The pressure, temperature and composition of ore fluids that resulted in gold deposition in the Archean, greenstone-hosted Hutti deposit have been studied using fluid inclusions and the compositions of arsenopyrite and chlorite. Five types of fluids have been identified in fluid inclusions in quartz veins associated with mineralization. They are (1) monophase CO2-rich fluid; (2) low-salinity (0 to 14wt% NaCl equivalent) and high-salinity (16 to 23wt% NaCl equiv.) aqueous fluids; (3) high-salinity (28 to 40wt% NaCl equiv.), polyphase aqueous fluids; (4) CO2H2ONaCl fluids of low salinity (08wt% NaCl equiv.); and (5) a few carbonic inclusions with halitenahcolite. The diversity of entrapped fluid composition is explained in terms of changes in fluid pressure and temperature which affect a more or less uniform supply of primary low-salinity CO2H2ONaCl fluid to the shear zone. Geothermobarometric studies indicate that during mineralization temperature ranged between 360 and 240C, and fluid pressure between 3,600 and 1,600bar. The data are interpreted in terms of the cyclic fault-valve mechanism for active shear zones. Deposition of gold and sulfides has been studied on the basis of constraints from the composition of wall-rock chlorite, ore-mineral assemblages, and textural features. Tubular channels, 20 to 100m wide and up to 500m long that arise from fractures and C-planes in sheared quartz veins are reported for the first time. The channels have pyrrhotite, arsenopyrite, pyrite and gold at their distal ends, with calcite filling up the remaining part. These channels form in response to increases in T and P, by dissolution of quartz grains, guided by dislocations in them. At the PT conditions of interest, gold and sulfide deposition takes place in the shears and fractures of quartz veins from CO2H2ONaCl ore fluid of low salinity and pH due to changes in phase compositions that occur during the process of shear failure of the enclosing rocks. In the wall rock where pH is buffered, gold deposition takes place from the predominant Au(HS)2 species with progressive sulfide deposition and decrease in S, from 0.01 to 0.001mol/kg as T falls from 360 to 240C.