Tracing fluid sources for the Salobo and Igarape Bahia deposits: implications for the genesis of the iron oxide copper-gold deposits in the Carajas province, Brazil

The Salobo and Igarape Bahia iron oxide copper-gold (IOCG) deposits stand out as economically important deposits in the Carajas Province. Whereas granitoids and gneisses host the Neoarchean Salobo deposit, the Igarape Bahia deposit occurs in volcanic rocks and associated sedimentary sequences. Paragenetic evolution of the IOCG alteration-mineralization evidences higher temperature conditions at Salobo (almandine-grunerite-biotite-magnetite) than at Igarape Bahia (tourmaline-carbonate-magnetite-chlorite). At Salobo, iron enrichment at 565 degrees +/- 50 degrees C was accompanied by hydrothermal fluids with magmatic or metamorphic compositions, as evidenced by grunerite (delta O-18(H2O) = 7.20-8.50 parts per thousand, delta D-H2O = -25.33 to -16.01 parts per thousand), garnet ((delta O-18(H2O) = 7.10-9.70 parts per thousand), and tourmaline ((delta O-18(H2O) = 5.07-7.37 parts per thousand, (delta D-H2O = -32.13 to + 11.60 parts per thousand). Fluids associated with potassic alteration at 565 degrees +/- 50 degrees C also have a typical magmatic/metamorphic composition, indicated by biotite (delta O-18(H2O) = 7.23-8.03 parts per thousand, delta D-H2O = -40.94 to -25.94 parts per thousand) and quartz (delta O-18(H2O) = 7.52 parts per thousand). Sulfur isotope signatures for chalcopyrite (0.81-1.28 parts per thousand) and bornite (-0.37 to + 1.63 parts per thousand) suggest a magmatic sulfur source at Salobo. For the Igarape Bahia deposit, fluids associated with tourmaline display magmatic or metamorphic signatures (delta O-18(H2O) = 5.07-7.37 parts per thousand, delta D-H2O = -34.02 to -19.74%, at 330 degrees +/- 50 degrees C), but those associated with calcite (delta O-18(H2O) = 1.68-3.10 parts per thousand, 330 degrees +/- 50 degrees C) and chlorite (delta O-18(H2O) = 1.92-3.20 parts per thousand, delta D-H2O = -57.36 to -21.34 parts per thousand, 255 degrees +/- 50 degrees C) evidence the input of O-18-depleted fluids. delta O-13(H2O) values (-9.32 to -4.93 parts per thousand) 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 Igarape Bahia were also magmatic-hydrothermal, the influx of O-18-depleted formation water was prominent during the later stages of ore genesis1144697718CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP481969/2013-6; 308365/2014-3; 457689/2014-5sem informação2016/13162-

Evolution of the Igarape Bahia Cu-Au deposit, Carajas province (Brazil) : early syngenetic chalcopyrite overprinted by IOCG mineralization

The Igarape Bahia IOCG Cu-Au deposit, located in the Carajas Domain, the northern part of the Carajas Province in the Amazon Craton, is one of the most economically important deposits in the province. The deposit is hosted in the metavolcanosedimentary Igarape Bahia Group and the metasedimentary Aguas Claras Formation. The Igarape Bahia Group encompasses a lower unit with metavolcanic rocks and metagabbros, and metasedimentary rocks (metarhythmites, epiclastic rocks, and banded iron formation) of the upper unit. Epidastic rocks are predominant in the Aguas Claras Formation. Basement xenoliths within the lower unit yielded an U-Pb zircon age of 2935 +/- 36 Ma, suggesting that a sialic crust was present prior to basin installation likely due to rifting. The U-Pb dating of detrital zircons yielded maximum deposition age at 2784 +/- 27 Ma for the upper unit, and 2763 +/- 32 Ma and 2774 +/- 19 Ma for the Aguas Claras Formation. Chalcopyrite nodules and layers are found within metarhythmites, concordant to primary structures, but without hydrothermal alteration halos and iron oxide. This chalcopyrite generation seems to have precipitated synchronously to the deposition of the Igarape Bahia Group. Chalcopyrite nodules and layers show delta(34)S(VCDT )values ranging from + 0.29 to +1.56 parts per thousand. These data indicate that most of its sulfur is likely derived from the metavolcanic rocks of the lower unit. Host rocks and chalcopyrite nodules and layers were overprinted by the IOCG mineralization. The latter formed extensive halos of hydrothermal alteration and was accompanied by ductile deformation and hydrothermal brecciation. These processes resulted in (tourmaline)-carbonate-magnetite, (tourmaline)-carbonate-chlorite and (tourmaline)-(biotite)-chlorite mylonites and breccias. Chalcopyrite from magnetite-rich zones (i.e. IOCG mineralization) displays delta S-34(VCDT) values from + 1.36 to + 5.35 parts per thousand. In addition to magmatic sulfur, seawater-derived sulfate may have been incorporated in sulfides via thermochemical sulfate-reduction reactions. Trace element geochemistry in distinct copper ores (i.e. nodules and layers versus magnetite-rich) also point to different origins of both styles of mineralization. The timing of the IOCG mineralization was constrained at 2559 +/- 34 Ma in the Alemao orebody. These data suggest that an IOCG-type metallogenetic event at ca. 2.5 Ga overprinted an older syngenetic-exhalative type copper mineralization. They also indicate that precipitation of early sulfide minerals within the Itacaiunas Supergroup may have created Cu-rich sequences that could have been remobilized, generating the broad group of the IOCG deposits at Carajas111CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP481969/2013-6; 308365/2014-3; 457689/2014-5não tem2016/13162-

Temporal evolution of the giant Salobo IOCG deposit, Carajás Province (Brazil): constraints from paragenesis of hydrothermal alteration and U-Pb geochronology

FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOThe giant Salobo copper-gold deposit is located in the Carajás Province, Amazon Craton. Detailed drill core description, petrographical studies, and U-Pb SHRIMP IIe and LA-ICP-MS geochronology unravel its evolution regarding the host rocks, hydrothermal alteration and mineralization. Within the Cinzento Shear Zone, the deposit is hosted by orthogneisses of the Mesoarchean Xingu Complex (2950 ± 25 and 2857 ± 6.7 Ma) and of the Neoarchean Igarapé Gelado suite (2763 ± 4.4 Ma), which are crosscut by the Old Salobo granite. Remnants of the Igarapé Salobo metavolcanic-sedimentary sequence are represented by a quartz mylonite with detrital zircon populations (ca. 3.1–3.0, 2.95, 2.86, and 2.74 Ga). High-temperature calcic-sodic hydrothermal alteration (hastingsite-actinolite) was followed by silicification, iron-enrichment (almandine-grunerite-magnetite), tourmaline formation, potassic alteration with biotite, copper-gold ore formation, and later Fe-rich hydrated silicate alteration. Myrmekitic bornite-chalcocite and magnetite comprise the bulk of copper-gold ore. All these alteration assemblages have been overprinted by post-ore hematite-bearing potassic and propylitic alteration, which is also recognized in the Old Salobo granite. In the central zone of the deposit the mylonitized Igarapé Gelado suite rocks yield an age of 2701 ± 30 Ma. Zircon ages of 2547 ± 5.3 and 2535 ± 8.4 Ma were obtained for the Old Salobo granite and for the high-grade copper ore, respectively. A U-Pb LA-ICP-MS monazite age (2452 ± 14 Ma) from the copper-gold ore indicates hydrothermal activity and overprinting in the Siderian. Therefore, a protracted tectono-thermal event due to the reactivation of the Cinzento Shear Zone is proposed for the evolution of the Salobo deposit525709732FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO573733/2008-22009/18371-02013/25659-5481969/2013-6308365/2014-

Timing of multiple hydrothermal events in the iron oxide–copper–gold deposits of the Southern Copper Belt, Carajás Province, Brazil

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOThe Southern Copper Belt, Carajas Province, Brazil, hosts several iron oxide-copper-gold (IOCG) deposits, including Sossego, Cristalino, Alvo 118, Bacuri, Bacaba, Castanha, and Visconde. Mapping and U-Pb sensitive high-resolution ion microprobe (SHRIMP) IIe zircon geochronology allowed the characterization of the host rocks, situated within regional WNW-ESE shear zones. They encompass Mesoarchean (3.08-2.85 Ga) TTG orthogneiss, granites, and remains of greenstone belts, Neoarchean (ca. 2.74 Ga) granite, shallow-emplaced porphyries, and granophyric granite coeval with gabbro, and Paleoproterozoic (1.88 Ga) porphyry dykes. Extensive hydrothermal zones include albite-scapolite, biotite-scapolite-tourmaline-magnetite alteration, and proximal potassium feldspar, chlorite-epidote and chalcopyrite formation. U-Pb laser ablation multicollector inductively coupled mass spectrometry (LA-MC-ICP-MS) analysis of ore-related monazite and Re-Os NTIMS analysis of molybdenite suggest multiple Neoarchean (2.76 and 2.72-2.68 Ga) and Paleoproterozoic (2.06 Ga) hydrothermal events at the Bacaba and Bacuri deposits. These results, combined with available geochronological data from the literature, indicate recurrence of hydrothermal systems in the Southern Copper Belt, including 1.90-1.88-Ga ore formation in the Sossego-Curral ore bodies and the Alvo 118 deposit. Although early hydrothermal evolution at 2.76 Ga points to fluid migration coeval with the Carajas Basin formation, the main episode of IOCG genesis (2.72-2.68 Ga) is related to basin inversion coupled with Neoarchean (ca. 2.7 Ga) felsic magmatism. The data suggest that the IOCG deposits in the Southern Copper Belt and those in the Northern Copper Belt (2.57-Ga Salobo and Igarap, Bahia-Alemo deposits) do not share a common metallogenic evolution. Therefore, the association of all IOCG deposits of the Carajas Province with a single extensive hydrothermal system is precluded.The Southern Copper Belt, Carajas Province, Brazil, hosts several iron oxide-copper-gold (IOCG) deposits, including Sossego, Cristalino, Alvo 118, Bacuri, Bacaba, Castanha, and Visconde. Mapping and U-Pb sensitive high-resolution ion microprobe (SHRIMP) IIe zircon geochronology allowed the characterization of the host rocks, situated within regional WNW-ESE shear zones. They encompass Mesoarchean (3.08-2.85 Ga) TTG orthogneiss, granites, and remains of greenstone belts, Neoarchean (ca. 2.74 Ga) granite, shallow-emplaced porphyries, and granophyric granite coeval with gabbro, and Paleoproterozoic (1.88 Ga) porphyry dykes. Extensive hydrothermal zones include albite-scapolite, biotite-scapolite-tourmaline-magnetite alteration, and proximal potassium feldspar, chlorite-epidote and chalcopyrite formation. U-Pb laser ablation multicollector inductively coupled mass spectrometry (LA-MC-ICP-MS) analysis of ore-related monazite and Re-Os NTIMS analysis of molybdenite suggest multiple Neoarchean (2.76 and 2.72-2.68 Ga) and Paleoproterozoic (2.06 Ga) hydrothermal events at the Bacaba and Bacuri deposits. These results, combined with available geochronological data from the literature, indicate recurrence of hydrothermal systems in the Southern Copper Belt, including 1.90-1.88-Ga ore formation in the Sossego-Curral ore bodies and the Alvo 118 deposit. Although early hydrothermal evolution at 2.76 Ga points to fluid migration coeval with the Carajas Basin formation, the main episode of IOCG genesis (2.72-2.68 Ga) is related to basin inversion coupled with Neoarchean (ca. 2.7 Ga) felsic magmatism. The data suggest that the IOCG deposits in the Southern Copper Belt and those in the Northern Copper Belt (2.57-Ga Salobo and Igarap, Bahia-Alemo deposits) do not share a common metallogenic evolution. Therefore, the association of all IOCG deposits of the Carajas Province with a single extensive hydrothermal system is precluded505517546CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPq [555065/2006-5, 472549/2009-0, 481969/2013-6]FAPESP [03/11163-603/01159-1, 2009/18371-0]FAPESP [573733/2008-2]FAPESP [01/2010 ICAAF 053/2011]555065/2006-5; 472549/2009-0; 481969/2013-603/11163-603/01159-1; 573733/2008-2; 01/2010 ICAAF 053/2011; 2009/18371-