X-ray imaging of uranium in individual fluid inclusions

The spatial distribution of major (K, Ca, Mn, Fe) and trace elements (Ti, C r, Cu, As, Br, Rb, Sr, Zr, Pb, Th, U) were determined in individual fluid i nclusions from quartz veins of the Streltsov uranium deposit, Russia, using synchrotron radiation X-ray fluorescence (SXRF). The analyses were perform ed on the beamline ID-ZZ Micro-FID (Fluorescence, Imaging, Diffraction) of the European Synchrotron Research Facility (ESRF, Grenoble, France). Fluore scence X-ray maps of single fluid inclusions show a relatively homogeneous distribution of most elements throughout the inclusion, whereas Fe and, to a lesser extent, Sr display highly localized count rates. This observation argues for the presence of minute, optically invisible, compounds that are precipitated inside the inclusion. Simple model calculations indicate that relatively diluted solutions (10-100 ppm U) trapped at geologically relevan t temperatures (e.g. 250 C) would precipitate submicron sized particles. Th ese particles would be highly reactive to the photon flux but not necessari ly visible under the microscope, These results indicate that third-generati on synchrotron light source can be a powerful technique to study the physic al processes undergone by the fluid. When combined with chemical data, this technique can help to clarify fluid transport properties in natural system s.