Elemental, lead and sulfur isotopic compositions of galena from Kola carbonatites, Russia – implications for melt and mantle evolution
Bibliographic record
Abstract
Abstract Galena from four REE -rich (Khibina, Sallanlatvi, Seblyavr, Vuoriyarvi) and REE -poor (Kovdor) carbonatites, as well as hydrothermal veins (Khibina) all from the Devonian Kola Alkaline Province of northwestern Russia was analysed for trace elements and Pb and S isotope compositions. Microprobe analyses show that the only detectable elements in galena are Bi and Ag and these vary from not detectable to 2.23 and not detectable to 0.43 wt.% respectively. Three distinct galena groups can be recognized using Bi and Ag contents, which differ from groupings based on Pb isotope data. The Pb isotope ratios show significant spread with 206 Pb/ 204 Pb ratios (16.79 to 18.99), 207 Pb/ 204 Pb (15.22 to 15.58) and 208 Pb/ 204 Pb ratios (36.75 to 38.62). A near-linear array in a 207 Pb/ 204 Pb vs. 206 Pb/ 204 Pb ratio diagram is consistent with mixing between distinct mantle sources, one of which formed during a major differentiation event in the late Archaean or earlier. The S isotopic composition (δ 34 S) of galena from carbonatites is significantly lighter (–6.7 to –10.3% Canyon Diablo Troilite (CDT) from REE -rich Khibina, Seblyavr and Vuoriyarvi carbonatites, and – 3.2% CDT from REE -poor Kovdor carbonatites) than the mantle value of 0%. Although there is no correlation between S and any of the Pb isotope ratios, Bi and Ag abundances correlate negatively with δ 34 S values. The variations in the isotopic composition of Pb are attributed to partial melting of an isotopically heterogeneous mantle source, while those of δ 34 S (together with Bi and Ag abundances) are considered to be process driven. Although variation in Pb isotope values between complexes might reflect different degrees of interaction between carbonatitic melts and continental crust or metasomatized lithosphere, the published noble gas and C, O, Sr, Nd and Hf isotopic data suggest that the variable Pb isotope ratios are best attributed to isotopic differences preserved within a sub-lithospheric mantle source. Different Pb isotopic compositions of galena from the same complex are consistent with a model of magma replenishment by carbonatitic melts/fluids each marked by quite different Pb isotopic compositions.
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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) | 0.000 | 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".