Research article: Time‐gated Raman and laser‐induced breakdown spectroscopy in mapping of eudialyte and catapleiite

Research group from the Department of Chemistry and Department of Biological and Environmental Science in the University of Jyväskylä, and Circuits and Systems Reasearch Unit in the University of Oulu, studied the rare earth elements (REE) containing rock samples by using laser-induced breakdown and time-gated Raman spectroscopy.

Time-gated Raman spectroscopy was used to study the mineralogical composition of REE-bearing rocks by revealing the chemical bonds between atoms trough their vibrations. LIBS and time-gated Raman spectroscopic methods were used for the study to find information regarding the elemental and mineralogical distributions in the measured samples. Time-gated Raman is an applicable option for mapping fluorescent REE minerals as it can suppress the fluorescence photons.

Absract

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 Kärr 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.

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