GEOLOGIA ESTRUTURAL E IDADE 40Ar/39Ar DO DEPÓSITO DE OURO PAU-A-PIQUE, FAIXA MÓVEL AGUAPEÍ, SUDOESTE DO ESTADO DE MATO GROSSO

Abstract

ResumoO depósito aurífero Pau-a-Pique localiza-se na porção sudoeste do Cráton Amazônico na parte sul da Faixa Móvel Aguapeí. O minério é constituído por sistemas de veios de quartzo e disseminações nas rochas da Formação Fortuna, porção basal do Grupo Aguapeí, de idade Mesoproterozóica. O mapeamento geológico do depósito Pau-a-Pique mostrou que o minério aurífero é controlado pela Zona de Cisalhamento Corredor. Esta estrutura estabelece o contato entre metaconglomeradodo Grupo Aguapeí e granito-gnaisses do Terreno Santa Helena. A deformação rúptil-dúctil imposta pelo cisalhamento regional converteu as rochas metassedimentaresem diversos tipos de milonitos, as quais facilitaram a percolação de fluidos hidrotermais. Em escala local, o minério é condicionado por falhas inversas subsidiárias a Zona de Cisalhamento Corredor, que colocam em contato o metaconglomerados com um corpo de anfibólio-biotita-clorita milonito xisto. O estudo petrográfico possibilitou a identificação de microtexturas de deformação e recuperação no minério. Datações 4°ArP9Ar em sericitas obtidas junto aos veios hidrotermais nos depósitos Pau-a-Pique e Ellus, porções norte e sul da Zona de CisalhamentoCorredor,apresentam idades entre 908,1 ± 0,9Ma e 927 ± lMa para a mineralização, as quais indicam circulação de fluidos hidrotermais nas rochas metassedimentares do Grupo Aguapeí durante as etapas finais de cisalhamento gerado pela Orogenia Sunsás-Aguapeí,dando um caráter epigenéticoà formação dos depósitos.Palavras chaves: Minério aurífero, rochas miloníticas, alteração hidrotermal, controles do minério, zona de cisalhamento, idades 4°ArP9Ar. Abstract THE PAU-A-PIQUE GOLD DEPOSlT OCURRS lN THE SOUTHWESTERN PORTION OF THE AMAZONlAN CRATON, STATE OF MATO GROSSO, CENTRAL BRAZlL.The ore is represented by quartz veins systems and disseminated in the metassedimentary rocks from the Aguapeí Group. These rocks was strongly deformed by the Sunsás-Aguapeí Orogeny (1.28-0.95Ga). The geological mapping of Pau-a-Pique deposit revealed that gold ore in the regional scale was controlled by the Corredor ShearZone. This structure forms the contact between the metaconglomerate,which belongs to the Group Aguapeí, with a granite-gneisses from the Santa Helena Terrane. The brittle-ductil deformation had converted the host-rock in many kinds of mylonite facilitating hydrothermal fluid percolation. ln local scale, ore is controlled by inverse faults subsidiary to Corredor Shear Zone, which form the contact between the metaconglomerateand an arnphibole-biotite-chlorite mylonite schist layer. The petrographic study identifieddeformationand recovery microtexturesin ore. 40ArP9Ar ages from sericite ofthe hydrothermalveins in the Pau-a-Pique and Ellus deposits, north and south portions ofthe Corredor Shear Zone, suggest 908.1 ± 0.9Ma e 927 ± lMa ages for mineralization.These ages indicate hydrothermalfluids circulationin the Aguapeí Group metassedimentaryrocks during the final stage ofthe Sunsás-AguapeíOrogeny. Geochronologicaland structural data combined with petrographic ...

A review of the tectonic evolution of the Sunsás belt, SW Amazonian Craton

“…As such the Aguapeí belt, in contrast with Sunsás orogenic framework (in Bolivia), exhibits only localized deformation and low-grade metamorphism (e.g., Geraldes et al, 2001), as given by gentle folds (upright to northeast dipping) and shears of NW trending. The deformation related to this event is characterized by recrystallized mylonites that yielded K/Ar and 40 Ar/ 39 Ar mica ages between 960-910 Ma (e.g., Geraldes et al, 1997;Fernandes et al, 2006;Ruiz et al, 2007).…”

“…Furthermore, these structures control occurrences of gold in the state of Mato Grosso (e.g., Fernandes et al, 2006) and in the Don Mario mineral district in Bolivia (Litherland et al, 1986). The latter district hosts important Au-Cu among other metals occurrences produced by hydrothermal mineralization , and is tectonically controlled by shear zones of the San Diablo front (see Fig.…”

Tectonic evolution of the southern margin of the Amazonian craton in the late Mesoproterozoic based on field relationships and zircon U-Pb geochronology

“…The Aguapeí Group exhibits pervasive deformation and low-grade metamorphism (e.g., Geraldes et al 2001, Ruiz 2005 Ma (e.g., Geraldes et al 1997, Fernandes et al 2006, Ruiz et al 2007). Because of the occurrence side by side of folded and sheared rocks (Sunsás and Aguapeí Groups) and flat-lying and unmetamorphosed rocks (Huanchaca and Ricardo Franco ridges), Santos et al (2002) prefer the usage of Aguapeí I for the folded and metamorphosed unit and Aguapeí II for the flat-lying cover.…”