DETAILED ASSESSMENT OF PLATINUM-GROUP MINERALS ASSOCIATED WITH CHROMITITE STRINGERS IN THE MERENSKY REEF OF THE EASTERN BUSHVELD COMPLEX, SOUTH AFRICA
Bibliographic record
Abstract
The minerals of the platinum-group elements (PGM) and their associated host minerals from the Merensky Reef at the Two Rivers platinum mine, South Africa, were investigated using an FEI 600F field emission Mineral Liberation Analyzer. Polished sections were prepared from intersections of upper and basal chromitite stringers collected from 12 boreholes drilled into a variety of Merensky Reef facies types. Primary minerals associated with the chromitite stringers, on the scale of a thin section, include orthopyroxene (30–60%), clinopyroxene (~2%), plagioclase (20–40%), and base-metal sulfides (up to 2%), whereas secondary silicates include tremolite (~4%), phlogopite (~1%), chlorite (<1%) and serpentine (<1%). The most abundant base-metal sulfides (BMS) occurring in the Merensky Reef in this area of the Bushveld Complex are pyrrhotite (46% of all BMS), pentlandite (32% of all BMS) and chalcopyrite (22% of all BMS). Abundances of the PGM (in area %, total PGM) are dominated by maslovite (PtBiTe, 29.7%), isoferroplatinum (Pt3Fe, 26.9%), braggite [(Pt,Pd,Ni)S, 13.3%], cooperite [(Pt,Pd,Ni)S, 11.9%] and laurite (RuS2, 8.3%), with michenerite (PdBiTe), sperrylite (PtAs2), stibiopalladinite (Pd5Sb2), geversite (PtSb), platarsite (PtAsS), and a variety of unnamed phases accounting for the remainder. There is a strong association of most PGM with pentlandite and chalcopyrite, but less so with pyrrhotite. Observed PGM–silicate mineral associations include a marked tendency for PGE antimonides, (sulf)arsenides, bismuthotellurides and sulfides to be associated with secondary silicates (in addition to BMS), which is taken as evidence for the redistribution of these PGMs by late fluids. The data presented here are consistent with existing models for mineralization within the Merensky Reef, which involve the separation of a sulfide melt from a silicate liquid, that then scavenged PGE while percolating downward until arrested by impermeable chromitite.
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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 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| 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".