A review of the Late Cretaceous Little Nahanni Pegmatite Group and associated rare element mineralization in the Selwyn Basin area, Northwest Territories
Bibliographic record
Abstract
The Late Cretaceous Little Nahanni Pegmatite Group (LNPG) is composed of more than 200 subvertical, lithium-cesium-tantalum (LCT) pegmatites, occurring in an area of approximately 55 km2. The pegmatite group is hosted by Selwyn Basin offshelf facies of the Neoproterozoic to Lower Cambrian Hyland Group and is located between, and subparallel to, major regional northwest-trending structures, such as the March Fault and the Fork Anticline. Since their discovery in 1961, these coarse-grained, mostly quartz, feldspar, and spodumene pegmatites have been investigated for economic concentrations of rare elements. Whole-rock geochemical analyses indicate granitic compositions and strong peraluminous signatures suggest an S-type affiliation. The depletion in rare earth element (REE) abundance, enrichment of Li, Ta, Cs, Sn, Rb, and Nb, and emplacement into low-pressure metamorphic rocks is typical of LCT pegmatites. There are similarities between the LNPG dykes and the Greenbushes pegmatite, Australia, which is rich in Sn, Ta, Nb, and Li (Wengzynowski, 2002). However, even closer geochemical comparisons can be made with examples of European late-Variscan, post-orogenic mineralized plutons and pegmatites. One such example, the Beauvoir granite, is suggested as an analog for the plutonic source of the LNPG dykes. Comparison of the setting and ages obtained for the emplacement of the LNPG with this well studied Variscan granite suggests a period of post-orogenic collapse and extension during the late Cretaceous period in this region of the northern Cordillera.
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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) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.007 | 0.009 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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 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".