Rare Earth Elements (REEs) in mine waste: a way to solve the rising worldwide REEs demand?

The increasing demand of Rare Earth Elements (REE) in the industry and their economic importance plays a crucial role in the mining exploration. More knowledge on unconventional deposits such as dumps and tailings should be gathered to recover REEs. Purwadi et al. (2018) studied the concentration and visible and near-infrared reflectance spectroscopy of REEs-bearing tailings of a closed tin mine located on the Bangka Island (Indonesia) but detected no REEs bearing minerals due to their low abundance (<1wt.%). Our study investigates quartz rich tailings from this tin mine by means of Electron Microprobe (EMP). The measurements on 12 samples have shown the occurrence of zircon ZrSiO4 and abundant REE bearing minerals such as monazite (Ce,La)PO4, xenotime YPO4, thorite (Th,U)SiO4, and uranite UO2. REEs bearing phases occur in quartz or at the grain boundaries, are approximately 5 to 50 µ large, and form relatively fresh (poorly altered) un-to subhedral grains suitable for EMP point analyses. Plotting the concentration of the monazite and xenotime REEs in the chondrite normalized diagram they show the typical monazite decreasing and xenotime increasing pattern with no obvious anomaly. Chemically monazites are characterized by high thorium (up to 18% ThO - mainly as huttonite component) and very high yttrium and xenotime component (up to 3.5 wt. % Y2O3) indicating a high monazite formation temperature. Additional ICP-OES analyses, elemental mappings and in situ dating on monazite, will show the REEs distribution, e.g. depleting and or enrichment triggered by fluids, and the geochemical signature of these tailings.