Fluid flows and metal deposition near basement /cover unconformity: lessons and analogies from Pb–Zn–F–Ba systems for the understanding of Proterozoic U deposits
Bibliographic record
Abstract
Geofluids (2010) 10 , 270–292 Abstract Fluid circulation at basement/cover unconformities is of first importance for metal transfer and especially the formation of Pb–Zn, F, Ba and U‐deposits. This is typically the case for world‐class Proterozoic U deposits (Canada, Australia, Gabon) in basins, which show many similarities with younger Pb–Zn–F–Ba systems (Irish Paleozoic Pb–Zn deposits, F–Pb–Zn–Ba deposits related to extensional tectonics from Spain, western France and Silesia and fluid movements related to continental rifting in the Rhine graben). As fluid mixing near the basement/cover unconformity is one of the key factors for ore formation, a series of parameters have been considered for both systems: the time gap between basin formation and metal deposit, the origin and nature of the ore fluids, the temperature of fluid end members and the style of migration. Results show great similarities in all fluid systems: (i) a wide range of fluid salinity indicating the lack of homogeneity of fluid chemistry at the scale of the reservoirs, (ii) the deep penetration of brines through faults and dense networks of microfractures within the basement below the unconformity, (iii) local fluid–rock interaction leading to porosity increase and significant fluid changes in fluid chemistry, (iv) a pulsatory fluid regime during fluid trapping, (v) anisothermal fluid mixing revealed by a systematic temperature gap between brines and recharge fluids, (vi) stages of fluid movements facilitated by discontinuous opening related to later tectonic/telogenetic stages linked to major geodynamic events, typically without related sedimentation and burial (exception in a few cases characterized by the synchronous production and penetration of surface brines and ore genesis). By analogy with younger systems, the conditions of burial and penetration of brines in the Archean basement suggest that thermal convection drove the brine movements, and was possibly linked to extensional tectonics in a part of the giant mid‐Proterozoic U‐deposits.
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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 | 0.001 |
| 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 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 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".