Drift prospecting applied to iron oxide alkali-altered systems and iron oxide copper-gold deposits in the Great Bear magmatic zone, Northwest Territories, Canada
Notice bibliographique
Résumé
This thesis provides foundations for the development of glacial drift prospecting techniques applied to iron oxide alkali-alteration systems (IOAA) that can host deposits from the broad iron oxide apatite (IOA) and iron oxide copper-gold (IOCG) families. The potential of using drift prospecting as an exploration tool in these complex metasomatic systems is explored with a till matrix geochemical study and an indicator mineral study within the Great Bear magmatic zone (GBMZ). Both of these drift prospecting methods offer promising leads towards exploration vectors for IOA and IOCG mineralization as well as their IOAA system footprint in glaciated terrain. The discontinuity of the till cover, the high compositional variability of the till due to heterogeneity within the source bedrock, the extensive size of alteration halos and the abundance of minor satellite mineralization in areas of interest complicate the application of surface exploration methods. However, Fe, Co, Ni, Cu, As, Mo, Bi, La, Th, U and W were identified as the most common potential vectoring elements towards mineralization in the GBMZ till matrix fraction based on a comparisons between a lithogeochemical dataset of the GBMZ (n= 707 samples) and a till geochemical dataset (n=101 samples). Anomalous concentration thresholds were established using the median values of elemental concentrations found in GBMZ background samples ± two times their standard deviation. Potential vectoring elements are dependent on the chosen analytical protocol, i.e. till matrix size fraction analyzed and digestion method used. In order to target the metasomatic halos of the mineralized systems, an innovative quantitative approach was developed based on the ratio of a selected element concentration from two analytical techniques. As such, mapping the ratios of the concentrations of either La or Th obtained from a near-total digestion method over those obtained from a partial digestion method in the silt+clay-sized fraction of till defines a more consistent target than any element concentrations from any single digestion method used alone. This ratio reflects a variation in the element host mineral caused by metasomatic alteration. This approach was tested for the Sue Dianne deposit due to the higher number of till samples collected in its vicinity.The potential of apatite to serve as an indicator of the presence of alteration systems and associated deposits in the GBMZ was also investigated. Apatite was selected due to its preservation in GBMZ till and its key role in the apatite-amphibole-magnetite assemblages as a signature alteration product of IOAA systems. The distinct fluorapatite chemistry that evolves within these systems can record metasomatic processes within IOA and IOCG deposits. Apatite from least-altered bedrock and from some IOAA systems have green to yellow-green cathodoluminescence responses. In contrast, apatite rich in REEs and poor in Mn, have a blue or blue and green-zoned cathodoluminescence response. REE-rich apatite crystals form during high temperature sodic-calcic-ferric/ferrous and calcic-ferric/ferrous metasomatism. As temperatures decline and the fluid chemistry evolves, localized REE leaching takes place within apatite and leads to the growth of secondary REE-bearing minerals. Apatite characteristics inherited from metasomatic history, such as irregular zoning, dissolution pits and mineral inclusions are visible in grains picked from the heavy mineral concentrates of till samples. Their presence may serve as a regional vector towards IOAA systems. The presence of blue cathodoluminescence response in apatite grains from till samples may serve as a local exploration tool for REE-rich IOA to IOCG prospects.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,002 | 0,003 |
| Études des sciences et des technologies | 0,001 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,001 |
| 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 source (Gemma direct ou Codex distillé), 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 ».