The Luohe iron deposit is a volcano-pneumato-hydatogenetic metasomatic deposit of late Mesozoic age. In addition to magnetite, this ore deposit contains abundant pyrite and anhydrite. The temperatures of mineralization and alteration may he estimated from sulfur isotopic fractionation between the coexisting anhydrite and pyrite. The fact that the estimated temperatures from the weakly altered zone using the sulfate-pyrite equation of H. Ohmoto and R. O. Rye (1979) coincide with those estimated by other means (e.g. fluid inclusion), but the opposite holds true with those from the strongly altered zone indicates the establishment of isotopic equilibrium between anhydrite and pyrite in the weakly altered zone.However,assuming δ^34SAub=δ^34SSO2 and δ^34Spy=δ^34SH2S and using the SO2-H2S equation,the isotopic temperatures from the strongly altered zone are reported to be coineident with the data from fluid inclusions and one formation on.So the authors consider that there was established an equilibrium between SO2 and H2S in hydrothermal fluids during strong alteration,and the mechanisms of formation of anhydrite and pyrite in the two altered zones are probably different.
