Geochronology, ore-forming processes and fluid sources of the Qinglonggou gold deposit, North Qaidam (NW China): Constraints from in-situ U-Pb dating of monazite and geochemistry of pyrite
Bibliographic record
Abstract
The Tanjianshan goldfield is the most important gold producer in the North Qaidam, NW China. Genesis of gold deposits in Tanjianshan is enigmatic, primarily because of uncertainties as to timing, mineralization processes and fluid sources. We investigate these uncertainties through a comprehensive study of the texture and geochemistry (LA-MC-ICPMS trace elements and sulfur isotopes) of pyrite and in-situ U-Pb dating of monazite from the Qinglonggou gold deposit. Six types of pyrite with distinct textures, trace element contents and sulfur isotopes have been identified, and provide constraints on two overprinting gold-related hydrothermal events. Stage I consists of Py1, occurring as veinlets parallel to S1 deformation in a schist, is characterized by extremely low Co/Ni ratios with high contents of Ni, and high δ34S values (+14.9 ‰ to +16.1 ‰), and were likely derived from metamorphism of the sedimentary strata in the Tanjianshan and Wandonggou Group. In stage II, Py2 occurs in the pyrite-quartz veins that cut Py1 veinlets. They have similar δ34S (+13.1 ‰ to +17.8 ‰) to Py1, indicating that sulfur was likely derived from the dissolution of Py1. The stage I and II veins formed during an early gold pre-concentration event, which is constrained at 429.1 ± 5.9 Ma by in-situ U-Pb dating of monazite that coexists with Py1. Stage III includes Py3 and Py4 which occur in the altered carbonaceous schist and accompanying quartz veins. Trace metals are highest in Py3 (Ag, Au, Sb, and Bi) which represent the most economic ore stage in the deposit, whereas the following Py4 shows low concentrations of most trace elements due to abundant Py3 precipitation. In contrast, trace elements contents increase in Py5 to similar levels as those seen in Py3, suggesting a new pulse of fluid in stage IV. Minor Py6 grains precipitated in the youngest quartz-calcite veins associated with stage V, and contain low concentrations of trace elements. The δ34S values of Py3 (+5.2 ‰ to +6.0 ‰) and Py4 (+4.2 ‰ to +6.1 ‰) are within the range of magmatic sulfur, suggesting a dominantly magmatic source. The δ34S values increase from Py3-4 to Py5 (+6.3 ‰ to +7.4 ‰), and to Py6 (+8.7 ‰ to +9.6 ‰), probably due to increasing contribution from the host rocks, as well as decreasing fO2, through incremental fluid-rock interaction. Stages III and IV represent a late gold-mineralizing event during Late Paleozoic to Early Mesozoic, while stage V is post-mineralization. The overprinting gold pre-concentration and mineralization events in the Tanjianshan goldfield correspond to orogenic evolution of the Proto-Tethys Ocean and Paleo-Tethys Ocean, respectively.
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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 | 0.001 |
| 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".