Mineralization of the Shuangwang Gold Deposit in the Western Qinling Orogen, China: Relations to Crust–Mantle Interactions and Tectonic Evolution
Bibliographic record
Abstract
Abstract The Shuangwang Au deposit in the western Qinling Orogen is hosted by a WNW–ESE‐trending breccia belt that is structurally controlled by the northern limb of the Yindonggou fold. Igneous rocks area in the deposit are part of the Xiba pluton, which comprises granodiorite and monzogranite that contains mafic microgranular envlaves (MMEs), and later mineralized granitic porphyry dikes. The mineralized granitic porphyry dikes were controlled by the same structures that controlled the ore bodies. Zircon LA‐ICP‐MS U‐Pb dating yields ages of 220.0 ± 1.9 Ma for the granodiorite, and 217.9 ± 1.9 Ma for the granitic porphyry, which is consistent with the mineralization ages reported in previous studies (220–218 Ma). Together with the similarity of alteration mineral assemblages between ore and mineralized granitic porphyry, we suggest that the mineralization was controlled by structure and Xiba pluton. The geochemical data show that the granodiorite and granitic porphyry are subalkaline and the MMEs are alkaline in composition. All samples have similar chondrite‐normalized rare earth element patterns with enrichment of light rare earth elements. The granodiorite and MMEs are depleted in Nb, Ta, Sr, P, and Ti and enriched in U, K, Pb, Zr, and Hf. The granitic porphyry is enriched in large‐ion lithophile elements but depleted in high‐field‐strength elements. The granodiorite and MMEs have low whole‐rock ε Nd ( t ) values (–10.90 to –2.32) and ( 87 Sr/ 86 Sr) i ratios (0.7000–0.7285), similar to coeval Triassic granites in the western Qinling Orogen. The ( 87 Sr/ 86 Sr) i ratios of the granitic porphyry have been affected by fluid metasomatism that results in higher ( 87 Sr/ 86 Sr) i values. The geochronological, geochemical, and isotopic evidence suggest that the Xiba pluton formed by partial melting of thickened lower crust that had been intruded by alkaline mafic magma, as documented by the MMEs, which were derived from a source metasomatized by subduction‐related fluids. The granodioritic and granitic porphyry magmas were relatively oxidized (fayalite–magnetite–quartz [FMQ] to magnetite–hematite (MH) buffer conditions; zircon Ce 4+ /Ce 3+ = 72–813; log( f O 2 ) = –22 to –8). We propose that magma mixing between lower crust and mantle‐derived mafic magma was triggered by the tectonic transition from a collisional to post‐collision setting, which provided the metals, S, fluids, and increase in magma oxygen fugacity that enabled the formation of the Shuangwang Au deposit. Since the Late Triassic, the western Qinling Orogen evolved from a syn‐collisional compressional to post‐collisional extensional environment. The mineralization of the Shuangwang Au deposit involved early formation of a tectonic breccia in the compressional stage. Subsequently, hydrothermal fluids derived from a magma ascended, migrated, mixed, and precipitated ores in the tectonic breccia during the later extensional stage to form the Shuangwang Au deposit.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 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 source (direct Gemma or distilled Codex), 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".