QUANTITATIVE PIXE MICROANALYSIS OF FLUID INCLUSIONS BASED ON A LAYERED YIELD MODEL

The PIXE microanalysis of geological material using the proton microprobe often involves the treatment of layered or complex three-dimensional samples. While many problems remain intractable, some specific cases lend themselves to quantitative analysis. In addition to thick targets, the two sample geometries that have been treated quantitatively at the CSIRO are fluid inclusions and mineral grains in polished thin sections. The analysis of synthetic targets of known thickness layers has been used to assess the accuracy of this calculation. Also, the effects of inclusion geometry and uncertainties in depth and thickness, on the deduced concentrations in the fluid, have been investigated. The method was applied to the in situ microanalysis of fluid inclusions in quartz. Direct optical measurements of depth and thickness were used, and the quartz matrix was analyzed separately. For many inclusions, the observed Cl K-alpha/K-beta ratio was used as a direct measure of inclusion depth. The results compared well with analyses obtained by the bulk crush-leach method.