U in coal and minerals

["Karam, Andrew" <Andrew_Karam@URMC.Rochester.edu>]

Good question (which is, I know, a poor answer).  I would guess that many of
these instances are site-specific.  For example, water flowing over
uraniferous igneous rocks would have more dissolved U than water flowing
over U-deficient rocks.  It could also be that, in a large coal swamp, the U
would precipitate near the edges of the swamp, leaving the central regions
less uraniferous.  

What I can say with regard to actual systems is that I have sampled
groundwater in parts of Ohio coal country that had high gross alpha and
gross beta activity that seemed correlated with high activity levels in the
local coal.  Surveys I have performed on some of these coals have resulted
in elevated count rates (up to a few thousand dpm with 1x1 NaI).  I have
also seen specimens taken from coal deposits consisting of wood in which
uranium minerals (typically uraninite) have replaced much of the original
wood.  It could also be that some of the other mines are in rock that is
elevated in U with respect to the coal or are in rock from which radon can
more easily escape the mineral structure.

According to The Chemistry of the Actinide Elements, organic shales,
organic-rich minerals such as thucolite and kolm, and lignite deposits
contain sufficient U to constitute low-grade ores in some places, although
the uraniferous regions are often only 1-10 feet thick.  It also notes that
"Uranium is often, but not always, found associated with carbonaceous
materials (plant remains, etc.) and indeed many fossilized logs, tree
branches, and leaves contain appreciable amounts of uranium."

My best guess is that we are looking at some sort of variations due to local
geology/geochemistry combined with zoning within large deposits.  But I am
perfectly willing to be contradicted or educated on this by someone who
knows more about the subject than I.  This is not a complete answer to your
question, but I hope it helps somewhat.

Andy

--Why, then, are coal mines low in radon compared to other mines?
This was a key point in concluding that radon was responsible for lung
cancer in some miners -- coal miners do not have an excess of lung cancer.  
Also, U in coal averages 1 ppm  vs 2.5 ppm in average rock. I was under
the impression that geochemistry worked against U and coal depositing
together
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