Fluid inclusion and stable isotope evidence for mixing of magmatic - hydrothermal fluids with meteoric water in vein-type Cu-Au-Bi deposits, southern New Brunswick, Canada
Bibliographic record
Abstract
Vein-type Cu-Au-Ag-Bi mineralization in the Caledonian Highlands, southern NB, Canada, is hosted within quartz-carbonate-rich shear zones cutting felsic lithic tuffs, intermediate intrusives and interbedded felsic and mafic flows of the Neoproterozoic Broad River Group. Mineralization in the veins consists of bornitechalcocite- hematite, coprecipitated with electrum and bismuthinite; ore minerals post-date quartz and REE-rich carbonates in the veins, with later supergene oxidation and hydration of the ores to cuprite-malachite. Wall-rock alteration is characterized by albitization and paragonitization. Replacement of bornite by chalcocite- hematite indicates changes in fluid redox with mineralization progression. Trails of secondary fluid inclusions in the quartz veins are two-phase liquid-vapour at room temperature. Homogenization occurs by vapour bubble disappearance between 150-270°C for all assemblages; individual assemblages show relatively narrow ranges (e.g., 173-191°C, n=22). Bulk salinities from final ice melting range from 4 to 13 wt% NaCl eq. with individual assemblages showing similarly narrow ranges. Stable isotope data (bulk separates, and in-situ by secondary ion mass spectrometry [SIMS]) for vein-stage quartz (d18Obulk = 13.7-15.1perthousand; d18OSIMS-qtz = 10.8±1.5 perthousand, 1c, n=32) and carbonate (d13Cbulk = -4.4 to -4.6 perthousand) combined with microthermometric data rule out unmodified, heated seawater and meteoric water as the dominant fluid components, and suggest that the metal-bearing fluids were magmatic in origin or represented saline formation waters modified through fluid-rock interaction with the host volcanic rocks (calculated d18Ofluid ~ 6-7 perthousand). However, significant variations in d18OSIMS-qtz are observed within single quartz crystals across growth zones and in massive quartz texturally predating sulfides and gold (from as low as 8.2 perthousand to 14.8 perthousand in quartz enclosed entirely within bornite-chalcocite). This indicates either (i) localized mixing of the metal-bearing fluid with low latitude meteoric water (calculated d18O = -1.0 to 0 perthousand), or (ii) fluctuations in fluid temperature during vein formation, with the lowest T portions of the vein associated with base metal-gold precipitation, or (iii) both. The isotopic composition of coeval quartz-carbonate predict a crystallization/final equilibration T of vein-stage at ~250- 270°C; if inclusions are primary, then a maximum Ptrapping = ~1.5 kbar, based on the lowest T assemblages, is estimated. Significant fluctuations in fO2, fluid temperature or fluid composition during vein precipitation highlight the importance of fluid mixing for mineralization. These characteristics, combined with the style of mineralization, link these deposits in NB genetically to much larger vein Cu deposits worldwide (e.g., Churchill, Davis-Keays, and Mamainse Point, Canada; Inyati, Zimbabwe; Copper Hills, Australia; Messina, South Africa; Cornwall, UK).
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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 | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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".