Unveiling the polyphasic evolution of the Neoarchean IOCG Salobo deposit, Carajás Mineral Province, Brazil: Insights from magnetite trace elements and sulfur isotopes
Bibliographic record
Abstract
The Salobo iron oxide copper-gold (IOCG) deposit host an important Cu-mineralization of the Carajás Mineral Province. The ore is characterized by an association of (bornite-chalcocite-digenite) hosted by magnetite and biotite-garnet schists. These rocks record distinct stages of superimposed hydrothermal alteration and dynamic metamorphism. Three different occurrences of magnetite constitute the magnetite bodies: a pristine to inclusion-poor Mgt I; inclusion-rich magnetite-bearing breccia Mgt II, and the granoblastic-foliated Mgt III. In general, the magnetite types present a similar trace element composition with some variations in Si, Al, Mg and K indicating that the magnetite types share the same magmatic-hydrothermal origin with post-formation processes (dissolution/reprecipitation) recorded in Mgt III. In addition, sulfur isotope signatures for chalcopyrite (1.3–3.35‰), pyrrhotite (0.88–1.98‰), and pyrite (1.7–5.04‰) associated with magnetite I and II, are consistent with a magmatic-hydrothermal sulfur source at Salobo without/or minimal external sulfur contributions. Our data indicate that ore-forming fluids for Salobo ore could have undergone sulfur disproportionation processes during sulfide formation due to magnetite precipitation, which results in the classic IOCG mineral association of chalcopyrite + magnetite described for the first time in this contribution. Therefore, the main mineralization event in the Salobo deposit could be coeval with similar IOCG deposits in the Carajás Mineral Province related to the Neoarchean magmatism at ca. 2.7 Ga. Subsequent deformation and low-grade dynamic metamorphism related to reactivation of the Cinzento Shear Zone (ca. 2.5 Ga) and A-type granite emplacement probably Paleoproterozoic in age resulted in remobilization-recrystallization of magnetite and Cu-sulfides.
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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 | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| 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".