Distribution of Te, As, Bi, Sb, and Se in Mid-Ocean Ridge Basalt and Komatiites and in Picrites and Basalts from Large Igneous Provinces: Implications for the Formation of Magmatic Ni-Cu-Platinum Group Element Deposits
Bibliographic record
Abstract
Abstract In magmatic nickel-copper-platinum-group element (PGE) deposits, the PGEs are found both in solid solution in base metal sulfides and as platinum group minerals (PGMs). Apart from S, the most common elements that the PGEs combine with to form PGMs are Te, As, Bi, Sb, and Sn (TABS). Whether the TABS play a role in collecting the PGEs or simply partition into the sulfide liquid along with the PGEs and later combine with PGEs when the sulfide phase becomes saturated with PGMs is not currently clear. This is in part because the concentrations of TABS in the magmas (picrites and basalts from large igneous province and komatiites) that form these types of deposits are not well established, and hence it is not evident whether the magmas contain sufficient TABS to control PGEs. In order to establish the concentrations of Te, As, Bi, Sb, and Se (TABS+) in these rock types and to document the processes affecting these concentrations, we have determined TABS+ concentrations in komatiites, in mid-ocean ridge basalt, and in picrites and basalts from large igneous provinces. Using TABS+ mantle-normalized diagrams, the affects of different mantle sources, crystal fractionation, crustal assimilation, degassing, and alteration are considered. We estimate the concentrations of TABS+ in komatiites to be approximately twice primitive mantle values. In picrites the concentrations vary: approximately 10 times primitive mantle values for As and Sb and decreasing through Bi to Te from 7 to 2 times primitive mantle. Assimilation of S-bearing sedimentary rocks is thought to be important in triggering sulfide saturation leading to the formation of Ni-Cu-PGE deposits. Assimilation of such sediments would enrich the magma in Th over Nb and in As, Sb, and Bi. Evidence of assimilation in the form of TABS and Th enrichment is clear in the PGE reef deposits of the Bushveld and Stillwater Complexes, but the deposits do not contain sufficient TABS to control the PGEs. This is also true in the Norilsk-Talnakh Ni-Cu-PGE deposits. However, at Norilsk degassing of the magma has resulted in the loss of TABS, which results in negative As, Bi, Se, and Te anomalies on primitive mantle-normalized plots.
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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) | 0.000 | 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".