Shearing and fluid evolution of the Porto Nacional orogenic gold district, western Brazil: microstructural, fluid inclusion, and C-O isotopic evidence

•Brazilian Porto Nacional Gold District is classified as an orogenic gold system.•Porto Nacional Gold District is composed of hypozonal and mesozonal deposits.•Veins and veinlets evolved from supralithostatic to hydrostatic pressure regimes.•Ore assemblages comprise graphite, pyrite, gold, and galena, chalcopyrite, gold.•Fluids source was metamorphic fluids and the graphite biogenic.