Evolution of High-Level Magmatic-Hydrothermal Systems: New Insights from Ore Paragenesis of the Veladero High-Sulfidation Epithermal Au-Ag Deposit, El Indio-Pascua Belt, Argentina
Bibliographic record
Abstract
Abstract The world-class Veladero high-sulfidation epithermal Au-Ag deposit is located in the Andean cordillera of Argentina near the northern end of the El Indio-Pascua metallogenic belt. The deposit comprises two nearly coalescing subhorizontal orebodies that are centered on an extensive zone of intense hydrothermal alteration. Intensely altered volcanic rocks are composed of fine-grained groundmass quartz that formed as a result of extreme acid leaching. These quartz grains contain ubiquitous rutile inclusions as well as healed microfractures of vapor-filled inclusions that record magmatic vapor streaming through the Miocene volcanic host succession. Condensation of the magmatic vapor into ambient groundwater generated the highly acidic waters responsible for the alteration. Alunite is present in the fine-grained groundmass quartz and fills vugs in the altered rocks. Stable isotope data indicate that the alunite formed through the disproportionation of SO2 in the condensed magmatic vapor. The fine-grained groundmass quartz is crosscut by later fracture-controlled euhedral quartz that is texturally associated with ore minerals. The euhedral quartz crystals show oscillatory growth zoning and contain rare primary fluid inclusions suggesting that quartz formation occurred at ~200°C from a moderately saline (<5 wt % NaCl equiv) liquid-phase hydrothermal fluid. High-fineness native Au grains are hosted in euhedral quartzlined void spaces and along fractures. In addition to native Au, vugs and fractures in the silicified volcanic rocks host Fe oxide/hydroxide and jarosite that are interpreted to represent the oxidation products of hypogene sulfide minerals that formed during and after the late stages of quartz formation. Results of previous jarosite dating suggest that pervasive oxidation of the orebody commenced during the waning stages of the hydrothermal activity or immediately thereafter. Oxidation of the orebody continued in the supergene environment for at least 3 m.y. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) showed that jarosite, which formed as a result of the oxidation of the orebody, is the principal host for Ag in Veladero ore, explaining the low (ca. 10%) Ag recovery from the oxide ore. The Veladero high-sulfidation epithermal deposit is interpreted to have formed in the shallow part of a magmatic-hydrothermal system. Early alteration related to magmatic vapor discharge was followed by later mineralization from liquid-phase hydrothermal fluids under reduced and slightly acidic to near-neutral conditions. This change from early vapor-dominated to later liquid-dominated magmatic-hydrothermal fluid flow was key in formation of the deposit.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| 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) | 0.003 | 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 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".