The Deposition of Elemental Gold from Gold(I)-Thiosulfate Complexes Mediated by Sulfate-Reducing Bacterial Conditions
Bibliographic record
Abstract
The role of sulfate-reducing bacteria in the precipitation of elemental gold through a geologic stratum was investigated using column experiments. The mixed culture, dominated by sulfate-reducing bacteria, was isolated from the Driefontein consolidated gold mine, Witwatersrand basin, Republic of South Africa. Bacterially mediated gold precipitation from the gold(I)-thiosulfate complex was more efficient than the corresponding abiotic experiments. In the bacterial systems, sulfate-reducing bacteria (i.e., Desulfovibrio sp.) deposited gold inside the cells as spherical nanoparticles. Over time, these nanoparticles of gold were released from the cells and deposited at cell surfaces and in the bulk solutions. Ultimately, these nanoparticles of gold contributed to the formation of micrometer-scale octahedral gold crystals, occasional framboidlike structures (~1.5-μm diam) and millimeter-scale gold foils, typically surrounding the silicate grains. Spherical gold particles (~1-μm diam) were precipitated in the abiotic experiments, and the formation of octahedral gold, framboidlike structures and gold foils were not observed in these experiments. The reduction and enrichment of elemental gold by sulfate-reducing bacteria occurred without the concomitant death of the bacteria, suggesting that in natural systems, this process could go on over geologic time scales, as long as nutrients and gold(I)-thiosulfate were provided to the system.
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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 | 0.000 | 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 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".