LATE AND MID-CRETACEOUS MINERALIZATION IN THE NORTHERN CANADIAN CORDILLERA: CONSTRAINTS FROM Re-Os MOLYBDENITE DATES
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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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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) | 0.027 | 0.001 |
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