THE TANCO PEGMATITE AT BERNIC LAKE, MANITOBA. XIII. EXOCONTACT TOURMALINE
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Bibliographic record
Abstract
The petalite-subtype Tanco granitic pegmatite, southeastern Manitoba, intrudes an amphibolite (metagabbro), which is metasomatically altered to tourmaline and magnesian annite close to the contact. The composition of exocontact tourmaline depends on the composition of the host rock and on the composition and amount of fluid injected from the pegmatite-forming melt into the host rock. Two compositional groups of tourmaline occur in the exocontacts at Tanco: (1) common feruvite – schorl – dravite (Ca- and Mg-rich), and (2) rare intermediate ternary tourmaline: elbaite – schorl – dravite (Na-, Al- and Li-rich). The Ca, Mg and Ti contents of group-1 tourmaline increase with distance from the contact between the pegmatite and the host rock. Group-1 and -2 tourmalines crystallize as a result of Na-, Al-, Li- and B-rich pegmatite-derived fluids infiltrating the Ca-, Mg-and Fe-rich host amphibolite, or as a chemical reaction between the pegmatite-forming melt and the host rock. The exocontact tourmaline is zoned, with a (Fe, Mg)-rich group-1 core and a Li-rich group-2 rim. Early consumption of Ca, Mg and Fe by crystallization of feruvite – schorl – dravite increased the chemical potential of Na, Al and Li in the fluid and promoted crystallization of elbaite – schorl – dravite. The rare ternary tourmaline of group 2 crystallized in the tourmaline aureole from fluids with high chemical potential of B, Al, Na and Ca, which are major constituents in tourmaline, but absent or minor in holmquistite. The influx of B-rich acidic fluids promoted crystallization of tourmaline and prevented crystallization of holmquistite.
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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) | 0.009 | 0.001 |
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 it