Mineralogy and Processing experiments of an unusual parasite bearing REE ore from northern Vietnam

The cabonatite-hosted Namxe rare earth element (REE) deposit in northern Vietnam has a total rare earth oxide (TREO) content of up to 2 wt% which is mainly hosted by parasite in the southern part of the deposit. Detailed mineralogical investigation of the rather complex mineralization revealed that parisite occurs in two geochemical varieties with slightly differing REE2O3/CaO ratios (5.8 ±0.2 vs. 6.8 ±0.35). Parisite occurs in dykes together with carbonates (ankerite, calcite) and barite and is often intergrown with fine-grained (sub 100µm size fraction) barite-celestine group minerals. The recognition of remnants of corroded bastnaesite suggest that REE enrichment is a result of a multi-stage process involving Sr- and CO3-rich fluids with mantle signature (δ13C values of -6.8 ‰ to -2.89 ‰) with no or little additional REE input.

We applied state-of-the-art techniques to propose a possible processing route of the ore, including experiments using sensor-sorting, selective comminution, magnetic separation (HIMS and WHIMS) and froth flotation. Sensor sorting turned out to be quite efficient as the basaltic host rock can be separated from the dyke material, resulting in a mass reduction of about 30% and a REE loss of less than 2%. Selective comminution experiments revealed similar results with the rejection of 27% of barren material and a slightly higher loss of REE (3.5%). Two step froth flotation of a model blend led to a concentrate with >40% TREO content.