The gold mineralization at the Enche Concha and Tunel prospects, northwestern portion of the Gurupi Belt, is hosted in dacites and phyllites that belong to the ca. 2160 Ma-old metavolcano-sedimentary Chega Tudo Formation. These host rocks are variably deformed, from a spaced cleavage to schistose and mylo-nitic varieties. The hosting structures have previously been defined as produced in the Paleoproterozoic. The hydrothermal alteration processes include carbonatization, sericitization, sulfidation, and quartz vei-ning. These processes are both pervasive and fissure-filling in style. Pyrite is largely predominant over chalcopyrite and sphalerite and gold occurs as a refractory phase in pyrite. Fluid inclusion, stable (O, H, C) and Sr isotopes studies indicate that the hydrothermal alteration and gold mineralization occurred betwe-en 260 and 370°C (mostly ~328°C), and 0.85 to 2.8 kbar, from a low-salinity (~5% NaCl), aqueous-carbo-nic (XCO2 = 0.03-0.13), relatively reduced (log fO2 = -32.1), and near neutral (pH = 5.0-6.2) metamorphic fluid (δ18O = +9.4 to +11.3‰, δD = -25 to -28‰). Contributions from deep-seated (lower crust and mantle) sources are suggested by a δ13CCO2 value of -7.6‰, and 87Sr/86Sr ratios between 0.702699 and 0.705141, which are lower than those found in the country rocks. Gold was transported by the Au(HS)2- complex and precipitation occurred in response to phase separation, identified by fluid inclusions, and fluid-rock interactions, given by the lowering of the δ13CCO2 values. The geological and genetic characteristics are equivalent to those of the orogenic gold system previously defined for the Gurupi Belt.
