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Ore characterization and textural relationships among gold, selenides, platinum-group minerals and uraninite at the granite-related Buraco do Ouro gold mine, Cavalcante, Central Brazil

Published online by Cambridge University Press:  02 January 2018

J. Menez  and
N. F. Botelho
J. Menez*
Affiliation:
Instituto de Geociências, Universidade de Brasília, Brasília, DF 70910-900, Brazil
N. F. Botelho
Affiliation:
Instituto de Geociências, Universidade de Brasília, Brasília, DF 70910-900, Brazil
*
*E-mail: jackiemenez@yahoo.com.br
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Abstract

Gold occurrences have been reported in the northeastern part of Goiás State since the beginning of the 18th Century. The main mineralization is associated with Paleoproterozoic peraluminous, syntectonic granites of the Aurumina Suite and associated metasedimentary,graphite-bearing country rocks of the Ticunzal Formation. In the Buraco do Ouro gold mine, the mineralization is hosted in muscovite-quartz mylonite in a silicified shear zone near the contact between biotite-muscovite granite and paragneiss of the Ticunzal Formation. The ore mineralogy consistsof gold, paraguanajuatite (Bi2Se3), kalungaite (PdAsSe), isomertieite [Pd11Sb2As2], mertieite II [Pd8(Sb,As)3], sperrylite (PtAs2), padmaite (PdBiSe), bohdanowiczite (AgBiSe2), clausthalite (PbSe),krutaite (CuSe2), ferroselite (FeSe2), uraninite (UO2) and unnamed Ag-Pb-Bi-Se minerals. Local magnetite concentrations and rare chalcopyrite and pyrite are also associated with both mineralized and barren mylonites in a gangue consisting of muscovite, quartzand rare tourmaline. High TiO2 muscovite clasts in the ore are interpreted as the magmatic muscovite of the original granite, and the mineralization is considered to be synchronous with the syntectonic granite intrusion during syn-emplacement shearing and alteration. The associationbetween granitic rocks and platinum-group element (PGE)-bearing gold mineralization observed in the Buraco do Ouro mine is uncommon and unique in the context of the Aurumina Suite and the Ticunzal Formation, where gold deposits and occurrences are gold-only. The chemical data suggest the possibilityof a solid solution between paraguanajuatite and bohdanowiczite. In addition, a complex intergrowth occurs between paraguanajuatite, clausthalite and Ag-Pb-Bi-Se phases, one of which, a Pb-Bi-Se phase could represent a new mineral. Uraninite is identified for the first time in this mineralassemblage and its concentration in the ore seems important, as revealed by high gamma spectrometric measurements in the samples collected in the mine. The association between gold and uranium constitutes a regional signature, observed in both gold and uranium deposits in the Cavalcante region.

Keywords

Buraco do Ouro gold mineselenidesgoldplatinum-group element
Type
Research Article
Information
Mineralogical Magazine , Volume 81 , Issue 3 , June 2017 , pp. 463 - 475
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2017

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