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Please use this identifier to cite or link to this item: http://repositorio.ufba.br/ri/handle/ri/3170

Title: Sm-Nd Age of the Fazenda Brasileiro Gabbro, Bahia, Brazil: Example of Robust Behavior of the Sm-Nd Isotopic System Under Extreme Hydrothermal Alteration
Other Titles: Anais da Academia Brasileira de Ciências
Authors: Pimentel, Márcio M.
Silva, Maria da Glória
Keywords: Rio Itapicuru greenstone belt;Fazenda Brasileiro;Paleoproterozoic;gold mineralization;Sm- Nd;hydrothermal alteration
Issue Date: 2003
Abstract: The Fazenda Brasileiro gold mineralization is hosted by a gabbroic sill, intrusive into metavolcanicmetasedimentary rocks of the Rio Itapicuru Greenstone Belt, São Francisco Craton. The 2.05 Ga old mineralization is associated with intense shearing and hydrothermal alteration, and the host gabbro is altered to a series of rocks rich in sericite, chlorite, actinolite, carbonate and quartz. Twelve whole-rock samples of the gold mineralization, representing varied degrees of alteration, from rocks with preserved igneous textures to the ore (quartz-carbonate-sulfide-chlorite), were studied by the Sm-Nd method. All analytical points resulted in an isochron (MSWD = 1.9) indicating the age of 2142 +/– 47 Ma (1s) and Epsilon Nd (T) of +1.2. Chlorite-sericite-carbonate rich hydrothermal rocks indicate the age of 2148 +/– 57 Ma and Epsilon Nd (T) of +1.1. The positive Epsilon Nd (T) suggest limited or no contamination with older continental crust, compatible with an oceanic setting for the tholeiites. Combined withREEdata, the Sm-Nd isotopic results reveal that the hydrothermal alteration, although intense, was unable to alter significantly the Sm/Nd ratios of the original igneous rocks and did not cause important scatter of the analytical points, providing a rare example of robust behavior of the isotopic system, even under intense hydrothermal alteration.
Description: p. 383-392
URI: http://www.repositorio.ufba.br/ri/handle/ri/3170
ISSN: 1678-2690
Appears in Collections:Artigos Publicados em Periódicos (IGEO)

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