Identification of monazite and estimation of its content in ores by cathodoluminescence imaging

Identification of rare earth element (REE)-bearing minerals in ores is important for the efficient exploration of mines that reserve REEs. This study presents a method to identify monazite, which is one of the principal REE-bearing minerals, and determines its content in ores via cathodoluminescence (CL) imaging. Monazite emitted pale red luminescence in CL images at 850–920 nm wavelengths in ores annealed at 1300 °C. No luminescence in 420–680 nm wavelength was observed. Apatite, xenotime, cheralite, quartz and potassium feldspar in the annealed ores emitted intense luminescence in CL images at 850–920 nm but also 420–680 nm wavelengths. Hence, we are able to distinguish monazite from other minerals by first finding areas with pale red luminescence in CL images in the 850–920 nm and subsequently in the 420–680 nm wavelengths. Areas with pale red luminescence in CL image in the 850–920 nm and no luminescence in the 420-680 nm wavelengths imply the presence of monazite. From the areas, monazite content in ores can then be estimated. The CL images can be obtained within 10 s. Therefore, the CL imaging method proposed in this study is applicable to the selection of ores with high content of monazite, which are needed in the precise quantitative analysis of ICP–MS, leading to a reduction in time to explore mines containing REEs.