FIELD VNIR-SWIR SPECTRORADIOMETRY FOR CLASSIFICATION OF MATERIALS IN THE VALDEFOREZ DEPOSIT (SPAIN) ACCORDING TO THE Li CONTENTS.

The Li mineralization of Valdeflórez (Cáceres province, Spain) is related to an extensive metasomatism of Ordovician metasedimentary rocks due to the circulation of B- and Li-rich magmatic hydrothermal fluids associated probably with a granite dome (Torres-Ruiz, et al., 1996). Li-rich micas mainly, and other Li-rich minerals like amblygonite-montebrasite, appear as consequence of this hydrothermal alteration. The aim of this study is to evaluate the use of the VNIR-SWIR spectroradiometry to the materials classification according to the Li content during the exploitation mining works and to the mining prospection in similar areas. The results of a study conducted by VNIR-SWIR portable spectroradiometry on 335 samples coming from representative cores of the mineralized area are shown. Complementary, a mineralogical study by XRD and chemical analysis by ICP were performed. Visible and infrared wavelength ranges were studied separately, and a classification of the high-resolution spectra was done to compare with the chemical and mineralogical composition of the samples. The spectra were classified into six groups according to their morphology in the near and short-wave IR range, and these groups correspond to a different mineralogy of major components, as logical.  However, there is not a clear relation among these groups and the Li-content because Li is mainly in micas as octahedral substitutions, which influence on the spectral features is neglectable. A higher content in micas does not imply a higher content in Li. Consequently, a spectral signature of Li could not be determined, because Li is not directly related to the content of a certain mineral, micas in this case. As a conventional spectral signature is not useful in this case, because it classified mineralogy but not Li-content, a detailed study of the hight resolution spectra obtaining different parameters (both from the spectra and from the second derivatives of the spectra) was performed. The joint statistical treatment of the hyperspectral, mineralogical, and chemical data allowed us to find a plot of the materials classification according to the Li content from the spectral data which means a very fast procedure for classification that could be automatized though IA.

Acknowledgement: TED2021-130440B-I00 funded by MCIN/AEI/10.13039/501100011033 and European Union NextGenerationEU/PRTR

Torres-Ruiz, J., Pesquera, P., Gil, P., Casas, J. 1996. Tourmalinites and Sn-Li mineralization in the Valdeflores area (Cáceres, Spain). Mineralogy and Petrology 56:209-223.