Basin-scale production of hyperacidic brines is critical for the formation of high-grade and large-tonnage uranium deposits in sedimentary basins
Bibliographic record
Abstract
Unconformity-related uranium deposits (URU deposits) in the Proterozoic Athabasca Basin (Canada) represent the largest and richest (with average grades ranging from 0.127 to 19.5 wt% U) U deposits in the world. Fluid inclusion studies and experimental data suggest that the ore-forming fluids of URU deposits are hyperacidic (pH < 3.5), oxidizing basinal brines carrying high concentrations of U (0.2 to 3700 ppm), which are several orders of magnitude higher than ordinary basinal and basement formation waters. While the oxidizing conditions of these fluids are well established, the mechanism responsible for the basin-scale generation of hyperacidic brines remains unknown. This paper aims to address this problem and to explain why the Athabasca Basin is exceptionally endowed with high-grade and large-tonnage uranium deposits. Based on petrographic and infrared hyperspectral logging data indicating basin-wide coexistence of kaolinite and illite in quartz-dominated sandstones, and fluid inclusion data showing high potassium (K) concentrations in diagenetic and ore-forming fluids within the Athabasca Basin, it is proposed that the production of hyperacidic brines resulted from a pervasive diagenetic reaction between K-rich brines and kaolinite: 3kaolinite [Al 2 Si 2 O 5 (OH) 4 ] + 2 K + ↔ 2illite [KAl 3 Si 3 O 10 (OH) 2 ] + 3H 2 O + 2H + . Geochemical modeling of fluid-rock reactions demonstrates that the basin-scale production of hyperacidic brines is achievable when a combination of three specific conditions is satisfied: 1) the presence of a thick package of compositionally mature sandstones, characterized by quartz-dominated framework grains with minimal (<1%) feldspar and the interstitial space filled with kaolinite; 2) the development of K-rich brines through seawater evaporation above the sandstone package; and 3) low fluid/rock ratios, which enable the reaction between kaolinite and K-rich brines to reach equilibrium and produce illite and H + . Recognizing the basin-scale development of hyperacidic brines and the specific conditions entailed offers insights into why the Athabasca Basin is exceptionally endowed with high-grade, large-tonnage U deposits. The conditions of hyperacidic brine production revealed in this study may be used for evaluating the U mineralization potential of other sedimentary basins.
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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 | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 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 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".