A 50 m.y. melting model for the rare metal−rich Koktokay pegmatite in the Chinese Altai: Implications from a newly identified Jurassic granite
Bibliographic record
Abstract
The petrogenesis of the world famous Koktokay No. 3 pegmatite in the Chinese Altai Mountains is still enigmatic due to its superenrichment of rare metals and the apparent absence of a parental granite. We present results from a granite apophysis that was recently discovered in the No. 3 pegmatite open pit. Results show that it has low K/Rb (32.35−38.76), Zr/Hf (13.78−23.30), Nb/Ta (1.00−6.02), and extremely low K2O/Na2O (0.12−0.20) ratios, which, together with its mica composition and the occurrences of garnet, indicate that it is a highly evolved muscovite albite granite. Columbite and apatite from the granite apophysis yielded U-Pb ages of 182.3 ± 1.0 Ma and 184.9 ± 4.3 Ma, respectively, which are younger than the Triassic ages (ca. 210 Ma) of the main magmatic stage but fall into the age range of the No. 3 pegmatite series (220−175 Ma). Both the granite and the apatite grains within it share nearly identical rare earth element patterns with the magmatic stage of the No. 3 pegmatite. The whole-rock εHf(t) values (t = 183 Ma) range from −0.11 to +1.32, consistent with those of the No. 3 pegmatite and indicating a similar source. We propose that the Jurassic granite represents a late pulse of magma injected as apophyses from a deep-seated magma chamber (perhaps from the lower crust), which overlapped with the early pegmatite and promoted the rare metal mineralization. The No. 3 pegmatite and the Jurassic granite may represent a continuous magmatic system with a 50 m.y. melting process, generating this unusual giant pegmatite intrusion with abundant rare metals.
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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 | 0.001 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 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".