Understanding the South Range Sudbury impact structure: a study of shear zones, impact breccias and PGE occurrences in the Vermilion and Crean Hill mines area, Sudbury, Canada
Bibliographic record
Abstract
The Sudbury impact structure formed when a bolide collided with the southern Superior craton margin ca. 1.85 Ga ago. During the impact, the target rocks were brecciated and melted, which resulted in the formation of a thick impact melt sheet, the Sudbury Igneous Complex (SIC), underlain by brecciated basement rocks. Nickel-copper-platinum group elements (Ni-Cu-PGE) deposits formed at the base of the SIC as contact deposits, in association with offset dikes that flowed from the melt sheet into the basement rocks (offset deposits), and as sulphide veins and pods of disseminated PGE mineralization that were emplaced into the brecciated basement rocks (footwall deposits). The deposits and their host rocks were subsequently modified by orogenic events that reworked the South Range of the impact structure. The thesis discusses the formation of syn-impact breccias below the SIC-basement contact, the structural and metamorphic modification of the impact structure during subsequent orogenic events, and the effect of syn- and post-impact processes on the formation and remobilization of (Ni-)Cu-PGE mineralization at the contact-type Crean Hill deposit and offset-type Vermilion deposit. The breccias formed by in situ shock melting of the footwall rocks during the impact, and were modified by contact metamorphism during cooling of the SIC and by syn-tectonic deformation and metamorphism after the impact. The latter resulted in the formation of regional folds and south-side-up-dextral shear zones during northwest-directed shortening of the impact structure. (Ni-)Cu-PGE mineralization at the Crean Hill and Vermilion deposits was emplaced as sulphide melts immediately after the impact and was remobilized by metamorphic semi-metal melt and hydrothermal fluids into the breccias and shear zones during and after regional deformation. These results illustrate how both syn- and post-impact processes contributed to the formation and modification of Ni-Cu-PGE deposits in Sudbury.
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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 | 0.004 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".