Artigo

The mineralizing fluid in the Piaba gold deposit, São Luís cratonic fragment (NW-Maranhão, Brazil) based on fluid inclusion studies in quartz veins

Piaba is the first gold mine to operate in the São Luís cratonic fragment, NW-Maranhão, northern Brazil. The geological setting comprises chiefly metavolcano-sedimentary sequences (Aurizona Group) and subduction-related granitoids (Tromaí Intrusive Suite), formed in island arc between 2240 and 2150...

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Autor principal: FREITAS, Saney Cecílio Ferreira de
Outros Autores: KLEIN, Evandro Luiz
Grau: Artigo
Idioma: eng
Publicado em: 2015
Assuntos:
Metalogênese
Inclusões fluídas
Ouro
CO2
Depósito aurífero de Piaba
Cráton São Luís
Maranhão - Estado
Acesso em linha: http://repositorio.ufpa.br/jspui/handle/2011/6434
id ir-2011-6434
recordtype dspace
spelling ir-2011-64342018-01-08T17:25:29Z The mineralizing fluid in the Piaba gold deposit, São Luís cratonic fragment (NW-Maranhão, Brazil) based on fluid inclusion studies in quartz veins O fluido mineralizador no depósito aurífero Piaba, Fragmento Cratônico São Luís (NW-Maranhão, Brasil), com base em estudos de inclusões fluidas em veios de quartzo FREITAS, Saney Cecílio Ferreira de KLEIN, Evandro Luiz Metalogênese Inclusões fluídas Ouro CO2 Depósito aurífero de Piaba Cráton São Luís Maranhão - Estado Piaba is the first gold mine to operate in the São Luís cratonic fragment, NW-Maranhão, northern Brazil. The geological setting comprises chiefly metavolcano-sedimentary sequences (Aurizona Group) and subduction-related granitoids (Tromaí Intrusive Suite), formed in island arc between 2240 and 2150 Ma. Gold mineralization is hosted in a fine-grained granophyric granodiorite (Piaba Granophyre) and in a subvolcanic andesite of the Aurizona Group. The mineralized zone is confined within the limits of the Piaba fault (ENE-WSW-trending brittle-ductile shear zone) and consists of quartz veins and veinlets and accompanying hydrothermal haloes (chlorite + muscovite + carbonate + pyrite + chalcopyrite + gold) disposed in stockwork geometry. Petrographic, microthermometric and microRaman spectroscopic studies of quartz have defined two- and three-phase aqueous-carbonic fluid inclusions produced by heterogeneous trapping during phase separation, in addition to late aqueous fluids. The mineralizing solution is an aqueous-carbonic fluid composed of CO2 (5 - 24 mol%), H2O (74 - 93 mol%), N2 (< 1 mol%) and CH4 (< 1mol%). It presents low salinity (5.5 wt.% NaCl equivalent) and density of 0.96 - 0.99 g/cm3). Ore deposition occurred at 267 - 302ºC and 1.25 - 2.08 kbars, corresponding to 4 - 7 km in depth, in agreement with the structural information. The P-T-X and reduced characteristics (log ƒO2 -31.3 to -34.3) of the fluid, combined with host rock sulfidation, altogether indicate that gold has been transported as a sulfur complex and that ore deposition occurred in response to phase separation and lowering of the sulfur activity and ƒO2 during fluid-rock interaction. O depósito aurífero de Piaba tornou-se a primeira mina em operação no fragmento cratônico São Luís, noroeste do Maranhão. Seu ambiente geológico compreende rochas metavulcanossedimentares do Grupo Aurizona e granitoides da Suíte Tromaí, entre outras unidades menores, formadas em ambiente de arcos de ilhas entre 2240 e 2150 Ma, juntamente com outras unidades menores. A mineralização é caracterizada por uma trama stockwork de veios e vênulas de quartzo com seus halos de alteração (clorita + muscovita + carbonato + pirita + calcopirita e ouro) hospedada em um granodiorito granofírico fino (Granófiro Piaba) e em rocha subvulcânica andesítica do Grupo Aurizona. O corpo mineralizado é espacialmente limitado à zona de cisalhamento ENE-WSW rúptil-dúctil (Falha Piaba). Estudos petrográficos, microtermométricos e por espectroscopia microRaman no quartzo definiram inclusões aquo-carbônicas bifásicas e trifásicas, produzidas por aprisionamento heterogêneo durante separação de fases, e fluidos aquosos tardios. A solução mineralizadora corresponde a um fluido aquo-carbônico composto por CO2 (5 - 24 mol%, densidade de 0,96 - 0,99 g/cm3), H2O (74 - 93 mol%), N2 (< 1 mol%), CH4 (<1mol%) e 5,5 % em peso NaCl equivalente. O minério depositou a 267 - 302ºC e 1,25 - 2,08 kbar, correspondendo a profundidades de 4 a 7 km, em consonância com o regime estrutural. A composição e o intervalo de P-T do fluido mineralizador, combinados com o caráter redutor (log ƒO2 -31,3 a -34,3) e a sulfetação da rocha hospedeira, sugerem que o ouro foi transportado como um complexo sulfetado. O minério foi depositado em consequência da separação de fase, redução da atividade de enxofre e da ƒO2 pela interação fluido-rocha. 2015-03-16T16:42:13Z 2015-03-16T16:42:13Z 2013-03 Artigo de Periódico FREITAS, Saney C. F. de; KLEIN, Evandro L. The mineralizing fluid in the Piaba gold deposit, São Luís cratonic fragment (NW-Maranhão, Brazil) based on fluid inclusion studies in quartz veins. Brazilian Journal of Geology, São Paulo, v. 43, n. 1, p. 70-84, mar. 2013. Disponível em: <http://ppegeo.igc.usp.br/pdf/bjg/v43n1/a07v43n1.pdf>. Acesso em: 10 mar. 2015. <http://dx.doi.org/http://dx.doi.org/10.5327/Z2317-48892013000100007>. 2317-4889 http://repositorio.ufpa.br/jspui/handle/2011/6434 eng Acesso Aberto application/pdf
institution Repositório Institucional - Universidade Federal do Pará
collection RI-UFPA
language eng
topic Metalogênese
Inclusões fluídas
Ouro
CO2
Depósito aurífero de Piaba
Cráton São Luís
Maranhão - Estado
spellingShingle Metalogênese
Inclusões fluídas
Ouro
CO2
Depósito aurífero de Piaba
Cráton São Luís
Maranhão - Estado
FREITAS, Saney Cecílio Ferreira de
The mineralizing fluid in the Piaba gold deposit, São Luís cratonic fragment (NW-Maranhão, Brazil) based on fluid inclusion studies in quartz veins
topic_facet Metalogênese
Inclusões fluídas
Ouro
CO2
Depósito aurífero de Piaba
Cráton São Luís
Maranhão - Estado
description Piaba is the first gold mine to operate in the São Luís cratonic fragment, NW-Maranhão, northern Brazil. The geological setting comprises chiefly metavolcano-sedimentary sequences (Aurizona Group) and subduction-related granitoids (Tromaí Intrusive Suite), formed in island arc between 2240 and 2150 Ma. Gold mineralization is hosted in a fine-grained granophyric granodiorite (Piaba Granophyre) and in a subvolcanic andesite of the Aurizona Group. The mineralized zone is confined within the limits of the Piaba fault (ENE-WSW-trending brittle-ductile shear zone) and consists of quartz veins and veinlets and accompanying hydrothermal haloes (chlorite + muscovite + carbonate + pyrite + chalcopyrite + gold) disposed in stockwork geometry. Petrographic, microthermometric and microRaman spectroscopic studies of quartz have defined two- and three-phase aqueous-carbonic fluid inclusions produced by heterogeneous trapping during phase separation, in addition to late aqueous fluids. The mineralizing solution is an aqueous-carbonic fluid composed of CO2 (5 - 24 mol%), H2O (74 - 93 mol%), N2 (< 1 mol%) and CH4 (< 1mol%). It presents low salinity (5.5 wt.% NaCl equivalent) and density of 0.96 - 0.99 g/cm3). Ore deposition occurred at 267 - 302ºC and 1.25 - 2.08 kbars, corresponding to 4 - 7 km in depth, in agreement with the structural information. The P-T-X and reduced characteristics (log ƒO2 -31.3 to -34.3) of the fluid, combined with host rock sulfidation, altogether indicate that gold has been transported as a sulfur complex and that ore deposition occurred in response to phase separation and lowering of the sulfur activity and ƒO2 during fluid-rock interaction.
format Artigo
author FREITAS, Saney Cecílio Ferreira de
author2 KLEIN, Evandro Luiz
author2Str KLEIN, Evandro Luiz
title The mineralizing fluid in the Piaba gold deposit, São Luís cratonic fragment (NW-Maranhão, Brazil) based on fluid inclusion studies in quartz veins
title_short The mineralizing fluid in the Piaba gold deposit, São Luís cratonic fragment (NW-Maranhão, Brazil) based on fluid inclusion studies in quartz veins
title_full The mineralizing fluid in the Piaba gold deposit, São Luís cratonic fragment (NW-Maranhão, Brazil) based on fluid inclusion studies in quartz veins
title_fullStr The mineralizing fluid in the Piaba gold deposit, São Luís cratonic fragment (NW-Maranhão, Brazil) based on fluid inclusion studies in quartz veins
title_full_unstemmed The mineralizing fluid in the Piaba gold deposit, São Luís cratonic fragment (NW-Maranhão, Brazil) based on fluid inclusion studies in quartz veins
title_sort mineralizing fluid in the piaba gold deposit, são luís cratonic fragment (nw-maranhão, brazil) based on fluid inclusion studies in quartz veins
publishDate 2015
url http://repositorio.ufpa.br/jspui/handle/2011/6434
_version_ 1832604243643596800
score 11.755432

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