MICROANALYSIS OF ORE-FORMING FLUIDS USING THE SCANNING PROTON MICROPROBE

Much of the uncertainty in our early method of microanalysis of fluid inclusions using PIXE stemmed from the heterogeneous internal structure of each inclusion, which typically contains a vapor bubble and daughter crystals, and the non-uniform beam dose distribution. This paper reports on recent work to improve the accuracy of quantitative analysis through the use of beam-scanning techniques which provide a controlled beam-dose distribution. Improvements have been made to the PIXE yield modelling to better account for large vapor bubbles, and all fluid inclusion analysis routines have been incorporated as standard features of the GeoPIXE software package, The method has been tested using synthetic fluid inclusions in quartz (solutions of Na, K, Zn, Rb and Cs chlorides). The results demonstrated an accuracy improved to similar to 10-15%. Examples show the application of the method for the analysis of ore-forming fluids in magmatic hydrothermal systems.