Garnet Geochemistry and Lu-Hf Geochronology of a Gold-Bearing Sillimanite-Garnet-Biotite Gneiss at the Borden Lake Belt
Bibliographic record
Abstract
The Kapuskasing Structural Zone transects the Wawa and Abitibi greenstone belts in the Superior province of the Canadian Shield. At the southern margin of the Kapuskasing Structural Zone (KSZ), the Borden Gold deposit hosts low-grade-gold mineralization within upper amphibolite- to granulite-facies sillimanite-garnet-biotite gneisses. Here, we present the geochemistry and Lu-Hf geochronological studies of a gold-hosting garnet-bearing gneiss to constrain the formation history of the deposit and regional geological history. The garnet is almandine-rich, and contains inclusions of quartz, biotite, pyrite, and zircon. The absence of chemical zoning in garnet is likely due to intracrystalline diffusion at peak metamorphic temperatures. The 176Lu-176Hf internal isochron of two garnet fractions and three corresponding whole-rock splits from a gneissic unit yield a precise internal isochron age at 2629.0 ± 4.3 Ma (MSWD = 0.66), with an initial 176Hf/177Hf = 0.281210 ± 0.000010 corresponding to an εHfi = +4.1. This signature suggests a mafic source, which was derived from a long-term depleted reservoir, for this metasediment. The Lu-Hf age is consistent with the youngest age population of zircons from the paragneisses, which were previously dated in the area. Our results thus provide upper constraints on the timing of retrograde upper-amphibolite metamorphism and gold mineralization at Borden.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.022 | 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".