Genesis of sediment‐hosted copper and silver mineralization at the Omatapati prospect, Kaoko Belt, Opuwo district, Kunene region, Namibia
Bibliographic record
Abstract
Abstract The Omatapati copper and silver prospect within the Kaoko Belt is located in the Opuwo district, Kunene region, Namibia. The prospect is hosted by dolomite and interbedded argillites of the Neoproterozoic Devede Formation, the Ombombo Subgroup. An ore body is exposed in shallow artisanal mining pits and drill‐cores of the prospect have grades of 0.4 to 5.2 wt% Cu, and 23 to 312 g/t Ag. The prospect was formed by both hypogene and supergene mineralization processes. The hypogene mineralization occurred in three stages. Stage 1 is represented by calcite veins containing chalcopyrite, bornite, sphalerite and galena. Stage 2 consists of quartz and calcite veins with chalcopyrite and bornite. Stage 3 consists of quartz‐calcite‐barite veins with chalcopyrite. The veins of stages 1 and 2 are subparallel or discordant to the foliation of argillites, and those of Stage 3 are NE‐striking and steeply dipping in the brecciated dolostone and argillite. The mineralization stages 1, 2, and 3 are overprinted by supergene chalcocite, digenite, annite, covellite, malachite, delafossite, hematite, and goethite. The supergene process forms a semi‐massive chalcocite‐covellite zone, which extends from the surface to ~50 m depth. The veins show average concentrations of 2.1 wt% Cu, 80 ppm Ag, and 532 ppm Pb for the stage 1, 3.1 wt% Cu, 118 ppm Ag, and 66 ppm Pb for the stage 2, and 18.6 wt% Cu, 675 ppm Ag, and 565 ppm Pb for the Stage 3 with supergene overprinting. Silver occurs as impurity in supergene chalcocite (6303 ppm Ag), digenite (4425 ppm Ag), and covellite (3060 ppm Ag). Fluid inclusions in quartz and calcite revealed that the hypogene mineralization occurred under a pressure >7–8 MPa. Temperatures of ore formation of the stages 1, 2, and 3 were >145–155 °C, >290–300 °C, and >190–230 °C, respectively. Large variation of salinities in each fluid inclusion assemblage suggests fluid mixing and dilution processes. Fluid inclusion gas compositions in the Stage 3 have weighted means of 98.98 mol% H2O, 0.75 mol% N2, 0.52 mol% CO2, 0.02 mol% CH4, 0.0021 mol% Ar, 0.0009 mol% H2S, and 0.00006 mol% He and indicate a signature of magmatic fluids mixed with meteoric waters or seawater. δ34SCDT values of sulfides in the stages 1, 2, and 3 in the prospect have three data clusters, (1) near 0 ‰ of chalcopyrite in the stages 1 and 2, (2) near −11 ‰ of bornite in the stage 2, and (3) +5 to +11 ‰ of the supergene chalcocite and covellite. Modes of occurrence of ores, fluid inclusions and sulfur isotope data show that the prospect is likely the same type as sediment‐hosted copper‐silver deposits with veining found in the Central African Copperbelt.
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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 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".