Características epigenéticas do depósito de cu-au chapada, arco magmático de goiás

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The Cu-Au Chapada deposit is located from 8km of Alto Horizonte-GO. The geologic picture is dominated by metavulcanic sedimentary sequences that integrate the Neoproterozoic Magmatic Arc of Mara Rosa, located in the central portion of the Tocantins Province. The framework of the deposit is represented by an antiform whose core is composed by association of the magnetite-biotite gnaisse and muscovite-biotite schist surrounded for amphiboles schist, biotite-muscovite schist, metacherts, metavulcanoclastics rocks, anfibolitics bodies and kyanite-quartz schist. These rocks are cut by pegmatite dikes oriented towards N40-60W. The core of biotite gneiss corresponding to a plutonic body acid to intermediate, typical of volcanic arc environment, with calc-alkaline character, and the association of metavulcanoclastics rocks, amphibolites and metacherts involving is related to a metavolcanic-sedimentary sequence. The Cu-Au Chapada ore is formed predominantly by the association chalcopyrite-pyrite-magnetite, whichever associations chalcopyrite-magnetite (magnetite ore) or chalcopyrite-pyrite (iron pyrites), with subordinate occurrence of galena, sphalerite and bornite. U-Pb data provided age of 884.99.4 Ma for kyanite-epidote-muscovite-biotite feldspathic schist, which represents the crystallization age of volcanic rocks, considered the protolith of association metavolcanosedimentary rocks, and an age of 864.95.6 Ma for biotite gneiss, corresponding to the age of crystallization of igneous protolith. The Sm-Nd isotopic data from rocks of the Cu-Au Chapada Deposit, with εNd positive and TDM between 0.92 and 1.73 Ga, show the juvenile character for the rocks. The deformational history of the Cu-Au Chapada Deposit comprises three phases of deformation. Phase Dn is represented by isoclinal recumbent folds, resulting in compressive stress EW to NW-SE, in association with amphibolite facies metamorphic. Phase Dn+1 is related to the Rio dos Bois shear zone, with drag and intrafolial folds which asymmetry indicate general vergence to the SE, in association with green-schist facies metamorphic. Phase deformational later, Dn+2, is related to regional smooth folding of foliation, oriented approximately EW and NS, resulting in an interference pattern like dome-and-basin. Phase Dn+2 is also associated with the development of NS and EW fractures responsible for the remobilization of Cu and Au and precipitation of carbonate and epidote. Two genetic hypotheses have been presented for the mineralization: one suggests that the deposit was generated by processes similar to those involved in the genesis of porphyry Cu-Au deposits, in arcs of intra-oceanic islands, while another defends on the combination of processes involving hydrothermal activities volcano-exalative and magmatic epithermal, followed by metamorphic remobilization in amphibolite facies, generally known as porphyritic epitermal system metamorphosed or modified. In this work, it is understood that only part of the formation of the Cu-Au Chapada deposit is associated with magmatic processes described in hydrothermal deposits of porphyry Cu-Au, between 900 and 850 Ma. Evidence shows that the genesis of the Cu-Au Chapada deposit is also related to epigenetic hydrothermal processes, marked by the transformation of magnetite-biotite gneiss to muscovite-biotite schist, associated with the deformation of Rio dos Bois shear zone at the end of the Brazilian Orogeny, between 600 and 560 Ma. In this sense, it is assumed that part of the deposit, called Capacete, is interpreted as an orogenic Cu-Au deposit or Intrusion Related developed during collisional magmatism stage syn to late-tectonic.

ASSUNTO(S)

epigenetic arco magmático neoproterozóico depósito de cu-au porfirítico geologia neoproterozoic magmatic arc deposit porphyry cu-au epigenético

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