Tools for Remote Exploration: A Lithium (Li) Dedicated Spectral Library of the Fregeneda–Almendra Aplite–Pegmatite Field

Abstract

The existence of diagnostic features in the visible and infrared regions makes it possible to use reflectance spectra not only to identify mineral assemblages but also for calibration and classification of satellite images, considering lithological and/or mineral mapping. For this purpose, a consistent spectral library with the target spectra of minerals and rocks is needed. Currently, there is big market pressure for raw materials including lithium (Li) that has driven new satellite image applications for Li exploration. However, there are no reference spectra for petalite (a Li mineral) in large, open spectral datasets. In this work, a spectral library was built exclusively dedicated to Li minerals and Li pegmatite exploration through satellite remote sensing. The database includes field and laboratory spectra collected in the Fregeneda–Almendra region (Spain–Portugal) from (i) distinct Li minerals (spodumene, petalite, lepidolite); (ii) several Li pegmatites and other outcropping lithologies to allow satellite-based lithological mapping; (iii) areas previously misclassified as Li pegmatites using machine learning algorithms to allow comparisons between these regions and the target areas. Ancillary data include (i) sample location and coordinates, (ii) sample conditions, (iii) sample color, (iv) type of face measured, (v) equipment used, and for the laboratory spectra, (vi) sample photographs, (vii) continuum removed spectra files, and (viii) statistics on the main absorption features automatically extracted. The potential future uses of this spectral library are reinforced by its major advantages: (i) data is provided in a universal file format; (ii) it allows users to compare field and laboratory spectra; (iii) a large number of complementary data allow the comparison of shape, asymmetry, and depth of the absorption features of the distinct Li minerals.

Analyses of Li-Rich Minerals Using Handheld LIBS Tool

“…This would require near real-time data processing based on chemometrics and artificial intelligence [44,45]. One previous data paper reported the acquisition of VNIR and SWIR spectra in the field from outcrops and various reference minerals [46] within the same project. As the LIBS handheld tool provides fast identification of trace elements, i.e., Li (Figure 1); here we aimed to establish the calibration curve of Li content in different matrices.…”

“…The database mainly includes laboratory LIBS spectra obtained from homogeneous Li-bearing minerals such as spodumene (LiAlSi 2 O 6 ), petalite (LiAlSi 4 O 10 ), amblygonite or montebrasite (LiAl(PO 4 )(F,OH)), lepidolite (K 2 (Li,Al) 5-6 (Si 6-7 Al 2-1 O 20 )(OH,F) 4 ), zinnwaldite (KLiFeAl(AlSi 3 )O 10 (OH,F) 2 ), and altered Li minerals [53]. Various LIBS analyses were also directly performed on Li-rich pegmatites at fresh outcrops in the field in Portugal by our Portuguese colleagues [46,54,55]. LIBS analyses were additionally performed on different powder pellets (obtained from the FAME project) and glasses made up of crushed powders from homogenized minerals.…”

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

“…The extraction of the wavelength, depth, and other geometric parameters of the absorption features was made using SpectraGryph software and the pysptools library. The complete spectral library and additional information on the equipment used and spectra processing can be found in Cardoso-Fernandes et al [45,46].…”

“…The main absorption features are highlighted, and sample photographs are provided. Each spectrum has a database code [45] providing information about the type of sample (L-Li-bearing minerals), mineralogy (Lep-lepidolite), sample provenance (FE-Feli mine and AL-Almendra), a three-digit numerical part representing the GPS code, a one-or two-digit code representing the spectra number or the averaged spectra numbers, and a reference to the spectroradiometer employed (sr-SR-6500; asd-FieldSpec 4). Dotted curves: fresh samples; full curves: samples with visible signs of weathering.…”

“…Dotted curves: fresh samples; full curves: samples with visible signs of weathering. Each spectrum has a database code [45] providing information about the type of sample (L-Li-bearing minerals); mineralogy (Pet-petalite); sample provenance (ALB-Alberto mine and BJ-Bajoca mine, FG-Fregeneda, and HD-Hinojosa de Duero); a three-digit numerical part representing the GPS code; a one-or two-digit code representing the spectra number or the averaged spectra numbers; and a reference to the spectroradiometer employed (sr-SR-6500; asd-FieldSpec 4). The main absorption features are highlighted, and sample photographs are provided.…”