Magmatic and Structural Controls on the Development of Porphyry Cu ± Mo ± Au Deposits
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Bibliographic record
Abstract
Abstract Porphyry Cu ± Mo ± Au deposits require the coincidence and positive interaction of a series of individually commonplace geological processes. They, and all their genetically associated deposits, are a natural consequence of convergent margin magmatism, and reflect the dynamic interplay between magmatic, hy-drothermal, and tectonic processes. Magmas generated during subduction rise into the upper crust, commonly along zones of lithospheric weakness, where they pond in tabular magma chambers at depths of 6 km or deeper. The chambers grow laterally by chamber floor depression (cantilever mechanism) and some roof lifting (piston mechanism). Apophyses rise from the parental magma chamber and intrude to within 1 to 3 km of the surface, where they may undergo volatile exsolution and crystallization as por-phyritic stocks. Emplacement of porphyry stocks is facilitated by structural anisotropy in the roof rocks. Ascending hydrothermal fluids exsolved from the porphyry stocks and the underlying parental magma chamber are focused into the cupola, taking advantage of vertical structural and rheological anisotropies introduced either before or during porphyry emplacement. From a structural standpoint, three recurrent processes enhance permeability in the form of fracture or breccia networks through which hydrothermal fluids pass and precipitate minerals. Fracture-producing events are related to intrusion of pre-, syn-, and post-mineral porphyry stocks or dikes to near-surface depths (1-3 km), phase separation and volume expansion of a hydrothermal fluid through a variety of mechanisms, and tectonically induced failure. Concentric and radial fracture patterns reflect magmatic processes whereas more linear arrays of veins reflect tectonic influences. The resulting different vein arrays are commonly vertically and temporally distributed in the porphyry system; concentric and radial arrays are more common above or in the upper parts of the stocks, whereas linear arrays dominate at depth, forming as the system cools and the pluton solidifies. Orthogonal and conjugate arrays of veins characterize all scales and all parts of porphyry systems. Veins from a particular paragenetic stage do not have unique orientations, but rather occur with all orientations typical of that system. The common conjugate to orthogonal inter-vein relationships in porphyry Cu deposits requires repetitive exchange of principal stress orientations, events that are facilitated by conditions of low differential horizontal stress. Such stress conditions indicate that many porphyry Cu deposits form in specific environments where the magmatic arc is under a near-neutral stress state. These conditions occur either in areas removed from active deformation, or during periods of stress relaxation and low strain in the magmatic arc. Achievement of these conditions in time and space is likely to be infrequent and transitory during the life of a convergent margin, which may explain the spatial and temporal clustering of deposits in large porphyry districts.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| 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) | 0.016 | 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 it