Multiple episodes of hematite mineralization indicated by U-Pb dating of iron-ore deposits, Marquette Range, Michigan, USA
Bibliographic record
Abstract
Abstract High-grade hematite ore (so-called “hard ore”) was first mined in the Lake Superior region of North America in A.D. 1848. The development of ore deposit models from the region has strongly influenced research on the origin of this deposit type worldwide. The inability to date high-grade hematite ores has hindered the testing of competing genetic models. In the Marquette Range, northern Michigan (USA), high-grade hematite ore is hosted by the 1.9–1.85 Ga Negaunee Iron Formation and unconformably overlying Goodrich Quartzite. Field relations and new in situ U-Pb geochronology of monazite and xenotime intergrown with hematite from six mines across the Marquette Range, Michigan, indicate that the formation of high-grade hematite ore bodies involved up to three events. The presence of pebbles of hematite ore in basal conglomerate of the Goodrich Quartzite indicates that the first episode of iron-oxide mineralization occurred after deposition and deformation of the Negaunee Iron Formation, but before the ca. 1.85 Ga Sudbury impact. Monazite in iron-ore deposits within the hinges of Penokean-aged folds yields an age of ca. 1.8 Ga, which is interpreted to record a second phase of hematite enrichment. Monazite and xenotime in iron-ore deposits along the limbs of regional folds give ages of ca. 1.77 Ga and are interpreted to record a later episode of hematite upgrading. The ca. 1.8 Ga and ca. 1.77 Ga phosphate ages coincide with the timing of regional tectonic events, suggesting hematite mineralization was coeval with the Penokean orogeny and Yavapai-interval accretion. Our results support the proposal that the formation of high-grade hematite ore bodies is a multistage process linked to discrete orogenic events.
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How this classification was reachedexpand
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) | 0.006 | 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 teacher head, 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".