Time-gated Raman and laser-induced breakdown spectroscopy in mapping of eudialyte and catapleiite

Raman analysis of rock samples containing rare earth elements (REEs) is challenging due to the strong fluorescence, which may mask the weaker Raman signal. In this research, time-gated (TG) Raman has been applied to the construction of the mineral distribution map from REE-bearing rock. With TG Raman, material is excited with a short subnanosecond laser pulse, and the Raman signal is collected within a picosecond-scale time window prior to the formation of a strong fluorescent signal by means of single-photon avalanche diode array. This allows signal readout with a significantly reduced fluorescence background. TG Raman maps are used to reveal the location of valuable minerals and are compared with the elemental distribution given by laser-induced breakdown spectroscopy. The analysis was carried out from a REE-bearing rock, nepheline syenite sample from the Norra Karr deposit, where REEs are mainly hosted in eudialyte and catapleiite. The combination of these two complimentary laser spectroscopic methods offers valuable elemental and mineralogical information about rocks.