Abstract: Geology and U-Pb geochronology of Mesoproterozoic magmatic sulphide mineralization in western Labrador
Bibliographic record
Abstract
Most orthomagmatic Ni-Cu-Co sulphide mineralization in Labrador is associated with Mesoproterozoic mafic plutonic suites, of which the best-known examples are the Voisey’s Bay intrusion (ca. 1332 Ma) and the Pants Lake intrusions (ca. 1338 and 1322 Ma). Magmatic sulphide mineralization also occurs in western Labrador, notably within the Michikamau Intrusion, where it is associated with troctolite and olivine norite that form part of a thick layered sequence. There are two main mineralized zones, one of which is situated close to the basal contact of the intrusion; however, the contact region itself has yet to be tested by drilling. Mineralization recently located at higher levels in the layered sequence appears to have generally higher metal grades. Disseminated sulphide mineralization was also discovered in a sheet-like gabbroic intrusion near Evening Lake, where it is also located near to its basal contact with sulphide-bearing metasedimentary country rocks. Small amounts of disseminated sulphides are also known locally within the Mount Fyne Intrusion. Both intrusions are traditionally grouped with the Shabogamo Gabbro suite. The grades of all these mineralized zones are relatively low, typically having sulphide metal contents of 1% to 2% Ni, as opposed to nearly 4% Ni at Voisey’s Bay. However, systematic exploration in western Labradior has to date been of limited extent, and the region retains significant potential. Mineralization in the Michikamau Intrusion was dated using a pegmatitic variant of the host leucotroctolite, adjacent to and gradational with a sulphide-bearing zone. Single-grain analyses of baddeleyite define a U-Pb age of 1469 ± 1 Ma, a result consistent with a previous age determination inferred to represent contact metamorphism. In the Evening Lake area, sulphide mineralization was dated using a dioritic variant of the gabbro, which gave a U-Pb zircon age of 1448 ± 2 Ma. This confirms the assignment of the host rocks to the Shabogamo Gabbro suite. A closely similar U-Pb zircon age of 1444 ± 4 Ma was previously obtained from gabbro of Mount Fyne Intrusion, which was emplaced into deeper level granitoid gneisses. The results confirm correlation of these mafic suites across major terrane boundaries; however, those in the north probably have greater prospectivity based on emplacement level and the presence of country rocks representing potential sources of sulphur.
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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) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".