Petrogenetic relationship of the variably Ni–Cu–platinum-group element (PGE)-mineralized intrusions of the Thunder Bay North Intrusive Complex, Midcontinent Rift, Canada: Implications for mineral exploration in mafic–ultramafic complexes
Bibliographic record
Abstract
Abstract The Thunder Bay North Intrusive Complex (TBNIC) of Canada comprises six variably Ni–Cu–platinum-group element (PGE)-mineralized mafic–ultramafic intrusions that intruded the Archean Quetico Subprovince. These are the Current, Escape, Lone Island, Greenwich, and 025 intrusions, with the former three aligned along an east–west-trending intrusion termed the East–West Corridor. These intrusions have a consistent igneous stratigraphy comprising, from bottom to top, peridotite, gabbros, and quartz gabbro. Only the Current and Escape intrusions are known to host sulfide mineralization in the peridotite. Despite the economic significance of the TBNIC, little work has been done to characterize its petrogenetic evolution and the causes of the apparent variable fertility. Our new ages for Escape (1107.6 ± 0.9 Ma) and Greenwich (1105.7 ± 0.9 Ma), combined with previously determined ages for Current (1106.6 ± 1.6 Ma) and Lone Island (1106.3 ± 2.1 Ma), demonstrate that the TBNIC was emplaced as part of the ca. 1.1 Ga Midcontinent Rift event. The similarities in their rare earth element geochemistry and consistently low Th/La–Sri values indicate that the intrusions crystallized from genetically related magmas that did not assimilate significant amounts of crustal material. Accordingly, their systematically negative εNdt values and Nb anomalies likely reflect that their parent magmas were largely sourced from the subdcontinental lithospheric mantle and not the Keweenaw Plume. Given their genetic relationship, the variable fertility of the intrusions cannot be related to processes that occurred in their mantle sources. Since the gabbros have systematically depleted Cu/Zr–Cu/Pd ratios and the peridotites have enriched ratios, the apparent variable fertility is likely related to the timing and location of sulfide segregation and accumulation, with the barren gabbros preserving magmas that lost sulfide liquid during transport to shallow crustal levels, and the mineralized peridotites recording accumulation of sulfide liquid. This interpretation has important implications for exploration as it implies that sulfide mineralization in the apparently barren intrusions may be located at depth in undiscovered ultramafic cumulates.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".