The Fraser Lakes Zone B U-Th-REE deposit and its host rocks : implications for pegmatite- and leucogranite-hosted U-Th-REE deposits in northern Saskatchewan, Canada
Bibliographic record
Abstract
The Fraser Lakes Zone B U-Th-LREE deposit is located approximately 50 km SE of the Key Lake uranium mine in the Wollaston Domain of Northern Saskatchewan, Canada. Here, a number of variably radioactive pegmatites and leucogranites intruded the highly sheared, unconformable contact between Paleoproterozoic Wollaston Group metasedimentary rocks and the underlying Archean orthogneisses, in a NNE-plunging antiformal fold nose. The U-Th-LREE mineralized pegmatites were subdivided into two groups based on their mineralogical and spatial differences. Both groups contain variable amounts of quartz, k-feldspar, plagioclase, biotite, magnetite, and ilmenite. The Group A pegmatites, in the eastern part of the fold nose, contain small amounts of uraninite, uranoan thorite, zircon, and rare coffinite and allanite, and are typically U- ±Th-enriched (Th/U ~1). The Group B pegmatites, in the central part of the fold nose, are Th- and LREE- enriched (Th/U up to ~20) and contain small amounts of monazite, uranoan thorite, and zircon, with rare allanite and pyrochlore-group minerals. The Group A pegmatites are interpreted to represent slightly more evolved crust melts that underwent higher degrees of restite unmixing, whereas the Group B pegmatites are postulated to have resulted from partial melting and incorporation of more restitic and peritectic material. Field relationships and chemical age dating of the pegmatites suggests that they formed between 1.85 to 1.80 Ga, during peak thermal metamorphism and ensuing decompression related to the ca. 1.9 to 1.8 Ga Trans-Hudson Orogen (THO). Examination of the pelitic gneiss host rocks at Fraser Lakes Zone B revealed that the area underwent high temperature (up to ~780°-800° C), low to medium pressure (max pressures of ~7-8 kbar), upper amphibolite to granulite facies metamorphism (accompanied by partial melting), followed by isothermal decompression (down to ~3 kbar) at approximately 1.81-1.80 Ga. After this, the rocks began to cool and retrograde metamorphism took place at amphibolite to greenschist facies. Later faulting and hydrothermal fluid flow served to alter the pegmatites and led to local remobilization of U and other metals in fractures and faults. The pegmatite-forming melts are interpreted to have formed by partial melting (via biotite-dehydration reactions) of U-, Th- and REE-enriched rocks similar to the Wollaston Group at depth. The melts migrated upwards to the emplacement level within and along major structural zones, including sheared fold limbs, metamorphic foliations, and the deformed Archean/Paleoproterozoic contact. The melt was concentrated in antiformal fold noses and other dilational zones, where it crystallized to form the pegmatite and leucogranite bodies. The style of mineralization and the structural control is similar to other pegmatite-hosted uranium deposits, including the Rössing alaskite-hosted deposit in Namibia. The knowledge gained from this study can be applied to exploration for similar deposits in northern Saskatchewan and other areas with similar geology.
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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 | 0.005 |
| Science and technology studies | 0.005 | 0.002 |
| Scholarly communication | 0.003 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.005 | 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".