GENESIS OF NATIVE COPPER LODES IN THE KEWEENAW DISTRICT, NORTHERN MICHIGAN: A HYBRID EVOLVED METEORIC AND METAMOPHOGENIC MODEL
Bibliographic record
Abstract
The Keweenaw Peninsula of northern Michigan is well known for early diagenetic sulfide-dominant sediment-hosted stratiform copper mineralization hosted mainly by basal siltstone-shale units of the Nonesuch Formation in the White Pine district, and later native copper lodes hosted mainly by flow-top breccias and amygdaloidal portions of flood basalts and interbedded conglomerates of the stratigraphically lower Portage Lake Volcanics. The native copper mineralization is generally attributed to downdip burial metamorphism of the host strata. An alternative model is proposed here, involving a complementary influx of evolved meteoric water (elevated in salinity and progressively equilibrating with its aquifers), similar to the fluid which formed the White Pine mineralization. This model has several advantages over the metamorphogenic model alone. It would provide the salinity (by dissolution of evaporites) and moderately oxidizing conditions (as a result of hematitization, i.e., reddening, of coarse continental rift sediments) necessary for copper transport, and the evolved meteoric water would have been an important cupriferous brine owing to the leaching of trace amounts of copper from the voluminous aquifers. Further reduction of the evolved fluid would also explain the updip deposition of native copper in association with dehematitized pumpellyite- and chlorite-dominant (i.e., reduced) hydrothermal mineral assemblages. At the same time, this influx of meteoric water from highlands adjacent to the Keweenaw rift basin would have provided a mechanism to move the deep-seated hot, dense ore brine upward along the aquifers of the Portage Lake Volcanics. On its ascent from deep portions of the rift basin, the gravity-driven evolved meteoric brine would have mixed with the fluid generated by burial metamorphism to form a hybrid evolved meteoric-metamorphogenic oreforming hydrothermal brine.
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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) | 0.000 | 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".