Multistep evolution of harzburgitic mantle underneath pipe 200 kimberlite, northern Lesotho: a study on xenoliths and their implication on diamond-barren nature of pipe 200 kimberlite
Bibliographic record
Abstract
Abstract The Pipe 200 kimberlite in northern Lesotho on the southeast margin of the Kaapvaal Craton is a diamond-poor deposit despite its proximity to economically viable kimberlites like the Liqhobong kimberlite. We study harzburgite xenoliths' mineral composition, geochemistry, and pressure–temperature evolution to understand factors influencing diamond destruction. The xenoliths are classified into five types based on their petrography and geochemistry. The diversity in the mineral assemblage correlates with a sampling depth of ~ 100 to 175 km (~ 2.8 to < 5.0 GPa). The signatures of metasomatism are evident in type 3 and 4 xenoliths, where garnet breaks down to form a cluster (henceforth assemblage) of phlogopite, chromite, and diopside. Fine-grained melts associated with an uplift in the mantle to shallower depths of < 90 km (< 2.3 GPa) encompass the minerals in the assemblage, which display resorption at the boundaries. Water contents (structural hydroxyl) of olivine and possibly orthopyroxene are lower in the xenoliths with metasomatism-induced breakdown of garnet. The structural hydroxyl distribution in the nominally anhydrous minerals shows flat distribution profiles of re-equilibration due to residence in the kimberlite magma. It is supported by the disruption of the inter-mineral water partition coefficient due to olivine water diffusion during residence in the kimberlite magma. The barren nature of the Pipe 200 kimberlite is attributed to the signatures of mantle metasomatism and residence in kimberlite magma, which led to the diamond destruction. Graphical abstract
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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 | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".