SEDEX mineralisation, Macmillan Pass (Yukon): petrography, mineralogy and bulk geochemistry of the Tom and Nidd deposits
Bibliographic record
Abstract
Sedimentary exhalative (SEDEX) deposits formed in the Selwyn Basin coeval with 3 magmatic episodes in the Cambrian, Silurian and Late Devonian. At Macmillan Pass, the Tom, Jason and Nidd deposits are hosted by Late Devonian strata and have well preserved vent complexes beneath overlying stratabound sulphide and sulphate facies. Drill core has been sampled from the vent complexes at Nidd and Tom. Detailed petrography (reflected and transmitted light, cathodoluminescence, back-scatter electron imaging) has developed a paragenesis and, at Tom, critically assessed textural relationships between the vent facies and the overlying stratabound sulphide and sulphate facies. The mineral chemistry of major phases has been determined from quantitative electron microprobe analyses in the vent and stratabound ore from Tom. The geochemical signatures of the hydrothermal vents (Tom, Nidd) are comprehensively characterized through bulk rock geochemical analysis of vent facies material for major, minor and rare earth elements. Detailed petrography has highlighted subtle feeder veins that preferentially replaced laminations leading to the formation of pseudo-bedded sulphide-rich layers in the grey facies rocks at Tom. This provides an important link between the vent and the overlying stratabound facies. Within the vent, main stage sulphide minerals succeeded destructive carbonate alteration, and were overprinted by pulses of sulphide minerals coeval with, and replacing, siderite, Ba-carbonate and barite. Aside from the ore components (Pb, Zn and Ba), vent facies samples are enriched above upper crustal values in Au, Ag, As, Cd, Cu, Ge, In, Mo, Sb, Sn and Ta. Notably, Au in two samples from Tom exceeds 100 ppb. Rare-earth element profiles broadly track the composition of un-mineralised shale in the area but have a positive Eu anomaly, likely attributable to the presence of Ba feldspar in the samples. This highlights the potential importance of the compositions of underlying strata in controlling the geochemistry of the hydrothermal fluids.
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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 | 0.001 |
| 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".