Raman Spectroscopic Analysis of Cyanobacteria in Apatite-Containing Rocks of the Tomtor Nb-REE Deposit (Russia)

Micro-Raman spectroscopy was employed to analyze apatite-containing samples from the Tomtor complex of ultrabasic rocks and carbonatites, located in the sharply continental region of Yakutia, Russia. Raman spectra excited at a wavelength of 532 nm revealed the characteristic vibrational bands of apatite, as well as bands attributed to carotenoid-type cyanobacteria. Additionally, as an artifact, the spectra exhibited bands resulting from the laser-induced photoluminescence of trivalent rare earth elements (REEs). Preresonance Raman spectra recorded at least two distinct C=C stretching modes of the β-carotene polyene chain, indicating the presence of this carotenoid component associated with apatite. Furthermore, three characteristic carotenoid bands were recorded in samples from the specific weathering crust on carbonatites that lacked apatite-related bands. These findings provide direct evidence of cyanobacteria in the studied samples, suggesting the likely involvement of microorganisms in the formation of Nb-REE-rich ores within the Tomtor field in Russia.