Tracing fluid sources for the Salobo and Igarapé Bahia deposits : implications for the genesis of the iron oxide copper-gold deposits in the Carajás Province, Brazil.
Nenhuma Miniatura disponível
Data
2019
Título da Revista
ISSN da Revista
Título de Volume
Editor
Resumo
The Salobo and Igarapé Bahia iron oxide copper-gold (IOCG) deposits stand out as economically important
deposits in the Carajás Province. Whereas granitoids and gneisses host the Neoarchean Salobo deposit, the
Igarapé Bahia deposit occurs in volcanic rocks and associated sedimentary sequences. Paragenetic evolution of
the IOCG alteration-mineralization evidences higher temperature conditions at Salobo (almandine-gruneritebiotite-magnetite) than at Igarapé Bahia (tourmaline-carbonate-magnetite-chlorite). At Salobo, iron enrichment at 565° ± 50°C was accompanied by hydrothermal fluids with magmatic or metamorphic compositions, as
evidenced by grunerite (δ18OH2O = 7.20–8.50‰, δDH2O = –25.33 to –16.01‰), garnet (δ18OH2O = 7.10–9.70‰),
and tourmaline (δ18OH2O = 5.07–7.37‰, δDH2O = –32.13 to +11.60‰). Fluids associated with potassic alteration at 565° ± 50°C also have a typical magmatic/metamorphic composition, indicated by biotite (δ18OH2O =
7.23–8.03‰, δDH2O = –40.94 to –25.94‰) and quartz (δ18OH2O = 7.52‰). Sulfur isotope signatures for chalcopyrite (0.81–1.28‰) and bornite (–0.37 to +1.63‰) suggest a magmatic sulfur source at Salobo. For the Igarapé Bahia deposit, fluids associated with tourmaline display magmatic or metamorphic signatures (δ18OH2O =
5.07–7.37‰, δDH2O = –34.02 to –19.74‰, at 330° ± 50°C), but those associated with calcite (δ18OH2O = 1.68–
3.10‰, 330° ± 50°C) and chlorite (δ18OH2O = 1.92–3.20‰, δDH2O = –57.36 to –21.34‰, 255° ± 50°C) evidence the input of 18O-depleted fluids. δ13CCO2 values (–9.32 to –4.93‰) for fluids in equilibrium with calcite
also imply magmatic sources. Our data indicate that the main source of the ore-forming fluids for Salobo was
derived from exsolved magmatic brines associated with crystallization of the coeval ca. 2.5 Ga granites. In
contrast, though the early fluids at Igarapé Bahia were also magmatic-hydrothermal, the influx of 18O-depleted
formation water was prominent during the later stages of ore genesis.
Descrição
Palavras-chave
Citação
MELO, G. H. C. de et al. Tracing fluid sources for the Salobo and Igarapé Bahia deposits: implications for the genesis of the iron oxide copper-gold deposits in the Carajás Province, Brazil. Economic Geology, v. 114, n. 4, p. 697-718, jun. 2019. Disponível em: <https://pubs.geoscienceworld.org/segweb/economicgeology/article/114/4/697/571772/Tracing-Fluid-Sources-for-the-Salobo-and-Igarap%C3%A9>. Acesso em: 10 mar. 2020.