This is an area that interests me as well as I have been dealing with monazites containing U an REE bearing minerals. Have you looked at the following article?

http://www.minersoc.org/pages/Archive-MM/Volume_49/49-353-495.pdf

Thank you Dr Jeffrey for your kind gesture. Best regards.

Dear Mr. Bute,

While U/Th may make sense, Rb/U does not as both elements are not chemically related with each other in termsof ionic radii or valence state. If you want to deal with this issue you should go a step  ahead and take a look at  the pegmatites which are similar in terms of the main constituents but reach a more advanced level as to the concentration of rare metals than many other granites can do.

I refer to DILL, H.G. (2015) Pegmatites and aplites: Their genetic and applied ore geology.- Ore Geology Reviews 69: 417-561.

In the section on U, Th and REE you may get an idea how they are related with each other, frequently controlled by the geodynamic setting and the crustal/subcrustal impact on their formation.

Good luck !

H.G.Dill

I'd suggest thorium as an indicator and phosphorus, chloride and (or) carbonate ions in fluids that would make possible uranium ions migration and accumulation. Note, that especially the kind and stability of the uranium plus carbonate complexes strongly depend on pH and redox potential. Arsenic ions may also influence the migration of uranium. Moreover, you must distinguish the hypo- to mesothermal mineralization, which commonly yields four-valent uranium, from  oxydation proces (late hydrothermal and supergene conditions) and phosphate, arsenate etc. mineralization, usually late hydrothermal or supergene. The paper which may be useful, is as follows: V. E. Boitsov, T. M. Kaikova, Uranium and arsenic in the hydrothermal process, Soviet Atomic Energy, April 1965, Volume 18, Issue 4, pp 473-479 (in English as the Springer Verlag translation)

With my best,

Andrzej Kozłowski

U+4 has the same charge and almost the same atomic radii as Ce Zr Pb, Hf, Ti and the light REEs.  So U+4 is often found as a substitute in RE fluorocarbonates and phosphates such as bastnaesite and monazite. 

I would suggest to approach the problem pragmatically.

1) Take some samples from granites or parts of granites which don't show or are not related to uranium mineralisation. 2) take some samples from granites or part of granites related to uranium mineralisation. 3) get some "pure" quartz grains out of these rocks. 4) analyse them by laser ablation ICPMS or INAA and look for contrast between the groups 5) why quartz; The mineral is rather intolerant of substitutions or inclusions; low background; quartz contains rare earth elements 6) if you find contrast between the two groups you may also use EPR or thermoluminesence. 7) See eg JC van Moort & Aung Pwa 2005 The use of quartz concentrates as a sample medium in lithogeochemistry GEEA 5:267-277 and alternative publications on EPR and trace elements in quartz.

JCvM

Trace elements and REE contents are important, because the trace element composition of the melt that forms the granite helps dictate the U mineral you have making up the mineralization. For instance, the mineralization I studied at Fraser Lakes Zone B consisted of higher U, lower Th, higher HREE lower LREE Group A, and higher Th, lower U, higher LREE Group B pegmatites/leucogranites. The most impressive difference between the two was the dominant U-Th-REE mineral (uraninite in Group A vs. monazite in Group B). There were other differences as well, including major element compositional variations.

The source of the melt, transport (degree of transport, amount of assimilation/fractional crystallization, i.e. AFC processes), and the composition of the rocks the mineralized granites are hosted in are all things that will dictate the composition of the granites.  Even major element ratios may be slightly thrown off, due to AFC processes. I saw this at Fraser Lakes Zone B.

Also, one must always keep in mind sampling biases due to inhomogeneity of the intrusive body when looking at your data.