Looking for U (traces?) by mapping?

[Julien]

Hi there,

I was in touch recently with a company that is looking for (trace) U in sand sample. They have no idea whether the uranium is present as UO2 particles or "hidden" in some sulfide or oxide, aka in trace amount. I am tempted to simply run a map through this sample to look for uranium, but I'm worried that a x-ray map might not reveal anything if the uranium is only at a couple (100?) ppm level within some particles... Did anyone already do such a "particle analysis" using mapping? What threshold for the detectability did you reach? If so, did you effectively run a map, or directly went from grain to grain to search for trace amount of uranium (or other element)?

Thanks for your help!

Julien

[Karsten Goemann]

Hi Julien,

Do you have access to an (usually SEM-based) automated mineralogy technique like MLA? If so, you could perform a quick automated search for small grains of uranium minerals. This is normally using a combined BSE/EDS approach which can be much faster than pure x-ray mapping in terms of spatial resolution and coverage. If not, you might be able to find them using BSE imaging as they're probably quite bright. One of our SEMs is set up to collect stitched BSE maps of whole samples quickly at fairly high resolution which we can then interrogate for "bright spots" for example.

If that doesn't return anything the next thing I'd probably do is a quick targeted search by EDS and/or WDS for a U peak in different minerals. If there are things like phosphate or carbonate minerals or zircons, certain oxides... in the sample they might be more likely candidates.

If the U is present as trace element in certain minerals it's probably difficult to find by WDS mapping within reasonable timeframes. Even targeted spot analyses by EPMA might be quite a bit of work unless you have U trace methods ready to go. It might be easier to do that by LA-ICP-MS?

Cheers,

Karsten