Low-Temperature Alteration at the World-Class LaRonde Penna Archean Au-Rich Volcanogenic Massive Sulfide Deposit, Abitibi Subprovince, Quebec, Canada: Evidence from Whole-Rock Oxygen Isotopes
Bibliographic record
Abstract
The oxygen isotope composition of 169 whole-rock samples from the world-class LaRonde Penna Au-rich volcanogenic massive sulfide deposit range from 6.5 to 22.0‰. Fractional crystallization from basalt to rhyolite accounts for a variation of approximately 2‰ in primary whole-rock δ 18O values. The remaining variance in whole-rock δ 18O values found at LaRonde Penna must therefore be ascribed to water-rock exchange with hydrothermal fluids. The metamorphosed, hydrothermally altered host rocks have been subdivided according to mineralogical assemblages, which display weak covariance with δ 18O values and whole-rock geochemical alteration indices. Water-rock equilibrium exchange models indicate that the high δ 18O values that characterize the LaRonde Penna deposit are compatible with low-temperature (~150oC) hydrothermal alteration at high water-rock oxygen atomic ratios (1–50). Zones of lower δ 18O values stratigraphically beneath the principal ore lens (20 North) indicate local zones of higher temperature hydrothermal alteration. The oxygen isotope composition of the hydrothermal fluid is estimated to have been ~5‰, as a consequence of mixing between seawater ( δ 18O ~0‰) and a component of magmatic water degassed from the volcanic and intrusive rocks associated with the LaRonde Penna deposit.
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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 | 0.001 | 0.001 |
| 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".