Mapping trace-metal (Cu, Zn, As) distribution in a single fluid inclusion using a third generation synchrotron light source

The concentration and spatial distribution of relatively dilute (10 to 100 ppm) trace metals (Cu, Zn and As) were determined for individual fluid incl usions from a gold-quartz vein at Brusson, western Italian Alps, using sync hrotron radiation X-ray fluorescence (SXRF). The analyses were performed on beamline ID-22 Micro-FID (Fluorescence, Imaging, Diffraction) of the Europ ean Synchrotron Research Facility (ESRF) Grenoble, France. The experimental set-up ensured a focal spot at the sample position of 2 X 7 mum and a flux of 10(10) photons/s. Fluorescence X-ray maps were collected for several fl uid inclusions, An example of the distribution of As in a fluid inclusion o riented at high angle to the wafer surface is presented. For each X-ray flu orescence spectrum, the (K alpha /K beta)(As) ratio of As was used as a mea ns of estimating;the thickness of quartz traversed by the photon beam. This value was used in turn for correcting As count rates. The correction proce dure resulted in uniformising the count rates of As in the liquid portion o f the inclusion and allowed visualizing the vapour bubble which contains on ly trace amounts of As. The strategy for computing the composition of the i nclusion fluid was to use one element from crush leach analysis (As) as an internal standard to calculate the concentrations of the other cations (Cu and Zn) present in the solution. Results of this calculation show that elem ent concentration estimates calculated using SXRF spectra are in relatively good agreement with those determined by crush-leach analysis. This indicat es that the fluid trapped in the sample studied was homogeneous with respec t to electrolyte composition. These results indicate that third generation synchrotron light source is a promising technique for tracking trace metals in individual inclusions (down to the tenths of ppm level) and, hence, as an invaluable tool for reconstructing the relative chronology of paleo-hydr othermal events responsible for the concentration of economic resources. (C ) 2001 Elsevier Science B.V. All rights reserved.