Interpretation of the Reflectance Spectra of Lithium (Li) Minerals and Pegmatites: A Case Study for Mineralogical and Lithological Identification in the Fregeneda-Almendra Area

Abstract

Reflectance spectroscopy has been used to identify several deposit types. However, applications concerning lithium (Li)-pegmatites are still scarce. Reflectance spectroscopic studies complemented by microscopic and geochemical studies were employed in the Fregeneda–Almendra (Spain–Portugal) pegmatite field to analyze the spectral behavior of Li-minerals and field lithologies. The spectral similarity of the target class (Li-pegmatites) with other elements was also evaluated. Lepidolite was discriminated from other white micas and the remaining Li-minerals. No diagnostic feature of petalite and spodumene was identified, since their spectral curves are dominated by clays. Their presence was corroborated (by complementary techniques) in petalite relics and completely replaced crystals, although the clay-related absorption depths decrease with Li content. This implies that clays can be used as pathfinders only in areas where argillic alteration is not prevalent. All sampled lithologies present similar water and/or hydroxide features. The overall mineral assemblage is very distinct, with lepidolite, cookeite, and orthoclase exclusively identified in Li-pegmatite (being these minerals crucial targets for Li-pegmatite discrimination in real-life applications), while chlorite and biotite can occur in the remaining lithologies. Satellite data can be used to discriminate Li-pegmatites due to distinct reflectance magnitude and mineral assemblages, higher absorptions depths, and distinct Al–OH wavelength position. The potential use of multi- and hyperspectral data was evaluated; the main limitations and advantages were discussed. These new insights on the spectral behavior of Li-minerals and pegmatites may aid in new Li-pegmatite discoveries around the world.

Sentinel-1 and ALOS data for lineament extraction: a comparative study

“…Meeting the demand for critical raw materials (CRM) and other commodities needed for the production and storage of "green" energy is crucial for achieving the decarbonization targets set by the European Climate Foundation by 2050 [1] . Such commodities can be found in pegmatite rocks and several recent works have been focused on their characterization for more efficient exploration and development of new tools [2][3][4][5] .…”

Multiscale (microscopic to remote sensing) preliminary exploration of auriferous-uraniferous marbles: A case study from the Egyptian Nubian Shield

“…For instance, in geological remote sensing, visible near-infrared (VNIR) bands are often included for discriminating iron-rich minerals due to the unique absorption features of these minerals at this spectral range. Short-wave infrared (SWIR) bands are the best choice for highlighting carbonates and OH-bearing minerals 42 , 82 , 83 . In the current research and due to the wide compositional variability of the exposed rock units, the best image composite differentiating the rock units was represented by SWIR, VNIR, and visible blue ranges through displaying Sentinel 2 band 12 (SWIR) in red, band 6 (VNIR) in green, and band 2 (blue) in blue channels.…”

The potential of spectral unmixing method applied to PRISMA hyperspectral images in the identification of Li minerals: an evaluation for prospecting purposes

“…Lepidolite was identified with higher scores in the n-D classes that correspond to the vegetation. When looking at the comparison of the pure spectra and the endmembers it can be seen that the characteristic water/OH absorption of Lepidolite (~1405 nm) 28 is negatively impacted by the water vapor absorption bands of the atmosphere. This may have negatively impacted the identification of this mineral.…”