Re-examination of the Aïn Allegua-Aguiba celestite-Pb-Zn salt diapir-related Mississippi Valley-type deposits (Nappes zone, Northwestern Tunisia): New conceptual model
Bibliographic record
Abstract
The celestite-rich and Pb-Zn-poor Aïn Allegua deposits are located at the northeastern extremity of the Dougas diapir in the Nappes zone of northern Tunisia. The Sr-Ba-Zn-Pb mineral system studied in this paper is enclosed in a Triassic breccia, labeled cap rock, located between the Triassic diapir and the surrounding Cretaceous to Lutetian marine sediments. It consists of evaporite dissolution float breccia where Triassic dolostone clasts are floating in a Triassic matrix of anhydrite and argillites. Five mineralizing stages are recognized, which are from early to late: celestite (stage 1); hydrothermal dolomite (stage 2); crosscutting galena-barite or sphalerite-galena-barite-calcite (stage 3); (4) fracture and karst filled by barite, celestite, and galena (stage 4); and late supergene mineralization (strontianite, smithsonite, and cerussite) (stage 5). The present study shows that the celestite and Pb-Zn mineralization formed from the circulation in the cap rock of at least three fluids : (1) fluid A (100-150°C; 10 to 25 wt.% NaCl eq.) deposited the celestite ; (2) fluid B (125 to 185°C; 29 to 34 wt.% NaCl eq.) deposited the hydrothermal dolomite, and (3) fluid C (temperatures around 90°C; 14 to 22 wt.% NaCl eq.) deposited the calcite that accompanied sphalerite and galena precipitation. The δ34S values for sphalerite and galena fall within a narrow range from +10.4‰ to +18.9‰ (avr. 13‰) indicating a homogeneous source of sulfur. The δ34S values of celestite and barite are also relatively homogeneous from +14.7 to +23‰ (ave. +16.5‰) and match those of Tunisian Triassic gypsum and Triassic marine sulfates (δ34S = +15‰). The temperature of deposition together with sulfur isotope data indicate that the reduced sulfur in sulfides was derived through thermochemical sulfate reduction of Triassic sulfate. The lead isotopes in galena show that Pb, and probably Zn and Ba were extracted from the upper crustal rocks. Part of the strontium is derived from the Triassic anhydrite and the other part is probably transported to the cap rock in formation waters. The tectonic setting, the carbonated nature of the host rocks, the epigenetic style of the mineralization, and the mineral associations, together with fluid inclusions data and sulfur and lead isotopes show that the Aïn Allegua deposit belongs to the diapir-related Mississippi Valley-type (MVT) deposits of the Eastern Maghreb salt diapirs province, that formed, as the most of the MVT deposits and districts in the world, from basinal brines with no mixing with metamorphic and/or magmatic fluid or involvement of a heat source from a concealed sill or magmatic intrusion.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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; both teacher heads agree on what is shown here.
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".