Genesis and metallogenic processes of the Potoumian Fe–Cu skarn deposit in western Guangdong: Evidence from garnet and magnetite geochemistry and Sr-Nd-Pb isotopes
Bibliographic record
Abstract
The Potoumian Fe–Cu skarn deposit is located on the northwestern margin of the Yangchun Basin in the Yunkai area. The orebodies are hosted in calc-silicate hornfels, skarn, and skarnized limestone proximal to the contact zone between Middle Jurassic granodiorite and Upper Devonian carbonate rocks. Based on the detailed investigation, this study focuses on the elemental and isotopic characteristics of garnet and magnetite from the Potoumian deposit. Two distinct generations of garnet are identified: early-stage cores (Grt I) consist of andradite (And 92-96 Spe 3-4 Gro 1-5 ) showing LREE enrichment, HREE depletion, and strong to weak positive Eu anomalies; late-stage rims (Grt II) are grandite (And 59-64 Spe 5-10 Gro 30-32 ) exhibiting inverse REE fractionation (LREE-depleted relative to HREE) with pronounced negative Eu anomalies. Grt I is significantly enriched in Sc, Ti, V, Cr, Co, Ni, Ga, Ge, Rb, Sn, Nb, Ta, Zr, and Hf, but depleted in As, Sr, In, W, Cu, Pb, Zn, U, and REEs compared to Grt II. The geochemical evolution from Grt I to Grt II reflects a transition in fluid conditions: early mineralization fluids were characterized by an open system with high oxygen fugacity, high water/rock ratios, weakly acidic pH, infiltration-dominated metasomatism, and significant influx of external fluids (e.g., meteoric water). In contrast, later fluids evolved toward a more closed system with reducing conditions, lower water/rock ratios, diffusion-dominated metasomatism, and minimal external fluid input. Magnetite geochemistry suggests a hydrothermal origin, with primary mineralization occurring under high and stable oxygen fugacity at temperatures exceeding 300 °C, which is consistent with classification as a skarn-type deposit. Sr–Nd–Pb isotopic analyses of magnetite yield I Sr ratios ranging from 0.71089 to 0.71096, ε Nd (t) values from −8.2 to −8.3, and narrow ranges of 206 Pb/ 204 Pb (19.285–19.327), 207 Pb/ 204 Pb (15.851–15.874), and 208 Pb/ 204 Pb (39.526–39.623). These isotopic signatures indicate that the ore-forming fluids and metals were likely related to granitic magma. Additionally, this study highlights the significant potential for W and Zn mineralization within the deposit, while Sn mineralization appears limited. The findings provide key mineralogical and isotopic insights into the metallogenic processes of the Potoumian Fe–Cu polymetallic 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 | 0.000 | 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".