Abstract Title: Close-Range Spectroscopic Techniques for Detection of Rare Earth Element Mineralization: Case Study from Siwana Ring Complex, Rajasthan, India

Abstract Submitted to: VOLCANOLOGY, GEOCHEMISTRY, AND PETROLOGY

Abstract Text:

Rare earth elements (REEs), which comprise of lanthanides (Z= 57-71) along with scandium and yttrium, are considered to be of high economic importance due to their use in various modern technological products. Situated in Barmer district, Rajasthan, India, The Siwana Ring Complex (SRC) is a collapsed caldera structure, comprising of peralkaline rocks which are a part of the Malani Igneous Suite. Previous workers have reported the REE potential of the area.
Sharp absorption features in the reflectance spectrum are observed in REE bearing minerals arising out of the 4f-4f intra configurational electronic transitions. Nd, which is known as a proxy for detection of REEs, exhibits prominent features at wavelengths 580 nm, 740 nm, 800 nm and 870 nm approximately.
Samples of peralkaline granites and rhyolites which host a variety of REE minerals are collected from this area after extensive field work and studied using laboratory-based imaging spectroscopy techniques. An ASD FieldSpec4 (350 nm – 2500 nm) and Fourier Transform Infrared (FTIR) spectroscopy (400-4000 cm-1) are used to collect spectra of the samples.
Distinctive absorption features in the VNIR region are seen in the spectral reflectance curves of the peralkaline granites and rhyolites at around 580 nm, 740 nm, 800 nm and 870 nm which indicate the presence of Nd3+. Characteristic CO32- absorption features present around 2300 nm point towards the presence of REE-fluorocarbonates. Features observed due to asymmetric bending (538 and 585 cm-1) and asymmetric stretching (1050 and 1097 cm-1) vibrations of P-O bond indicate the presence of monazite.
Trace and bulk rock geochemistry confirm the abundance of LREEs (ΣLREE = 662-3799 ppm). Ce (306-1772 ppm) and Nd (153-843 ppm) are the most abundant REEs. Presence of monazite-Ce, REE fluorocarbonates and allanite-Ce are confirmed by mineral chemistry along with the occurrence of zircon, sphene and apatite which correlate with the abundance of LREEs.
Mineral chemistry and geochemical analyses seem to be in concurrence with the spectral data. It is observed that imaging spectroscopy can be used as an effective low-cost technique for detection of REE mineralization before further exploration. Based on the spectral data obtained from the proven regions, other areas can be studied which have not been explored previously