The Diamantina Monazite: A New Low‐Th Reference Material for Microanalysis
Bibliographic record
Abstract
Most monazite reference materials ( RM s) for in situ U‐Pb geochronology are rich in Th; however, many hydrothermal ore deposits contain monazite that is low in trace element contents, including Th, U and Pb. Because of potential problems with matrix effects and the lack of appropriate matrix‐matched RM s, such variations can bias dating of hydrothermal deposits. In this paper, we describe a polycrystalline low‐U and low‐Th Diamantina monazite from the Espinhaço Range, SE Brazil. It has a U‐Pb ID ‐ TIMS weighted mean 207 Pb * / 235 U ratio of 0.62913 ± 0.00079, 206 Pb * / 238 U of 0.079861 ± 0.000088 and 207 Pb * / 206 Pb * of 0.057130 ± 0.000031, yielding a weighted mean 206 Pb * / 238 U date of 495.26 ± 0.54 Ma (95% c.l.). In situ dates acquired with different methods ( LA ‐(Q, SF , MC )‐ ICP ‐ MS and SIMS ) are within uncertainty of the ID ‐ TIMS data. U‐Pb LA ‐(Q, MC )‐ ICP ‐ MS runs, using Diamantina as a primary RM , reproduced the ages of other established RM s within < 1% deviation. The LA ‐ MC ‐ ICP ‐ MS analyses yielded homogeneous Sm‐Nd isotopic compositions ( 143 Nd/ 144 Nd = 0.511427 ± 23, 2 s ; 147 Sm/ 144 Nd = 0.1177 ± 13, 2 s ) and εNd (495 Ma) of −18.7 ± 0.5 (2 s ). SIMS oxygen isotope determinations showed measurement reproducibility better than ± 0.3‰ (2 s ), confirming Diamantina's relative homogeneity at test portion masses below 1 ng.
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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 | 0.003 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".