Scheelite texture and composition fingerprint skarn mineralization of the giant Yuku Mo-W deposit, Central China
Notice bibliographique
Résumé
• The scheelite REE pattern is controlled by substitution mechanisms and affected by REE-bearing mineral coprecipitation. • The scheelite Eu anomaly can be used to assess fluid oxygen fugacity. • The scheelite Mo concentration should be used with other parameters to assess fluid oxygen fugacity. • The scheelite Mo concentration is valuable for distinguishing between orogenic and skarn deposits. Scheelite is widely used to reveal ore-forming redox environments and track hydrothermal evolution processes in W-bearing deposits. Yuku, situated in Central China, is a typical skarn Mo-W deposit discovered recently in the Luanchuan Mo-W-Zn-Pb ore district. This study determined the compositions of the Yuku scheelite via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and electron microprobe analysis (EMPA) techniques. Based on the textural characteristics and mineral assemblages, three types of scheelite were categorized, including Sch A1, Sch A2, and Sch B. In general, Sch A1 formed during the prograde stage, mostly occurring as euhedral grains that distributed discretely within the interstices of skarn minerals. Sch A2 predominantly formed as the rim of Sch A1 or crosscut Sch A1. It is commonly associated with sulfides, such as pyrrhotite, pyrite, and molybdenite. Sch B is primarily observed in the quartz-sulfide veins or within pyrrhotite crystals, occurring later than Sch A1 and Sch A2. Geochemically, Sch A1 contains a significantly higher Mo content (>14,300 ppm) and is characterized by a negative inclined chondrite-normalized rare earth element (REE) pattern, while Sch B has Mo contents lower than 10,300 ppm and exhibits an M-type tetrad REE pattern. Sch A2 contains a Mo content ranging from 146 ppm to 89,000 ppm (mean 27,900 ppm) and displays an intricate REE pattern that partially overlaps with Sch A1 and Sch B. The difference of REE concentrations among different scheelite generations is controlled by substitution mechanisms and also influenced by the precipitation of garnet and pyroxene. Sch A1 and Sch B exhibit a linear 1:1 trend between Na (atom) and ΣREE – Eu + Y (atom), indicating the important role of substitution via 2Ca 2+ = REE 3+ + Na + . The concentrations of Nb, Ta and V are notably low, supporting only a small amount of REE incorporation into Sch A1 through Ca 2+ + W 6+ = REE 3+ + (Nb + Ta + V) 5+ . The REE patterns of Sch A1 and partly Sch A2 resemble those of the causative intrusions, indicating that substituting the site vacancy in scheelite lattice is another crucial mechanism. All three substitution mechanisms play roles in REE incorporation during the scheelite mineralization process. Negative Eu anomalies prevail in Yuku scheelite (mean δEu = 0.77), although positive Eu anomalies are also observed, particularly in Sch B (mean δEu = 1.11). Additionally, there is a conspicuous decreasing trend in the Mo content from the prograde to late stage, suggesting that the Mo-W mineralization at Yuku likely experienced a decrease in oxygen fugacity and/or temperature. Furthermore, in a comparative analysis of scheelite Mo content and Eu anomaly with other deposits, it was observed that Mo content in skarn deposits is generally higher than that in orogenic deposits (mostly <100 ppm), providing a tool for distinguishing deposit types utilizing scheelite geochemical characteristics.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| 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 | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 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 tête enseignante, pas un consensus.
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