Drift prospecting applied to iron oxide alkali-altered systems and iron oxide copper-gold deposits in the Great Bear magmatic zone, Northwest Territories, Canada
Bibliographic record
Abstract
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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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".