Structural control and genesis of the Au-quartz veins from the Serra do Cavalo Magro orogenic gold deposit, southern Ribeira Belt, Brazil

Detalhes bibliográficos
Autor(a) principal: Malta, Isaac Siles
Data de Publicação: 2018
Tipo de documento: Dissertação
Idioma: eng
Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
Texto Completo: https://www.teses.usp.br/teses/disponiveis/44/44143/tde-30052019-103210/
Resumo: The Serra do Cavalo Magro orogenic gold deposit is located in the southern Ribeira Belt, Brazil. Gold-quartz veins are hosted by Calymmian (1500-1450 Ma) metasedimentary and metabasic rocks and Ediacaran (610-600 Ma) granitic rocks. Petrological modeling indicates peak metamorphic conditions from 560°C and 7 kbar (chlorite-biotite phyllite) to 625°C and 6.8 kbar (garnet-biotite phyllite) recorded in immediate host rocks. Gold mineralization occurs in extensional and shear quartz veins structurally-controlled by NE-trending second-third order sinistral transcurrent shear zones. NNW-trending, vertical and subhorizontal extensional veins are oriented 55-85° in relation to the fault planes, indicating that the shear zones were severely misoriented for frictional react ivation. Deformation within the shear zones was accommodated by bulging recrystallization of quartz aggregates, while feldspar aggregates from granitic protoliths underwent cataclastic flow or were replaced by sericite-epidote producing phyllonites. Gold precipitated during stages of vein deformation within microfractures in my lonitized shear veins with quartz previously subjected to bulging recrystallization. Ore-fl uids are recorded in coexisting C02-N2, l-hO-NaCl-CaCh and H20-C02-N2-NaCI-CaCh fluid inclusions oflow to moderate salinities (1-18 w1.%NaCl eq.). Microthennometric data indicate entrapment conditions of240-260 °C and 0.4-2.5 kbar, recording hydrostatic to supralithostatic fluid pressure conditions. High-temperature l-hO-NaCl-CaCh-KCl brine inclusions (up to 475 DC, 25-33 wt.% aCl eq.) are considered unrelated with gold mineralization. Strong fluid pressure fluctuations from 0.4 to 1.6 kbar are associated with earthquake cycles and the faultvalve behavior. In this scenario, gold mineralization was associated with fluid immiscibility. There is evidence for restricted fluid mixing, but this process is interpreted as unrelated with gold mineralization. Available geochronological data and structural-petrological relationships with host rocks and shear zones indicate that mineralization was formed within 580-540 Ma in post-peak metamorphic episodes. The hydrothermal ore-fluids were likely produced by devolatilization reactions during prograde metamorphism at deeper levels. Subsequently, the metamorphic-hydrothermal fluids were channeled upwards within the strike-slip shear zones into rocks that have been metamorphosed and devolatilized at earlier times.
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spelling Structural control and genesis of the Au-quartz veins from the Serra do Cavalo Magro orogenic gold deposit, southern Ribeira Belt, BrazilStructural control and genesis of the Au-quartz veins from the Serra do Cavalo Magro orogenic gold deposit, southern Ribeira Belt, BrazilAu-quartz veinsComportamento falha-válvulaDepósito de ouro orogênico da Serra do Cavalo MagroFault-valve behaviorFluid inclusionsGold precipitationInclusões fluídasPrecipitação de ouroProcessos de falhamento sísmicoSeismic faulting processesSerra do Cavalo orogenic gold depositVeios de quartzo auríferosThe Serra do Cavalo Magro orogenic gold deposit is located in the southern Ribeira Belt, Brazil. Gold-quartz veins are hosted by Calymmian (1500-1450 Ma) metasedimentary and metabasic rocks and Ediacaran (610-600 Ma) granitic rocks. Petrological modeling indicates peak metamorphic conditions from 560°C and 7 kbar (chlorite-biotite phyllite) to 625°C and 6.8 kbar (garnet-biotite phyllite) recorded in immediate host rocks. Gold mineralization occurs in extensional and shear quartz veins structurally-controlled by NE-trending second-third order sinistral transcurrent shear zones. NNW-trending, vertical and subhorizontal extensional veins are oriented 55-85° in relation to the fault planes, indicating that the shear zones were severely misoriented for frictional react ivation. Deformation within the shear zones was accommodated by bulging recrystallization of quartz aggregates, while feldspar aggregates from granitic protoliths underwent cataclastic flow or were replaced by sericite-epidote producing phyllonites. Gold precipitated during stages of vein deformation within microfractures in my lonitized shear veins with quartz previously subjected to bulging recrystallization. Ore-fl uids are recorded in coexisting C02-N2, l-hO-NaCl-CaCh and H20-C02-N2-NaCI-CaCh fluid inclusions oflow to moderate salinities (1-18 w1.%NaCl eq.). Microthennometric data indicate entrapment conditions of240-260 °C and 0.4-2.5 kbar, recording hydrostatic to supralithostatic fluid pressure conditions. High-temperature l-hO-NaCl-CaCh-KCl brine inclusions (up to 475 DC, 25-33 wt.% aCl eq.) are considered unrelated with gold mineralization. Strong fluid pressure fluctuations from 0.4 to 1.6 kbar are associated with earthquake cycles and the faultvalve behavior. In this scenario, gold mineralization was associated with fluid immiscibility. There is evidence for restricted fluid mixing, but this process is interpreted as unrelated with gold mineralization. Available geochronological data and structural-petrological relationships with host rocks and shear zones indicate that mineralization was formed within 580-540 Ma in post-peak metamorphic episodes. The hydrothermal ore-fluids were likely produced by devolatilization reactions during prograde metamorphism at deeper levels. Subsequently, the metamorphic-hydrothermal fluids were channeled upwards within the strike-slip shear zones into rocks that have been metamorphosed and devolatilized at earlier times.o deposito de aura orogemco da Serra do Cavalo Magro localiza-se na Faixa Ribeira Meridional, Brasil. Os veios de quartzo de ouro estao hospedados em rochas metassedimentares e metabasicas caliminianas (1500-1450 Ma) e rochas graniticas ediacaranas (610-600 Ma). A modelagem petrologica indica que as condicoes de pico metamorfico das rochas hospedeiras imediatas aos veios ocorreram a 560°C e 7 kbar (clorita-biotita filito) e a 625°C e 6,8 kbar (granada-biotita filito). A mineralizacao aurifera ocorre tanto em veios de quartzo extensionais como em veios de cisalhamento estruturalmente control ados por zonas de cisalhamento transcorrentes sinistrais de segunda e terceira ordem de direcao NE. Os veios extensionais verticais e sub-horizontais NNW sao orientados entre 55 a 85° em relacao aos planos de falhas, indicando que as zonas de cisalhamento foram severamente desorientadas para reativacao friccional. A deforrnacao nas zonas de cisalhamento foi acomodada pel a recristalizacao de agregados de quartzo por bulging, enquanto agregados de feldspato derivados de protolitos graniticos sofreram fluxo cataclastico ou foram substitufdos por epidoto-sericita produzindo filonitos. 0 ouro precipitou durante estagios de deforrnacao dos veios ao longo de microfraturas em veios de cisalhamento milonitizados com quartzo previamente submetido arecristalizacao por bulging. Os fluidos mineralizantes registram a coexistencia de inclusoes fluidas de C02-N2, I-hO-NaCI-CaCh e H20-C02-N2-NaCI-CaCh de baixas a moderadas salinidades (1-18% em peso de NaCI eq.). Dados microtermometricos indicam condicoes de aprisionamento de 240 a 260°C e de 0.4 a 2.5 kbar, registrando variacoes hidrostaticas a supralitostaticas da pressao de fluidos. Inclusoes hipersalinas aquosas e multifasicas (I-hO-NaCI-CaCh-KCI) de alta temperatura (475°C, 25-33% em peso de NaCI eq.) sao consideradas nao relacionadas com a mineralizacao de ouro. Fortes flutuacoes de pressao de fluidos na ordem de 0.4 a 1.6 kbar estao associadas a ciclos de terremotos e ao comportamento falha-valvula. Nesse cenario, a mineralizacao aurffera estaria associada aimiscibilidade de fluidos. Ha evidencias de mistura fluidos restrita, mas esse processo e interpretado como nao relacionado amineralizacao. Dados geocronologicos disponfveis e relacoes estruturais-petrologicas das rochas hospedeiras e zonas de cisalhamento sugerem que a mineralizacao foi formada entre 580-540 Ma durante episodios apos 0 pico metarnorfico. as fluidos hidrotermais mineralizantes foram provavelmente produzidos por reacoes de devolatilizacao durante 0 metamorfismo progressivo em nfveis profundos, os quais foram subsequentemente canalizados ao longo de sistemas de falhas e zonas de cisalhamentos transcorrentes em rochas que ja foram metamorfizadas e devolatilizadas em epocas anteriores.Biblioteca Digitais de Teses e Dissertações da USPFaleiros, Frederico MeiraMalta, Isaac Siles2018-12-21info:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/masterThesisapplication/pdfhttps://www.teses.usp.br/teses/disponiveis/44/44143/tde-30052019-103210/reponame:Biblioteca Digital de Teses e Dissertações da USPinstname:Universidade de São Paulo (USP)instacron:USPLiberar o conteúdo para acesso público.info:eu-repo/semantics/openAccesseng2023-08-02T11:39:59Zoai:teses.usp.br:tde-30052019-103210Biblioteca Digital de Teses e Dissertaçõeshttp://www.teses.usp.br/PUBhttp://www.teses.usp.br/cgi-bin/mtd2br.plvirginia@if.usp.br|| atendimento@aguia.usp.br||virginia@if.usp.bropendoar:27212023-08-02T11:39:59Biblioteca Digital de Teses e Dissertações da USP - Universidade de São Paulo (USP)false
dc.title.none.fl_str_mv Structural control and genesis of the Au-quartz veins from the Serra do Cavalo Magro orogenic gold deposit, southern Ribeira Belt, Brazil
Structural control and genesis of the Au-quartz veins from the Serra do Cavalo Magro orogenic gold deposit, southern Ribeira Belt, Brazil
title Structural control and genesis of the Au-quartz veins from the Serra do Cavalo Magro orogenic gold deposit, southern Ribeira Belt, Brazil
spellingShingle Structural control and genesis of the Au-quartz veins from the Serra do Cavalo Magro orogenic gold deposit, southern Ribeira Belt, Brazil
Malta, Isaac Siles
Au-quartz veins
Comportamento falha-válvula
Depósito de ouro orogênico da Serra do Cavalo Magro
Fault-valve behavior
Fluid inclusions
Gold precipitation
Inclusões fluídas
Precipitação de ouro
Processos de falhamento sísmico
Seismic faulting processes
Serra do Cavalo orogenic gold deposit
Veios de quartzo auríferos
title_short Structural control and genesis of the Au-quartz veins from the Serra do Cavalo Magro orogenic gold deposit, southern Ribeira Belt, Brazil
title_full Structural control and genesis of the Au-quartz veins from the Serra do Cavalo Magro orogenic gold deposit, southern Ribeira Belt, Brazil
title_fullStr Structural control and genesis of the Au-quartz veins from the Serra do Cavalo Magro orogenic gold deposit, southern Ribeira Belt, Brazil
title_full_unstemmed Structural control and genesis of the Au-quartz veins from the Serra do Cavalo Magro orogenic gold deposit, southern Ribeira Belt, Brazil
title_sort Structural control and genesis of the Au-quartz veins from the Serra do Cavalo Magro orogenic gold deposit, southern Ribeira Belt, Brazil
author Malta, Isaac Siles
author_facet Malta, Isaac Siles
author_role author
dc.contributor.none.fl_str_mv Faleiros, Frederico Meira
dc.contributor.author.fl_str_mv Malta, Isaac Siles
dc.subject.por.fl_str_mv Au-quartz veins
Comportamento falha-válvula
Depósito de ouro orogênico da Serra do Cavalo Magro
Fault-valve behavior
Fluid inclusions
Gold precipitation
Inclusões fluídas
Precipitação de ouro
Processos de falhamento sísmico
Seismic faulting processes
Serra do Cavalo orogenic gold deposit
Veios de quartzo auríferos
topic Au-quartz veins
Comportamento falha-válvula
Depósito de ouro orogênico da Serra do Cavalo Magro
Fault-valve behavior
Fluid inclusions
Gold precipitation
Inclusões fluídas
Precipitação de ouro
Processos de falhamento sísmico
Seismic faulting processes
Serra do Cavalo orogenic gold deposit
Veios de quartzo auríferos
description The Serra do Cavalo Magro orogenic gold deposit is located in the southern Ribeira Belt, Brazil. Gold-quartz veins are hosted by Calymmian (1500-1450 Ma) metasedimentary and metabasic rocks and Ediacaran (610-600 Ma) granitic rocks. Petrological modeling indicates peak metamorphic conditions from 560°C and 7 kbar (chlorite-biotite phyllite) to 625°C and 6.8 kbar (garnet-biotite phyllite) recorded in immediate host rocks. Gold mineralization occurs in extensional and shear quartz veins structurally-controlled by NE-trending second-third order sinistral transcurrent shear zones. NNW-trending, vertical and subhorizontal extensional veins are oriented 55-85° in relation to the fault planes, indicating that the shear zones were severely misoriented for frictional react ivation. Deformation within the shear zones was accommodated by bulging recrystallization of quartz aggregates, while feldspar aggregates from granitic protoliths underwent cataclastic flow or were replaced by sericite-epidote producing phyllonites. Gold precipitated during stages of vein deformation within microfractures in my lonitized shear veins with quartz previously subjected to bulging recrystallization. Ore-fl uids are recorded in coexisting C02-N2, l-hO-NaCl-CaCh and H20-C02-N2-NaCI-CaCh fluid inclusions oflow to moderate salinities (1-18 w1.%NaCl eq.). Microthennometric data indicate entrapment conditions of240-260 °C and 0.4-2.5 kbar, recording hydrostatic to supralithostatic fluid pressure conditions. High-temperature l-hO-NaCl-CaCh-KCl brine inclusions (up to 475 DC, 25-33 wt.% aCl eq.) are considered unrelated with gold mineralization. Strong fluid pressure fluctuations from 0.4 to 1.6 kbar are associated with earthquake cycles and the faultvalve behavior. In this scenario, gold mineralization was associated with fluid immiscibility. There is evidence for restricted fluid mixing, but this process is interpreted as unrelated with gold mineralization. Available geochronological data and structural-petrological relationships with host rocks and shear zones indicate that mineralization was formed within 580-540 Ma in post-peak metamorphic episodes. The hydrothermal ore-fluids were likely produced by devolatilization reactions during prograde metamorphism at deeper levels. Subsequently, the metamorphic-hydrothermal fluids were channeled upwards within the strike-slip shear zones into rocks that have been metamorphosed and devolatilized at earlier times.
publishDate 2018
dc.date.none.fl_str_mv 2018-12-21
dc.type.status.fl_str_mv info:eu-repo/semantics/publishedVersion
dc.type.driver.fl_str_mv info:eu-repo/semantics/masterThesis
format masterThesis
status_str publishedVersion
dc.identifier.uri.fl_str_mv https://www.teses.usp.br/teses/disponiveis/44/44143/tde-30052019-103210/
url https://www.teses.usp.br/teses/disponiveis/44/44143/tde-30052019-103210/
dc.language.iso.fl_str_mv eng
language eng
dc.relation.none.fl_str_mv
dc.rights.driver.fl_str_mv Liberar o conteúdo para acesso público.
info:eu-repo/semantics/openAccess
rights_invalid_str_mv Liberar o conteúdo para acesso público.
eu_rights_str_mv openAccess
dc.format.none.fl_str_mv application/pdf
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dc.publisher.none.fl_str_mv Biblioteca Digitais de Teses e Dissertações da USP
publisher.none.fl_str_mv Biblioteca Digitais de Teses e Dissertações da USP
dc.source.none.fl_str_mv
reponame:Biblioteca Digital de Teses e Dissertações da USP
instname:Universidade de São Paulo (USP)
instacron:USP
instname_str Universidade de São Paulo (USP)
instacron_str USP
institution USP
reponame_str Biblioteca Digital de Teses e Dissertações da USP
collection Biblioteca Digital de Teses e Dissertações da USP
repository.name.fl_str_mv Biblioteca Digital de Teses e Dissertações da USP - Universidade de São Paulo (USP)
repository.mail.fl_str_mv virginia@if.usp.br|| atendimento@aguia.usp.br||virginia@if.usp.br
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