Sulfur isotopic composition and origin of sulfide sulfur in epithermal Au-Ag vein-type deposits in Japan

Epithermal Au-Ag vein-type deposits in Japan are divided into two major types, Green tuff-type and non-Green tuff-type, based on their country rocks. delta(34)S values of sulfides and other geochemical and mineralogical features (delta(13)C and delta(18)O of carbonates, salinity of inclusion fluids, Ag/Au total production ratio, association of metals, gangue minerals) are different in two types of-deposits. These differences can be explained by the influences of country rocks. The Green tuff-type deposits are affected by marine rocks containing marine sulfates and carbonates and interstitial water of seawater origin with high chloride concentration, resulting to higher delta(34)S, delta(13)C, salinity, and Ag/Au total production ratio and enrichment of base metals (Cu, Pb, Zn, Mn, Fe), whereas the non-Green tuff-type deposits are by subaerial rocks. Sedimentary sulfur and organic carbon were involved in ore fluids for the non-Green tuff-type deposits, resulting to relatively low delta(34)S of sulfides and delta(13)C of carbonates. The differences in the association of metals in the deposits, and Ag/Au total production ratio of ores are reasonably explained in terms of HSAB principle by Pearson (1963). According to this principle, H2S and HS- tend to form thio-complexes combined with soft element such as Au and Hg which are enriched in the non-Green tuff-type, whereas Cl- tends to form chloro-complexes with Ag and base metals (Cu, Pb, Zn, Mn) which are relatively enriched in the Green tuff-type.