Niobium, Critical Metal, and Progeny of the Mantle
Notice bibliographique
Résumé
Abstract Niobium is a critical metal in high demand because of technological advances and the supply risk created by the fact that over 90% of its production is by a single country (Brazil). In this paper, we review the geology of the deposits that are currently being mined and other potentially economic deposits as well as develop models for their genesis. With the exception of the Lovozero deposit (Russia), which is hosted by a layered silica-undersaturated alkaline igneous complex, all the deposits that are currently being mined for niobium are hosted by carbonatites, and most of the deposits with economic potential are also hosted by these rocks. Niobium owes its concentration in carbonatites and alkaline silicate rocks to its highly incompatible nature and the small degree of partial melting of the mantle required to generate the corresponding magmas. The primary control on the concentration of niobium to economic levels in alkaline silicate magmas is fractional crystallization, partly prior to but mainly after emplacement. In the case of silica-undersaturated magmas, the final residue saturates in minerals like eudialyte and loparite to form niobium-rich horizons in the layered complexes that crystallize from these magmas. The final residue, in the case of silica-saturated magmas, crystallizes the pegmatites that are the hosts to the economic niobium mineralization, which commonly takes the form of pyrochlore. In contrast, carbonatitic magmas undergo little to no fractional crystallization prior to emplacement. Moreover, fractional crystallization on emplacement has minimal impact on the concentration of niobium to economic levels. Instead, we propose that the metasomatic interaction of the carbonatitic magmas with their hosts to form rocks like phlogopitite (glimmerite) consumes much of the magma, leaving behind a phoscoritic residue from which pyrochlore crystallizes in amounts sufficient to form economic deposits. Although many niobium deposits display evidence of intense hydrothermal alteration, during which there can be major changes in the niobium mineralogy, the extremely low solubility of niobium in aqueous fluids at elevated temperature precludes significant mobilization and, thus, enrichment of the metal by hydrothermal fluids. However, weathering of carbonatite-hosted niobium deposits leads to supergene enrichment (due largely to the dissolution of the carbonate minerals) that can double the niobium grade and make subeconomic deposits economic. Pyrochlore is the principal niobium mineral in these laterite-hosted deposits, although its composition differs considerably from that in the primary mineralization. This paper evaluates the processes that appear to be responsible for the genesis of niobium ores and provides a framework that we hope will guide future in-depth studies of niobium deposits and lead to more effective strategies for their successful exploration and exploitation.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,001 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».