Evidence of gold related to Neoarchean alkaline magmatism in the Abitibi greenstone belt (Canada) from mineral parageneses and microscale trace element geochemistry on pyrite
Bibliographic record
Abstract
Most of Archean gold deposits are classified as orogenic gold systems (OGS), precipitated by metamorphic fluids during compressional deformation at convergent plate margins. However, Neoarchean gold deposits are also found spatially related to post-collisional alkaline intrusions such as syenites, suggesting a genetic link between gold and magmas. To bring novel evidence on this relation, ore parageneses related to Bachelor/O’Brien, Beattie, Douay and Golden Arrow gold deposits were studied together with trace elements distribution at micron-scale in Au-bearing pyrites. Further, the δ34Spyrite signature in the Beattie deposit were compared to epithermal Phanerozoic analogues in post-collisional tectonic settings. Except for Golden Arrow, results show a paragenetic assemblage of K-feldspar-albite-anhydrite-barite-celestite-apatite-rutile-calcite-dolomite which is also common in Phanerozoic magmatic-hydrothermal systems. Gold-bearing pyrites are characterized by a higher abundance of most trace elements compared to OGS. Positive Au-Ag-Bi-Te-Tl-W-anomalies – which are not observed in OGS – suggest deposition from highly oxidized fluids, while Au precipitation in OGS is mainly controlled by reduced fluids. The presence of highly oxidized environments is also confirmed by very low δ34Spyrite values ranging from −17.3‰ to −13.9‰ VCDT found at Beattie, in the range of those found in Phanerozoic deposits of Tuvatu and Emperor in Fiji. It is proposed that Archean gold related with late alkaline continental magmatism is deposited both at the top of porphyritic system and in epithermal environment, before the acme of deformation and metamorphism.
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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 | 0.000 | 0.001 |
| 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".