Percival, and 7 co-authors, reported in 2018 that infrared (Visible-Near Infrared-Shortwave Infrared (VNIR-SWIR)) spectroscopy is a cost-effective technique for mineral identification in the field. Modern hand-held spectrometers are equipped with on-board spectral libraries that enable rapid, qualitative analysis of most minerals and facilitate recognition of key alteration minerals for exploration. Spectral libraries can be general or customized for specific mineral deposit environments.
To this end, careful collection of spectra in a controlled environment on pure specimens of key minerals was completed using the National Mineral Reference Collection (NMC) of the Geological Survey of Canada. The spectra collected from specimens in the ‘Kodama Clay Collection’ were processed using spectral plotting software and each new example was validated before being added to a group of spectra considered for incorporation into the on-board library of the handheld ASD-TerraSpec Halo near-infrared (NIR) mineral identification instrument. Spectra from an additional suite of mineral samples of the NMC containing REE, U, Th, and/or Nb are being prepared for a new, publicly available spectral library. These minerals commonly occur in carbonatite or alkali intrusive deposits, and as such will assist in the exploration for critical metals.
The authors concluded that progress over the last few decades in field instrumentation has facilitated acquisition of in situ, nondestructive, rapid, mineralogical and mineral-chemical analyses using near-infrared spectroscopy. In some environments, these key infrared-active alteration minerals can provide robust vectors to ore. For some users, custom libraries are needed and this should be achieved through the collection of VNIR-SWIR spectra
of pure reference minerals in a controlled manner. To encourage the expansion of these techniques, collection of VNIR-SWIR spectra on clay minerals of the Kodama Clay Collection, part of the vast national mineral collection at the Geological Survey of Canada, has been completed (Percival et al., 2016a).
As indicated in that 2016a study, infrared spectroscopy can also identify REE-U-Th-Nb-bearing minerals relevant for exploration for critical metals and work is underway to expand the GSC infrared spectral database to include these minerals. These large mineral collections represent a valuable asset for geoscientists. As national collections become more recognized for their value in Earth sciences research, these data must be available publicly. Building spectral libraries of unique and common minerals ensures the legacy of collections and adds to their scientific and cultural value.
[Note: the development in spectroscopy will be especially useful in the off-world geological exploration programs to come, either remotely or by on-site human activities. Remote acquisition of spectral data is already underway on Mars.]
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