The Genesis of Regolith-Hosted Heavy Rare Earth Element Deposits: Insights from the World-Class Zudong Deposit in Jiangxi Province, South China
Bibliographic record
Abstract
"The Zudong heavy rare earth element (HREE) deposit in South China is the largest regolith23 hosted HREE deposit in the world with a resource of ~17,600 t of REO, at an average grade of ~0.1 wt. % REO. Despite more than 40 years of exploration and exploitation, the genesis of this deposit is poorly understood. Subtropical weathering of the parent A-type granite formed ore bodies hosted mainly within the lower B to upper C horizons of the resulting soil, which is developed on the hillsides of a moderately incised landscape (relief ~150m). The thickness of the ore bodies varies from a few meters to up to 10 m. Rare earth element concentrations increase from ~300 ppm in the A horizon to ~1500 ppm in the lower B to upper C horizons and decrease with further depth in the profile. The entire soil profile is HREE-enriched with (La/Yb)N ratios <1, but the REE-enriched lower B horizon is less HREE-enriched ((La/Yb)N values up to 0.9) than the underlying upper C horizon. Exchangeable REEs, representing REEs that are adsorbed in the deposit, constitutes ~65% of the bulk REE content; the LREEs are preferentially adsorbed. The main minerals adsorbing the REEs are kaolinite and halloysite; the proportions of REEs adsorbed by Fe-Mn oxyhdyroxides and organic matter are negligible. The remaining REE content is hosted by supergene chernovite [YAsO4] and residual aeschynite/euxenite36 group and fergusonite-group minerals, xenotime-(Y), zircon, and thorite. The Zudong deposit formed from weathering of a HREE-enriched A-type granite, containing between ~200 and ~450 ppm REE dominantly as synchysite-(Y), yttrian fluorite, gadolinite-(Y), hingganite-(Y), and yttrialite-(Y), which are susceptible to chemical weathering. Decomposition of these minerals released REEs to the weathering fluid, and the interaction between alkali feldspar, muscovite and the weathering fluid produced halloysite and subordinate illite and smectite. With progressive weathering, these minerals accumulated together with quartz, refractory zircon, xenotime43 (Y), and aeschynite/euxenite-group and fergusonite-group minerals. In the upper parts of the soil profile, where conditions were acidic, dissolution of REE minerals is promoted and the REEs tend to remain in solution. Deeper in the profile (lower part of the B horizon and upper part of the C horizon), conditions become less acidic leading to adsorption of the REEs and As (released by weathering from an adjacent coal unit) on the surface of halloysite. With time, halloysite, a metastable phase in respect to kaolinite, gradually transforms to the latter, releasing As and variable proportions of the adsorbed REEs. The released REEs and As are transported downwards, partially re-adsorbed by clay minerals and the remaining REEs combined with As to precipitate supergene chernovite-(Y). Ongoing operation of this eluviation-illuviation process at Zudong has gradually enriched the soils in HREEs to form a resource that now supplies much of the world’s HREE."@eng
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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 | 0.003 | 0.004 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".