Corundum in Sulfide Ore at the Thompson Mine, Manitoba, Canada: An Unusual Occurrence of Cr- and Ni-Bearing Corundum
Bibliographic record
Abstract
Abstract A novel type of corundum host environment is described from the Thompson Mine, northern Manitoba, where corundum occurs within a high-grade metamorphic reaction zone between boudinaged metaperidotite bodies, sulfide ore, and Al-rich pelitic schist of the Pipe Formation (Ospwagan Group). Zoned corundum porphyroblasts, up to 20 mm across, contain coevally formed sulfide inclusions, zircon, rutile, abundant exsolved rutile needles, and secondary sulfide inclusions formed within fractures. Retrograde alteration products of corundum include greenish muscovite (in contact with the schist) and diaspore (in contact with sulfides). The median concentrations of trace elements in Thompson corundum are as follows (in µg/g): 119 Mg, 1720 Ti, 69.9 V, 390 Cr, 8.2 Mn, 1924 Fe, 9.1 Ni, and 106 Ga. The geochemical signature of Thompson corundum (enrichment in Fe, Cr, and Ni) resembles that of ruby in other metamorphic and metasomatic mafic-ultramafic-hosted deposits, and the Cr concentration is comparable to the low range of rubies. Thompson corundum contains high Ni concentrations relative to most Cr-enriched corundum occurrences, a result of formation in an exceptionally Ni-rich environment. The high abundance of exsolved rutile inclusions imparts a dominantly brownish-gray color to the corundum, which precludes it from being of gem quality. Chromium-bearing corundum has been suggested as a possible indicator mineral for metamorphosed massive sulfide deposits, however, it is an indirect indicator that risks yielding false positives. Further investigation into Ni concentrations in corundum, a potential indicator of formation in a Ni-rich environment, is recommended.
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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 | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".