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The Archean-Paleoproterozoic terrane of central Brazil is an exotic and allochthonous part of the Tocantins Province, a large Brasiliano/Pan-African orogen of the South American Platform formed during the Brasiliano orogeny. The terrane amalgamated to the province during the late stages of the orogeny as a crustal segment consisting of six Archean orthogneiss complexes and five low-grade metamorphic, in part Paleoproterozoic (Rhyacian) greenstone belts. The Uvá complex is the southernmost orthogneiss association of the Archean-Paleoproterozoic terrane of central Brazil. New U–Pb LA-ICP-MS data from zircon crystals show that the complex formed at least during two magmatic stages. The older consists of polydeformed tonalite and granodiorite batholitic and diorite stock protoliths with igneous age of 3040 Ma to 2930 Ma. The youngest comprises tonalite, monzogranite and granodiorite tabular bodies formed between 2876 and 2846 Ma. As compared to the orthogneisses of the northern portion of the terrane, both the oldest and youngest granitogenesis stages of the Uvá complex are, in average, about 150 Ma older. This suggests that the northern and southern orthogneisses formed during different times as independent crustal segments, but when and why they amalgamated is still under investigation. [ABSTRACT FROM AUTHOR]

The Mamão gold deposit, located in the eastern portion of the Amazonian Craton, northern Brazil, is hosted by mafic rocks of the Mesoarchean Andorinhas greenstone belt. An underground mine was operated in this area by Troy Resources Ltd., which produced approximately 350 koz of gold between 2008 and 2015. The hydrothermal alteration halos are characterized by a distal zone (10- to 80 m wide) with a chlorite-albite-epidote-actinolite assemblage, an intermediate zone (5- to 20 m wide) marked by calcite-albite-chlorite-actinolite-quartz, a proximal zone (0.5–5 m wide) composed of biotite-quartz-calcite-pyrite-(gold) and a quartz vein-hosted orebody zone (0.5- to 6 m wide) composed by quartz-calcite-pyrite-(gold). Geochemical data indicate that the metabasalt, metandesite and metadacite host rocks display a tholeiitic N-MORB signature, suggesting that they were formed in ancient oceanic spreading centers. Hydrothermal chlorite of the Mamão deposit is classified as ripidolite and brunsvigite. Biotite is the main mica and increases in modal content from the distal alteration to the vein zone, displaying compositions within the annite domain. Muscovite occurs as very fine lamellae and is generally located in the intermediate zone of the altered region. Amphiboles are calcium-rich and display compositions mostly varying from hornblende (Mg-hornblende to Fe-hornblende) in the distal zone, to actinolite in the intermediate zone. Sulfidation occurs in all hydrothermal alteration zones, with both fine- and coarse-grained pyrite as the main sulfide phase, and lesser amounts of chalcopyrite, pyrrhotite, cobaltite and sphalerite. Fine-grained pyrite contains many gold inclusions and is typical of the orebody zone preferentially in close contact with the proximal hydrothermal zone, whereas coarse-grained pyrite (without recoverable gold) occurs in the veins. From the edges to the core of the hydrothermal alteration halos, the As, Sb, Ag and Au contents in the pyrite increase, whereas Pb, Co and Mo decrease. Gold occurs as free crystals (2- to 0.1 mm) disseminated within the gangue or as inclusions in the fine-grained pyrite. Temperature estimated via chlorite geothermometer ranges from 284- to 320 °C, with pressure between 1.12 and 1.34 kbar according to biotite geobarometer calculations for the hydrothermal zones. The C–O–S isotope analyses of the calcite and pyrite from the orebody zone yielded δ13C, δ18O and δ34S values ranging from −4.23 to −3.54‰, 8.60–9.77‰ and 3.37–3.52‰ respectively, which suggests that the hydrothermal fluid is predominantly of metamorphic origin. The εNd (3.0) calculated using isotopic analyses of the metavolcanic host rocks varies between +0.11 and + 4.25. A whole-rock Sm–Nd isochron age of 2952 ± 14 Ma was obtained from the host rocks, while a post-mineralized pyrite yielded a Sm–Nd isochron age of 2446 ± 35 Ma. The deposit exhibits mineralogical and isotopic characteristics consistent with those of orogenic type containing gold-bearing, sulfide-rich quartz veins. The Mamão deposit's host rocks are among the oldest rocks described so far in the Carajás Province. The age of the mineralizing event is limited between 2.95 and 2.45 Ga (probably ca. 2.7 Ga), which is the major metallogenic event of gold-deposit formation in several granite-greenstone terrains worldwide. [Display omitted] • Characterization of hydrothermal alteration halos. • Geochemistry and mineral chemistry of hydrothermal alteration minerals. • P-T conditions and source of hydrothermal fluid. • Sm–Nd and C–O–S isotopes of orogenic gold deposit. • Archean gold deposit in the Amazonian Craton. [ABSTRACT FROM AUTHOR]

The Carajás province (CP) is the largest preserved Archean core of the Amazonian craton. In this paper we present a detailed work about the Tucumã area located in the northwestern portion of the Rio Maria domain of the CP, where more detailed studies had not yet been carried out. The new geological and geochemical data obtained allowed the identification of Mesoarchean granitoids of different natures that resemble typical late-Archean granitoids (TTG, leucogranites, sanukitoids and hybrid granites) identified in several cratons around the world. The most extensive unit in the Tucumã area is the Leucomonzogranitic batholith which is intrusive in a tonalite crust of TTG affinity, that exhibits an older N-S structural pattern commonly found in oldest rocks (greenstone belt sequence). The batholith is coeval with small granitoid intrusions that occur as lenses controlled by NE-SW and E-W direction anastomosed shear zones. Apart from the tonalite, these granitoids show affinity with the calc-alkaline series and are individualized in four units. The porphyritic granodiorite is a magnesium-rich unit that has moderate K 2 O/Na 2 O ratio and higher levels of Ba, K and Th, indicating similarities with the Transitional TTG suites (Yilgarn craton). Equigranular granodiorites are equivalent of sanukitoid suites; they show enrichment in Sr and compatible elements (Mg, Cr, and Ni) and depletion in HREE. Hybrid granitoids were identified as High-HFSE granites (medium- and high-Ba) that share some geochemical affinities with Closepet granite of the Dharwar craton. The Leucomonzogranite is enriched in LILE and exhibit negative Eu anomalies, which indicate crustal reworking processes. This granitoids are syntectonic bodies that underwent a progressive deformation processes that started before the magma crystallization was complete, under high temperatures (>500 °C) conditions compatible with those of the amphibolite facies. Two phases of magmatism are recorded in the RMD, which would be responsible for the formation of these granitoids. The first phase (2.98-2.92 Ga) is related to formation of a thick TTG crust from parcial melting of an oceanic plateau or a thickened mafic crust. The second magmatism phase (~2.87 Ga) initiated due to thermal events in a collisional setting, where both crustal rework processes and generation of juvenile magmatism occurred at the same time, resulting in the formation of heterogeneous plutons, at different crustal levels that were emplaced by mechanisms analogous to diapirs. Image 1 • Origin of high-HFSE granitoids require interaction of mantle- and crust-derived materials. • 2.87 Ga - Syntectonic magmatism formed in collisional setting. • Shear zones conditioned the ascent and emplacement of Tucumã magmas. • Syn-tectonic plutonism and crustal anataxis. • The role of crustal anatexis and mantle-derived magmas in the genesis of synorogenic Mesoarchean granitoids. [ABSTRACT FROM AUTHOR]

Metamorphosed mafic-ultramafic rocks from the central portion of the Rio Grande do Norte Domain of the Borborema Province (BP), northeastern Brazil, have been studied here with the objective of gaining a better understanding of the Archean evolution of this portion of the BP. The study area is underlain by gneissic-migmatitic basement as well as biotite schists and paragneisses of the Seridó and Jucurutu formations of the Seridó Group. The mafic-ultramafic rocks (serpentinites, amphibole-schists and amphibolites) occur in lenses for 30 km along strike following the NNE regional foliation. The serpentinites occur as relatively small exposures of elongated bodies within paragneisses of the Jucurutu Formation and orthogneisses of the Caicó Complex. They consist of xenoblastic serpentine (75–99%) that has replaced the primary ferromagnesian minerals of the protolith. The amphibole schists and amphibolites are whitish gray to green, depending on the dominant mineral phase, tremolite, talc or actinolite. The mafic-ultramafic rocks present high MgO, Ni and Cr 2 O 3 contents and very low TiO 2 , Na 2 O and K 2 O contents, being compositionally similar to mafic-ultramafic rocks from other Archean greenstone belts worldwide. U-Pb (SHRIMP) dating of zircons returned concordia ages of 3526 ± 5 Ma (MSWD = 0.0084) for the serpentinites of the Serra Verde Mine and 3747 ± 12 Ma (MSWD = 9.8) for serpentinites from the Oiticica Mine. The petrographic and geochemical characteristics as well as the Eo to Paleoarchean ages of the studied rocks are significant as the basement of this portion of the BP is dominantly of Paleoproterozoic age. It is envisaged that these results will lead to further debate and a greater understanding of crustal evolution of the BP. We propose that these mafic-ultramafic rocks are part of a dismembered Archean greenstone belt, which present the oldest ages so far determined for the South American Platform. • The mafic-ultramafic rocks have geochemical signatures akin to Archean komatiites. • The mafic-ultramafic rocks may be a part of a dismembered greenstone belt. • Zircon U-Pb dating indicates Eo to Paleoarchean crystallization ages for the protoliths. • Archean crust in this part of Borborema Province may be more extensive than previously thought. [ABSTRACT FROM AUTHOR]