GEOCHEMICAL FRACTIONATION OF Nb-Ta OXIDES IN Li-BEARING PEGMATITES FROM THE BARROSO-ALVAO PEGMATITE FIELD, NORTHERN PORTUGAL
Bibliographic record
Abstract
The Barroso–Alvao granitic pegmatite field, located in northern Portugal, is known for its numerous occurrences of Li-bearing pegmatites, especially spodumene- and petalite-bearing bodies. Recent work on this pegmatite field characterized other types of pegmatites, and complex mineralization and mineral associations. Minerals of the columbite–tantalite group are found in all the LCT (Li–Cs–Ta) pegmatites from Barroso–Alvao: spodumene pegmatites, petalite pegmatites, and lepidolite pegmatites. In the petalite and lepidolite pegmatites, the columbite–tantalite group of minerals are found spatially associated with cassiterite. Cassiterite is not present in the spodumene pegmatites. The columbite-group minerals have Ta/(Ta + Nb) and Mn/(Mn + Fe) values ranging from 0.20 to 0.60, except in the lepidolite pegmatites, where Mn/(Mn + Fe) is close to 1. The fractionation trend starts in the Mn-poor columbite-(Fe) field (spodumene pegmatites) toward Mn- and Ta-enrichment (lepidolite pegmatites). Our results suggest that Mn enrichment is not controlled by silicate or phosphate phases, but instead by the increasing activity of fluorine. The Ta enrichment, on the other hand, may well be controlled by fractional crystallization. We also observe a decrease in the Ti of the columbite-group minerals from the spodumene to the lepidolite pegmatites, which we consider an evolutionary trend.
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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 | 0.000 |
| 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".