The Papagaios Gold Deposit: Record of Multiple Hydrothermal Mineralization Events in the Pitangui Greenstone Belt, Brazil
Bibliographic record
Abstract
Abstract The Papagaios gold deposit in the Pitangui greenstone belt, Brazil, exhibits a complex metallogenic evolution characterized by multiple hydrothermal events. This study presents the first comprehensive characterization of its geology, petrography, lithogeochemistry, and mineral chemistry to elucidate the gold mineralization evolution. The mineralization is hosted in granitoids and a metavolcanic-sedimentary sequence metamorphosed to amphibolite facies (~630°C, garnet-biotite geothermobarometry) and is structurally controlled by east-northeast to west-southwest shear zones. Four hydrothermal stages have been identified based on their relationship to the Sn foliation. The pre-Sn stage features Mn-rich dolomite and talc-dolomite-chlorite-actinolite veins, with gold-bearing pyrite disseminated in metabasalts and volcaniclastic rocks, suggesting a possible Archean volcanic-hosted massive sulfide (VHMS)-like system. Syn-Sn mineralization is hosted in silicified zones with carbonate-chlorite halos, where free gold is associated with sulfide assemblages. Chlorite chemistry points to formation temperatures of 180° to 475°C under oxidizing conditions, while lithogeochemistry reveals an Au-Cu-Pb-Zn signature. Syn- to late-Sn Na-Ca alteration halos envelop Neoarchean granitic intrusions, suggesting a high-temperature and saline magmatic-hydrothermal process consistent with intrusion-related systems. The post-Sn stage shows propylitic and phyllic alteration with Au-Fe-As–rich sulfide-oxide assemblages formed between 190° and 390°C under reducing conditions, according to chlorite chemistry, while tourmaline chemistry suggests saline fluids, and white mica points to formation pressures around 2 kbar. This stage may reflect a late Neoarchean magmatic-hydrothermal fluid release or a Paleoproterozoic overprint. The multistage evolution of the Papagaios deposit is distinct from other mineral deposits within the Pitangui greenstone belt and Quadrilátero Ferrífero metallogenic scenario, and implies an interplay of VHMS, orogenic, and intrusionrelated gold systems.
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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 | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 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".