Emplacement of sharp-walled sulphide veins during reactivation of impact-related structures at the Broken Hammer Mine, Sudbury, Ontario
Bibliographic record
Abstract
Broken Hammer is a hybrid, Cu-Ni-Platinum Group Element (PGE) footwall deposit in the North Range of the ca. 1.85 Ga Sudbury impact structure. The sulphide vein system and associated low sulphide PGE mineralization were mined as an open pit operation over a 15-month period, providing a unique opportunity to study a complete 90-meter vertical section across a footwall deposit. The deposit is hosted within Archean basement rocks and impact-induced Sudbury breccia, 1.5 km north of the Sudbury Igneous Complex (SIC) – basement contact. The low sulphide mineralization consists of disseminated to blebby chalcopyrite (<5%), minor pyrite, chalcocite, galena, sphalerite and platinum group minerals, associated with Ni-bearing chlorite overprinting alteration patches of epidote, actinolite and quartz. The veins comprise massive chalcopyrite and minor magnetite, chalcocite, millerite, and rare sperrylite, surrounded by thin epidote, actinolite and quartz selvedges. They are grouped into five, steeply-dipping, NE-, SW-, SE-, S- and EWstriking sets, which intersect in a common line controlling the plunge (60°) and trend (220°) of ore shoots. The veins were emplaced along syn-impact fractures that were reactivated multiple times during stabilization of the impact crater floor. Early reactivation of the fractures created pathways for the migration of hydrothermal fluids from which quartz and chlorite precipitated sealing the fractures. Renewed slip and reactivation shattered the quartz-chlorite veins into fragments that were incorporated in massive sulphide veins that crystallized from strongly fractionated sulphide melts or high temperature (400°C-500°C) hydrothermal fluids which migrated outward into the basement rocks from a cooling and crystallizing impact melt sheet represented by the SIC. Hydrothermal fluids syn-genetic with the epidote-actinolite-quartz alteration distributed the PGE into the footwall rocks, or late hydrothermal fluids associated with the Ni-bearing chlorite leached Ni and PGM’s from the sulphide veins and re-distributed them within the footwall rocks, forming the low-sulphide high-PGE mineralization. During post-impact tectonic events, reactivation and slip at temperatures below the brittle-ductile transition for chalcopyrite (<200°C-250°C) produced striations along the vein margins. The Broken Hammer deposit exemplifies how Cu-Ni-PGE footwall deposits formed by the reactivation of syn-impact fractures that provided conduits for the migration of melts and hydrothermal fluids.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".