AbstractGold 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.
