Geology, mineralogy, S and Sr isotope geochemistry, and fluid inclusion analysis of barite associated with the Lemarchant Zn–Pb–Cu–Ag–Au-rich volcanogenic massive sulphide deposit, Newfoundland, Canada
Bibliographic record
Abstract
Barite in the approximately 513 Ma Lemarchant volcanogenic massive sulphide (VMS) deposit, Newfoundland, consists of granular and bladed barite intimately associated with mineralization. Regardless of type, the composition of barite is homogeneous at bulk rock and mineral scale containing predominantly Ba, S, and Sr, with minor Ca and Na. The barite has homogeneous sulphur isotope compositions (δ34Smean = 27‰), similar to Cambrian seawater sulphate (25–35‰) and Sr isotope compositions (87Sr/86Sr = 0.706905 to 0.707485). These results are consistent with barite having formed from fluid–fluid mixing between Cambrian seawater and VMS-related hydrothermal fluids. The 87Sr/86Sr values in the barite are lower than mid-Cambrian seawater, which suggests that some of the Sr was derived from the underlying Neoproterozoic basement. Fluid inclusions in bladed barite are low-salinity, CO2-rich inclusions with homogenization temperatures between 245°–250 °C, and average salinity of 1.2 wt.% NaCl equivalent. Estimated minimum trapping pressures of between 1.7 to 2.0 kbars were calculated from aqueous–carbonic fluid inclusion assemblages. The fluid inclusion results reflect regional metamorphic reequilibration during younger Silurian regional metamorphism, rather than primary fluid signatures, despite the preservation of primary barite and fluid inclusion textures. These results illustrate that barite in VMS deposits records the physicochemical processes associated with VMS formation and the sources of fluids in ancient VMS deposits, as well as seawater sulphate and basement isotopic compositions. The results herein are not only relevant for the Lemarchant deposit but also for other barite-rich VMS deposits globally.
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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 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 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".