Breaking up the temporal link between granitic magmatism and iron oxide-copper-gold (IOCG) deposits in the Carajs Mineral Province, NW Brazil

Iron oxide-copper-gold (IOCG) deposit genesis is often genetically linked to magmatism due to temporal association between granite and mineralization and participation of magma-derived components. In the Carajas Mineral Province, NW Brazil, a set of ca. 2.6-2.5 Ga IOCG deposits has been interpreted to be genetically linked to contemporary granite, which are located along the Cinzento Shear Zone, in the northern part of the province. Despite the apparent temporal correlation, the understanding of ca. 2.5 Ga ages as magmatic may be misleading, since ca. 2.6-2.5 Ga reset ages have been previously reported for deformed and hydrothermally altered granites crystallized at ca. 2.74 Ga. We studied the morphology, texture, and composition of 2.74-2.73 Ga, 2.68 Ga, 2.64-2.62 Ga, and 2.59-2.55 Ga zircons from variably deformed and metasomatized granites located along the Cinzento Shear Zone. Our study reveals re-equilibrated magmatic, deformed, and newly grown zircon domains with compositional changes (Ta, U, Y, and LREE enrichment relative to chondrite) that inconsistently follow textural patterns. The overprint arises from diffusion-reaction, coupled-dissolution-reprecipitation processes, and alteration of metamict zircons, likely aided by alkaline (Na-K-rich) and F-Cl-rich hydrothermal fluids that circulated regionally in the Carajas Province. Such processes account for disturbances and resetting of the U-Th-Pb isotopic system in zircon; therefore, the geochronological record in granites from our study can be associated with the first (ca. 2.72-2.68 Ga) and the second (ca. 2.6-2.5 Ga) IOCG-forming hydrothermal events rather than to igneous crystallization. In this context, we rule out a temporal link between granitic magmatism and the IOCG deposits at Carajas.