Non-hydrothermal origin of apatite in SEDEX mineralization and host rocks of the Howard’s Pass district, Yukon, Canada
Bibliographic record
Abstract
The Howard’s Pass district (HPD) comprises 14 Zn-Pb sedimentary exhalative (SEDEX) deposits and is located within the Selwyn basin, Yukon, Canada. Although the HPD is renowned for its large accumulation of base-metal sulfides, in places the Late Ordovician to Early Silurian host rocks also contain abundant carbonate-bearing fluorapatite (CBFA). This mineral is present stratigraphically below, within, and above the SEDEX deposits and occurs as fine-grained layers that are interbedded with cherty carbonaceous mudstone. Electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometric analysis reveal that mineral compositions and rare earth element-yttrium (REE-Y) systematics, respectively, are remarkably similar throughout the stratigraphic succession. North American Shale Composite (NASC)-normalized La/Sm and La/Yb ratios indicate that the original REE compositions in CBFA have undergone only minor compositional modification subsequent to deposition. Uniformly negative Ce anomalies indicate that the mineral formed in analogous manner to modern and ancient sedimentary phosphorites under suboxic bottom-water conditions. Europium anomalies are mostly absent, indicating that reduced, slightly acidic high-temperature hydrothermal fluids were not a major source of REE-Y to CBFA. The chemical homogeneity of the mineral irrespective of its stratigraphic position indicates that a common process was responsible for its deposition within the sedimentary rocks of the HPD. On the basis of the similarity of the REE patterns to modern and ancient phosphorites, and the absence of positive Eu anomalies, we conclude that the CBFA is of hydrogenous origin, and not hydrothermal as suggested by previous workers. As such, phosphorite formation in the HPD is casually related to SEDEX Zn-Pb deposit formation.
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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 | 0.002 | 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".