Petrogenesis of PGE mineralised intrusions in the floor of the northern Bushveld Complex
Bibliographic record
Abstract
Abstract The floor rocks of the northern lobe of the Bushveld Complex host several sill-like mafic-ultramafic bodies. In the present paper we evaluate whole rock data generated by exploration companies for sills on the farms Townlands, Amatava, Uitloop, Turfspruit and Rietfontein, located to the north of Mokopane, in order to constrain the origin of the sills and their mineralisation. Key observations include: (i) The sills have geochemical affinities to the Lower Zone (LZ) or Lower Critical Zone (LCZ). (ii) Most sills are enriched in sulphides and platinum-group elements (PGE) relative to most other LZ and LCZ cumulates. (iii) Most PGE mineralised intrusives have been emplaced into the carbonaceous-pelitic Duitschland Formation. (iv) The sills are spatially associated with the Mokopane gravity anomaly, possibly representing a major feeder zone to the Bushveld Complex. (v) The sills show evidence for assimilation of the sedimentary host rocks in the form of locally elevated δ34S, incompatible trace element contents and the presence of carbonaceous and pelitic country rock xenoliths. (vi) There is no correlation between PGE abundance and indicators of crustal contamination. Based on these data we propose that in the vicinity of the putative Mokopane feeder zone relatively fertile, unevolved magmas ascended through the crust initially as dykes. When intersecting the relatively fissile Duitschland Formation the mode of magma emplacement changed to one of sills. This facilitated contamination with sulphide- and graphite-rich carbonate and shale, triggering sulphide melt saturation. The sulphides were locally entrained and upgraded within the sills before precipitating, likely within flow dynamic traps.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.009 | 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 teacher head, 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".