Geologia, petrografia e geocronologia das rochas do depósito aurífero Ouro Roxo, Província Tapajós, Jacareacanga (PA), Brasil

Abstract

The Ouro Roxo gold deposit lies near the city of Jacareacanga, Tapajós Gold Province, southwestern of Pará, Brazil. The Ouro Roxo deposit comprises a hydrothermal system of sulfide quartz veins hosted by mylonite granitoid Tropas Intrusive Suit of Paleoproterozoic age and controlled by the N-S trending Ouro Roxo-Canta Galo shear zone (OCSZ). The host granitoids are oxidized calc-alkaline granodiorite and tonalite of magmatic arc filiation. The OCSZ is a sinistral oblique ductile-brittle shear, which belongs to the third deformation event of the Tapajós Province and has turned the granitoids into protomylonites, mylonites and breccias. The NNE-SSW mylonitic foliation dipping to ESE and stretch lineation in quartz grains indicate the tectonic movement to NW. Mineralized quartz veins and pipes are hosted by mylonites and breccias and surrounded by hydrothermal alteration halos. Besides silicification and sulfidation, concentrated in the ore bodies, three types of wall-rock alteration occur: propilitization (chlorite + phengite + carbonate); phylic alteration (phengite + quartz + carbonate + pyrite); carbonatization. Besides magmatic quartz and microcrystalline quartz of mylonites, five generations of hydrothermal quartz were recognized in the lodes. The isotopic Pb-Pb data do not support a genetic relationship between the gold deposit and the Tropas granitoids, being the deposit coeval to Maloquinha granite. The orogenic environment, the veining style, the structural control, the hydrothermal alteration and the metallic association (Au + Cu + Bi), are all consistent with a mesozona-epizona orogenic model for the genisis of the Ouro Roxo deposit.