HIGH-PRECISION U-Pb ZIRCON-BADDELEYITE DATING OF THE J-M REEF PLATINUM GROUP ELEMENT DEPOSIT IN THE STILLWATER COMPLEX, MONTANA (USA)
Bibliographic record
Abstract
The Stillwater Complex, Montana (USA), is one of the world’s largest layered intrusions and hosts the Johns-Manville (J-M) Reef, a world-class platinum group element (PGE) deposit. In this study, zircon and baddeleyite were successfully extracted from three mineralized samples of the J-M Reef. The samples, which were collected over 15 km of strike length of the deposit, provide high-precision crystallization ages for the reef and the Stillwater Complex. All samples are coarse grained to pegmatitic and range in composition from olivine-bearing gabbronorite to anorthosite and troctolite. Irregular (anhedral) morphology and prominent sector zoning characterize interstitial zircon. U-Pb crystallization zircon ages determined by chemical abrasion thermal ionization mass spectrometry (CA-TIMS) for the three samples are indistinguishable within uncertainty: Frog Pond adit (2709.11 ± 0.56 Ma), East Boulder mine (2709.28 ± 0.32 Ma), and West Fork area (2709.00 ± 0.45 Ma). A U-Pb baddeleyite date from the Frog Pond adit sample (2708.85 ± 0.46 Ma) is identical within uncertainty with the zircon dates. Collectively, the results illustrate that the J-M Reef is an intrusion-wide time marker that formed at ca. 2709 Ma during crystallization of the Lower Banded series of the Stillwater Complex. The recognition that zircon can be successfully extracted from mafic-ultramafic rocks associated with magmatic ore deposits provides new opportunities for testing the timing of mineralization and duration of mineralization processes in layered intrusions worldwide.
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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 | 0.000 | 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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.018 | 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".