The Genesis of Regolith-Hosted Heavy Rare Earth Element Deposits: Insights from the World-Class Zudong Deposit in Jiangxi Province, South China
Notice bibliographique
Résumé
"The Zudong heavy rare earth element (HREE) deposit in South China is the largest regolith23 hosted HREE deposit in the world with a resource of ~17,600 t of REO, at an average grade of ~0.1 wt. % REO. Despite more than 40 years of exploration and exploitation, the genesis of this deposit is poorly understood. Subtropical weathering of the parent A-type granite formed ore bodies hosted mainly within the lower B to upper C horizons of the resulting soil, which is developed on the hillsides of a moderately incised landscape (relief ~150m). The thickness of the ore bodies varies from a few meters to up to 10 m. Rare earth element concentrations increase from ~300 ppm in the A horizon to ~1500 ppm in the lower B to upper C horizons and decrease with further depth in the profile. The entire soil profile is HREE-enriched with (La/Yb)N ratios <1, but the REE-enriched lower B horizon is less HREE-enriched ((La/Yb)N values up to 0.9) than the underlying upper C horizon. Exchangeable REEs, representing REEs that are adsorbed in the deposit, constitutes ~65% of the bulk REE content; the LREEs are preferentially adsorbed. The main minerals adsorbing the REEs are kaolinite and halloysite; the proportions of REEs adsorbed by Fe-Mn oxyhdyroxides and organic matter are negligible. The remaining REE content is hosted by supergene chernovite [YAsO4] and residual aeschynite/euxenite36 group and fergusonite-group minerals, xenotime-(Y), zircon, and thorite. The Zudong deposit formed from weathering of a HREE-enriched A-type granite, containing between ~200 and ~450 ppm REE dominantly as synchysite-(Y), yttrian fluorite, gadolinite-(Y), hingganite-(Y), and yttrialite-(Y), which are susceptible to chemical weathering. Decomposition of these minerals released REEs to the weathering fluid, and the interaction between alkali feldspar, muscovite and the weathering fluid produced halloysite and subordinate illite and smectite. With progressive weathering, these minerals accumulated together with quartz, refractory zircon, xenotime43 (Y), and aeschynite/euxenite-group and fergusonite-group minerals. In the upper parts of the soil profile, where conditions were acidic, dissolution of REE minerals is promoted and the REEs tend to remain in solution. Deeper in the profile (lower part of the B horizon and upper part of the C horizon), conditions become less acidic leading to adsorption of the REEs and As (released by weathering from an adjacent coal unit) on the surface of halloysite. With time, halloysite, a metastable phase in respect to kaolinite, gradually transforms to the latter, releasing As and variable proportions of the adsorbed REEs. The released REEs and As are transported downwards, partially re-adsorbed by clay minerals and the remaining REEs combined with As to precipitate supergene chernovite-(Y). Ongoing operation of this eluviation-illuviation process at Zudong has gradually enriched the soils in HREEs to form a resource that now supplies much of the world’s HREE."@eng
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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 | 0,003 | 0,004 |
| Études des sciences et des technologies | 0,001 | 0,001 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,001 |
| 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 ».