Petrologic and geochemical examination of the Early Devonian, Evandale porphyry Cu-Mo-(Au) deposit, southern New Brunswick: geothermobarometric analysis of petrogenesis
Bibliographic record
Abstract
Porphyry Cu-Mo-(Au) systems associated with the granitoid rocks in eastern North American orogenic belts have been researched using current deposit models; however, relatively few studies have examined the potential for late stage fine-grained porphyritic to aplitic intrusive phases being host to mineralization. The Evandale Granodiorite is an example of a well- preserved Mid-Devonian (U-Pb zircon age of 391.2 ± 3.2 Ma for the coarser granitoid, and 390.2 ± 1.6 Ma for the aplite) polyphase pluton intruding through deformed Silurian sedimentary and mafic volcanic rocks of the Mascarene Basin in southern New Brunswick. The two intrusive phases have been identified as I type granites with a minor sedimentary component. The pluton is separated both petrochemically and texturally into two distinct phases. The coarser phase ranges from medium- to coarse-grained seriate to porphyritic granodiorite to monzogranite and the later finer stage layered aplite ranges from a monzogranite to syeno-granite. INAA analysis of each phase found that the highest concentrations of Cu and Au (108 ppm Cu, and 33 ppb Au) are associated with pyrite, chalcopyrite, and arsenopyrite within the aplitic dykes sampled, whereas concentrations of up to 6 ppm Mo were detected within the c.g. granite. Current models suggest that the transport of metals (particularly Cu and Au) are sourced from secondary two-phase fluids at shallow depths (approximately 2 kb), and is controlled primarily by Cl fugacity of the magma. Analyses of biotite phenocrysts from both the aplite and granite contain an average of 0.21 wt% Cl, which is similar to other high grade Cu-Mo-(Au) porphyry deposits. Average zircon saturation temperatures were calculated to be 818°C for the aplite and 787°C for the granitoid. Average apatite saturation temperatures were found to be 880°C for the aplite and 934°C for the granitoid phase. Hornblendeplagioclase thermometry revealed the crystallization temperature of the granite to be 642°C and 600°C for the aplite, cooler than most deposits of the same type. Al in hornblende geobarometery indicates crystallization depths of ~2.1 kb for hornblende in the aplite and ~0.7 kb for the c.g. granite. The aplitic dykes were subject to higher crystallization pressures and lower crystallization temperatures suggesting that their formation may either be a result of pressure quenching of the melt during rapid ascent or by the sub-solidus recrystallization of the melt as pyroclastic flows.
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 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".