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1. Till Geochemistry as a Vector to Metasomatic Iron and Alkali-Calcic Systems and Associated Deposits in the Great Bear Magmatic Zone, Northwest Territories, Canada.

Author

Normandeau, Philippe X., McMartin, Isabelle, and Corriveau, Louise

Subjects
*GEOCHEMISTRY, *GLACIAL drift, *IRON, *BEDROCK, *IRON ores, *COPPER, *PLATINUM group
Abstract

Recent advances in the characterization of metasomatic iron and alkali-calcic (MIAC) systems with associated iron-oxide apatite (IOA) prospects and iron-oxide–copper–gold (IOCG) and metasomatic cobalt deposits of the Great Bear magmatic zone were used to determine if the geochemistry of glacial sediments can unveil pathfinder elements indicative of mineralization and associated alteration. Analysis of variance within bedrock lithogeochemical (n = 707 samples) and till geochemical datasets (n = 92 samples) are compared. Results show that Fe, Co, Ni, Cu, As, Mo, Bi, La, Th, U, and W were identified as potential vectoring elements in different fractions of till due to their anomalous concentrations down-ice of various mineralized outcrops within the study area. For instance, Fe, Co, Cu, and Mo were established as the most useful vectoring elements in the locally derived till (<2 km down-ice) near the Sue Dianne IOCG deposit, and Fe, Co, Ni, Cu, Mo, W, Bi, and U near the Fab IOCG prospect. At the Sue Dianne deposit, the ratios of near-total (4-acid digestion) versus partial (modified aqua regia digestion) concentrations in the silt + clay-sized till fraction (<0.063 mm) for both La and Th reflect the mineralization alteration signature and define a more consistent dispersal train from mineralization compared to element concentrations mapped alone. Additional testing in an area of continuous till cover near an isolated point source is recommended to further develop the elemental ratio method for exploration of MIAC systems. [ABSTRACT FROM AUTHOR]

Published
2024
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2. The conjunction of factors that lead to formation of giant gold provinces and deposits in non-arc settings.

Author

Groves, David I., Goldfarb, Richard J., and Santosh, M.

Abstract

It is quite evident that it is not anomalous metal transport, nor unique depositional conditions, nor any single factor at the deposit scale, that dictates whether a mineral deposit becomes a giant or not. A hierarchical approach thus is required to progressively examine controlling parameters at successively decreasing scales in the total mineral system to understand the location of giant gold deposits in non-arc environments. For giant orogenic, intrusion-related gold systems (IRGS) and Carlin-type gold deposits and iron oxide-copper-gold (IOCG) deposits, there are common factors among all of these at the lithospheric to crustal scale. All are sited in giant gold provinces controlled by complex fundamental fault or shear zones that follow craton margins or, in the case of most Phanerozoic orogenic giants, define the primary suture zones between tectonic terranes. Giant provinces of IRGS, IOCG, and Carlin-type deposits require melting of metasomatized lithosphere beneath craton margins with ascent of hybrid lamprophyric to granitic magmas and associated heat flux to generate the giant province. The IRGS and IOCG deposits require direct exsolution of volatile-rich magmatic-hydrothermal fluids, whereas the association of such melts with Carlin-type ores is more indirect and enigmatic. Giant orogenic gold provinces show no direct relationship to such magmatism, forming from metamorphic fluids, but show an indirect relationship to lamprophyres that reflect the mantle connectivity of controlling first-order structures. In contrast to their province scale similarities, the different giant gold deposit styles show contrasting critical controls at the district to deposit scale. For orogenic gold deposits, the giants appear to have formed by conjunction of a greater number of parameters to those that control smaller deposits, with resultant geometrical and lithostratigraphic complexity as a guide to their location. There are few giant IRGS due to their inferior fluid-flux systems relative to orogenic gold deposits, and those few giants are essentially preservational exceptions. Many Carlin-type deposits are giants due to the exceptional conjunction of both structural and lithological parameters that caused reactive and permeable rocks, enriched in syngenetic gold, to be located below an impermeable cap along antiformal “trends”. Hydrocarbons probably played an important role in concentrating metal. The supergiant Post-Betze deposit has additional ore zones in strain heterogeneities surrounding the pre-gold Goldstrike stock. All unequivocal IOCG deposits are giant or near-giant deposits in terms of gold-equivalent resources, partly due to economic factors for this relatively poorly understood, low Cu-Au grade deposit type. The supergiant Olympic Dam deposit, the most shallowly formed deposit among the larger IOCGs, probably owes its origin to eruption of volatile-rich hybrid magma at surface, with formation of a large maar and intense and widespread brecciation, alteration and Cu-Au-U deposition in a huge rock volume. [ABSTRACT FROM AUTHOR]

Published
2016
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3. Rare earths and other trace elements in minerals from skarn assemblages, Hillside iron oxide–copper–gold deposit, Yorke Peninsula, South Australia.

Author

Ismail, Roniza, Ciobanu, Cristiana L., Cook, Nigel J., Teale, Graham S., Giles, David, Mumm, Andreas Schmidt, and Wade, Benjamin

Subjects
*RARE earth metals, *SKARN, *TRACE elements, *IRON oxides, *COPPER mining
Abstract

The Hillside Cu–(Au) deposit, Yorke Peninsula, South Australia, is a recently-discovered ore system within the 1.6Ga World-class Olympic iron oxide–copper–gold (IOCG) Province. The deposit is characterized by a skarn-style alteration zone. Analyses of feldspar, calcite, skarn minerals (garnet, pyroxene, clinozoisite and actinolite) and accessories (titanite, apatite and allanite), and grain-scale element mapping by laser-ablation inductively-coupled plasma mass spectrometry are used to assess the distributions of rare earth element (REE), incompatible and ore-forming elements in host rocks, prograde and retrograde skarn. Garnet is a major repository of HREE, especially in prograde skarn, whereas LREE-enriched clinozoisite is the principal REE-host in retrograde skarn. REE distribution patterns define a pronounced partitioning of elements among the dominant coexisting minerals. Compositional variation between assemblages, and also within individual grains, defines an evolution from early feldspar–pyroxene skarn through main-stage calcic skarn to the ore-stage. A switch from a prograde, HREE-dominant signature to a LREE-enriched signature is observed in both retrograde and distal skarn. Zr-in-titanite geothermometry supports transition from magmatic to hydrothermal, skarn-forming processes at temperatures of ~660°C; the initiation of ore-stage is about 100°C lower. Understanding REE distributions in all minerals within a complex, multistage ore system assists the development of vectoring tools that use trace element chemistry in exploration for similar IOCG deposits beneath regolith cover across the Olympic Province. Titanite and apatite show particular promise because of their characteristically distinct REE patterns in magmatic and hydrothermal stages, trace element responses to redox changes, and their widespread abundance throughout different lithologies in the area. [ABSTRACT FROM AUTHOR]

Published
2014
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4. Constraining models of the tectonic setting of the giant Olympic Dam iron oxide–copper–gold deposit, South Australia, using deep seismic reflection data

Author

Drummond, Barry, Lyons, Patrick, Goleby, Bruce, and Jones, Leonie

Subjects
*SEISMOLOGY, *MORPHOTECTONICS, *EARTHQUAKE zones, *IRON oxides
Abstract

Abstract: In the Gawler Craton, the completeness of cover concealing the crystalline basement in the region of the giant Olympic Dam Cu–Au deposit has impeded any sufficient understanding of the crustal architecture and tectonic setting of its IOCG mineral-system. To circumvent this problem, deep seismic reflection data were recently acquired from ∼250 line-km of two intersecting traverses, centered on the Olympic Dam deposit. The data were recorded to 18 s TWT (∼55 km). The crust consists of Neoproterozoic cover, in places more than 5 km thick, over crystalline basement with the Moho at depths of 13–14 s TWT (∼40–42 km). The Olympic Dam deposit lies on the boundary between two distinct pieces of crust, one interpreted as the Archean–Paleoproterozoic core to the craton, the other as a Meso–Neoproterozoic mobile belt. The host to the deposit, a member of the ∼1590 Ma Hiltaba Suite of granites, is situated above a zone of reduced impedance contrast in the lower crust, which we interpret to be source-region for its ∼1000 °C magma. The crystalline basement is dominated by thrusts. This contrasts with widely held models for the tectonic setting of Olympic Dam, which predict extension associated with heat from the mantle producing the high temperatures required to generate the Hiltaba Suite granites implicated in mineralization. We use the seismic data to test four hypotheses for this heat-source: mantle underplating, a mantle-plume, lithospheric extension, and radioactive heating in the lower crust. We reject the first three hypotheses. The data cannot be used to reject or confirm the fourth hypothesis. [Copyright &y& Elsevier]

Published
2006
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5. The conjunction of factors that lead to formation of giant gold provinces and deposits in non-arc settings

Author

M. Santosh, David I. Groves, and Richard J. Goldfarb

Subjects
Lithosphere, 010504 meteorology & atmospheric sciences, Metamorphic rock, Geochemistry, Earth and Planetary Sciences(all), 010502 geochemistry & geophysics, Iron oxide copper gold ore deposits, 01 natural sciences, Sedimentary depositional environment, Intrusion-related gold systems, Carlin deposits, 0105 earth and related environmental sciences, Terrane, geography, geography.geographical_feature_category, lcsh:QE1-996.5, Orogenic gold, Giant gold deposits, lcsh:Geology, Craton, Magmatism, General Earth and Planetary Sciences, Shear zone, Iron oxide-copper-gold deposits, Geology
Abstract

It is quite evident that it is not anomalous metal transport, nor unique depositional conditions, nor any single factor at the deposit scale, that dictates whether a mineral deposit becomes a giant or not. A hierarchical approach thus is required to progressively examine controlling parameters at successively decreasing scales in the total mineral system to understand the location of giant gold deposits in non-arc environments. For giant orogenic, intrusion-related gold systems (IRGS) and Carlin-type gold deposits and iron oxide-copper-gold (IOCG) deposits, there are common factors among all of these at the lithospheric to crustal scale. All are sited in giant gold provinces controlled by complex fundamental fault or shear zones that follow craton margins or, in the case of most Phanerozoic orogenic giants, define the primary suture zones between tectonic terranes. Giant provinces of IRGS, IOCG, and Carlin-type deposits require melting of metasomatized lithosphere beneath craton margins with ascent of hybrid lamprophyric to granitic magmas and associated heat flux to generate the giant province. The IRGS and IOCG deposits require direct exsolution of volatile-rich magmatic-hydrothermal fluids, whereas the association of such melts with Carlin-type ores is more indirect and enigmatic. Giant orogenic gold provinces show no direct relationship to such magmatism, forming from metamorphic fluids, but show an indirect relationship to lamprophyres that reflect the mantle connectivity of controlling first-order structures. In contrast to their province scale similarities, the different giant gold deposit styles show contrasting critical controls at the district to deposit scale. For orogenic gold deposits, the giants appear to have formed by conjunction of a greater number of parameters to those that control smaller deposits, with resultant geometrical and lithostratigraphic complexity as a guide to their location. There are few giant IRGS due to their inferior fluid-flux systems relative to orogenic gold deposits, and those few giants are essentially preservational exceptions. Many Carlin-type deposits are giants due to the exceptional conjunction of both structural and lithological parameters that caused reactive and permeable rocks, enriched in syngenetic gold, to be located below an impermeable cap along antiformal “trends”. Hydrocarbons probably played an important role in concentrating metal. The supergiant Post-Betze deposit has additional ore zones in strain heterogeneities surrounding the pre-gold Goldstrike stock. All unequivocal IOCG deposits are giant or near-giant deposits in terms of gold-equivalent resources, partly due to economic factors for this relatively poorly understood, low Cu-Au grade deposit type. The supergiant Olympic Dam deposit, the most shallowly formed deposit among the larger IOCGs, probably owes its origin to eruption of volatile-rich hybrid magma at surface, with formation of a large maar and intense and widespread brecciation, alteration and Cu-Au-U deposition in a huge rock volume.

Published
2016
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6. Geological and metallogenetic characterization of the Pantera IOCG, Rio Maria domain, Carajás-PA

Author

Ananda Melo Lopes, Moreto, Carolina Penteado Natividade, 1985, Xavier, Roberto Perez, 1958, Assis, Rafael Rodrigues de, Santos, Ticiano José Saraiva dos, Universidade Estadual de Campinas. Instituto de Geociências, Programa de Pós-Graduação em Geociências, and UNIVERSIDADE ESTADUAL DE CAMPINAS

Subjects
Crátons - Amazônia, Metalogenia, Depósitos de oxido de Fe-Cu-Au, Metallogeny, Craton - Amazon, Iron oxide-copper-gold deposits
Abstract

Orientadores: Carolina Penteado Natividade Moreto, Roberto Perez Xavier Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Geociências Resumo: A Província Carajás localizada na porção sudeste do Cráton Amazônico e do Estado do Pará, representa hoje uma das províncias mais importantes do mundo e destaca-se por apresentar a maior quantidade conhecida de depósitos de óxidos de ferro-cobre-ouro (IOCG) de alta tonelagem (e.g., Sossego, Salobo, Igarapé Bahia/Alemão, Cristalino, Alvo 118, Igarapé Cinzento/Alvo GT46). O depósito Pantera é hospedado por rocha de composição granodiorítica (2909 ±15Ma; U-Pb LA-ICP-MS em zircão) e por diferentes tipos de diques que compreendem quartzo diorito porfirítico (2900 ±10Ma, U-Pb LA-ICP-MS em zircão), quartzo-feldspato pórfiro e diábasio, e representa a primeira ocorrência de depósitos da classe IOCG no domínio Rio Maria. O granodiorito hospedeiro apresenta evidências de deformação heterogênea referentes às distintas zonas milonitizadas que se apresentam intimamente relacionadas ao melhor desenvolvimento das zonas de alteração hidrotermal. A partir da descrição de testemunhos de sondagem e de estudos petrográficos detalhados, foi possível reconstituir o zoneamento espacial das alterações hidrotermais que apresentam padrão vertical a sub-vertical, e com distribuição fortemente controlada por zonas de cisalhamento. A sequência de alteração hidrotermal em direção às zonas proximais ao minério incluem zonas de alteração sódico-cálcica com actinolita e albita, seguida por alteração cálcica caracterizada por aumento substancial na abundância de actinolita, que gradam para zonas de alteração férrico-cálcica com magnetita e actinolita. A partir disto, o sistema hidrotermal evidência diminuição de temperatura de acordo com as últimas alterações hidrotermais reconhecidas no depósito representadas por alteração potássica constituída por biotita, hastingsita e feldspato potássico subordinados, acompanhada por silificicação, mineralização cuprífera e zonas de alteração clorítica. A mineralização IOCG no depósito Pantera está essencialmente associada ao estágio de alteração potássica e apresenta estilos de mineralização que variam entre veios, vênulas, brechas hidrotermais e disseminações na foliação milonítica que hospedam uma associação de minério constituída principalmente por magnetita, pirita e calcopirita, que é o principal mineral de minério. Infere-se para o estágio de precipitação do minério condições moderadas de fO2 e pH levemente ácido a neutro em temperaturas em torno de 300 ºC. A alteração tardia venular com predominância de quartzo, feldspato potássico pode indicar a circulação de fluidos hidrotermais ainda posteriores ao evento hidrotermal principal, sugerindo a existência de um segundo sistema hidrotermal de menor intensidade sobreposto, formado em regime rúptil de deformação. Composições isotópicas de enxofre obtidas em sulfetos (calcopirita e pirita) das zonas de minério (?34S = 4,22 a 5,07¿) e da alteração tardia (?34S = 4,67 a 4,79¿) possibilitaram a correlação da origem do enxofre com fluidos evaporativos residuais, com possível contribuição de enxofre magmático ou lixiviado de rochas ígneas a partir de mecanismos de interação fluido-rocha Abstract: The Carajás Province is located in the southeastern portion of the Amazon Craton and the State of Pará. Nowadays it represents one of the most important provinces in the world and stands out for having the highest known amount high tonnage of iron-copper-gold oxide (IOCG) deposits (eg, Sossego, Salobo, Igarapé Bahia / Alemão, Cristalino, Alvo 118, Igarapé Cinzento/ Alvo GT46). The Pantera deposit is hosted by rocks of granodioritic composition (2909 ±15M; U-Pb LA-ICP-MS in zircon) and by different types of dikes comprising porphyritic diorite quartz diorite (2900 ±10Ma, U-Pb LA-ICP-MS in zircão), feldspar quartz porphyry and diabase, and represents the first occurrence of IOCG deposits in the Rio Maria domain. The host granodiorite presents evidence of heterogeneous deformation related to the different milonitized zones that are closely related to the better development of the of hydrothermal alteration zones. Basead on detailed drill core description and petrographic studies, it was possible to reconstitute the spatial zoning of the hydrothermal alterations that display vertical to subvertical patterns with distribution strongly controlled by shear zones. The hydrothermal alterations sequence towards ore zones includes sodic-calcic zones with actinolite and albite, followed by calcic alteration characterized by a substantial increase in the abundance of actinolite, which pass to iron-calcic alteration zones with magnetite and actinolite. From this point on, the hydrothermal system evidences decrease in temperature according to the last hydrothermal alterations recognized in the deposit represented by potassic alteration with biotite, hastingsite and subordinate potassic feldspar and associated silificication, cooper ore, and zones of chlorite alteration. The IOCG mineralization in the Pantera deposit is essencially related to the potassic alteration stage and presents mineralization styles ranging from veins, veinlets, hydrotermal breccias and disseminations along mylonitc foliation, which host ore assemblage mainly composed of magnetite, pyrite and chalcopyrite which as the main ore mineral. It is infered for ore precipitation conditions of moderate fO2 and slightly acidic to neutral pH with temperatures around 300 ºC. The late venular alteration with predominancy of quartz and potassic feldspar may indicate the circulation of hydrotermal fluids after the stablishment of the main hydrotermal event, suggesting the existence of a second hydrotermal system superimposed, formed in a brittle conditions. Isotopic compositions of sulfur obtained in sulphides (chalcopyrite and pyrite) from the ore zones (?34S = 4,22 a 5,07¿) and from late venular alteration (?34S = 4,67 a 4,79¿) allowed the correlation of the sulfur sources with residual evaporative fluids, with possible contribution of magmatic sulfur or leached from igneous rocks by fluid-rock interaction mechanism Mestrado Geologia e Recursos Naturais Mestra em Geociências CNPQ 132033/2016-0

Published
2018

7. Evolução temporal e fonte de fluidos dos depósitos IOCG Salobo e Igarapé Bahia, Província Carajás

Author

Melo, Gustavo Henrique Coelho de, 1989, Monteiro, Lena Virginia Soares, 1970, Xavier, Roberto Perez, 1958, Villas, Raimundo Netuno Nobre, Oliveira, Claudinei Gouveia de, Assis, Rafael Rodrigues de, Mesquita, Maria José Maluf de, Universidade Estadual de Campinas. Instituto de Geociências, Programa de Pós-Graduação em Geociências, and UNIVERSIDADE ESTADUAL DE CAMPINAS

Subjects
Isótopos estáveis, Depósitos de oxido de Fe-Cu-Au, Minerios de cobre, Depositos hidrotermais, Copper ores, Iron oxide-copper-gold deposits, Hydrothermal deposits, Stable isotopes
Abstract

Orientadores: Lena Virgínia Soares Monteiro, Roberto Perez Xavier Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Geociências Resumo: Os depósitos Salobo e Igarapé Bahia representam importantes depósitos de óxido de ferro¿cobre¿ouro (IOCG) da Província Carajás. O depósito Salobo é hospedado por gnaisses do Complexo Xingu, granitoides da Suíte Igarapé Gelado e por unidades metasedimentares. Alteração hidrotermal formou rochas miloníticas ricas em grunerita¿almandina¿faialita¿magnetita¿(turmalina) e (grunerita¿almandina)¿magnetita¿biotita. O depósito Igarapé Bahia é hospedado por rochas metavulcanossedimentares do Grupo Igarapé Bahia e metassedimentares da Formação Águas Claras. Xenólitos embasamento ocorrem no depósito e forneceram idades de 2935 ±36 Ma (MSWD = 0,85), sugerindo uma crosta ensiálica prévia a instalação da bacia. Idades U¿Pb de zircão detritítico das metagrauvacas do Grupo Igarapé Bahia (2,82 ¿ 2,88 Ga e 2,94 ¿ 2,99 Ga) e da Formação Águas Claras (2,81 ¿ 2,89 Ga e 2,91 ¿ 3,03 Ga) apontam para predominância de fontes do embasamento mesoarqueano. Nódulos e layers de calcopirita em metarritmitos da unidade superior representam uma mineralização singenética coeva à deposição do Grupo Igarapé Bahia no Neoarqueano. A composição isotópica de enxofre dessa geração de calcopirita (+0,29 e +1,56¿) e os seus elevados conteúdos de Ni, Co e Bi apontam para enxofre e metais lixiviados das rochas metavulcânicas da unidade inferior. Extensas zonas de alteração hidrotermal com rochas ricas em (turmalina)¿carbonato¿magnetita e (turmalina)¿carbonato¿clorita envelopam a mineralização IOCG. Geocronologia U¿Pb em monazita forneceu idade 2559 ±34 Ma no corpo Alemão. A assinatura geoquímica de minério com elevados valores de ?ETR e conteúdos significativos de U, Mo, Sn, W, Y, Nb e Sr são característicos da mineralização IOCG. No depósito Salobo, fluidos em equilíbrio com grunerita (?18OH2O = +6,66 a +7,96¿, ?DH2O = ¿10,65 a ¿1,33¿), granada (?18OH2O = +6,88 a +7,77¿) e turmalina (?18OH2O = +4,11 a +6,41¿, ?DH2O = ¿15,40 a +5,12¿), a 429 ±45 ºC, e fluidos em equilíbrio com biotita (?18OH2O = +7,16 a 7,96¿, ?DH2O = -36,96 a -21,93¿) e quartzo (?18OH2O = +6,88 ± 0,35¿), a 520 ± 45 ºC, apresentam composição semelhante à da água magmática. No depósito Igarapé Bahia, fluidos associados com a formação de turmalina (?18OH2O = +5,54 a 6,24¿, ?DH2O = ¿46,98 a ¿32,70¿) e calcita (?18OH2O = +1,68 a +3,10¿; ?13CCO2 = ¿9,04 a ¿4,65¿, 398 ± 85°C) também evidenciam fontes magmáticas. A participação de fontes externas no Igarapé Bahia é marcada pela clorita (?18OH2O = +2,13 e +3,41¿). Isótopos de enxofre apontam para fontes magmáticas no depósito Salobo (¿0,37 e +1,63¿) e externa para o Igarapé Bahia (+1,36 e +5,35¿). Isótopos de boro em turmalina nos depósitos Salobo (+3,4 a +17,0¿), Igarapé Bahia (+3,4 a +14,6¿), Furnas (+13,1 a +17,2¿), Grota Funda (+8,2 a +13,6¿) e GT-46 (+5,4 a +6,4¿) sugerem a participação de fontes híbridas, que incluem salmoras derivadas de fluidos hidrotermais submarinhos e/ou evaporação da água do mar associada com boro proveniente de salmoras magmáticas. A sobreposição de episódios de mineralização de Cu¿Au reflete os diversos eventos tectônicos e magmáticos do Domínio Carajás Abstract: The Salobo and Igarapé Bahia deposits represent important iron oxide-copper-gold (IOCG) deposits at Carajás Province. The Salobo deposit is hosted by gneiss from the Xingu Complex, granites from the Igarapé Gelado suite and by metasedimentary units. Hydrothermal alteration formed grunerite¿almandine¿fayalite¿magnetite¿(tourmaline) and (grunerite¿almandine)¿magnetite¿biotite mylonitic rocks. The Igarapé Bahia depositi is hosted by metavolcanosedimentary rocks from the Igarapé Bahia Group and metasedimentary sequences from the Águas Claras Formation. Basement xenoliths occur within the deposit with ages of 2,935 ±36 Ma (MSWD = 0.85), evidencing the presence of an ensialic crust prior to rifting. U-Pb ages in detrital zircon of the metagraywackes of the Igarapé Bahia Group (2.82 ¿ 2.88 Ga e 2.94 ¿ 2.99 Ga) and of the Águas Claras Formation (2.81 ¿ 2.89 Ga and 2.91 ¿ 3.03 Ga) point to mesoarchean basement sources. Chalcopyrite nodules and layers within metarhytmites of the upper sequence represent a syngenetic mineralization coeval with deposition of the Igarapé Bahia Group in the Neoarchean. Sulfur isotopes in this chalcopyrite generation (+0.29 and +1.56¿) and elevated contents of Ni, Co and Bi suggest that sulfur and metals were leached from the metavolcanic rocks of the lower sequence. Zones of hydrothermal alteration with (tourmaline)¿carbonate¿magnetite and (tourmaline)¿carbonate¿chlorite envelop the IOCG mineralization. U-Pb geochronology in monazite yielded ages of 2,559 ±34 Ma in the Alemão orebody. Ore geochemistry signature at IOCG mineralization exhibit elevated ?ETR values and expressive contents of U, Mo, Sn, W, Y, Nb and Sr. In the Salobo deposit, fluids associated with grunerite (?18OH2O = +6.66 to +7.96¿, ?DH2O = ¿10.65 to ¿1.33¿), garnet (?18OH2O = +6.88 to +7.77¿) and tourmaline (?18OH2O = +4.11 to +6.41¿, ?DH2O = ¿15.40 to +5.12¿), at 429 ± 45 ºC, and fluids in equilibrium with biotite (?18OH2O = +7.16 to 7.96¿, ?DH2O = -36.96 to -21.93¿) and quartz (?18OH2O = +6.88 ±0.35¿), at 520 ± 45 ºC, fall into the magmatic water field. In the Igarapé Bahia deposit, fluids in equilibrium with tourmaline (?18OH2O = +5.54 to 6.24¿, ?DH2O = ¿46.98 to ¿32.70¿) and calcite (?18OH2O = +1.68 to +3.10¿; ?13CCO2 = ¿9.04 to ¿4.65¿, 398 ± 85°C) also point to magmatic sources. External sources in the Igarapé Bahia deposit is constrained by chlorite (?18OH2O = +2.13 e +3.41¿). Sulfur isotopes point to magmatic sources at Salobo (¿0.37 and +1.63¿) and external sources for Igarapé Bahia (+1.36 and +5.35¿). Boron isotopes in tourmaline at Salobo (+3,4 to +17,0¿), Igarapé Bahia (+3,4 to +14,6¿), Furnas (+13.1 to +17.2¿), Grota Funda (+8.2 to +13.6¿) and GT-46 (+5.4 to +6.4¿) evidence the participation of exhalative fluids and/or evaporated seawater brines associated with magmatic brines. These results suggest that seawater and magmatic boron sources took part in the mineral system during distinct Neoarchean tectono-magmatic events separated in time Doutorado Geologia e Recursos Naturais Doutor em Ciências CNPQ 481969/2013-6 CAPES 2016/13162-7 FAPESP 2016/13162-7

Published
2018

8. A fluid inclusion and stable isotope (O, H, S and C) study of the Archean IOCG Cristalino deposit, Carajás mineral Province, Brazil: Implications to ore genesis.

Author

Craveiro, Gustavo Souza, Villas, Raimundo Netuno Nobre, and Xavier, Roberto Perez

Subjects
*STABLE isotopes, *CARBON dioxide, *ORES, *MINERALS, *ARCHAEAN, *FLUID inclusions, *PYRITES, *SULFIDE minerals
Abstract

• Cristalino is a world-class IOCG deposit which lies in Carajás Province, Brazil. • The two major ore association consist of Ccp-Py-Mag-Au and Ccp ± Py ± He ± Au. • The Cristalino hydrothermal history evolved from >550° to ~250 °C with f O2 increase. • Stable isotope data support magmatic sources for ore fluid, sulfides and carbonates. • Fluid salinity decreased (>55–7.9%) due to mixing of magmatic with surficial water. The hydrothermal history of the Archean Cu-Au Cristalino deposit is recorded in moderately to intensely altered host rocks, which evolved from ~550 °C to ~150 °C. Distal sodic and proximal calcic-ferric, potassic and propylitic alterations developed successively with variable intensity. Two main mineralization types are also recognized: an earlier one characterized by a chalcopyrite + pyrite + magnetite + Au association that occurs as disseminations and breccias in calcic-ferric zones, and a later one represented by a chalcopyrite ± pyrite ± hematite ± Au association that occurs as breccias and veins mainly in potassic and propylitic zones. Estimated pressures (0.6 to 2.6 Kbar) are consonant with brittle and ductile-brittle deformational environments where both alteration and mineralization took place. The ore-bearing fluid was hot (T as high as ~550 °C), acidic and hypersaline (55.1% wt. NaCl equiv.) and chemically approached by the H 2 O-NaCl-CaCl 2 -CO 2 ± MgCl 2 ± FeCl 2 system. Salinity might have exceeded 55 wt% NaCl equiv. in the early alteration stages but decreased progressively to 7.9 wt% NaCl equiv. from 250 °C onwards, due to incursion of surficial water into the deposit site. The fluid was initially 18O-enriched and D-depleted (δ 18O v-smow = +9.73 to +6.48‰; δ D v-smow = −30.17 to −40.25‰) and most likely derived from magmatic sources. As result of dilution caused by mixing with meteoric water, the fluid became relatively 18O-depleted and D-enriched (δ 18O v-smow = +5.57 to −0.28‰; δ D v-smow = −19.15 to −22.24‰). The δ 13C v-pdb values for vein and breccia calcite (−6.5 to −3.8‰) are consistent with a deep source for CO 2 , likely of mantellic origin. Most δ 34S v-cdt values for chalcopyrite show narrow variation (+1.6 to +3.5‰) and could indicate a homogeneous reservoir for sulfur. However, a few samples reveal significant influence of sedimentary rocks on their isotope composition (δ 34S v-cdt = −32.6‰), showing that sulfur may have been sourced from various reservoirs. It is inferred that most Cu and Au were transported as chloride complexes (>350 °C), and precipitated in response to decrease in temperature and Cl− activity, and increase in pH. The formation of the chalcopyrite ± pyrite ± hematite ± Au association was especially favored by an oxygen fugacity increase during the late stages of the hydrothermal alteration. Secondary fluid inclusions reveal that an aqueous, colder (200–150 °C) and relatively less saline (21–3.1 wt% NaCl equiv.) fluid of uncertain origin circulated in the Cristalino deposit area, which is likely related to a nearby Paleoproterozoic granitic intrusion. In comparison with other Archean Carajás IOCG deposits, particularly those that lie in the southern sector of the Carajás Domain, the Cristalino deposit shows similar structural styles, hydrothermal assemblages, and ore fluid composition and evolution. The data presented here support previous interpretations that consider Cristalino as of IOCG typology. [ABSTRACT FROM AUTHOR]

Published
2020
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