Disponível on-line no endereço www.igc.usp.br/geologiausp -45 -Resumo A região de Santana do Araguaia, foco deste trabalho, localiza-se no sudeste do Estado do Pará, que, por sua vez, fica no sudeste do Cráton Amazônico. Sob o ponto de vista tectônico, posiciona-se no Domínio Santana do Araguaia, interpretado como um terreno arqueano afetado pelo Ciclo Transamazônico. Um estudo petrográfico e geocronológico, com suporte de dados de campo, foi empreendido em granitoides da região com o intuito de desvendar a evolução desse domínio. Em termos modais, as rochas estudadas compõem-se de biotita monzogranito, biotita metagranodiorito, hornblenda-biotita granodiorito, hornblenda-biotita metatonalito e enderbito. Essas rochas apresentam-se não deformadas a moderadamente deformadas, com algumas particularidades: o biotita metagranodiorito apresenta foliação seguindo um trend E-W; o hornblenda-biotita metatonalito possui uma foliação seguindo a direção NW-SE, com mergulhos normalmente altos a subverticais; o biotita monzogranito é isotrópico e os litotipos hornblenda-biotita granodiorito e enderbito apresentam apenas uma leve orientação de seus cristais, perceptível principalmente em lâmina delgada. Esses litotipos foram analisados pelo método de evaporação de Pb de zircão, tendo sido obtidas as seguintes idades: biotita metagranodiorito, 3066 ± 3 Ma e 2829 ± 13 Ma, hornblenda-biotita metatonalito, 2852 ± 2 Ma; biotita monzogranito (ML-08), 2678 a 2342 Ma; hornblendabiotita granodiorito, 1990 ± 7 Ma; e enderbito, 1988 ± 4 Ma. Os dados geocronológicos indicam que as rochas cristalizaram tanto no Arqueano quanto no Paleoproterozoico, contudo, não foram detectadas evidências que comprovem a ação do Ciclo Transamazônico na região.Palavras-chave: Santana do Araguaia; Granitoides; Geocronologia; Arqueano; Paleoproterozoico. AbstractThe region of Santana do Araguaia, focus of this study, is located in the southeast of Pará State, which, in its turn, lies in the southeastern Amazonian Craton. From the tectonic point of view, it is positioned in the Domain Santana do Araguaia, interpreted as an Archean terrain affected by the Transamazonic Cycle. A petrographic and geochronological study, supported by field data, was undertaken in granitoids of the region in order to unravel the evolution of this field. In modal terms, the studied rocks consist of biotite monzogranite, biotite metagranodiorite, hornblende-biotite granodiorite, hornblende-biotite metatonalite and enderbite. These rocks present themselves undeformed to moderately deformed, with some particularities: the biotite metagranodiorite presents foliation following an E-W trend; the hornblende-biotite metatonalite has a foliation following the NW-SE direction, usually with high to subvertical dives, the biotite monzogranite is isotropic, and lithologies hornblende-biotite granodiorite and enderbite show only a slight orientation of their crystals, mainly noticeable in thin section. These rock types were analyzed by evaporating Pb zircon method and the following ages were obt...

Evidence of massive manganese was found in the northwest of the State of Mato Grosso, in the municipality of Comodoro. The area is located in the southwest portion of the Amazonian Craton, in the Calimian Jauru Tectonic Domain, which comprises metasedimentary rocks of the Rio Galera Complex and calc-alkaline granites of the Pindaituba Intrusive Suite (Praia Alta and Rio Piolho granites). Chemical analysis of the manganese--bearing sample yielded the following oxide and element concentrations: MnO = 61.4%, BaO = 13.2%, Cu = 751 ppm, Mo = 417 ppm, Pb = 4642 ppm, U = 107.8 ppm and Ce = 1608 ppm. Petrographic analysis allowed the identification of pyrolusite as the manganese mineral totaling 95% of the analyzed sample and 5% of gangue minerals.

The Trincheira Mafic-ultramafic Complex comprises a Mesoproterozoic layered intrusion hosted in metasedimentary rocks of the southwestern portion of the Amazonian Craton. This intrusion has an outcropping area of approximately 35 km 2 , however, it has been associated to a larger ellipsoidal magnetic anomaly with N-S elongated shape. The Trincheira Complex is composed of partially metamorphosed pyroxenites, websterites, gabbros and anorthosites. The complex hosts Cr-rich layers associated to relevant concentrations of Ni. High concentrations of Cu, Co and V have also been detected. Preliminary analysis performed with portable X-ray diffraction indicates up to 13% Cr and occurrence of cochromite, a special variety of chromite enriched in cobalt, nickel and iron, whereas ICP-MS analyses returned concentrations of up to ~3600 ppm Cr.