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A Basic Intro To Xrf Guns For Prospecting


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Great introduction, Jason.  I was familiar with using microprobe analysis with electron microscopes to identify elements in microscopic targets such as plankton shells for research back in the 80’s, (it was basically the same as XRF, but not a very portable version), and am amazed at seeing how portable the technology has become!  I don’t need a hand held XRF gun, but when those GPXRF 8000 mono coils are finally released to the public for doing lead discrimination, I will be one of the first wanting to pre-order it! 😁

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I've been thinking about trying to build a homebrew scanning electron microscope for like 15 years. One of those things that will probably always be a month off in the horizon and never get around to though. Like cleaning out my garage. :smile:

I was in school in the early 2000's and even then XRF's were totally beyond the range of affordability even for the university so we never could play with them, though we did have a SEM which was cool. The last 5 years or so have really brought units that could be used for prospecting onto the used market finally. It really feels like a Star Trek tri-corder type device to me in many ways, sorta unreal.

Discrim only works to a whopping 1/100th of a inch or so though unfortunately on the GPXRF 8000. :laugh:

 

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51 minutes ago, jasong said:

I've been thinking about trying to build a homebrew scanning electron microscope for like 15 years. One of those things that will probably always be a month off in the horizon and never get around to though. Like cleaning out my garage. :smile:

I was in school in the early 2000's and even then XRF's were totally beyond the range of affordability even for the university so we never could play with them, though we did have a SEM which was cool. The last 5 years or so have really brought units that could be used for prospecting onto the used market finally. It really feels like a Star Trek tri-corder type device to me in many ways, sorta unreal.

Discrim only works to a whopping 1/100th of a inch or so though unfortunately on the GPXRF 8000. :laugh:

 

Oh man, you want to make a SEM too?!  I saw that project on hackaday and it was on my bucket list too, but have you seen the scanning tunneling microscope? That would be a really cool build, looks easier than the SEM also.  Pretty cool to be able to get a image of atomic structures up close like that, hu?

 

You have to see the author's image gallery, too - examples of gold atoms and crystals there too:

https://dberard.com/home-built-stm/image-gallery/

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That's cool, I saw a similar one except it was on a forum back in 2003 or so that dealt with building coilguns and railguns and a guy posted a SEM DIY tutorial. These newer ones look like better designs, and easier. I actually have most the stuff in the SEM guide other than the HV Arduino shield, I even have that finite element analysis program they are using, it's not really needed though.

I've been thinking about making videos again except not prospecting/detecting since so many people are making those nowadays. I thought it'd be fun to build amazing stuff like this that few have heard of, out of stuff laying around. My first project is going to be building a laser out of common household trash I find laying around McGuyver style (semi cheating since I've done this before out of 50% trash basically so I have a rough idea ahead of time what to look for), then I might look at a microscope.

Those crystalline gold STM photos are cool. I wonder if cryptocrystalline structure pattern analysis could be used to track/match placer gold to it's lode source. I don't think anyone has ever studied that, mostly they just do elemental fingerprinting.

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Great post and some really good information with the reading of this subject.

At one time I had given it some thought about one of those, but now see the reasons not to get one. The way I have banged up and dropped some of my tools, I would have it out of calibration in no time.

I think I will just learn these detectors my grandfather left me and be happy once I can find time to get out and hunt.

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Hi Jasong

Our company owns an olimpus vanta. I have also used the Nitton gold3+ too. It costs $50 000 aud + extras so it a bit out of reach of the hobby prospector.

For gold exploration you need the Rhodium xray tube as the accuracy with the other tubes (tungsten or silver) is very low on Au and PGM's. And a lot of the gold areas we are chasing have mostly free gold and little of the pathfinder elements accociated with them. Although the pathfinders are always elevated near the deposit in relation to the backgound norm for the areas, they may only have a small halo and this may only be slightly elevated. This is probably due to the large amount of water we get in such a little time here with our tropical wetseason. Which can render the pathfinders of little use to the explorer up here in parts of northern Australia. But in the more arid areas they are of much greater use. Our xrf has the gold and pathfinders suite but we also got the rare earth and base metals suite's too. But each program is expensive and an added extra.

A suitable xrf is an essential tool in a modern technologically advanced exploration company. We have developed 2 special ways that we prepair our samples which increase the accuracy of the scanner and allow it to accuratly detect down in the lower end of its recomended minimum ppm. Our results closely mirror our assay results since developing these methods. Which further increased the usfulness and reliability of the xrf results for field use.

The scanner saves the savvy user 1000's in assays and weeks in waiting time for assays which can be a real pain if you are in a remote location, as you may have to return after good results to resample a hot area further. It is much easier to be able to make on the spot decisions on the viability of further samples and when a hot area is discovered you can concentrate your efforts on that area rather than just taking grid samples and sending them to assay. 

There is also another technology that is of use to the modern gold explorer it is called LIBS. LIBS as an Emerging Analytical Tool for Mineral Exploration - SciAps
https://www.sciaps.com/newly-published-research-libs-as-an-emerging-analytical-tool-for-mineral-exploration/

I am are looking at ways of increasing libs usefulness in gold exploration. Its limiting factor is that it only scans a very small area which can give you inaccurate results but Im trying to addapt the same technology but from a different sector where they use it in a different way that should prove very useful when addapted to exploration.

 

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Nice writeup, Jason.  The one thing you didn't emphasize (at least I didn't see it) is that for typical materials the depth the measaurements are made is quite shallow -- effectively surface effects for many materials.  It varies greatly with atomic number of the material as well as the energy of the impinging X-ray.

Most people are familiar with X-rays due to their medical diagnostic applications, particularly in dental use.  Those tend to be X-rays at  higher energy (approaching 100 keV).  Also skin and bone are composed of low atomic number elements and thus easier for X-rays to penetrate.  If you recall seeing dental x-rays, the metal fillings (e.g. silver amalgam from the 'old days') show up clearly but nothing behind them.  Another 'advantage' of medical x-ray diagnostics is that they are monitoring transmission only.  (That's why they put the detector -- used to be film -- in your mouth!)  The XRF guns work by transmission + absorption/excititation + de-excitation + retransmission, with each step robbing the process of efficiency.  And then they have to sort out signal from noise and measure the energy of the few (relatively speaking) relevant signals.

There are parallels between how these guns work and how a standard metal detector works.  The strength of the magnetic fields from the target in the ground (what the detector relies on to sound off) is tiny compared to the magnetic fields the detector transmitted initially.

It's pretty impressive how well these hand-held devices work, given all the sophisticated components (including software) it takes to run them.  The progress made in the last decade or so is analagous to the evolution of the hand-held computer (aka cell phone) from the desktop computer.

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