Structural analysis and metamorphism of the Barlow Fault Zone, Chibougamau area, Neoarchean Abitibi Subprovince: implications for gold mineralization
Bibliographic record
Abstract
Faults and deformation zones are important features of Archean terranes because of their significance for structural evolution and the formation of large gold districts. In the Chibougamau area, northeastern portion of the Abitibi Subprovince, an Apogee Metal Earth seismic reflection survey identified an association between an exceptional shallow-dipping subsurface reflector zone and the Barlow Fault Zone visible at the surface. This fault zone is located adjacent to the Opatica Subprovince and shares many characteristics with well-documented major gold-bearing faults in the more gold-endowed southern portion of the Abitibi Subprovince. This study aimed to reconstruct the kinematic evolution of the Barlow Fault Zone, determine its position within the structural setting of this section of the Abitibi Subprovince, and evaluate its importance for gold potential in the northern part of the Chibougamau area. The fault zone can be divided into three segments that differ markedly in dip. Structural reconstruction and field observations are compatible with a reverse south-over-north movement related to a ductile north–south shortening event, which culminated with amphibolite metamorphism. A late normal movement is deduced at the final stage. Geothermobarometers indicate peak metamorphism conditions of 550 ± 50 °C and 6 ± 1.2 kbar. Results from this study suggest that amphibolite facies metamorphism covers a much wider area within the Chibougamau region than previously documented. The Barlow Fault Zone shares similar geometric characteristics and evolutionary history with other gold-bearing structures in the Abitibi Subprovince, but ultimately it was unable to provide optimal conditions for channelling fluid and precipitating gold. High-grade metamorphism and the limited crustal extent of the fault likely prevented the tapping of deep metamorphic fluid and magma reservoirs. The Barlow Fault Zone is interpreted as a back-thrust fault that belongs to a more extensive south-dipping fault system encasing juxtaposed tectonic slivers. This system, with amphibolite facies metamorphism, is a defining feature of the northern portion of the Chibougamau area and developed during the accretion between the Opatica and Abitibi subprovinces.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 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 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".