The distribution of trace elements in sulfides and magnetite from the Jaguar hydrothermal nickel deposit: A potential link between IOA and IOCG deposits within the Carajás Mineral Province? (original) (raw)
Related papers
Structure and iron mineralisation of the Carajás Province
Applied Earth Science, 2006
The Carajá s Province presents several volcano-sedimentary sequences that comprise the Itacaiú nas Supergroup. The rocks represent bimodal volcanism, and clastic and chemical sedimentation in relatively unstable basins subject to recurrent structural events with subsidence and volcanism. The Grã o Pará Group represents one of these sequences with mafic volcanic rocks that enclose discontinuous jaspilite lenses, with development of large high-grade orebodies (Fe.65%). This unit is named the Carajá s Formation and presents peculiar characteristics compared with other iron districts in the world, thereby departing from the classic Lake Superior or Algoma iron formation types. Owing to the dense vegetation, lack of outcrops and harsh landscape, the structural analysis of the district can only be accomplished by combination of regional field work, detailed structural work on the open pits and remotely sensed image interpretation, in this case Landsat ETM7, JERS-1 images and the shuttle radar topography mission (SRTM) digital terrane model. The regional trend of the several sequences of the area is approximately N-S and the structure is dominated by a flattened flexural fold system with axes moderately dipping WNW, intersected by several strike-slip faults subparallel to their axial plane. The Serra dos Carajá s represents an s-shaped synform-antiform pair, herein named the Carajá s Fold. This regional structure is partially disrupted by the Carajá s Shear Zone that divides it in the northern (Serra Norte) and the southern (Serra Sul) Ranges and also probably prepared the terrane with the development of pathways for mineralising hydrothermal fluids forming large highgrade massive iron bodies. Syntectonic granitic bodies played an important role in the structural evolution of the area as well. They caused localised ductile flattening deformation and thermal contact metamorphism in surrounding terranes. The Estrela pluton, for instance, was responsible for the discontinuity of the regional trend between the Serras do Rabo and Leste. The Carajá s Province is regionally the upper crustal product of a very shallowly eroded dome-and-keel geometry of Neo-Archaean volcano-sedimentary units intruded by syntectonic calc-alkaline intrusives and overlying pre-existing infracrustal rocks. The lithostructural data suggest continental-margin back-arc basin development and closure in an oblique collision belt, with N-S shallow crustal shortening, parallel to the inferred pre-existing strike of the stratigraphy.
Revista Brasileira de Geociências
O deposito de sulfeto de níquel de Boa Vista está localizado na extremidade noroeste do greenstone belt de Crixás. O depósito está associado a uma estreita sequência de rochas metavulcânicas máficas e ultramáficas com 7 km de extensão e direção geral E-W. Embora essa sequência de rochas vulcânicas tenha sido submetida à deformação e metamorfismo regional, feições primárias estão ainda preservadas em low-strain zones. Dois tipos de derrames ultramáficos são reconhecidos (derrames com textura spinifex e derrames não diferenciados). As rochas ultramáficas apresentam feições texturais e geoquímicas diagnósticas de derrames komatiíticos. O teor de MgO (22,1 a 28,7 % peso) em derrames com textura spinifex e derrames não diferenciados é característico de komatiitos peridotíticos. Variações geoquímicas entre os elementos maiores indicam a importância da cristalização fracionada de olivina. A dispersão dos dados geoquímicos sugere alterações na composição química primária durante o metamorfismo regional. A mineralização sulfetada está restrita a base de uma sequência metavulcânica ultramáfica sobreposta à uma sequência metavulcânica máfica. A espessura do horizonte mineralizado é variável mas geralmente nao ultrapassa alguns metros. Quatro tipos de minério são reconhecidos no depósito de Boa Vista. Esses tipos compreendem, em ordem decrescente de abundância, minério venulado, minério disseminado, minério maciço e minério silicate ocluso. A mineralogia do minério sulfetado e característica de sulfetos magmáticos associados à komatiitos. O minério consiste essencialmente de pirrotita (70 % do volume) associada a pentlandita e calcopirita e com magnetita e esfalerita como acessórios. O minério sulfetado de Boa Vista tem teores de Fe-Ni-S compatível com uma origem magmática. Análises geoquímicas do minério sulfetado recalculadas para 100% de sulfeto têm composição no campo da monosulfide solid solution à elevadas temperaturas. A razão Ni/Cu do minério sulfetado e elevada (± 10) e comparável com a maioria dos depósitos de sulfeto associados a komatiitos do arqueano. O depósito de Boa Vista representa a primeira oportunidade de estudo do ambiente formador de depósitos de níquel sulfetado no greenstone belt de Crixás. Depósitos de sulfeto de níquel associados a komatiitos estão geralmente confinados a unidades ultramáficas específicas nas sequências do tipo greenstone belt mineralizadas. Desta forma, estudos geológicos e petrológicos no depósito de Boa Vista podem subsidiar a prospecção mineral nos extensos terrenes do tipo greenstone belt do Brasil central. Palavras-chave: komatiito, níquel, sulfeto, greenstone belt, Crixás.
Mineralium Deposita, 2011
The Alvo 118 iron oxide-copper-gold (IOCG) deposit (170 Mt at 1.0 wt.% Cu, 0.3 g/t Au) lies in the southern sector of the Itacaúnas Shear Belt, Carajás Mineral Province, along a WNW-ESE-striking, 60-km-long shear zone, close to the contact of the~2.76-Ga metavolcanosedimentary Itacaiúnas Supergroup and the basement (~3.0 Ga Xingu Complex). The Alvo 118 deposit is hosted by mafic and felsic metavolcanic rocks and crosscutting granitoid and gabbro intrusions that have been subjected to the following hydrothermal alteration sequence towards the ore zones: (1) poorly developed sodic alteration (albite and scapolite); (2) potassic alteration (biotite or K-feldspar) accompanied by magnetite formation and silicification; (3) widespread, pervasive chlorite alteration spatially associated with quartz-carbonate-sulphide infill ore breccia and vein stockworks; and (4) local post-ore quartz-sericite alteration. The ore assemblage is dominated by chalcopyrite (~60%), bornite (~10%), hematite (~20%), magnetite (10%) and subordinate chalcocite, native gold, Au-Ag tellurides, galena, cassiterite, F-rich apatite, xenotime, monazite, britholite-(Y) and a gadolinite-group mineral. Fluid inclusion studies in quartz point to a fluid regime composed of two distinct fluid types that may have probably coexisted within the timeframe of the Cu-Au mineralizing episode: a hot (>200°C) saline (32.8‰ to 40.6 wt.% NaCl eq.) solution, represented by salt-bearing aqueous inclusions, and a lower temperature (<200°C), low to intermediate salinity (<15 wt.% NaCl eq.) aqueous fluid defined by twophase (L H2O +V H2O ) fluid inclusions. This trend is very similar to those defined for other IOCG systems of the Carajás Mineral Province. δ 18 O H2O values in equilibrium with calcite (−1.0‰ to 7.5‰ at 277°C to 344°C) overlap the lower range for primary magmatic waters, but the more 18 O-depleted values also point to the involvement of externally derived fluids, possibly of meteoric origin. Furthermore, sulphide δ 34 S values (5.1‰ to 6.3‰), together with available boron isotope and Cl/Br-Na/Cl data provide evidence for a significant component of residual evaporative fluids (e.g., bittern fluids generated by seawater evaporation) in this scenario that, together with magmaderived brines, would be the main sources of the highly saline fluids involved in the formation Alvo 118 IOCG deposit. The restricted high temperature sodic alteration, the pervasive overprinting of the potassic alteration minerals by chlorite proximal to the ore zones, ore breccias with openspace filling textures in brittle structures, microthermometric and stable isotope data indicate, collectively, that the Alvo 118 IOCG system developed at structurally high levels and may be considered the shallower representative of the IOCG systems of the CMP.
Mineralium Deposita, 2007
The Igarapé Bahia Cu-Au deposit in the Carajás Province, Brazil, is hosted by steeply dipping metavolcanosedimentary rocks of the Igarapé Bahia Group. This group consists of a low greenschist grade unit of the Archean (∼2,750 Ma) Itacaiúnas Supergroup, in which other important Cu-Au and iron ore deposits of the Carajás region are also hosted. The orebody at Igarapé Bahia is a fragmental rock unit situated between chloritized basalt, with associated hyaloclastite, banded iron formation (BIF), and chert in the footwall and mainly coarse-to fine-grained turbidites in the hanging wall. The fragmental rock unit is a nearly concordant, 2 km long and 30-250 m thick orebody made up of heterolithic, usually matrix-supported rocks composed mainly of coarse basalt, BIF, and chert clasts derived from the footwall unit. Mineralization is confined to the fine-grained matrix and comprises disseminated to massive chalcopyrite accompanied by magnetite, gold, U-and light rare earth element (LREE)minerals, and minor other sulfides like bornite, molybdenite, cobaltite, digenite, and pyrite. Gangue minerals include siderite, chlorite, amphibole, tourmaline, quartz, stilpnomelane, epidote, and apatite. A less important mineralization style at Igarapé Bahia is represented by late quartz-chalcopyritecalcite veins that crosscut all rocks in the deposit area. Fluid inclusions trapped in a quartz cavity in the ore unit indicate that saline aqueous fluids (5 to 45 wt% NaCl+CaCl 2 equiv), together with carbonic (CO 2 ±CH 4) and low-salinity aqueous carbonic (6 wt% NaCl equiv) fluids, were involved in the mineralization process. Carbonates from the fragmental layer have δ 13 C values from −6.7 to −13.4 per mil that indicate their origin from organic and possibly also from magmatic carbon. The δ 34 S values for chalcopyrite range from −1.1 to 5.6 per mil with an outlier at −10.8 per mil, implying that most sulfur is magmatic or leached from magmatic rocks, whereas a limited contribution of reduced and oxydized sulfur is also evident. Oxygen isotopic ratios in magnetite, quartz, and siderite yield calculated temperatures of ∼400°C and δ 18 O-enriched compositions (5 to 16.5 per mil) for the ore-forming fluids that suggest a magmatic input and/or an interaction with 18 O-rich, probably sedimentary rocks. The late veins of the Igarapé Bahia deposit area were formed from saline aqueous fluids (2 to 60 wt% NaCl+CaCl 2 equiv) with δ 18 O fluid compositions around 0 per mil that indicate contribution from meteoric fluids. With respect to geological features, Igarapé Bahia bears similarity with syngenetic, volcanic-hosted massive sulfide (VHMS)-type deposits, as indicated by the volcano-sedimentary geological context, stratabound character, and association with submarine volcanic flows, hyaloclastite, and exhalative beds such as BIF and chert. On the other hand, the highly saline ore fluids and the Miner Deposita
Mello et al Mineralium Deposita Mar2006
U-Pb sensitive high resolution ion microprobe mass spectrometer (SHRIMP) ages of zircon, monazite and xenotime crystals from felsic intrusive rocks from the Rio Itapicuru greenstone belt show two development stages between 2,152 and 2,130 Ma, and between 2,130 and 2,080 Ma. The older intrusions yielded ages of 2,152±6 Ma in monazite crystals and 2,155±9 Ma in zircon crystals derived from the Trilhado granodiorite, and ages of 2,130± 7 Ma and 2,128±8 Ma in zircon crystals derived from the Teofilândia tonalite. The emplacement age of the syntectonic Ambrósio dome as indicated by a 2,080±2-Ma xenotime age for a granite dyke probably marks the end of the felsic magmatism. This age shows good agreement with the Ar-Ar plateau age of 2,080±5 Ma obtained in hornblendes from an amphibolite and with a U-Pb SHRIMP age of 2,076±10 Ma in detrital zircon crystals from a quartzite, interpreted as the age of the peak of the metamorphism. The predominance of inherited zircons in the syntectonic Ambrósio dome suggests that the basement of the supracrustal rocks was composed of Archaean continental crust with components of 2,937±16, 3,111±13 and 3,162±13 Ma. Ar-Ar plateau ages of 2,050±4 Ma and 2,054±2 Ma on hydrothermal muscovite samples from the Fazenda Brasileiro gold deposit are interpreted as minimum ages for gold mineralisation and close to the true age of gold deposition. The Ar-Ar data indicate that the mineralisation must have occurred less than 30 million years after the peak of the metamorphism, or episodically between 2,080 Ma and 2,050 Ma, during uplift and exhumation of the orogen.
Ore Geology Reviews, 2019
The 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 2,935 ± 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 2,784 ± 27 Ma for the upper unit, and 2,763 ± 32 Ma and 2,774 ± 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 δ 34 S VCDT 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 magnetiterich zones (i.e. IOCG mineralization) displays δ 34 S VCDT 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 2,559 ± 34 Ma in the Alemão orebody. These data suggest that an IOCG-type metallogenetic event at ca. 2.5 Ga overprinted an older syngeneticexhalative 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.
Mineralium Deposita, 2023
The Montecristo district, northern Chile, is one of the few places worldwide where there is a direct relationship between magnetite-(apatite) (MtAp) mineralization and iron oxide-copper-gold (IOCG) mineralization. The MtAp mineralization includes Ti-poor magnetite, fluorapatite, and actinolite and is crosscut and partially replaced by a younger IOCG mineralization that includes a second generation of actinolite and magnetite with quartz, chalcopyrite, pyrite, and molybdenite. The MtAp stage at Montecristo is interpreted as the crystallized iron-rich melts that used the pre-existing structures of the Atacama Fault System as conduits. These rocks later acted as a trap for hydrothermal IOCG mineralization. Geochronology data at Montecristo indicate that the host diorite (U-Pb zircon 153.3 ± 1.8 Ma, 2-sigma), MtAp mineralization (40 Ar-39 Ar in actinolite, 154 ± 2 Ma and 153 ± 4 Ma, 2-sigma), and the IOCG event (Re-Os on molybdenite, 151.8 ± 0.6 Ma, 2-sigma) are coeval within error and took place in a time span of less than 3.4 Ma. The εHf i and εNd i values of the host diorite are + 8.0 to + 9.8 and + 4.3 to + 5.4, respectively. The whole-rock 87 Sr/ 86 Sr i values of the IOCG mineralization (0.70425 to 0.70442) are in the lower end of those of the MtAp mineralization (0.70426-0.70629). In contrast, εNd i values for the IOCG mineralization (+ 5.4 and + 5.7) fall between those of the MtAp rocks (+ 6.6 to + 7.2) and the host diorite, which suggests that the IOCG event was related to fluids having a more crustal Nd (εNd i < + 5.7) composition than the MtAp mineralization. This likely reflects the mixing of Nd from the MtAp protolith and a deep magmatic-hydrothermal source, very likely an unexposed intrusion equivalent to the host diorite. Sulfur isotope compositions (δ 34 S, + 0.3 to + 3.4‰) are consistent with a magmatic source.
Geology, petrology and geochemistry of the
Mineralium Deposita, 2011
The "Americano do Brasil" Complex (ABC) is part of a cluster of coeval synorogenic mafic-ultramafic intrusions emplaced during the Brasiliano/Pan-African Orogenic Cycle in Brazil. The medium-sized ABC consists of interlayered dunite, peridotite, websterite, and gabbronorite. High Fo values of olivine (up to Fo88) and the crystallization sequence of the ABC (Ol + Chr ≥ Ol + Opx + Chr ≥ Cpx + Opx ≥ Opx + Pl + Cpx ≥ Opx + Pl + Cpx + Ilm + Mag) suggest crystallization from tholeiitic high-MgO parental magmas. Light rare earth element (REE)-enriched mantle-normalized REE profiles and ɛNd(T) values of +2.4 for cumulate rocks from the ABC suggest a depleted mantle source for the parental magma. The ABC Ni-Cu sulfide deposit (3.1 Mt at 1.12 wt.% Ni and 1.02 wt.% Cu) consists of three distinctively different orebodies (S1, S2, and G2). The S2 orebody, an unusual occurrence of stratiform massive sulfide hosted by dunite and peridotite in the interior of a layered intrusion, results from sulfides accumulated at the transient base of the magma chamber following a new influx of parental magma. The G2 orebody has an irregular and roughly cylindrical shape, consisting mainly of net-textured sulfides. The G2 orebody is hosted by peridotite and pyroxenite and located stratigraphically below the S1 orebody. S2 and G2 orebodies are characterized by low Cu/Cu + Ni ratios (mainly below 0.4). The S1 orebody, hosted by websterite and gabbronorite in the more fractionated sequence of the ABC, is a cluster of several irregular discontinuous orebodies of Ni-Cu disseminated sulfides. The sulfides of the S1 orebody have high Cu/Cu + Ni ratios (mainly between 0.5 and 0.8) and are highly depleted in PGE. The S1 orebody is interpreted to result from a later event of sulfide segregation in the magma chamber, possibly following the event that originated the G2 orebody. The bulk of δ34S values for sulfides of the ABC orebodies and their host rocks fall in the range of 0 ± 2‰. Higher δ34S values (between 3‰ and 5‰) are restricted to pyrite from xenoliths of gneiss located close to the S1 orebody and sulfides from the S1 orebody. Crustal xenoliths and chemical data (lithogeochemistry and sulfur isotope composition) provide evidence of crustal contamination of the igneous rocks hosting the S1 orebody, suggesting that sulfur saturation was induced by contamination with sulfide-bearing crustal rocks. The ABC deposit is an example of Ni-Cu sulfide mineralization hosted by synorogenic mafic-ultramafic intrusions. The S2 orebody is the first documented example of an economic stratiform massive sulfide orebody located within layered intrusions, expanding the opportunities for exploration of Ni-Cu sulfides in orogenic regions worldwide.