3-D Distribution of Sulphide Minerals in the Merensky Reef (Bushveld Complex, South Africa) and the J-M Reef (Stillwater Complex, USA) and their Relationship to Microstructures Using X-Ray Computed Tomography
Bibliographic record
Abstract
Large mafic-ultramafic layered intrusions may contain layers enriched in platinum-group elements (PGE). In many cases, the PGE are hosted by disseminated sulphides. We have investigated the distribution of the sulphides in three dimensions in two oriented samples of the Merensky Reef and the J-M Reef. The aim of the study was to test the hypothesis that the sulphides crystallized from a base metal sulphide liquid that percolated through the cumulate pile during compaction. The distribution of sulphides was quantified using: (1) X-ray computed tomography; (2) microstructural analysis of polished thin sections oriented parallel to the paleovertical; (3) measurement of dihedral angles between sulphides and silicates or oxides. In the Merensky Reef and the J-M Reef, sulphides are connected in three dimensions and fill paleovertical dilatancies formed during compaction, which facilitated the downward migration of sulphide liquid in the cumulate. In the melanorite of the Merensky Reef, the sulphide content increases from top to bottom, reaching a maximum value above the underlying chromitite layer. In the chromitite layers sulphide melt connectivity is negligible. Thus, the chromitite may have acted as a filter, preventing extensive migration of sulphide melt downwards into the footwall. This could partially explain the enrichment in PGE of the chromitite layer and the observed paucity of sulphide in the footwall.
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 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".