DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
Navegar
8 resultados
Resultados da Pesquisa
Item The hydrothermal evolution of the Alvo Açaí Cu (Au, Mo) skarn deposit, Carajás Province, Brazil.(2023) Fernandes, Kamila Gomes; Xavier, Roberto Perez; Moreto, Carolina Penteado Natividade; Melo, Gustavo Henrique Coelho de; Boyce, Adrian JosephThe Alvo Açaí Cu (Au, Mo) skarn deposit forms part of several poorly explored copper deposits in the western sector of the Carajás province in Brazil. Here, a 2.86 Ga metasyenogranitic basement and a 2.71 Ga quartzite of the Liberdade Group are crosscut by diabase and granitic pegmatite dikes in the deposit area. The sequence of hydrothermal alteration at Alvo Açaí is marked by (1) early pervasive calcic-sodic alteration (hastingsite- albite) and (2) potassic iron alteration (biotite-almandine-grunerite) overprinted by (3) silicification (quartz), (4) prograde (grossular-hedenbergite), and (5) retrograde (actinolite-biotite-epidote) skarn stages. Late per- vasive chloritization along with epidote-calcite veinlets crosscut the previous alteration zones. The main stage of copper mineralization (I) is spatially and temporally related to the retrograde skarn alteration for which three chalcopyrite-bearing mineral assemblages are distinguished on the basis of textural relationships and mineral associations: (1) actinolite-chalcopyrite-pyrrhotite-pyrite-magnetite-molybdenite, (2) biotite-chalcopy- rite-pyrite-magnetite, and (3) epidote-pyrite-chalcopyrite-sphalerite. Minor chalcopyrite occurs along rare late- stage epidote-calcite veinlets (mineralization II). The evolution of a single hot H2O-NaCl-CaCl2–dominated magmatic fluid of moderate salinity (22.8–28.6 wt % NaCl + CaCl2 equiv) toward a cooler H2O-NaCl fluid, with likely variable amounts of FeCl2, MgCl2, and KCl of low to moderate salinity (0.1–33.2 wt % NaCl equiv). Fluid evolution as a result of progressive crystallization of the granitic pegmatite was likely the trigger for mineraliza- tion I as supported by calculated δ18OH2 O values from retrograde quartz. The chalcopyrite and pyrite δ34S values (–1.5, –1.1, and –0.7‰) point to a magmatic origin for the sulfur, which was most probably leached from sur- rounding igneous host rocks. The evolution of the Alvo Açaí deposit encompasses the development of the first copper skarn mineralization recognized in the Carajás province.Item Magmatic-hydrothermal fluids leaching older seafloor exhalative rocks to form the IOCG deposits of the Carajás Province, Brazil : evidence from boron isotopes.(2021) Melo, Gustavo Henrique Coelho de; Monteiro, Lena Virginia Soares; Hunger, Raphael Bianchi; Toledo, Poliana Iara Freitas; Xavier, Roberto Perez; Zhao, Xin-Fu; Su, Zhi-Kun; Moreto, Carolina Penteado Natividade; Jesus, Silvandira dos Santos Goes Pereira deThe notable group of iron oxide-copper–gold (IOCG) deposits at the Carajas Province (Amazonian Craton, Brazil) contain remarkable copper reserves due to a complex Neoarchean metallogenetic evolution. The overlay of diachronic hydrothermal-mineralizing events is revealed by two clusters of boron isotope compositions of hy- drothermal tourmaline obtained in IOCG deposits (Salobo, Igarap ́e Bahia, GT-46, Grota Funda and Furnas) with (i) high δ11B (+8.2 to +17.2‰) and (ii) low δ11B (+3.4 to +9.8‰) values. The isotopically heavy boron sig- natures, recorded in tourmaline cores, are inherited from the volcano-sedimentary sequences of the ca. 2.76 Ga Itacaiúnas Supergroup, which includes exhalative tourmaline and spilites formed in extensive exhalative systems prior to the IOCG formation. During the main IOCG event at ca. 2.55 Ga, the regional circulation of magmatic- hydrothermal boron-rich fluids originated tourmaline rims and new crystals with lower δ11B values. We describe the critical role of an older volcano-sedimentary as a source for boron and likely metals leached by magmatic- hydrothermal fluids to form the IOCG deposits of the Carajas ́ Province.Item The Santa Lúcia Cu-Au deposit, Carajás Mineral Province, Brazil : a Neoarchean (2.68 Ga) member of the granite-related copper-gold systems of Carajás.(2021) Hunger, Raphael Bianchi; Melo, Gustavo Henrique Coelho de; Xavier, Roberto Perez; Moreto, Carolina Penteado Natividade; Talavera, Cristina; Su, Zhi-Kun; Zhao, Xin-FuThe Santa Lúcia copper-gold deposit lies in the southeastern portion of the Carajás Mineral Province, along NW-SE splays of the Carajás Fault. The deposit is hosted by a rhyolitic subvolcanic rock, which is crosscut by pegmatite intrusions. The paragenetic evolution at Santa Lúcia encompasses an early stage of chlorite alteration, followed by potassic alteration with microcline, greisenization (quartz-muscovite-tourmaline), copper-gold ore precipitation, and late sericite and hematite vein formation/ fracture infill. Copper mineralization is dominantly represented by chalcopyrite-sphalerite-pyrrhotite-pentlandite-pyrite breccias, which are spatially associated with greisen alteration and characterized by the enrichment of light rare earth elements (LREE), Ni, Co, and Cr. The alteration types, mineralization styles, and ore assemblage suggest that the Santa Lúcia deposit could represent a member of the Paleoproterozoic (ca. 1.88 Ga) granite-related copper-gold systems of Carajás (e.g., the Breves and Estrela deposits). However, the in situ U-Pb analyses of ore-related monazite yield a weighted average 207Pb/206Pb age of 2688 ± 27 Ma, thereby constraining the timing of mineralization at Santa Lúcia to the Neoarchean. Moreover, tourmaline from the pegmatite and within the ore zones has a range of δ11B values from − 3.7 to − 0.6‰, therefore linked to a magmatic boron source. Collectively, these results indicate that the Santa Lúcia deposit is the first reduced magmatic-hydrothermal, iron oxide–poor system formed in the Neoarchean, coeval with the 2.72–2.68 Ga metallogenic event responsible for the genesis of important iron oxide copper-gold (IOCG) deposits in the Carajás Mineral Province.Item Mesoarchean migmatites of the Carajás Province : from intra-arc melting to collision.(2021) Silva, Marco Antonio Delinardo da; Monteiro, Lena Virginia Soares; Santos, Ticiano José Saraiva dos; Moreto, Carolina Penteado Natividade; Sousa, Soraya Damasceno; Faustinoni, Jackeline Monteiro; Melo, Gustavo Henrique Coelho de; Xavier, Roberto Perez; Toledo, Benfica A. M.In the Carajás Domain, northern Carajás Province, Amazonian Craton, the oldest units encompass the Mesoarchean migmatites of the Xicrim-Cateté Orthogranulite and Xingu Complex. The Xicrim-Cateté Orthogranulite underwent early dehydration and late water-fluxed partial melting. The first process resulted in net-structured and schollen migmatites with a pargasite-bearing mafic granulite paleosome. The F-pargasite breakdown produced a neosome with peritectic enstatite, diopside, and plagioclase and a residual amphibole-free mafic granulite. The late water- fluxed partial melting generated quartzofeldspathic leucosomes in shear bands of the NW-SE-trending high-angle transcurrent shear zones. The Xingu Complex is composed of stromatic, net-structured, schollen and schlieren migmatites developed in the late water-fluxed partial melting event. These migmatites have orthogneiss and am- phibolite paleosome and syn-tectonic quartzofeldspathic leucosome and biotite-rich melanosome oriented along a low angle NE-SW to NW-SE gneissic foliation. The Xicrim-Cateté paleosome age remains undefined, but the U–Pb zircon ages of the pyroxene-bearing neosome constraint the dehydration-melting to c. 3.06–2.93 Ga. The εHf data (−2.2 to +1.2) of the neosome tie the dehydration-melting of the pargasite-bearing granulite to the underplate of mantle melts. The Zr-Ti-Y content and Ti/V ratios of the pargasite-bearing granulite suggest a compositional shift of their protoliths from MORB to IAT, characterizing a scenario of subduction installation and magmatic evolution. The Xicrim-Cateté pyroxene-bearing neosome is geochemically similar to the Xingu orthogneiss. Both rocks have a TTG affinity and similar εHf values (+0.8 to +1.6) and crystallization ages (2.94 Ga). It indicates a common source for them and suggests that the dehydration partial melting of the primitive mafic crust produced a signif- icant portion of the TTG felsic continental crust of the Carajás Domain. It probably occurred during the island-arc setting evolution between 3.06 and 2.93 Ga when supra-subduction mantle melts started to trigger the composi- tional differentiation of the mafic crust. The late water-fluxed partial melting was controlled by fluid influx into the structures developed during the regional deformation of the Carajás Domain at c. 2.89–2.85 Ga, likely associated with a collisional event in the Carajás Province.Item Stable isotopes and fluid inclusion constraints on the fluid evolution in the Bacaba and Castanha iron oxide-copper-gold deposits, Carajás Mineral province, Brazil.(2020) Pestilho, André Luiz Silva; Monteiro, Lena Virginia Soares; Melo, Gustavo Henrique Coelho de; Moreto, Carolina Penteado Natividade; Juliani, Caetano; Fallick, Anthony Edward; Xavier, Roberto PerezThe evolution of the Bacaba and Castanha iron oxide-copper-gold deposits, located in the Carajás Mineral Province, Brazil, is discussed based on petrography, scanning electron microscopy, stable isotopes, and fluid inclusion analyses. The Castanha deposit is mainly hosted by ca. 2.75 Ga subvolcanic and volcanic rhyodacitic rocks, and gabbros. Early sodic (albite, scapolite) alteration was followed by high-temperature calcic-iron (actinolite-magnetite), potassic (biotite), and minor chlorite and sericite alteration. Calcite, REE carbonate, and epidote represent a late and proximal alteration to ore bodies. Ore breccias with Durchbewegung structure comprise chalcopyrite + pyrrhotite + pyrite ± cobaltpentlandite ± sphalerite ± marcasite and are notable due to their nickel-(zinc) enrichment. The Bacaba Deposit is hosted by the ca. 3.00 Ga Bacaba Tonalite, 2.85 Ga Serra Dourada Granite, and gabbro bodies. Early (ca. 2.70 Ga) alteration at Bacaba includes sodic (albite, scapolite), iron (magnetite), and potassic-iron (K feldspar-magnetite, biotite) associations. Well-developed late chlorite, albite, sericite, calcite-hematite-(musketovite) alteration formed during a Paleoproterozoic overprinting (ca. 2.06 Ga). The Bacaba ore is composed of (I) chalcopyrite ± magnetite ± bornite, and (II) chalcopyrite ± pyrite ± hematite/musketovite, related to early potassic-iron and late alteration, respectively. The Castanha deposit was formed from magmatic fluid (δ18OH2O = 9.5 ± 0.5‰ to 5.2 ± 1.0‰, at 500 to 400 °C) and sulfur (δ34S = 0.1–3‰) sources, with a limited contribution of externally-derived fluids during its evolution. Ore precipitation progressed under considerably low fS2 and fO2 conditions, at relatively high temperatures (> 370 ± 50 °C). Fluid inclusion analyses indicate greater proximity of the Castanha deposit to the source of a hot overpressured magmatic fluid, suggesting its formation in a high-temperature hydrothermal center. Fluidrock interaction coupled with increasing pH might have been the critical factors in destabilizing the metalchloride complex in the Castanha deposit. The Bacaba deposit evolved from a fluid-mixing between hot (> 450 °C) hypersaline CaCl2-NaCl-bearing magmatic brine (> 30 mass % equivalent) and a less saline, colder, and 18O-depleted and D-enriched fluid (e.g., seawater or low-latitude meteoric water). Mixing resulted in an oxidizing environment, dilution (salinities between 35 and 4 mass % equivalent), and temperature drop (160–190 °C), triggering the ore precipitation. At Bacaba, the slightly higher δ34S values (1.3–5.4‰) may reflect an additional contribution of externally-derived sulfur through the thermochemical reduction of oxidized sulfur species. In the Southern Copper Belt, the regional spatial distribution of the sulfur isotope compositions shows the highest δ34Ssulfide values close to the Paleoproterozoic Sossego Orebody and the Alvo 118 deposit. This might suggest significant involvement of externally-derived components (e.g., diluted fluids and sulfur) during late stages of a protracted hydrothermal evolution in the Carajás IOCG deposits.Item Multistage evolution of the Neoarchean (ca. 2.7 ga) Igarapé Cinzento (GT-46) iron oxide copper-gold deposit, Cinzento shear zone, Carajás province, Brazil.(2019) Toledo, Poliana Iara de Freitas; Moreto, Carolina Penteado Natividade; Xavier, Roberto Perez; Gao, Jianfeng; Matos, José Henrique da Silva Nogueira de; Melo, Gustavo Henrique Coelho deThe Igarapé Cinzento (GT-46) iron oxide copper-gold deposit is located in the northwestern part of the Cinzento shear zone in Carajás province, Brazil. Copper mineralization in the deposit is hosted by a hydrothermally altered metavolcanosedimentary sequence that consists of interlayered amphibolites, (actinolite)-biotite schists, almandine-biotite schists, and metamorphosed banded iron formations, intruded by granitoids (tonalite to granite) and mafic dikes. The complex evolution of the deposit involved (1) deposition of a volcanosedimentary sequence (2774 ± 19 Ma U-Pb zircon), (2) a tectonometamorphic event (Dn = upper amphibolite facies), restricted in time between 2.77 and 2.72 Ga, (3) development of the Cinzento shear zone (Dn + 1) at 2.72 Ga, with associated hydrothermal activity and deposit formation, (4) superimposed hydrothermal events (ca. 2.6 and 2.5 Ga), and (5) granitoid emplacement at ca 2.5 Ga in the region. The GT-46 deposit is the result of overprinting hydrothermal stages with at least two distinct mineralization events. Variations in alteration styles are a consequence of changes in the mechanisms of fluid control, first regulated by ductile deformation and later by brittle fracturing. Early hydrothermal alteration is characterized by zones of sodic-calcic and potassic alteration as well as iron metasomatism with associated disseminated mineralization I, controlled by ductile structures (chalcopyrite-bornite-magnetite, 2718 ± 56 Ma, Re-Os molybdenite). Veins and breccias with chalcopyrite-magnetite(-chlorite-calcite-quartz) represent an overprinting episode of mineralization (II) at ca. 2.6 Ga. Late alteration stages (ca. 2.5 Ga) represent fluid remobilization with chloritization zones and crystal growth spatially related to pegmatite intrusions. Re-Os molybdenite ages of 2503 ± 51 and 2449 ± 44 Ma provide evidence for younger episodes of hydrothermal fluid circulation in the deposit. Fluid inclusion study reveals aqueous-saturated, highly saline (32–>50 wt % NaCl equiv, total homogenization temperature [Tht] = 203°–>450°C) and carbonic fluids (CO2 melting temperature [TmCO2] = –56.3° to –54.5°C) for early alteration zones and saline (2.1–27.5 wt % NaCl equiv, Tht = 153.3°–215.5°C) solutions for late alteration zones. These data provide evidence for several alternative fluids involved in the evolution of the deposit: (1) hypersaline fluids derived from hydrothermal-magmatic brines or evaporative brines/evaporite-derived fluids, (2) saline solutions generated by progressive dilution of primary hypersaline fluids with shallower, colder, and less saline fluids (e.g., meteoric, seawater), and (3) carbonic components sourced from magmatic fluids, devolatilization of carbonate units and, partially, metamorphic fluids. Sulfur is interpreted to have been leached from country rocks in the earlier hydrothermal stages (mineralization I, δ34S = 0.01–1.99‰), and to have come from mixed granitic and external oxidized sources for later overprinting events (mineralization II, δ34S = 9.75–11.25‰). These data provide evidence for the recurrence of hydrothermal activity, indicating the existence of different potential sources of metals and sulfur during the evolution of the deposit.Item 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.(2019) Melo, Gustavo Henrique Coelho de; Monteiro, Lena Virginia Soares; Xavier, Roberto Perez; Moreto, Carolina Penteado Natividade; Santiago, Érika Suellen BarbosaThe 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.Item Evolution of the Igarapé Bahia Cu-Au deposit, Carajás Province (Brazil) : early syngenetic chalcopyrite overprinted by IOCG mineralization.(2019) Melo, Gustavo Henrique Coelho de; Monteiro, Lena Virginia Soares; Xavier, Roberto Perez; Moreto, Carolina Penteado Natividade; Arquaz, Raul Mendes; Silva, Marco Antonio Delinardo daThe Igarapé Bahia IOCG Cu–Au deposit, located in the Carajás Domain, the northern part of the Carajás Province in the Amazon Craton, is one of the most economically important deposits in the province. The deposit is hosted in the metavolcanosedimentary Igarapé Bahia Group and the metasedimentary Águas Claras Formation. The Igarapé 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. Epiclastic rocks are predominant in the Águas 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 Águas 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 Igarapé Bahia Group. Chalcopyrite nodules and layers show δ34SVCDT values ranging from +0.29 to +1.56‰. 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 δ34SVCDT values from +1.36 to +5.35‰. 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 Alemão 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 Itacaiúnas Supergroup may have created Cu-rich sequences that could have been remobilized, generating the broad group of the IOCG deposits at Carajás.