A reference library of thermal infrared mineral reflectance spectra for the HyLogger-3 drill core logging system

Abstract

ABSTRACTA new reference library of thermal infrared spectral reflectance measurements of the major rock-forming and alteration minerals has been compiled to support and enhance analysis of data acquired using the CSIRO HyLogger-3 drill-core logging system. The HyLogger-3 is a robotic system that acquires large volumes of bidirectional reflectance spectra from diamond drill core within the wavelength range of visible light, the near infrared and shortwave infrared (400–2500 nm) as well as the thermal infrared from 6000 to 14 000 nm. The library samples were selected as single pure solid mineral crystals or monomineralic hand samples judged to have a similar bidirectional spectral response to that of typical diamond drill cores. Furthermore, a large number of individual mineral samples were chosen to cover the various natural spectral variations within single mineral groups such as, for example, a range of solid solutions of plagioclase. Owing to the bidirectional measurement geometry of the HyLogger-3, spectral variations caused by crystal orientation effects are also expected. Accordingly, reflectance measurements were made for multiple surfaces/facets of each sample, and also for orthogonal orientations of the plane of incidence illumination for each facet measured. All measured spectra were compared with existing library spectra or with spectra measured from validated samples to judge whether the mineral samples could be regarded as pure and, where possible, their chemical composition and mineralogy were validated by X-ray fluorescence and X-ray diffraction. For quality control, all such relevant metadata, including macroscopic descriptions of each sample, were collated in an associated database. In total, the spectral library contains more than 2000 spectra, from 562 specimens, representing 130 mineral groups. This library focuses on the most common rock-forming minerals of relevance to metalliferous exploration and mining, with a few limitations resulting from availability of suitable samples, which will be addressed as new samples become available. Comparisons with emission spectra from existing spectral libraries show good agreement, indicating that this spectral library will also be useful in the remote sensing domain.