Título:	Geologia e controle estrutural dos veios mineralizados em ouro dos depósitos cocal e ouro fino, grupos Paranoá e Serra da Mesa, norte de Goiás
Autor(es):	Lobo, Ricardo Luiz de Morais
Orientador(es):	Souza, Valmir da Silva
Assunto:	Geologia estrutural Ouro orogênico Quartzo Ouro
Data de publicação:	22-Jun-2018
Data de defesa:	29-Set-2017
Referência:	LOBO, Ricardo Luiz de Morais. Geologia e controle estrutural dos veios mineralizados em ouro dos depósitos cocal e ouro fino, grupos Paranoá e Serra da Mesa, norte de Goiás. 2017. 131 f., il. Dissertação (Mestrado em Geologia)—Universidade de Brasília, Brasília, 2017.
Abstract:	The Cocal and Ouro Fino deposits are comprised of a system of structurally controlled gold bearing quartz veins situated in the footwall and hangingwall respectively of the Rio Maranhão Fault. These deposits are hosted by the metamorphosed sediments of the Paranoá e Serra da Mesa Groups. These Groups are an important part of the Brasília Belt colisional accretionary orogen of the Tocantins Province and formed progressively in the concluding stages of the Brasiliano Orogeny. Rock types identified within the area are schists, phyllites, quartzites and carbonates with the first three hosting the mineralised system. These rocks were metamorphosed to greenschist facies , chlorite and biotite zones. The gold bearing quartz veins have been worked since the 18th Century and some areas are still being worked by informal miners (‘Garimpeiros’). Several Mining Companies have conducted exploration work within the area and have reported grades of up to 45 grams/Tonne of gold. Three principal phases of deformation have been identified in the deposits studied. The first phase was a compressive event in an E-W direction developed in a principally ductile lithosphere and generating the S1 foliation with a regional and pervasive character and generating veinlets of quartz-carbonate, gold mineralisation in low angle shear zones, isoclinal folds, flattening and stretching in coaxial or non-coaxial regimes. A second phase of deformation under brittleductile lithosperic conditions generated extensional fractures which host veins of gold bearing quartz (±carbonate), and also reactivated older structures. A third phase of brittle deformation generated fractures and faults, some quite deep, and intruded by basic magnetic dykes. Three principal families of quartz (± carbonate) veins and veinlets have been identified. The first family is syn-tectonic with S1 deformation and is locally gold bearing and is designated as Syn-tectectonic Veining (VST). A system made up of two vein families with gold mineralisation is associated with the generation of extensional fractures during the second phase of deformation, and is denominated as Late Tectonic Veining VTT1 (Cocal) and VTT2 (Ouro Fino). In the Cocal Deposit gold occurs free and/or as inclusions in masses or within subhedral crystals of pyrite and with silver contents from 4.87 to 17.69%. Hydrothermal alteration has resulted in enrichment of the rocks in Si. (quartz), Ca. (carbonates), K. (micas), B. (tourmalines), S. (sulphides), Fe. (pyrite, magnetite), gold and silver. Preliminary isotope geochemistry of carbon, oxygen and sulphur from the Cocal Deposit seems to exclude the possibility that mineralising fluids originated in the lower crust (or mantle) or from organic carbon in sediments and suggest the fluids originated in the upper crust and especifially from chemical sediments (marine limestones). The regional concentration of gold mineralisation within the Paranoá and Serra da Mesa Groups along the trace of the Rio Maranhão Fault allows the definition of an Orogenic Gold Belt at least in the northern part of the Brasília Belt. The Cocal and Ouro Fino deposits show lithological and structural controls which allow them to be classed as Orogenic Gold Deposits as described by Mitchell & Garson (1981) and Groves et al. (1998).
Unidade Acadêmica:	Instituto de Geociências (IG)
Informações adicionais:	Dissertação (mestrado)—Universidade de Brasília, Instituto de Geociências, Programa de Pós-Graduação em Geologia, 2017.
Programa de pós-graduação:	Programa de Pós-Graduação em Geologia
Licença:	A concessão da licença deste item refere-se ao termo de autorização impresso assinado pelo autor com as seguintes condições: Na qualidade de titular dos direitos de autor da publicação, autorizo a Universidade de Brasília e o IBICT a disponibilizar por meio dos sites www.bce.unb.br, www.ibict.br, http://hercules.vtls.com/cgi-bin/ndltd/chameleon?lng=pt&skin=ndltd sem ressarcimento dos direitos autorais, de acordo com a Lei nº 9610/98, o texto integral da obra disponibilizada, conforme permissões assinaladas, para fins de leitura, impressão e/ou download, a título de divulgação da produção científica brasileira, a partir desta data.
Aparece nas coleções:	Teses, dissertações e produtos pós-doutorado

Os itens no repositório estão protegidos por copyright, com todos os direitos reservados, salvo quando é indicado o contrário.