Are there elephants hiding in the Jurassic of Yukon? A tectonomagmatic perspective on porphyry prospectivity
Bibliographic record
Abstract
Within British Columbia, Triassic-Jurassic felsic plutonic and intrusive rocks of the Stikinia and Quesnellia terranes are very much considered mp;lt;"elephant countrymp;gt;", and are spatially and genetically associated with some of the most significant porphyry Cu-Mo deposits in North America. However, where these terranes meet and merge in central Yukon, little significant mineralization has been discovered in similarly aged felsic plutonic rocks and they host only one operating Cu mine, despite outcrop covering hundreds of square kilometres. The reasons for this discrepancy are not clear. In order to provide assessment of the tectonomagmatic setting and porphyry prospectivity of Jurassic plutonic rocks within Yukon, 65 unmineralized samples from across the district have been analyzed for their whole rock major and trace element geochemistry, and their zircon Ce4+/Ce3+ ratios were determined by laser ablation ICP-MS. Most samples plot within calc-alkaline to high K calc-alkaline fields within a plot of SiO2 vs. K2O, although data display significant scatter and lack any strong trend, suggestive of later disturbance of the K content. Rocks from all sampling locations show HFSE depletions and negative Nb anomalies characteristic of suprasubduction zone environments, and commonly depleted HREE patterns are suggestive of melt generated below the depth of garnet stability. Plots of Sr/Y vs. Y and La/YbN vs. YbN both indicate significant adakite-like and adakitic characteristics in a subset of the samples analysed. Taken together, the suprasubduction zone character and presence of adakite-like magmatism have been suggested as strong indicators of high porphyry potential in other parts of the world. Zircon Ce4+/Ce3+ values were highly variable and ranged up to more than 2100, an order of magnitude greater than previous studies have suggested as a porphyry prospectivity threshold. However, aluminum-inhornblende data and Cu and Mo contents well below crustal abundances suggest that Jurassic plutonic rocks may represent the mid-crustal, volatile-depleted residue of porphyry-related magmatism that has been eroded away. Future exploration for Cu-Mo-Au mineralization within Yukon will depend on understanding of tectonic uplift across the region, and better constraint on the genesis of known mineralization.
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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 | 0.002 | 0.002 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".