Stable isotope analyses were carried out on sulfides from three mesothermal gold deposits of the Rio Itapicuru greenstone belt (Fazenda Brasileiro, Maria Preta, and Ambrosio mines) to constrain the source of the hydrothermal solutions. The ores are hosted in a volcanic-sedimentary sequence that evolved in an Archean cratonic area reworked during the Transamazonic event (ca. 2.1 Ga). The ore bodies were deposited by hydrothermal solutions in polycyclic shear zones generated by Paleoproterozoic dynamothermal metamorphism. In the Fazenda Brasileiro deposit, δ34S values for arsenopyrite from mineralized quartz veins range from 5.5‰ to +1.0‰; pyrites from Au-rich mineralized veins from the Maria Preta deposit yielded δ34S values ranging from +8.9‰ to +6.9‰, in agreement with published δ34S data (+0.1‰ to +6.6‰). A narrow spread in the δ34S values for Au-rich sulfides from both deposits indicates that gold deposition occurred under conditions involving a small range of fO2 and fH2O. A barren, galena-rich vein f...