The world-class Howard’s Pass SEDEX Zn-Pb district, Selwyn Basin, Yukon. Part II: the roles of thermochemical and bacterial sulfate reduction in metal fixation
Bibliographic record
Abstract
The Howard’s Pass district of sedimentary exhalative (SEDEX) Zn-Pb deposits is located in Yukon Territory and comprises 14 Zn-Pb deposits that contain an estimated 400.7 Mt of sulfide mineralization grading 4.5 % Zn and 1.5 % Pb. Mineralization is hosted in carbonaceous and calcareous and, to a lesser extent, siliceous mudstones. Pyrite is a minor but ubiquitous mineral in the host rocks stratigraphically above, within, and below mineralization. Petrographic analyses reveal that pyrite has a complex and protracted growth history, preserving multiple generations of pyrite within single grains. Sulfur isotope analysis of paragenetically complex pyrite by secondary ion mass spectrometry (SIMS) reveals that sulfur isotope compositions vary with textural zonation. Within the Zn-Pb deposits, framboidal pyrite is the earliest pyrite generation recognized, and this exclusively has negative δ34S values (mean = −16.6 ± 4.1 ‰; n = 55), whereas paragenetically later pyrite and galena possess positive δ34S values (mean = 29.1 ± 7.5 and 22.4 ± 3.0 ‰, n = 13 and 13, respectively). Previous studies found that sphalerite and galena mineral separates have exclusively positive δ34S values (mean = 16.8 ± 3.3 and 12.7 ± 2.8 ‰, respectively; Goodfellow and Jonasson 1986). These distinct sulfur isotope values are interpreted to reflect varying contributions of bacterially reduced seawater sulfate (negative; framboidal pyrite) and thermochemically reduced seawater sulfate and/or hydrothermal sulfate (positive; galena, sphalerite, later forms of pyrite). Textural evidence indicates that framboidal pyrite predates galena and sphalerite deposition. Collectively, the in situ and bulk sulfur isotope data are much more complex than δ34S values permitted by prevailing genetic models that invoke only biogenically reduced sulfur and coeval deposition of galena, sphalerite, and framboidal pyrite within a euxinic water column, and we present several lines of evidence that argue against this model. Indeed, the new data indicate that much of the base metal sulfide mineralization was emplaced below the sediment-water interface within sulfidic muds under reducing conditions during early diagenesis. Furthermore, thermochemical sulfate reduction provided most of the reduced sulfur within the Zn-Pb deposits.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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".