The nature and origin of the Nechalacho rare metal deposit (REE, Nb, Zr), Northwest Territories, Canada
Notice bibliographique
Résumé
The Nechalacho REE-Nb-Zr deposit at Thor Lake, Northwest Territories, Canada, consists of layers of hydrothermally altered eudialyte syenite. With combined measured, indicated and inferred resources of 269 Mt grading 1.47 wt. % REE-oxide, 0.35 wt. % Nb2O5 and 2.59 wt. % ZrO2, the deposit is one of the largest REE deposits in the World. The principal primary magmatic REE-Nb-mineral is kentbrooksite (eudialyte). Strong hydrothermal alteration led to its replacement by fergusonite-(Y), samarskite-(Y), columbite-(Fe) and -(Mn), xenotime-(Y), monazite-(Ce), bastnäsite-(Ce), parisite-(Ce), synchysite-(Ce), allanite-(Ce) and zircon. The host aegirine-nepheline syenite was metasomatically replaced by a phlogopite-quartz-magnetite-ankerite-fluorite assemblage. Peripheral pegmatites, the T-, R- and S-Zones, contain high-grade Li, Be, REE and Nb mineralization. The host to the Nechalacho REE-Nb-Zr deposit is an agpaitic nepheline syenite intrusion, the Nechalacho Layered Suite, which crosscuts the anorogenic 2176 Ma Blatchford Lake Igneous Complex. The laccolithic intrusion has a diameter of ~1.9 km, is >1.1 km thick and displays modal layering of nepheline, sodalite, end-member aegirine and annite, K-feldspar, albite and eudialyte. A U-Pb zircon concordia age of 2176.0 ± 2.7 Ma shows that the nepheline syenites are contemporaneous with the other units of the complex. The initial εNd(2176 Ma) was between 1.1 and 3.1, averaging 2.0, and δ18Omelt and δDmelt values calculated from magmatic minerals are 5.1 to 7.8‰ and 60‰, respectively. In the earlier alkaline granite and quartz syenites of the complex (Grace Lake Granite, Thor Lake Syenite, Rim Syenite), δ18Omelt and δDmelt were 6.7 to 8.1‰ and -99 to 93‰, respectively. Combined with whole-rock trace element profiles, this indicates that the units of the complex formed from melt batches extracted from a deep crustal feeder magma chamber in which a mantle-derived, heterogeneous mafic parental melt, that was similar to modern ocean island basalt, underwent fractional crystallization. The Nechalacho Layered Suite formed from the youngest and most evolved batch, which was magnesium-free and enriched in Zr, REE, Nb, carbon species, fluorine and chlorine. Mineral equilibria indicate that at ~800 to <500 °C and a pressure of ~4 kbar, oxygen fugacity was initially below FMQ+0.2 to FMQ+1.3, and later increased in response to auto-oxidation of the melt by annite crystallization. In situ fractional crystallization proceeded upwards and downwards and REE, Nb and Zr were enriched in an iron-rich residual melt until the magma became saturated with respect to eudialyte. Mineral fractionation led to variations in light/heavy REE, Zr/Hf and Nb/Ta, with the Basal Zone recording the strongest heavy REE enrichment. Magmatic-hydrothermal auto-metasomatism associated with ankerite-bastnäsite-(Ce) mineralization is indicated by trends of δ13C from -6.3 to 2.7‰ and of δ18O from 11.3 to 15.0‰ for hydrothermal carbonates. Ankerite from the T-Zone has similar values, demonstrating a genetic link to the peripheral pegmatites at the magmatic-hydrothermal interface. U-Pb and Th-Pb ages of hydrothermal monazite-(Ce) from the Basal Zone (1871 ± 14 to 1835 ± 57 Ma) indicate a late regional hydrothermal overprint associated with faulting along the southern margin of the Slave Craton. Hydrothermal temperatures determined using oxygen isotopes are ~300 °C and the fluids had δ18O of 3.1-9.3‰ and δD of 24‰, suggesting a crustal origin. Mineral equilibria indicate that the alteration fluid was reducing (FMQ+2.0 to +3.7) and that pH was moderately acidic to mildly alkaline (between 3.7 and 5.7). Likely, the alteration fluid was initially acidic and neutralized upon reaction with the nepheline syenites. This external crustal fluid was Mg-bearing and caused the in situ replacement of eudialyte by multiple REE-Nb minerals and phlogopite-magnetite-quartz alteration.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
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 | 0,001 |
| Études des sciences et des technologies | 0,002 | 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) | 0,002 | 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 ».