CLAY MINERALOGY AND LA-ICP-MS DATING OF SUPERGENE U-Cu NONTRONITE-BEARING MINERALIZATION AT NABBURG-WOLSENDORF, SOUTHEASTERN GERMANY
Bibliographic record
Abstract
Nontronite has been reported from a wide range of mineral deposits on the continent and in marine environments, commonly associated with basic igneous rocks, base-metal sulfides, Fe sulfides, Fe–Mn oxide–hydroxides and gold. This smectite-type phyllosilicate forms during the low-temperature alteration of sulfide-bearing parent material. In contrast, nontronite from vein-type fluorite mineralization at Nabburg–Wolsendorf, in southeastern Germany, developed in a sulfur-deficient environment under supergene conditions associated only with uranyl phosphates, mainly uranocircite. It was investigated by XRD, IR spectrometry, XRF, CEC analysis and SEM–EDX. Phyllosilicates and uranium mica are coeval and of Pliocene age. A U–Pb age of 4.0 ± 0.1 Ma was determined using Laser-Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA–ICP–MS). Some younger ages cluster, possibly indicating a multiphase history of crystallization. Both minerals came into existence at temperatures around 30°C when the region underwent pervasive chemical weathering under humid tropical climatic conditions. Uranium was derived from the decomposition of uraninite and coffinite in the veins and from the weathering of U-bearing accessory minerals in the granite, whereas the major elements and barium in uranocircite originated from the alteration of the granitic country-rocks. The vein minerals, e.g. , fluorite acted solely as bedrock, but were not involved in this supergene mineralization. Nontronite–uranocircite mineralization can develop in almost all granitic terranes under supergene conditions like those described. The log Al3+/H+ 3 and log Ca2+/H+ 2 values are decisive as to whether nontronite, kaolinite or green opal (nontronite plus opal) comes into existence. Both types of supergene alteration minerals, kaolinite and green opal, developed side-by-side with the nontronite–uranocircite mineralization during the Neogene in this area. Uranium–lead dating using the LA–ICP–MS technique serves to constrain the age of this mineralization.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 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".