Rapid determination of the approximate content of bastnäsite in ores using cathodoluminescence imaging

A rapid determination of the rough content of the major rare earth element (REE)-bearing minerals (bastnäsite, monazite, and xenotime) can lead to a drastic reduction of the time required to analyze mineral ores for the extraction of REE metals, thus enabling the efficient exploration of mines with REE reserves. This study presents a method of using cathodoluminescence (CL) imaging to identify bastnäsite in mineral ores and determine the rough bastnäsite content rapidly. By investigating the luminescence colors in CL images and the peaks in CL spectra emitted by minerals in ores that include bastnäsite, the author found that bastnäsite can be identified by detecting dark red or red-orange luminescence in CL images of the ores in the wavelength range 420-680 nm or by detecting areas that emitted no luminescence in the 420-680 nm CL images but that do emit pale red luminescence in CL images in the broader wavelength range 350-1000 nm. The bastnäsite content in the ores can be estimated roughly from the fractional areas identified as bastnäsite in the CL images. The CL images can be obtained within 30 s. Therefore, CL imaging can prescreen mineral ores for subsequent more precise quantitative analyses (e.g., using inductively coupled plasma mass spectrometry or electron-probe microanalysis) by identifying mineral ores having a probable high bastnäsite content. This approach can drastically reduce the time required to explore mines with potential REE reserves.