Episodic magmatism contributes to sub-seafloor copper mineralization: Insights from textures and geochemistry of zoned pyrite in the Ashele VMS deposit
Bibliographic record
Abstract
Abstract Prolonged and episodic magmatic-hydrothermal processes have been proposed to be important in forming large-tonnage Cu volcanogenic massive sulfide (VMS) deposits but are difficult to document and remain poorly understood in ancient VMS systems. In this study, we combine textural evidence and in situ analysis of sulfur isotopic composition with trace elements of pyrite from the well-preserved, large-tonnage Ashele VMS deposit (Central Asian Orogenic Belt, NW China) to elucidate the origin of the ore-forming materials and controlling factors of VMS deposits. The distribution of hydrothermal alteration and mineralization allows the Ashele deposit to be divided into five zones: massive sulfide, quartz-pyrite, chlorite-chalcopyrite-quartz-pyrite, quartz-chlorite-sericite-pyrite, and quartz-sericite-pyrite zones. Cu mineralization is mainly hosed in the massive sulfide and chlorite-chalcopyrite-quartz-pyrite zones. Three texturally and compositionally distinct types of pyrite from the Cu mineralization zones have been recognized. The first type of growth zones with high Cu, As, and volatile elements (e.g., Hg and Tl) concentrations and negative δ34S values (−7.83‰ to −0.35‰) are observed in pyrite grains from the massive sulfide zone most likely formed from the input of magmatic volatiles degassed from the underlying magmatic systems. The second type of Cu-As-rich growth zones in pyrite grains from the chlorite-chalcopyrite-pyrite zone is not enriched in volatile elements and has positive δ34S values (2.59–6.56‰), which are interpreted to have precipitated during fluid boiling. The third type of growth zone, without Cu-As enrichment but having positive δ34S values (0.30–9.76‰) in pyrite grains from both mineralization zones, was probably formed without boiling or magmatic volatile input. Our results suggest that multi-stage magmatic degassing or fluid boiling accompanied by Cu precipitation recorded in individual pyrite grains can reveal episodic magmatic-hydrothermal activity, which is an essential factor in forming large-tonnage VMS deposits.
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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 | 0.000 | 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 | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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".