Hyperspectral Imaging Applications in the Mining Industry: Refining Alteration Footprints

• Author / Creator

  Lypaczewski, Philip

• The mining industry generates vast amounts of geological material and diamond drill core throughout the life-cycle of any exploration or mining project. This material needs to be examined, logged, and assayed where appropriate. Currently this is generally performed through visual observations by professional geologists. However, as hydrothermal alteration often produces fine-grained alteration, it may be difficult to correctly identify mineralogy with the unaided eye. Geological descriptions are therefore relatively subjective, as differences may exist between geologists investigating the same material.
  Hyperspectral imaging is a spectroscopic method that acquires reflectance spectra of a sample in a spatially contiguous manner, generating high-resolution imagery (e.g., at 1 mm/pixel) of a target sample. Reflectance spectra can be used to uniquely identify mineralogy, and in some cases can also provide information on mineral chemistry. In this thesis, the use of hyperspectral imaging is investigated, with emphasis on practical applications to the mining industry. Three specific research areas are examined: 1) the spectral response of biotite and chlorite is investigated for pure samples, and correlations are established to their respective mineral chemistries, 2) applied use of hyperspectral imaging is investigated at the Canadian Malartic disseminated gold deposit, with emphasis on vectoring towards mineralization using spectral parameters, and 3) applied use of hyperspectral imaging is investigated at the Highland Valley Copper porphyry deposits, with emphasis on detection of mineralized sample, which would allow for efficient ore-sorting.
  In Chapter 2, shortwave infrared (SWIR, 1000-2500 nm) reflectance spectra of biotite and chlorite are investigated to establish quantitative relationships between spectral metrics and mineral chemistry, determined by electron microprobe analysis (EMPA). Samples spanning a broad range of mineral compositions are used to establish regression equations to Mg#, which can be estimated to ±3 and ±5 Mg#, and to AlVI content, which can be estimated to ±0.044 AlVI (11 O) and ±0.09 AlVI (14 O), respectively for biotite and chlorite. As both minerals have several absorptions at common positions (1400, 2250, 2330 nm), spectral interference may occur in mineral mixtures. For an equivalent Mg#, absorptions of chlorite are offset to 1-15 nm higher wavelengths relative to those of biotite. If the incorrect mineral is identified, errors in the estimation of composition may occur. Recommendations to mitigate these issues are presented.
  In Chapter 3, applied use of hyperspectral imaging is investigated at the Canadian Malartic gold deposit, located in the Abitibi region of Québec, Canada. High-resolution hyperspectral imagery (0.2-1.0 mm/pixel) in both shortwave infrared (SWIR, 1000-2500 nm) and longwave infrared (LWIR, 8000-12000 nm) is acquired for over two thousand meters of drill core and is used to visualize changes in mineralogy and mineral chemistry related to metamorphism and hydrothermal alteration. Unaltered metasedimentary rocks contain metamorphic white mica with AlVI contents varying between 1.90 and 1.75 apfu (2195-2203 nm), depending on metamorphic grade. Hydrothermal alteration is characterized by white mica which becomes progressively more phengitic with increasing alteration intensity, with AlVI contents ranging from 1.70 to 1.50 apfu (2204 to 2212 nm). LWIR hyperspectral data is used in drill core to estimate the degree of silicification, and was generally in good agreement with the silicification abundance estimated by core logging.
  In Chapter 4, applied use of hyperspectral imaging is investigated at the Highland Valley Copper (HVC) district in British Columbia, Canada. Hyperspectral imagery is acquired on 755 rock samples and several hundred meters of continuous drill core. Simple spectral metrics (absorption depths and spectral slopes) are utilized to identify and quantify the relative abundance of 12 minerals commonly present in HVC samples. Coarse-grained white mica occurs as vein selvages and is closely associated with mineralization, and can regionally be detected up to 4 km away from the deposits. Kaolinite is present within 2 km of the mineralized centers, but does not necessarily occur within strongly mineralized intervals. Prehnite occurs as veinlets and vein selvages and is ubiquitous 4 to 8 km from the deposits. Prehnite is the most distant spectrally detectable alteration mineral, and may serve as an effective pathfinder mineral towards mineralized centers. A simple and easily adjustable spectral alteration score based on the presence or absence of a set of minerals could serve as a vector towards mineralization on regional scales.

• Subjects / Keywords

  • Infrared spectroscopy
  • Hyperspectral imaging
  • Canadian Malartic
  • Highland Valley Copper

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-36vm-ky95

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.