Multistage evolution of gold mineralization in the Kibali gold district: Insights from pyrite analyses
Notice bibliographique
Résumé
The Kibali gold district, located on the Congo Craton, comprises a Neoarchean gold resource exceeding 28.7 Moz. The district is located within a westerly-verging stacked fold-and-thrust belt associated with a compressional tectonic regime active from ca. 2.64–2.60 Ga. Deposits are hosted by a major fault zone that consists of a complex series of smaller thrust faults, shear zones, and folds, which extend over 60 km. Gold deposits are primarily hosted in BIF and clastic sedimentary rocks. The gold and associated sulfides are in veins and disseminated in NE-to NNE-trending ore shoots within the deformed and metamorphosed volcanosedimentary rocks. Pyrite is the dominant sulfide mineral and hosts both solid solution gold and free gold. Because of its strong association with the gold mineralization, our study focusses on unravelling the metallogeny of the area by considering pyrite textural analyses, in situ trace element analyses using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), and S isotopic composition (δ 34 S) analyses using Secondary Ion Mass Spectrometry (SIMS). Eight distinct pyrite types were identified, including microcrystalline sooty (py-0a), small grains (<40 μm) (py-0b), aggregate recrystallized (py-1), core-rich inclusion (py-2), vein-like (py-3), non-zoned (py-4a), oscillatory As-bands zoned (py-4b), and cubic euhedral (py-5) pyrite. The ore-forming processes occurred over a polyphase evolution. Syn-diagenetic pyrite py-0a in volcaniclastic layers of older basin sediments served as the primary repository of Au (15.6 ppm median) with a near-zero δ 34 S value. Late diagenetic or early metamorphic pyrite (py-0b) was found in younger basin sediments. Py-1 resulted from solid-state recrystallization of py-0a and py-0b. During the early ore stage, porous py-2 with high Au concentrations (3.1 ppm) and various trace element enrichments precipitated due to fluid-rock interaction. Metal precipitation occurred through sulfidation and carbonation of wall rock with a relatively reduced fluid undergoing 34 S-depletion. However, py-3 displayed notable trace element depletion and a complex mineral association. In a second ore stage, py-4a and zoned py-4b deposition occurred, dominated by an over-pressured fluid fracturing brittle rock. Py-4b, rich in Au (5.5 ppm) concentrated in oscillatory zoned As-rich bands, resulted from interactions during pulsed fluid flow. This process involved fluid phase separation, non-equilibrium conditions, 32 S-depletion, and precipitation of py-4b with a high δ 34 S value (6.4 ‰ mean). Subsequently, pyrite (0–4) generations underwent deformation during a later ductile deformation event, leading to the remobilization and concentration of invisible gold into adjacent gold grains within the high-grade shoot plunging NE. This process involved shearing, boudinaging, and folding ore minerals in tightly folded structures. Late-stage py-5 formed under gold-poor fluid conditions or inefficient gold depositional conditions. Brittle fracturing of these grains later provided local sites for remobilized gold. The study contributes insights into the origin and evolution of gold mineralization in the Kibali gold district, supporting a multistage ore-forming fluid system. • Identified eight distinct pyrite types, each revealing unique mineral-forming processes. • Early syn-diagenetic py-0a serves as a repository of gold and trace elements. • Two ore stages (py-2 and py-4) involve dissolution-reprecipitation and overpressured fluid injection into low-permeability rocks. • Heavy positive δ 34 S isotope signatures linked to fluid-pressure pulses and phase separation. • Deformation processes connect to visible gold concentrations, upgrading to high-grade shoot.
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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 | 0,001 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,002 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,001 |
| Science ouverte | 0,001 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 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 ».