Origin and Evolution of the Iron-Rich Upper Unit and Fe–Ti–V Mineralization of the Neoarchean Lac Doré Layered Intrusion, Chibougamau, Québec
Bibliographic record
Abstract
Abstract The Lac Doré Complex (LDC) is a metamorphosed Neoarchean (ca. 2728 Ma) tholeiitic layered intrusion with an estimated thickness of 7–8 km. The Layered zone (magnetitite, anorthosite, and gabbro mostly, and ferrodunite locally) is located in the upper part of the LDC, and it corresponds to an Fe–Ti oxide-bearing unit currently being explored for Fe–Ti–V magmatic deposits. Previous studies documented lithological, textural, and chemical heterogeneities in the Layered zone from the NW, NE, and S limbs of the LDC. This study integrates detailed chemical and petrological investigation of Fe-rich rocks across the Layered zone to evaluate the impact of magmatic processes (contamination, magma replenishment events, and fractional crystallization) on the evolution of the upper part of the LDC. Field data point to fractional crystallization (upward increase of quartz, apatite, and ilmenite, and decrease of titanomagnetite) and to efficient mineral sorting within flow currents (modal layering) in the S limb, where the Layered zone is thick, possibly as a result of frequent replenishment events. Petrological observations and bulk rock chemistry indicates that the magma emplaced at the NW limb was more evolved (Si richer) than the Fe-rich magmas emplaced at the NE and S limbs, explaining the limited economic potential of the NW limb. The chemistry of Fe–Ti oxides indicates that the least evolved Fe-rich magma (magma most enriched in V, Cr, and Ni) emplaced at the NE limb and subsequently interacted with Si–Ca–poor carbonate-facies iron formation. The chemistry of Fe–Ti oxides, as well as ƒO2 estimates, points to additional chemical heterogeneities across the Layered zone, which are interpreted to result from several injections of a chemically heterogeneous residual tholeiitic melt (Fe rich) followed by inefficient homogenization process. We conclude that Fe-rich residual melts produced by prolonged crystallization of silicates during most of the evolution of the LDC were extracted from the Lower zone (anorthosite- and gabbro-dominated unit) and migrated upward to form the Layered zone. Successive extraction of the Fe-rich melt in response to regional and/or local deformation event translates as replenishment events for the Layered zone that then evolved through contamination (NE limb), fractional crystallization (NW, NE, and S limbs), and mineral sorting (S limb).
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| 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 teacher head, 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".