New insights into mineralogy and geochemistry of allanite-bearing Mediterranean coastal sands from Northern Greece

摘要

Allanite-bearing black coastal sands of Kavala (N. Greece) were studied using a combination of single-crystal XRD, EMPA, mu-XRF, bulk ICP-MS, LA-ICP-MS, mu-XANES and gamma-ray spectrometry. The sands are rich in REE (Sigma REE + Y: 4010 to 10,810 mg/kg), Th (236-1205 mg/kg) and other critical metals such as Nb, Ta and Co. The main REE- and Th-hosts are allanite and titanite. The allanite unit cell parameters were calculated whereas its formula was found to be (REE0.470Ca1. 499Th0.031) (Ti0.031Fe1.089+3Al1.880) (Si-2.906Al0.094O12) (OH). The mu- XANES spectra showed that LREE are present in trivalent oxidation state. Analyses of the non-magnetic sand fractions showed higher LREE (12,470 mg/kg) due to accumulation of allanite. The materials showed elevated radioactivity ranging from 885 +/- 13 to 3467 +/- 20 Bq/kg. The obtained results provide new insights on the provenance of the sands, the abundance of REE, Th, and other immobile elements, and offer new clues for potential exploration and exploitation.