Tokyoite, As-Rich Tokyoite, and Noélbensonite: New Occurrences From the Postmasburg Manganese Field, Northern Cape Province, South Africa
Bibliographic record
Abstract
Samples of manganese-rich rock containing two compositional varieties of tokyoite in association with noelbensonite were retrieved from a drill core obtained from the Postmasburg area in the Northern Cape Province of South Africa. The samples consist of fine-grained braunite, hematite, and hausmannite. Within this material abundant vugs are observed that are filled with witherite, baryte, and barytocalcite. In addition, As-rich tokyoite, tokyoite, and noelbensonite occur in the center of the vugs, in fine aggregates 0.1 to 1 mm in size. Individual As-rich tokyoite grains are typically 20–200 μm in size. The outer walls of the vugs are lined with microcrystalline K-feldspar, witherite, and/or serandite. Textural evidence of the Ba-rich mineral phases in association with As-rich tokyoite suggest an epigenetic mode of formation of the observed assemblages, caused by V- and As-bearing alkali-rich fluids interacting with pre-existing Mn-rich minerals. Electron microprobe analysis (EMPA), electron backscatter diffraction analysis (EBSD), and Raman spectroscopy show that the As-rich tokyoite is a mineral belonging to the brackebuschite mineral group. Its measured mineral composition corresponds to the formula (Ba 1.92 Sr 0.05 Pb 0.03 ) ∑2.00 (Mn 3+ 0.98 Fe 3+ 0.02 ) ∑1.00 [(As 1.050 V 0.950 ) ∑2.00 O 8 )](OH). Electron backscatter diffraction analysis results point to a monoclinic, P 2 1 / m space group, with cell parameters a 9.121 A, b 6.142 A, c 7.838 A, α = γ = 90°, β = 112°, Z = 2. The structure is therefore similar to gamagarite. Raman spectra of As-rich tokyoite were compared to spectra of arsenbrackebuschite and arsentsumebite, and those of noelbensonite to spectra of hennomartinite and lawsonite. The indexing of Raman peaks in As-rich tokyoite, by similarity with arsentsumebite, suggests a possible ordering of the AsO 4 and VO 4 tetrahedra. This observation, correlated with mineral chemistry and specifically an As:V ratio of ~1:1, suggest that the As-rich tokyoite may in fact represent a possible new mineral with ordering of As and V at tetrahedral positions, or at least an unknown As analogue of tokyoite.
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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 | 0.001 | 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) | 0.002 | 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 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".