Rare Earth Elements: Conventional and Non-Conventional Deposits

• Joan Carles Melgarejo ^[1]
  1. [1] Universitat de Barcelona

     Universitat de Barcelona

     Barcelona, España

     
• Localización: Seminarios de la Sociedad Española de Mineralogía, ISSN-e 2659-9872, ISSN 1698-5478, Vol. 12, 1 1 (Huelva, 30 de junio 2015), 2015 (Ejemplar dedicado a: Los Elementos de las Tierras Raras), págs. 13-91
• Idioma: inglés
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• Resumen

  • The renovated interest for the REE elements compels to strengthen and promote the study of their classical outcrops and the discovery of new elements of the same group along the same lines China followed over the last years. In magmatic outcrops, REE tend to concentrate in the most alkaline typologies (undersaturated and oversaturated) and in carbonatites, especially in their latest stages, being these pegmatitic or associated to hydrothermal fluids, frequently saline and rich in F or B. In addition, other mechanisms of transport of REE can occur. However, to obtain an economic deposit, sometimes these pre-concentrations need improve their cut-off grades by means of supergene enrichment. Deposits of hydrothermal origin are associated with hypersaline fluids with the resulting hydrothermal alterations (albitizations, scapolitizations…) or fluids very rich in F or B. Consequently, some skarns, IOCG or U deposits associated to unconformities constitute the hydrothermal deposits more given to contain REE. In addition, fluids associated with shear zones, rich in CO2, also transport REE. In the exogenous medium REE can efficiently be concentrated in saline environments, as caliches, evaporites, primary or diagenetic phosphorites, submarine muds and Fe-Mn submarine crusts, while more stable minerals, as monazite or xenotime concentrate in placers. The combustion of carbons can result in differentiated residue rich in REE. Moreover, laterites, bauxites and clays, product of the weathering of other rocks, can become enriched in REE. The potential in REE is explored in geothermal fluids and manganese deposits, as well as in ancient sedimentary series including hard grounds or diagenetic zeolite deposits, or even some deposits associated with reductive geochemical traps, like red beds or series including black shales.