Veining, alteration and genesis of the Dongan epithermal Au deposit, Northeast China
Bibliographic record
Abstract
• The Dognan epithermal Au–Ag deposit related to Cretaceous andesitic to rhyolitic rocks, is characterized by alteration and ore zonation. • Ore precipitation is related to low-pressure (<10 MPa), low-temperature (mostly <300 °C) dilute fluids at a proposed depth of 200–600 m. • Boiling, together with fluid–rock interaction, desulfurization, and fluid mixing, promoted the precipitation of Au from near neutral, reduced fluids. Dongan, located in the Lesser Xing’an Range district of NE China, is a large epithermal Au deposit with an estimated resource of 70 t Au. The auriferous veins are hosted in Jurassic granites and Cretaceous andesitic to rhyolitic rocks. The alteration system around the deposit is zoned from adularia–sericite in the center of the mineralized system through albite–illite–clay to an outer chlorite–sericite–actinolite shell. Four vein stages are recognized, including quartz–pyrite veins, quartz–adularia ± pyrite veins/bands, quartz–actinolite–sulfide veins/breccias, and late quartz–fluorite–carbonate veins with time. Microthermometric measurements on primary fluid inclusions in quartz indicate that the vein minerals precipitated directly from low-pressure (mainly <10 MPa), low-temperature (mostly <300 °C) and dilute fluids (up to 5.7 wt% NaCl equiv) at a proposed minimum depth of 200–600 m. Pyrite yields δ 34 S values of –3.0 to + 1.3 ‰, with the values becoming more positive from stage I to stage III, probably related to reducing process, fluid cooling and fluid–rock interaction. The decreasing oxygen (δ 18 O fluid = 1.9 to –11.4 ‰) and hydrogen (δD fluid = –103.7 to –128.3 ‰) isotopic values of the hydrothermal fluids are interpreted to be a result of progressive addition of meteoric water to the hydrothermal system over time. Boiling and desulfurization exerted a first-order control on generating the low sulfur (logƒS 2 ) and oxygen fugacities (–30 to –32 log ƒO 2 ) that characterize the mineralized systems, and promoted the precipitation of Au from near neutral, reduced fluids.
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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 | 0.000 |
| 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) | 0.001 | 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 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".