Dating and isotopic characteristics (Pb and S) of the Fe oxide–Cu–Au–U–REE Igarapé Bahia ore deposit, Carajás mineral province, Pará state, Brazil

The Igarapé Bahia ore deposit is located in the Carajás mineral province, southeast of the Amazonian Craton in northern Brazil. The deposit is hosted by the Archean Igarapé Bahia Group, which consists of mafic metavolcanic, metapyroclastic, and metasedimentary rocks, in addition to banded iron-formations and hydrothermal breccias. Mafic dikes cut these lithological varieties. The Cu–Au mineralization is best developed in breccias that lie between the mafic metavolcanic and metapyroclastic/metasedimentary units. Chalcopyrite, pyrite, bornite, and chalcocite are the main sulfides and are associated with Fe-rich chlorite, magnetite, siderite, and subordinate amounts of tourmaline, fluorite, REE-bearing minerals, and calcite. Dating of chalcopyrite from the hydrothermal breccias and metavolcanic, metapyroclastic, and dike rocks by the Pb–Pb method yields ages of 2772 ± 46, 2756 ± 24, 2754 ± 36, and 2777 ± 22 Ma, respectively. A similar age of 2744 ± 12 Ma of gold from the hydrothermal breccia, mafic metavolcanic rocks, and gossan is also obtained and considered the age of the mineralization, contemporaneous with the formation of the volcanosedimentary sequences of the Igarapé Bahia Group (2745–2747 Ma). These geochronological data support a genetic link between the volcanic processes and the Igarapé Bahia Cu–Au mineralization. Pb–Pb analyses of chalcopyrite leachates from the hydrothermal breccias reveal ages of 2385 ± 122 and 2417 ± 120 Ma, which suggest remobilization, likely due to regional tectonic reactivations related to the development of the Carajás and Cinzento strike-slip fault systems. Pb isotopic analyses show highly radiogenic samples that indicate magmas derived from sources in the upper crust enriched in U and Th. δ34S values (−2.1 to +4.2) are consistent with the derivation of sulfides from magmatic fluids, but a submarine environment similar to that of Archean VMS mineralization in which evaporites have been deposited cannot be ruled out.