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|Type:||Artigo de periódico|
|Title:||Geological and SHRIMP II U-Pb constraints on the age and origin of the Breves Cu-Au-(W-Bi-Sn) deposit, Carajis, Brazil|
|Abstract:||The Breves deposit in the Carajds Copper-Gold Belt, Brazil, a member of the Cu-Au-(W-Bi-Sn) group of deposits, contains about 50 Mt of 1.22% Cu, 0.75 g/t Au, 2.4 g/t Ag, 1,200 g/t W, 70 g/t Sri, 175 g/t Mo and 75 g/t Bi. It is hosted by sandstones and siltstones of the Aguas Claras Formation (minimum age of 2,681 +/- 5 Ma) in the roof zone of a complex, highly altered granite intrusion. The mineralisation is disseminated in a greisenized zone, resulting from alteration of probable monzogranites and syenogranites. The ore-bearing greisen contains abundant xenomorphic quartz in association with Fe-chlorite and muscovite. The gangue assemblage also includes fluorite, tourmaline, and minor amounts of monazite, xenotime, chlorapatite, thorite, zircon, calcite, siderite and bastnaesite. Copper mineralisation is dominated by chalcopyrite associated with pyrite, arsenopyrite, pyrrhotite and molybdenite. Gold particles, in equilibrium with native bismuth, are common as inclusions in chalcopyrite. The greisen contains sub-economic concentrations of tungsten and mobium that are related to the presence of ferberite, qitianlingite and Nb-rutile. SHRIMP II zircon dating of the host granites gives Pb-207/Pb-206 ages of 1,878 +/- 8 and 1,880 +/- 9 Ma for two phases, and a combined age of 1,879 +/- 6 Ma. SHRIMP II dating of monazite and xenotime grains in late- to post-mineralisation veins gives a combined Pb-207/Pb-206 age of 1,872 +/- 7 Ma, indistinguishable from the ages of the granites. This provides a genetic connection between the Breves deposit and the ca. 1.88 Ga A-type granite magmatism that typifies the Carajas Belt as part of a much larger, intracratonic magmatic province that extends over much of the Amazonian Craton. The recognition of this association has exploration implications, not only for the geophysical signature of the granite roof zones, but also for likely geochemical dispersion around the deposits of this type.|
SHRIMP II geochronology
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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