Seafloor-hydrothermal Si-Fe-Mn exhalites in the Pecos greenstone belt, New Mexico, and the redox state of ca. 1720 Ma deep seawater
Bibliographic record
Abstract
Mineralogical and geochemical data for ca. 1720 Ma Si-Fe-Mn seafloor-hydrothermal sedimentary rocks (exhalites) near the Jones Hill Zn-Cu-Pb-Ag-Au volcanogenic massive sulfide (VMS) deposit, northern New Mexico, provide valuable insights into the redox state of late Paleoproterozoic deep sea-water. Distal exhalites ~1200 m south of the deposit form beds 0.5–2 m thick composed of interlayered iron formation and metachert. The iron formation consists mostly of quartz and magnetite, and includes 0.3–3-cm-thick laminae of fine-grained garnet-quartz rock, which in places contains as much as 9.4 wt% MnO that resides chiefly in spessartine-rich garnet (coticule). Shale-normalized rare earth element data for an unaltered, low-Al quartz-magnetite iron formation show no Ce anomaly, which rules out fully oxic deep waters during exhalative mineralization. The garnet-quartz rocks and coticules mostly have small positive Ce anomalies, which are larger for calculated detrital-free compositions, thus precluding deposition in anoxic waters. Significant amounts of ferric iron are inferred for protoliths of the iron formation, based on the presence of abundant magnetite laminae, and of magnetite inclusions in cores of the spessartine garnets. Protoliths of the garnet-quartz rocks and coticules probably consisted largely of clays and Fe-Mn oxyhydroxides. Together these mineralogical and geochemical data suggest that the Jones Hill exhalites were deposited from deep sea-water having low concentrations of dissolved O2 corresponding to suboxic conditions, and not the sulfidic conditions proposed for late Paleoproterozoic deep seawater by other workers. Exhalites associated with Cu-rich VMS deposits, when effects of alteration and detrital components are considered, can be important proxies for evaluating the evolving redox state of ancient deep oceans.
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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 | 0.000 | 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) | 0.001 | 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".