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Título

THE PANTERA IOCG DEPOSIT: A SYN-KINEMATIC COPPER MINERALIZATION ALONG THE CANAÃ SHEAR SYSTEM, CARAJÁS DOMAIN

Texto do resumo

The tectonic setting of the Carajás Province, southern portion of the Amazon craton, is formed by the Rio Maria Domain to the south and the Carajás Domain to the north. The Rio Maria Domain comprises typical greenstone belt sequences and TTGs of Mesoarchean, whereas the Carajás Domain consists of Neoarchean volcano-sedimentary sequences overlying Mesoarchean basement rocks and crosscut by roughly coeval mafic-ultramafic and granitoids intrusions. The Carajás Domain is structurally divided into three main shear-systems: Canaã, Cinzento and Carajás. The Canaã shear system is an E-W trend anastomosing lineament that controls, on a regional scale, the spatial distribution of several economically important 2.7 Ga iron-oxide-copper-gold (IOCG) deposits, including the Pantera deposit (20.8 Mt @ 1.7 % Cu and 0.2 g/t Au). The regional deformation at the Pantera IOCG deposit has been investigated based on field work data, kinematic analyses on macroscopic and microscopic scales, and integrated with in situ titanite U-Pb geochronology. The Pantera IOCG deposit is hosted by granitoids of the Mesoarchean Ourilândia plutonic suite particularly where affected by the Ourilândia shear zone, a splay of the Canaã shear system. The deformed granitoids along the Ourilândia shear zone show an east-west strike and have subvertical (>70°) mylonitic foliation, containing strike-slip (10-14° to W-ESE) and oblique (15-40° to NE) lineations. The sheared host granitoids display distinct hydrothermal alteration zones the following order of formation: sodic-calcic (albite-epidote-hastingsite-titanite 2), calcic-iron (actinolite-apatite-magnetite-chalcopyrite) and potassic-silicifica (biotite-quartz). In thin section, amphibole of sodic-calcic alteration shows sigmoid microstructure indicating sinistral shear sense. A syn-kinematic actinolite on paragenesis with chalcopyrite string shows crystals with domino fragmentation favorable to Ourilândia shear zone nucleation. Hydrothermal titanite syn-kinematic to these amphibole microstructures and preferentially oriented in the S-C’ foliation of the sodic-calcic altered mylonitic granitoids yield a formation age of 2.7 Ga. At the shear zone boundaries, synthetic en echelon veins are related to antithetic shear fractures filled by albite-epidote. The late potassium-silicifica alteration stage is controlled by microstructures with dextral sense of shear along the Ourilândia shear zone. For instance, biotite occurs orientated along the C-C’ foliation, shear band boudin, magnetite δ-type porphyroclast and kink bands. Titanite of the sodic-calcic alteration and titanite located along kink band show recrystallization ages ranging from 2.2 to 2.0 Ga. Recrystallized titanite crystals and microstructures show evidences of a dynamic metamorphism at the Ourilândia shear zone. It highlights a Rhyacian reactivation period in the shear zone during the Transamazonic event that promotes the remobilization and reworking of the copper mineralization at the Pantera IOCG deposit.

Palavras Chave

U-Pb geochronology; Structural; Heterogeneous strain