A visible-near infrared spectral library for critical metals exploration

Optical remote and proximal sensing instruments, collecting reflectance spectra of rocks and sediments in the visible to near infrared (VNIR) wavelength range (350 to 1200 nm) of the electromagnetic spectrum at high spectral and spatial resolution, provide a unique fingerprint of a wide range of rock forming, alteration and ore minerals. This paper presents a newly compiled VNIR spectral reference library, comprising reflectance spectra of 249 mineral samples over the 350 to 1350 nm wavelength range, which were acquired by the CSIRO from single crystals, crystal aggregates, pulp and rock samples. The collection comprises representatives from the following mineral groups: sulfides, oxides, hydroxides, carbonates, sulfates, phosphates, molybdates/tungstates, nesosilicates, cyclosilicates, inosilicates and phyllosilicates. Many mineral species amongst those mineral groups are host minerals of critical metals, such as Co, Ga, Ge, Sb, Sc, W, and Rare Earth Elements (REE). Importantly, the spectral library also comprises gangue minerals common to the respective commodities, such as iron oxides in regolith-hosted REE-deposits. In addition to the VNIR, the short-wave infrared (SWIR) region, between 1300-2500 nm, was also collected and is only provided here for comparison purposes rather than detailed spectral peak assignment/analysis. The validation of the 249 mineral reference reflectance spectra is an ongoing process. Based on completed X-ray diffractometry, the reflectance spectra currently comprise 98 pure mineral species samples, 117 samples that are impure, but where the target minerals form an assemblage with typically associated minerals. Selected samples may require further validation methods, such as scanning electron microscopy, inductively coupled plasma spectrometry and Fourier transform infrared spectroscopy.

Presented at the 2025 IEEE International Geoscience and Remote Sensing Symposium.