Scanning Microscopy


The complementary techniques of EPMA and micro-PIXE are reviewed in the context of spatially resolved trace element analysis of sulfide minerals. Attention is focussed on methods of standardization and of fitting EDX spectra. Sphalerites and chalcopyrites from various sources are used as specimens. For Ag in chalcopyrites, the two techniques agree well. Sphalerites pose problems such as Zn-Fe replacement and the presence of minor elements, both of which influence matrix corrections ; these are addressed in detail. The necessity for absorbers in the micro-PIXE work prevents detection of minor elements lighter than Zn ; these are determined by EPMA and the results used in the micro-PIXE fitting and matrix corrections. For Cd, Ag, Ga, Ge there is acceptable agreement between the two techniques given uncertainties and constraints on samples, but EPMA results for Hg are notably lower than micro-PIXE results. The improvement in detection limits afforded by micro-PIXE over EPMA in these sulfide minerals ranges from ~ 3 for Ga, Ge, Hg to 10-30 for Se, Ag, Cd, In ; possible further gains are discussed for both techniques.

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