Trace element distribution in sulphide assemblages of the Levack-Morrison ore system, Sudbury, Ontario: looking for chemical fingerprints of mineralization processes
Bibliographic record
Abstract
One challenge in the exploration for Cu-Ni-PGE mineralization in the footwall of the Sudbury Igneous Complex (SIC) is the uncertainty of its origin. The relative proximity of mineralization to the SIC is consistent with models of magmatic fractionation, but the common association of ore in the SIC footwall with amphibole and epidote alteration is consistent with a hydrothermal origin. Although these processes are not mutually exclusive (e.g. ores of magmatic origin could have been later remobilized by hydrothermal fluids), better constraints on which processes operated would greatly assist exploration. This project is a pilot study to assess whether chemical fingerprints can be established for four distinct mineralization types in the Levack-Morrison ore system: (a) contact; (b) a transition zone between contact and footwall ore; (c) sharpwalled veins; and (d) disseminated, S-poor, PGE-rich ores. Sulphide assemblages consisting primarily of pyrrhotite, chalcopyrite, and pentlandite were characterized in detail (petrography, SEM, EPMA, LA-ICP-MS). The results indicate that (a) Se content increases with depth; and (b) some trace elements (e.g. Cd vs. Se in chalcopyrite, Co vs. Se in pentlandite and pyrrhotite) can discriminate among different ore types. Calculated partition coefficients (± 2?) for Se in chalcopyrite and pentlandite (1.2 ± 0.1 for contact and transition ores, 0.5 ± 0.2 for sharp-walled veins) are significantly different, which is consistent with different mineralization processes for those ore types. In addition to trace element content calculation in major sulphides, element distribution maps were created from LA-ICP-MS spectra of sulphide assemblages. Some contact-style samples contained abundant euhedral pyrite but pyrite was also present in samples of other ore types. The maps showed complex trace element zonation (e.g. Se, Co, and As) in pyrite in contact ore, as well as some PGE minerals (notably Ir and Os). In contrast, no PGEs were detected in any of the other sulphides or any compositional zoning. Because Ir has very low solubility under most hydrothermal conditions, Co-rich, Ir-bearing pyrite was interpreted to have formed from the cooling of a sulphur-rich sulphide liquid. Such pyrite (when present) could be used as an indicator of a magmatic signature. To further refine these results, future work would need to focus on three areas: (1) analyses of additional samples from the Morrison-Levack ore system to validate the discrimination diagrams for different ore types; (2) similar work would need to be undertaken elsewhere in the Sudbury mining district, to establish if the proposed discrimination plots are applicable basin-wide; (3) better constraints would need to be established for the origin of the Co-rich, PGE-bearing pyrite to enable it to be used as a marker of ore type.
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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) | 0.001 | 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".