Evolution of High-Level Magmatic-Hydrothermal Systems: New Insights from Ore Paragenesis of the Veladero High-Sulfidation Epithermal Au-Ag Deposit, El Indio-Pascua Belt, Argentina
Notice bibliographique
Résumé
Abstract The world-class Veladero high-sulfidation epithermal Au-Ag deposit is located in the Andean cordillera of Argentina near the northern end of the El Indio-Pascua metallogenic belt. The deposit comprises two nearly coalescing subhorizontal orebodies that are centered on an extensive zone of intense hydrothermal alteration. Intensely altered volcanic rocks are composed of fine-grained groundmass quartz that formed as a result of extreme acid leaching. These quartz grains contain ubiquitous rutile inclusions as well as healed microfractures of vapor-filled inclusions that record magmatic vapor streaming through the Miocene volcanic host succession. Condensation of the magmatic vapor into ambient groundwater generated the highly acidic waters responsible for the alteration. Alunite is present in the fine-grained groundmass quartz and fills vugs in the altered rocks. Stable isotope data indicate that the alunite formed through the disproportionation of SO2 in the condensed magmatic vapor. The fine-grained groundmass quartz is crosscut by later fracture-controlled euhedral quartz that is texturally associated with ore minerals. The euhedral quartz crystals show oscillatory growth zoning and contain rare primary fluid inclusions suggesting that quartz formation occurred at ~200°C from a moderately saline (<5 wt % NaCl equiv) liquid-phase hydrothermal fluid. High-fineness native Au grains are hosted in euhedral quartzlined void spaces and along fractures. In addition to native Au, vugs and fractures in the silicified volcanic rocks host Fe oxide/hydroxide and jarosite that are interpreted to represent the oxidation products of hypogene sulfide minerals that formed during and after the late stages of quartz formation. Results of previous jarosite dating suggest that pervasive oxidation of the orebody commenced during the waning stages of the hydrothermal activity or immediately thereafter. Oxidation of the orebody continued in the supergene environment for at least 3 m.y. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) showed that jarosite, which formed as a result of the oxidation of the orebody, is the principal host for Ag in Veladero ore, explaining the low (ca. 10%) Ag recovery from the oxide ore. The Veladero high-sulfidation epithermal deposit is interpreted to have formed in the shallow part of a magmatic-hydrothermal system. Early alteration related to magmatic vapor discharge was followed by later mineralization from liquid-phase hydrothermal fluids under reduced and slightly acidic to near-neutral conditions. This change from early vapor-dominated to later liquid-dominated magmatic-hydrothermal fluid flow was key in formation of the deposit.
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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) | 0,001 | 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 | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,003 | 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.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».