On the Origin of Bastnaesite (La,Nd,Y) in the Nissi (Patitira) Bauxite Laterite Deposit, Lokris, Greece

Rare Earth Deposits & Mining

Kalatha, and 3 co-authors, reported in 2017 that a detailed geochemical study and a mineralogical description of the rare-earth elements (REE)-minerals and associated minerals were carried out on samples from two outcrop exposures of approximately 4 meters within the Nissi (Patitira) bauxite laterite deposit, Lokris, Greece. The samples examined are characterized by the presence of goethite in small sizes resembling bacterial cell coated by goethite and a significant REE enrichment. The enrichment of the REE concentrated in bastnaesite-group minerals,the intergrowths between REE-minerals and Al–Ni–silicates with significant sulfur contents and their association with goethite microtextures were interpreted as bacteriomorphic, indicate REE remobilization along with iron bio-leaching and re-precipitation on karstified limestone.

In addition to the previous-reported hydroxyl bastnaesites, a (La,Nd,Y)(CO₃)F member of the bastnaesite-group associated with Al–Ni–silicates were identified, the stability of which may reflect the dependence on the source rocks and the local variations of pH-Eh. Interaction between recharging groundwater and carbonate rocks seems to be a very effective mechanism for REE fluorocarbonates deposition under alkaline and reducing conditions.

Based on the mineralogical and geochemical data presented in this study combined with information from the current literature, the authors have concluded:

• In addition to the hydroxyl bastnaesites described by previous authors in the Nissi (Patitira) laterite deposit, a (La,Nd,Y)(CO₃)F member of the bastnaesite group, associated with Al–Ni–silicates, has been identified.

• The enrichment of the REE at the Nissi (Patitira) concentrated in bastnaesite-group minerals, the intergrowths between REE-minerals and Al–Ni–silicates and their association with goethite microtextures have been interpreted as bacteriomorphic support the remobilization of REE along with iron downward and re-precipitation on karstified limestone.

• The stability of the (La,Nd,Y)(CO₃)F may reflect this dependence on the source rocks and the local variations of pH-Eh present in the recharging groundwater.