Space and ground based spectroscopic studies and mineral chemistry of rare earth element bearing peralkaline rocks from Siwana Ring Complex, Rajasthan, India

Abstract

The Neoproterozoic Siwana Ring Complex (SRC) in Barmer district, Rajasthan, India, contains a promising concentration of rare earth elements (REEs). This study uses PRISMA hyperspectral data to map potential high-REE locations using the Spectral Angle Mapper (SAM) classifier. Also, laboratory-based spectroscopy is used to analyse rock samples of peralkaline granite and rhyolite, using spectroradiometer in 400-2500 nm and Fourier Transform Infrared (FTIR) Spectroscopy in 400-4000 cm⁻1 regions. Diagnostic absorption features in the Visible Near Infrared (VNIR) and Short-Wave Infrared (SWIR) regions indicate the presence of REEs, alongside pyroxenes, amphiboles, and phyllosilicates. The data from the FTIR indicates the presence of minerals possessing Si-O, P-O and O-H bonds. Mineral chemistry and geochemistry confirm these findings, indicating the occurrence of REE-bearing minerals such as monazite, REE silicates, and apatite. Ce is found to be the most abundant REE. However, only absorption features related to Nd and Er or Ho are observed which means that these elements are indicators of high concentration of total REE in the samples. The map generated from the PRISMA data aligns well with geochemical data, proving the value of hyperspectral remote sensing in early exploration. This study also highlights laboratory spectroscopy as a valuable complementary tool in mineral exploration. This study provides spectral information for reference for future use on REE bearing peralkaline rocks.