A contribution to physicochemical conditions for the formation of syngenetic sulfide ores

The results of thermodynamic calculations demonstrate that the pH and Eh values for bottom sea water enriched in organic matter tend to decrease drastically as a result of bacterial reduction of sulfates in sea water. Syngenetic sulfide ore beds associated with the Jiashengpan strata-bound Pb-Zn-S ore deposit are believed to have been precipitated under the conditions of pH varying from 7.08 to 7.17 and Eh from −0.232 to −0.418V. It is established that in the reducing system in sea water where reduction of sulfates by anaerobic bacteria took place, paleosalinity is an important factor affecting pH and Eh changes and controlling the formation of sulfide ore beds. The present study shows that the quantitative evaluation of physicochemical conditions can be effected from thermodynamic calculations on the basis of geochemical data.