Advanced Identification and Quantification of In-Bearing Minerals by Scanning Electron Microscope-Based Image Analysis

Abstract

The identification and accurate characterization of discrete grains of rare minerals in sulfide base-metal ores is usually a cumbersome procedure due to the small grain sizes (typically <10 μm) and complex mineral assemblages in the material. In this article, a new strategy for finding and identifying indium minerals, and quantifying their composition and abundance is presented, making use of mineral liberation analysis (MLA) and electron probe microanalysis (EPMA). The method was successfully applied to polymetallic massive sulfide ores from the Neves-Corvo deposit in Portugal. The presence of roquesite and sakuraiite could be systematically detected, their concentration quantified by MLA measurements, and their identity later confirmed by EPMA analyses. Based on these results, an almost complete indium deportment could be obtained for the studied samples. This validates the approach taken, combining automated mineralogy data with electron microprobe analysis. A similar approach could be used to find minerals of other common minor and trace elements in complex base-metal sulfide ores, for example Se, Ge, Sb, or Ag, thus permitting the targeted development of resource technologies suitable for by-product recovery.

The geometallurgical assessment of by-products—geochemical proxies for the complex mineralogical deportment of indium at Neves-Corvo, Portugal

“…The aim was to cover most major ore types, and thus study the effect of varying modal mineralogy on indium deportment. As noted in ESM Tables A1 and A2, about one third of our samples have already been described elsewhere (Relvas et al 2006a;Bachmann et al 2017). Drill core samples were mostly quarter core, > 10 cm in length, while hand specimens were generally larger than 10 × 10 cm, weighing > 500 g each.…”

“…Actual indium deportments are only estimated in one recent study (Bachmann et al 2017). However, the methodological focus of this study means that results are restricted to a small number of ore samples (n = 5).…”

“…Ore samples were selected based on mineralogical/ chemical variability and high bulk indium content (> 10 ppm) as determined on drill core by the mine and onhand specimens in previous studies (Relvas et al 2006a;Bachmann et al 2017). The aim was to cover most major ore types, and thus study the effect of varying modal mineralogy on indium deportment.…”

Advances and Opportunities in Ore Mineralogy

“…Automated mineralogy is increasingly used for the identification of unconventional or less common ore minerals and to understand the distributions of minor and trace elements. For example, Bachmann et al (2017) [93] describe new strategies, combining MLA and EPMA, for the systematic detection and identification of small particles containing the critical element indium. Correct interpretation of automated mineralogy data does, however, require a sound mineralogical understanding of the material, and thus should not be considered as a direct substitute for that.…”

Description of Ore Particles from X-Ray Microtomography (XMT) Images, Supported by Scanning Electron Microscope (SEM)-Based Image Analysis

“…From hereon we will refer to these false color images obtained by the MLA system as MLA images/data. More detailed information about the functionality of the MLA system can be found in Fandrich et al (2007), whereas details regarding data processing are shown in Bachmann et al (2017). Additional information on the measurements with the MLA of the ore used in this study can be found in Heinig et al (2015).…”