The effect of Li on the petrogenesis of granitic pegmatites
Bibliographic record
Abstract
The effect of Li on the petrogenesis of Li-bearing pegmatites was studied through a combination of experimental research and field investigations. Crystallization experiments were conducted under H2O-saturated and H2O-undersaturated conditions at 400-800 °C and 500 MPa, using a common granitic starting material (Li-free) and the same granitic material enriched with ~3700 ppm Li (Li-bearing). Comparison of the two sets of experiments highlighted the role of Li as an effective fluxing component of the pegmatite-forming melt; the presence of Li decreased the melting and crystallization temperatures, constrained the degree of undercooling at the onset of formation of pegmatitic textures to 85-110 °C, and increased the growth rates of feldspar crystals to 13 cm/y, one order of magnitude faster than feldspars grown in the Li-free system. Graphic and granophyric quartz-feldspar intergrowths, the characteristic textures encountered in pegmatites, were reproduced early in the Li-bearing experiments, followed by the development of K-feldspar, albite and quartz monomineralic zones at later stages, and the crystallization of Li-aluminosilicates close to the solidus.The experiments showed that Li preferentially partitioned in the melt, reaching ~12000 ppm at 80% crystallization. A new series of dissolution, crystallization and melting experiments at 550-750 °C and 500 MPa estimated the solubility of Li at the saturation of spodumene and petalite and defined the maximum saturation curve for Li-aluminosilicates. The results of these experiments suggested extreme Li enrichment of the pegmatite-forming melt before the formation of Li-aluminosilicate phases, often to the point of supersaturation (~22000 ppm Li at 600 °C). A comparison between the experimental results and information obtained from natural samples from the Moblan pegmatite in Quebec supported the extreme enrichment of the pegmatite-forming melt in Li, strengthening the plausibility of the supersaturation hypothesis. Lastly, based on the experimental results and the field observations on the Moblan pegmatite, the Li concentration of feldspar crystals was proposed as a useful exploration tool for the distinction between Li-free and Li-bearing pegmatites as well as the identification of Li-rich sections in an individual pegmatitic body. The geochemical signature of Li in feldspar, and possibly quartz as well, shows a promising potential as an inexpensive means to optimize targeting of Li-rich ore resources in pegmatites.
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 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".