Host: The Japanese Association of Mineralogists, Petrologists and Economic Geologists
The Hishikari low-sulfidation Epithermal gold deposit, Southern Kyushu, Japan is one of the biggest gold veins with extremely high grade. The Hishikari gold deposit comprises of Honko, Sanjin and Yamada deposits. Rock samples from several veins and the adjacent host rocks from Hishikari epithermal Au deposit were analyzed for their sulfur isotopic compositions to establish the source of the hydrothermal fluids. The sulfur isotopic ratio varies from zero to +2 permil for the Kurozonsan and Shishimano dacites, and mostly from -3 to +16 permil for the hydrothermal sulfide minerals obtained from the veins and the adjacent host rocks. The heavier values of +11 to +16 permil were obtained from the pyrites in the latest druze of the Yamada and Sanjin deposits. Most of the values are in the range of -3 to +4 permil, which are similar to those of the magmatic sulfide in the Kurozonsan and Shishimano dacites. These data suggest that the sulfur in the hydrothermal fluid is originated in magma. The heavier values are probably from sulfate. The hydrothermal reduced species of sulfur might be oxidized in the overlaid volcanic rock of magnetite series and/or by mixing with oxic meteoric water to form sulfate ions. The isotopic ratio of sulfate should be heavier. If these ions descend into the Shimanto super group, the sulfate might be reduced to HS or H2S. If the reduction would be completed, the isotopic ratio of H2S and the derived pyrite might be also heavy. The evidence that the heavier values of the sulfide formed at the later stage supports this idea.
