LATE AND MID-CRETACEOUS MINERALIZATION IN THE NORTHERN CANADIAN CORDILLERA: CONSTRAINTS FROM Re-Os MOLYBDENITE DATES
Bibliographic record
Abstract
New Re-Os molybdenite dates are presented from three deposits (Casino, Cash, and Mt. Nansen) in the Dawson Range, Yukon, northern Canadian Cordillera. The Re-Os molybdenite dates provide constraints on the timing of sulfide mineralzation, and together with 40 Ar/ 39 Ar and K-Ar mineral dates yield estimates for the longevity of the porphyry hydrothermal system. At the Casino deposit, Re-Os molybdenite dates associated with the potassic (75.05 ± 0.28; 74.69 ± 0.28 Ma) alteration are nominally older to overlapping with Re-Os molybdenite dates (~74.4 ± 0.28 Ma, n = 2) with phyllic alteration and suggest that it is likely that potassic and phyllic mineralization-alteration was contemporaneous. The Re-Os molybdenite dates are significantly older than hydrothermal K feldspar 40 Ar/ 39 Ar and K-Ar biotite dates (~72 Ma), which most likely reflect the cessation of the porphyry hydrothermal system. The molybdenite age data combined with silicate hydrothermal mineral dates suggest a porphyry hydrothermal system longevity of 4.16 to 1.94 (Casino), 8.66 to 6.44 (Cash), and 2.47 to 1.48 Ma (Mt. Nansen). These longevity estimates for porphyry hydrothermal systems are greater than previously proposed (~ 50°C/km) may control the disparate Re-Os molybdenite and 40 Ar/ 39 Ar K feldspar dates of the porphyry systems of this study. The contrasting Re-Os and 40 Ar/ 39 Ar dates clearly show the Re-Os isotope system in molybdenite is resistant to prolonged (~1 Ma) interaction with a high-temperature (400°-500°C) hydrothermal fluid, and that the Re-Os isotope systematics in molybdenite unambiguously record directly the timing of sulfide mineralization. This ability to directly date sulfide mineralization has identified mid- (Pattison, Idaho Creek, ~102-104 Ma) and Late Cretaceous (Zappa-Koffee, ~74.5 Ma) mineralization, which is hosted by the mid-Cretaceous (~104-102 Ma) Casino Plutonic Suite. The Late Cretaceous date is very similar to that for molybdenite mineralization at Casino, and we suggest that the Zappa-Koffee mineralization is an area of Late Cretaceous porphyry mineralization, for which the host pluton has not yet been discovered.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.003 | 0.002 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 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".