Mineralization of the Bayan Obo Rare Earth Element Deposit by Recrystallization and Decarbonation
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Bibliographic record
Abstract
Abstract The genesis of the Bayan Obo giant rare earth element (REE) deposit has been debated for several decades. Here, we report the isotopic effects of dynamic recrystallization in the H8 carbonatite, which is the principal ore carrier in the deposit. We studied fresh drill core to a depth of 1.78 km and documented the elemental and C-O-Sr isotope evolution of rock-forming dolomite during its deformation and reaction with fluids. The precursor dolomite and the products of its recrystallization differ in δ13CVienna-PeeDee Belemnite (V-PDB) (–1.09 to 2.37 vs. –3.59 to 0.79‰, respectively) and 87Sr/86Sr (0.70241–0.70394 vs. 0.70288–0.71409, respectively), and show a similar δ18Ovienna-standard mean ocean water (V-SMOW) range (10.3–16.9‰). The strong negative shift in δ13CV-PDB indicates that, locally, there was as much as 40% loss of CO2 from the precursor dolomite, although most of the recrystallized dolomite experienced decarbonation on a smaller scale. Clumped monazite grains associated with apatite in paragenetically similar samples yielded variable in situ Th-Pb dates (980–340 Ma), whereas those in monomineralic veinlets give a consistent age of ~400 Ma and consistent initial Nd isotope ratios. This indicates that the wide range of dates may not represent real REE depositional events and that the primary REE minerals deposited in the Mesoproterozoic underwent isotopic reequilibration and REE remobilization in the mid-Paleozoic. Recrystallization and decarbonation of dolomite in the H8 unit were facilitated by its reaction with subduction-derived silica- and halogen-rich fluid, genetically linked to plate-convergence processes along the northern margin of the North China craton, and did not require an influx of REEs from an external source.
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.009 | 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 it