Major and Trace Element Concentrations in Chromite and Silicate Minerals of the Critical Zone of the Bushveld Complex, South Africa: Effects of Reequilibration and Crystal Fractionation on Chromite Composition
Bibliographic record
Abstract
Abstract The Rustenburg Layered Suite of the Bushveld Complex, South Africa, contains the world’s largest resource of chrome and platinum group elements (PGEs). Both Cr and PGEs are found in chromitite layers within an approximately 1,000-m-thick section of ultramafic to mafic rocks known as the Critical zone. Neither the process of how the chromitite layers form nor the role that chromite plays in collecting the PGEs is clear. Major and trace element contents of chromite and silicate minerals from each of the 13 chromitite layers, and from chromite in the adjacent peridotites and norites, have been determined. The concentrations of PGEs in both chromite and silicates are less than detection levels (10–20 ppb). Thus, neither are the host of the PGEs in these rocks. The Cr# and Fe# of the chromites from chromitite layers are similar to those found in experiments carried out to model the crystallization of the initial magma (B1) of the Bushveld, with the same decrease in Cr# with increase in Fe#. The fO2 of the experiments Δ 0 FMQ (where FMQ = fayalite-magnetite-quartz buffer) and those of the chromitite chromite calculated from the Fe3+/FeTotal ratios and the V contents of the chromite are similar. Variations in trace element contents of the chromitite chromite can also be modeled using the B1 composition and allowing for ~40% crystal fractionation across the stratigraphy.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| 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) | 0.000 | 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".