Optimising Analyses of Geological Material with an Analytical Scanning Electron Microscope

English Abstract:

The need to determine the precise composition of geological material is ever growing and the data widely used in multiple fields such as geochemistry and metamorphic petrology. Although routinely used, electron microscopes analyses are not always optimized nor is the surface of the sample perfectly prepared.

This study presents advances in scanning electron microscopy (SEM) coupled with an EDS (SiLi) detector on thin-sections of amphiboilte-facies pelitic schists and garnet grains therein. The purpose is to optimize the various operating parameters, such as probe current, accelerating voltage, working distance, live acquisition time and concentrations of major and trace elements within the sample. We present examples of optimized analyses and their limits for several applications including: 1) characterization of polished surface condition using secondary electron imaging; 2) zoning profile for major elements in garnet; 3) x-ray maps for major elements in garnet. In order to verify the possibility of quantification with this optimized method, our results are then compared to those obtained for the same samples using the electron microprobe, the customary instrument for such analyses. This methodology will further be used to optimize data acquisition for a new analytical SEM coupled with both WDS and EDS (SDD) detectors, acquired by the Centre for Characterization and Microscopy of Materials (CM)² of Polytechnique Montreal.