Nanoscale Characteristics of Carlin-Type Auriferous Pyrite from the Nadaleen Trend, Yukon
Notice bibliographique
Résumé
Abstract Gold deposits of the Nadaleen trend in central Yukon host over 1.7 million ounces (Moz) of Au and share many characteristics in common with Nevada’s Carlin-type deposits, including similar host rock types, structural setting, alteration, and geochemistry, as well as the occurrence of gold in hydrothermal arsenian pyrite. We examined the textures, minor and trace element geochemistry, and δ34S signatures of precursor pyrite and hydrothermal pyrite overgrowths in samples grading over 35 g/t Au from the Sunrise and Conrad deposits. In the Osiris limestone at Sunrise, hydrothermal pyrite occurs as rims ranging from <1 to 5 µm overgrowing subhedral to euhedral sedimentary pyrite grains that are 20 to 100 µm in diameter; as rims (<1 to 3 µm thick) of hydrothermal pyrite that cement together the individual aggregates (measuring <1 to 5 µm) in framboidal pyrite; and as disseminated hydrothermal pyrite grains (<1 µm) that may be single stage. The hydrothermal pyrite in our Sunrise samples contains up to 45 ppm Au, 29 ppm Cu, 1,053 ppm As, and 15 ppm Ag, with δ34S compositions that are 1 to 8‰ higher than the sedimentary pyrite. The hydrothermal pyrite is zoned at the nanoscale, with the highest Au concentrations typically in the outermost portion of the rims. In the Conrad gabbroic dike, hydrothermal pyrite occurs as rims ranging from <1 to 5 µm overgrowing earlier pyrite grains that are 5 to 100 µm in diameter. The inner rims of the hydrothermal pyrite contain up to about 20 ppm Au, 900 ppm As, 60 ppm Ag, and 50 ppm Cu, whereas the outer margins of the hydrothermal pyrite contain up to about 670 ppm Au, 23,400 ppm As, 385 ppm Ag, and 115 ppm Cu. Relatively coarse hydrothermal rims (up to 5-µm) occur on the coarsest grains of precursor pyrite, suggesting that the substrate partially controls the texture of the hydrothermal pyrite, potentially due to the availability of Fe during sulfidation. The δ34S plateau values of the hydrothermal rims range from 1.2 to 11.0‰. Bayesian stable isotope modeling shows that the δ34S compositions of the hydrothermal pyrite can be generated by mixing the locally present sedimentary rocks with locally present magmatic sulfur. The modeling indicates that additional sources are not required, although they cannot be ruled out. At high Au concentrations, the modeling shows that most of the sulfur in the hydrothermal pyrite comes from a magmatic source, potentially from buried plutons visible as aeromagmetic anomalies. The modeling does not differentiate between whether (1) these magmatic rocks contributed sulfur and metals during passive leaching by an amagmatic hydrothermal fluid or (2) cooling magmas exsolved a sulfur- and metal-bearing fluid that led to magmatic-hydrothermal mineralization. We favor the latter interpretation, since the available geochronological evidence suggests that mineralization on the Nadaleen trend occurred during or shortly after Late Cretaceous emplacement of volumetrically limited, mantle-derived gabbroic dikes. Collectively, the evidence supports a Carlin-type origin for the gold deposits on the Nadaleen trend. Continued study is needed to link site-specific characteristics and processes to the regional metallogenic setting.
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Comment cette classification a été obtenuedéplier
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) | 0,004 | 0,001 |
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; les deux têtes enseignantes s’accordent sur ce qui est montré ici.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».