to a higher specific gravity on the Ir.
too bad Ir is only $745/.ozt current spot.