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Multi-Scale X-Ray Computed Tomography Analysis to Aid Automated Mineralogy in Ore Geology Research
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.ORCID iD: 0000-0003-3593-3786
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.ORCID iD: 0000-0001-9846-1793
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.ORCID iD: 0000-0003-4711-7671
Geological Survey of Finland (GTK), Espoo, Finland.
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2021 (English)In: Frontiers in Earth Science, E-ISSN 2296-6463, Vol. 9, article id 789372Article in journal (Refereed) Published
Abstract [en]

Ore characterization is crucial for efficient and profitable production of mineral products from an ore deposit. Analysis is typically performed at various scales (meter to microns) in a sequential fashion, where sample volume is reduced with increasing spatial resolution due to the increasing costs and run times of analysis. Thus, at higher resolution, sampling and data quality become increasingly important to represent the entire ore deposit. In particular, trace metal mineral characterization requires high-resolution analysis, due to the typical very fine grain sizes (sub-millimeter) of trace metal minerals. Automated Mineralogy (AM) is a key technique in the mining industry to quantify process-relevant mineral parameters in ore samples. Yet the limitation to two-dimensional analysis of flat sample surfaces constrains the sampling volume, introduces an undesired stereological error, and makes spatial interpretation of textures and structures difficult. X-ray computed tomography (XCT) allows three-dimensional imaging of rock samples based on the x-ray linear attenuation of the constituting minerals. Minerals are visually differentiated though not chemically classified. In this study, decimeter to millimeter large ore samples were analyzed at resolutions from 45 to 1 μm by AM and XCT to investigate the potential of multi-scale correlative analysis between the two techniques. Mineralization styles of Au, Bi-minerals, scheelite, and molybdenite were studied. Results show that AM can aid segmentation (mineralogical classification) of the XCT data, and vice versa, that XCT can guide (sub-)sampling (e.g., for heavy trace minerals) for AM analysis and provide three-dimensional context to the two-dimensional quantitative AM data. XCT is particularly strong for multi-scale analysis, increasingly higher resolution scans of progressively smaller volumes (e.g., by mini-coring), while preserving spatial reference between (sub-)samples. However, results also reveal challenges and limitations with the segmentation of the XCT data and the data integration of AM and XCT, particularly for quantitative analysis, due to their different functionalities. In this study, no stereological error could be quantified as no proper grain separation of the segmented XCT data was performed. Yet, some well-separated grains exhibit a potential stereological effect. Overall, the integration of AM with XCT improves the output of both techniques and thereby ore characterization in general.

 

Place, publisher, year, edition, pages
Frontiers Media S.A., 2021. Vol. 9, article id 789372
Keywords [en]
x-ray computed tomography, automated mineralogy, mineral segmentation, ore, trace metals
National Category
Geosciences, Multidisciplinary
Research subject
Ore Geology; Fluid Mechanics; Experimental Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-85847DOI: 10.3389/feart.2021.789372ISI: 000741835600001Scopus ID: 2-s2.0-85121840567OAI: oai:DiVA.org:ltu-85847DiVA, id: diva2:1570752
Note

Validerad;2022;Nivå 2;2022-01-01 (johcin);

Artikeln har tidigare förekommit som manuskript i avhandling

Available from: 2021-06-22 Created: 2021-06-22 Last updated: 2025-01-08Bibliographically approved
In thesis
1. Improving trace metal characterisation of ore deposits through multi-modal, multi-scale, and multi-dimensional micro-analysis
Open this publication in new window or tab >>Improving trace metal characterisation of ore deposits through multi-modal, multi-scale, and multi-dimensional micro-analysis
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The variety and amount of metals consumed by human society is ever increasing. Meeting the demand requires exploration for new ore deposits, efficient production of active mines, and improved efficiency in metal recycling. A key element in mining-related enterprises is the improvement of ore characterisation. The study of the geology and mineralogy of ore deposits allows us to infer the processes behind ore genesis. This knowledge guides important exploration and processing decisions. Over the last few decades, technological advancements have enabled ore characterisation at increasing levels of detail. This has brought the trace metal mineralogy of ore deposits into focus. In many cases, trace metals occur as extremely fine-grained minerals or as lattice-bound impurities in the more common minerals in ore deposits. Hence, their study requires the use of micro-analytical techniques. Trace metals and their minerals can carry crucial information on the conditions of ore formation. They can be of economic value, harmful to the environment, or of strategic economic and geopolitical interest (e.g. Critical Raw Materials). Trace metal characterisation is therefore highly relevant to research, industry, and society.  In this project, micro-analysis was performed on the Liikavaara Östra Cu-(W-Au) deposit in northern Sweden to research the trace metal mineralogy of Au, Ag, Bi, Mo, Re, and W. The main goal of the project was the development, optimisation, and integration of various micro-analytical techniques for ore characterisation. The project was subdivided into four studies (scientific contributions): (1) Drill core logging, whole-rock geochemistry, and light microscopy were applied to identify lithology, alteration, and mineralisation of the deposit. An intrusion in the footwall, potentially related to ore genesis, was dated with LA-ICP-MS. Scanning electron microscopy with energy dispersive spectrometry was used to gain insight into the trace metal mineralogy of the deposit. This study provided an overview of the geology and mineralogy of the deposit and served as a basis for sample selection and data interpretation of subsequent studies. (2) A polished thin section of the ore containing trace metal minerals was scanned by automated mineralogy (QEMSCAN) at Boliden AB to assess the potential of trace metal mineral quantification in a production-focused environment. To delineate instrument limitations from operator input the same sample was also scanned at Camborne School of Mines, UK. Detection of trace metal minerals was generally difficult due to their fine-grained nature. Yet, quantification could be improved by optimisation of the mineral classification library. (3) Four polished epoxy-mounted drill core pieces of ore were analysed by automated mineralogy (Mineralogic) and x-ray computed tomography (XCT). In two samples, a smaller region of interest was drilled and re-analysed at higher resolution. Results from automated mineralogy were used to segment and interpret the XCT data. Vice versa, XCT data provided 3D spatial context for the 2D scans. (4) Three polished thin section pieces with grains of molybdenite, pyrite, and native Bi, all with Au-inclusions, were analysed by synchrotron radiation x-ray fluorescence mapping at the NanoMAX beamline of the MAX IV synchrotron facility in Lund, Sweden. Element fluorescence maps down to 50 nm pixel size revealed the distribution of micro- and nano-inclusions and lattice-bound impurities in the mineral grains. The studies demonstrated benefits and challenges of the various micro-analytical techniques, and how and what they may contribute to ore characterisation. Results allowed linking and integrating the techniques into a smart analytical flow to optimise the characterisation of trace metal minerals in ore deposits. This is useful for both ore geology research and the mining industry. 

Place, publisher, year, edition, pages
Luleå University of Technology, 2021
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Geosciences, Multidisciplinary
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-85848 (URN)978-91-7790-897-5 (ISBN)978-91-7790-898-2 (ISBN)
Public defence
2021-10-22, F1031, Luleå University of Technology, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2021-06-22 Created: 2021-06-22 Last updated: 2025-01-08Bibliographically approved

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Warlo, MathisBark, GlennWanhainen, ChristinaForsberg, FredrikLycksam, Henrik

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