**5. Conclusions**

This study investigated the potential of comprehensive routine quantitative mineralogical characterization of uncrushed rock samples by QEMSCAN ® (as an example of ASEM) in the mining industry, with emphasis on trace mineral quantification. Analytical quality and methodology between an industrial and a scientific application of the QEMSCAN ® system were compared. It was shown that in comparison to a scientific application, the quality of the industry data was largely reliant on the quality of the species identification protocol (SIP) or mineral library used. Especially, the capability to identify di fferent gangue minerals and trace phases and to resolve mixed spectra was inferior for the analysis with settings for an industrial application. The resolution of mixed spectra was achieved through the "boundary phase processor" after modification of the SIP (the preferred method for the scientific analysis) proved too time intensive. It was demonstrated that by modification of the SIP for the analysis using industrial settings, gangue mineral di fferentiation could be improved. Additionally, the identification and quantification of trace minerals (in this case, Au-minerals) was significantly improved by the addition of single-element entries to the top of the SIP. Due to a potential of erroneous spectra caused by, e.g., a deflected electron beam, a threshold value had to be added to the single-element SIP. The lowest possible threshold value to avoid errors had to be determined experimentally (25% signal intensity for Au) and by verification with another analytical method (SEM-EDS). For a routine application, continuous verification is time consuming and thereby implausible, but a conservative threshold value could be implemented at the expense of missing some pixels of trace minerals. With this method, a 5 μm field scan was able to identify Au grains of less than 2 μm. It was also successfully tested for Ag. However, no information on trace metal mineralogy, grain size, and shape was collected. It thus cannot be compared to the data quality achievable with a 1 μm phase-specific search. However, as an add-on to routine quantitative mineralogical analysis focused on major ore minerals this method can also produce quantitative data and information on mineral association for trace minerals whose

metals may be potential by-products in a mining operation. This method will then lay the foundation for further targeted analysis of, for instance, precious- and critical trace metals.

While this study was performed on a single thin section sample only, the method developed to quantify trace minerals should be reproducible for other samples as well. In general, the more complex the mineralogy and textures of a sample and the finer the trace minerals, the more challenging an analysis will be. Additionally, the quality of the analysis is dependent on the quality of polishing (issues with beam deflections). Although this may impact the threshold value necessary to exclude errors, it should not affect the usability of the method itself.

**Author Contributions:** Conceptualization, M.W., C.W., G.B. and A.R.B.; Data curation, M.W., D.B. and G.K.R.; Formal analysis, M.W., I.M., D.B. and G.K.R.; Investigation, M.W., D.B. and G.K.R.; Methodology, M.W., I.M., D.B. and G.K.R.; Supervision, M.W., C.W., G.B. and A.R.B.; Validation, M.W.; Writing—original draft, M.W.; Writing—review & editing, M.W., C.W., G.B., A.R.B., I.M., D.B. and G.K.R.

**Funding:** This research received no external funding.

**Acknowledgments:** We kindly thank Boliden AB for letting us test their methodology, to develop their operation, and for permission to publish the findings. This work was carried out as part of a doctoral project (MW) financed by CAMM<sup>2</sup> (Centre for Advanced Mining & Metallurgy, Luleå University of Technology) and Boliden Mineral AB. The authors appreciate the in-depth discussions with Thomas Riegler on earlier versions of the manuscript, and three anonymous reviewers are thanked for improving the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
