Análise microtectônica em zonas de alteração hidrotermal e mineralização do depósito pantera, provincia carajás, cráton amazônico

Abstract

The Carajás Province (3.0–2.5 Ga), located in the southeastern portion of the Amazonian Craton, is recognized for having several types of world-class mineral deposits, with emphasis on iron oxide, copper and gold deposits (iron-copper-gold oxide (IOCG) deposits from the Neoarchean (ca. 2.7 and 2.5 Ga) and Paleoproterozoic (ca. 1.8 Ga). The province was divided into Carajás (north) and Rio Maria (south) domains. The IOCG mineralization data show that the superimposition of hydrothermal events is frequent in the formation of deposits. Furthermore, the percolation of mineralizing fluids is strongly controlled by shear zone features (eg. S surfaces; extensional shear bands, among others). Therefore, the advance in the understanding of the temporal relationship between mineralization and deformation depends on detailed studies, with a special focus on microtectonics. Considering this knowledge gap, the work used the microstructural to characterize the hydrothermal alteration and deformation of the IOCG mineralization of the Pantera reservoir located in the northern region of the Rio Maria Domain controlled by subsidiary structures of the Canaã Shear Zone (WNW-ESE). One methodological approach involved the description of thin and thin-polished sections of zones of hydrothermal alteration and mineralization of the reservoir. This provided an identification of features related to deformation in the shear zone among the hydrothermal paragenesis of the reservoir in different zones. The mineral paragenesis described in protomylonites is compatible with the range 250-500°C and 500-700°C, with conversion of dynamic recrystallization and static recrystallization occurring with fluid pressure between 50 and 100 Mpa respectively for the ranges. Comparing in parallel the temperature and pressure conditions of the greenschist facies and lower amphibolite facies. It is interpreted from the microstructural data that the protomilonita with hydrothermal paragenesis shared by the mineralization, are post magmatic crystallization and syntectonic.