Paragenetic Evolution of the Robertson Deposit: Eocene Reduced Intrusion-Related Gold Deposit in the Northern Shoshone Range, Nevada
Notice bibliographique
Résumé
Abstract The Robertson deposit, formerly known as Tenabo, is an Eocene reduced intrusion-related gold deposit located 5 km north of Pipeline, a world-class 20+ Moz Carlin-type gold deposit in the northern Shoshone Range, Nevada. This study is the first in-depth examination of Robertson describing gold mineralization, hydrothermal alteration, petrology of the intrusive rocks, and geochronology of the magmatic and hydrothermal events. We present six new U/Pb zircon ages of intrusive phases, one vein-hosted molybdenite Re/Os age, and one hydrothermal orthoclase 40Ar/39Ar age. Gold mineralization is spatially and temporally related to an intrusive complex referred to as the Tenabo stock, which is composed of successive intrusive phases including an early ilmenite-bearing diorite, andesite dikes, hypabyssal dacitic porphyry dikes, composite ilmenite-bearing granodiorite, granitic porphyry dikes, and hypabyssal rhyolitic dikes. Emplacement of the Tenabo stock resulted in contact metamorphism of the host siliciclastic rocks, yielding quartz, biotite, and calc-silicate hornfels that formed an aureole up to 1 km from the stock. Through petrographic observations and geochemical analyses, distinct alteration assemblages are identified, encompassing sodic-calcic, potassic, calcic, sericitic, and chloritic alteration. Petrographic observations of veins at Robertson indicate the succession of three main stages referred to as (1) pregold, (2) syngold, and (3) postgold. The pregold stage consists of barren quartz veins, potassic alteration veins comprising biotite veinlets and quartz-K-feldspar, quartz-arsenopyrite, quartz-chalcopyrite, and quartz-molybdenite veins. The syngold stage is composed of quartz-gold ± Bi-Te-Se-Pb-Ag–bearing sulfosalt veins containing native visible gold observed as single grains in quartz and/or rimming pyrrhotite, arsenopyrite, chalcopyrite, and loellingite (FeAs2) grains. The postgold veins encompass pyrite ± quartz, quartz-calcite-polymetallic sulfide veins with Pb-Zn-Sb-Ag-Sn base metal sulfides, bull quartz veins, and calcite veins. Crosscutting relationships, along with U/Pb zircon dating of intrusive phases, Re/Os molybdenite dating, and 40Ar/39Ar orthoclase dating, indicate two distinct magmatic phases at Robertson. Phase one is an early phase associated with hydrothermal activity, and phase two is a late phase associated with hypabyssal rhyolitic dikes. The period of gold mineralization at Robertson is linked with the initial phase of magmatism and subsequent hydrothermal activity, which was found to occur between 39.6 and 39.0 Ma. This study demonstrates that gold mineralization is spatially and temporally related to the emplacement of an upper Eocene 39.6 Ma reduced ilmenite-bearing intrusive complex into Paleozoic siliciclastic sedimentary rocks. This produced a high-tonnage, low-grade gold deposit characterized by an Au-As-Bi-Te-Cu metal association. Mineral assemblages observed at Robertson, comprising native bismuth, Bi sulfosalts, arsenopyrite, pyrrhotite, and loellingite (FeAs2), are characteristic of low-sulfidation and oxidation states akin to reduced intrusion-related gold deposits and gold skarns described globally.
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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 | 0,001 | 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 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 ».