Characterization of the hydrothermal alteration and ore zones of The Rio Vermelho Prospect: A new iocg mineralization in The Carajás province

The Rio Vermelho prospect is located in the eastern sector of the Carajás Mineral Province, near to the contact with the metasediments of the Araguaia Fold Belt. The mineralization is located in a horse splay zone of the Carajás Fault, near to the Cristalino IOCG deposit. The ore is hosted by Archean deformed granitoids affected by multi-stages hydrothermal alteration controlled by NNW-SSE structures. Geological mapping and detailed drill core logging associated to petrographic studies allowed the identification of different hydrothermal stages. The hydrothermal alteration starts with a sodic system, preserved only in distal areas, in which albite replaces the original feldspars in regional deformed granites and fills a stockwork vein system in metadiorite/metagabbro rocks. The excess of silica after original feldspars transformation forms quartz in the sodic paragenesis. The presence of actinolite in metadiorite/metagabbro, although restricted to distal areas, might be suggestive of local coeval calcic alteration. Pervasive potassification, represented by the crystallization of microcline together with quartz, overprints the albite paragenesis and occurs proximal to the ore zone. Chloritization occurs in two different stages, pre- and syn-mineralization. The pre-mineralization is characterized by pervasive lamellar chlorite I associated with epidote and quartz. The syn-mineralization is marked by fibro-radial chlorite II, enriched in FeAl and Mn, and associated with iron oxide and copper sulfides filling veins and breccias. Before the mineralization stage, silicification marks the beginning of the brecciacion phase producing quartz veins. The copper mineralization stage, with ore filling breccias dominated by chalcopyrite with subordinate bornite, occurs associated with abundant hematite replacing early magnetite crystals. Sericitization is a continuous post-mineralization process producing pervasive finely scaled white mica that is followed by epidote and carbonate formation during the last hydrothermal alteration phase. The hydrothermalism starting with sodic-calcic phases and ending with low-k potassic phase suggests a temperature ranging from >500 to <300 °C. The transition from high temperature sodic and potassic alteration to low temperature in the ore zone in a ductil-brittle environment, suggest a possible input of externally-derived fluids. The abundant hematite derived from magnetite transformation indicates extremely oxidized fluids and suggests a depositional temperature <350° during the ore formation. The hydrothermal characteristics of the copper mineralization of the Rio Vermelho Prospect suggest a shallow IOCG type dominated by hematite. Its regional position at the borders of the Araguaia Fold Belt, possibly not affected by the Neoproterozoic processes, opens a new area for exploration in the easternmost part of the Carajás Domain.