Novel technique for the preparation and analysis of powder-based polished sections by automated optical Mineralogy: Part 1 – Comparative study of representativity

Abstract

Reflected optical microscopy is an affordable technique that can be used for automated quantitative mineralogical analysis. Polished sections are a common format used to analyze representative powdered mineral samples. The epoxy resin used to make polished sections for quantitative automated mineralogy is known to cause preferential sedimentation (or segregation) of the particles through the polished section. This phenomenon results in biased polished sections. Carbon-based resin preparation is now widely used to overcome this problem. This study presents a new resin for polished section preparation, acrylic resin, which can provide ready-to-analyze polished sections in less than three hours (instead of more than 10 h for other resins).This work investigated the effect of other polished section resin preparation protocols and compared them, including rheological measurements and automated optical microscopy analyses. The aim was to compare the polished section preparation techniques aiming at determining the technique which allows a reliable mineral abundance while not introducing a bias due to segregation in the polished sections. To do so, standard mineral powders were prepared using different pure opaque minerals at a calibrated size fraction of 20–75 μm. The results suggest that the rheological behavior of the fast-hardening acrylic resin allowed an accurate modal composition to be obtained while avoiding any preferential sedimentation of the particles compared to the other studied resins.