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Petrography, magnetic susceptibility and geochemistry of the Rio Branco Granite, Carajás Province, southeast of Pará, Brazil

2013; Sociedade Brasileira de Geologia; Volume: 43; Issue: 1 Linguagem: Inglês

10.5327/z2317-48892013000100002

2317-4889

Patrick Araújo dos Santos, Gilmara Regina Lima Feio, Roberto Dall’Agnol, Hilton Túlio Costi, Cláudio Nery Lamarão, Marco Antônio Galarza,

Geochemistry and Elemental Analysis

The Paleoproterozoic Rio Branco stock intrudes the Archean Cruzadão biotite monzogranite.It occurs west of the Canaã dos Carajás city, close to the Sossego copper mine in the Carajás Province.It is constituted by undeformed and isotropic, hololeucocratic syenogranites, showing equigranular texture.The granite is formed essentially by perthitic alkali feldspar, quartz, and plagioclase, with additional variable amounts of chloritized biotite.Fluorite, allanite, and zircon are common accessory minerals, whereas pyrite and chalcopyrite are scarces.Albitization and subordinate greisenization are the main alteration processes that affected the granite.The secondary mineralogy is represented by albite, fluorite, topaz, chlorite, muscovite, siderophyllite, and iron oxides.Magnetic susceptibility values are systematically low and vary between 1.3 x 10 -5 a 6.9 x 10 -4 (SI).The Rio Branco Granite is metaluminous to peraluminous and shows high FeOt/(FeOt + MgO).It has geochemical affinities with ferroan, reduced A2-subtype granites.The rare earth element (REE) patterns are flat with little heavy REE fractionation and show accentuated negative Eu anomalies (Eu/Eu* = 0.08 -0.13).These characteristics are typical of evolved granites, derived from volatile-enriched liquids responsible by the intense subsolidus hydrothermal alteration.The dating of the Rio Branco granite did not give conclusive results, but the obtained data, associated with geological evidence, suggest that it is of Paleoproterozoic age.The comparison between the Rio Branco granite and Paleoproterozoic A-type suites of the Carajás Province suggests that the Rio Branco granite has more affinity with the Velho Guilherme suite and, in lesser degree, with the Serra dos Carajás suite.On the other hand, is clearly different from oxidized A-type granites of the Jamon suite.Despite its similarities with tin-specialized granites, the Rio Branco Granite is not associated with tin mineralizations.