|Petrography of sectioned drill cutting as seen under optical microscope, Scanning Electron Microscope, and QEMSCAN|
(the image is not part of the conference paper below)
Examples of Automated Petrography systems (MLA/QEMSCAN) used in the Minerals Industry
Dirk van der Wal, Hans Kruesemann
FEI Company , PO Box 80066, 5600 KA Eindhoven, The Netherlands
Petrology is a Geoscience involved with understanding the provenance of rocks, such as depositional environment in the case of hydrocarbon reservoir rocks, or metamorphism in the case of “hard rocks”. Petrography is a branch of Petrology that involves microscopic description of mineral content and texture (microstructure) to aid interpretation of provenance.
The predominant petrographic system is a polarized optical microscope, used to identify minerals from their optical properties in crossed polarized light such as birefringes. Due to the manual and laborious nature of the technique, the Minerals Industry has struggled to deploy petrography in industrial use cases such as Geometallurgy or Mineral Processing.
Scanning Electron Microscopy (SEM) based Automated Petrography systems have been developed since the late 1980’s, predominantly in Australia (CSIRO, Univ. of Queensland), known as QEMSCAN® and Mineral Liberation Analyzer (MLA) respectively. Mineral classification technology based on backscattered electron intensity and elemental composition from energy dispersive spectroscopy has been developed over decades and provides a robust solution of automated fast mineral classification with the superior spatial resolution obtained from electron microscopy.
There are currently more than 150 Automated Petrography systems in use worldwide, predominantly in the precious and base metal mining industries. They are used to measure ore properties such as ore typing, precious metal host mineralogy, mineral associations (e.g. mineral liberation) or phase purity from core samples or grinded material.
Recent developments include advances in sample preparation and speed of analysis, aiming at reducing sample turn-around time to a point where data can be used near real-time to optimize the grinding and flotation circuit.
In this contribution, the Automated Petrography technology will be introduced and use cases illustrated from the precious metal (e.g. Pt, Au, U) and base metal mining industries (e.g. Cu, Fe).