2004 Volume 55 Issue 1-2 Pages 19-30
Sulfur isotopic ratio,δ34SCDT, was determined on 50 sulfide samples from the Cretaceous (with one Paleogene locality) granitic terrain of the Kitakami Mountains, and the data, together with 8 analyses already published, were examined in view of the ore genesis. The studied ore deposits and quarries are 37. The δ34S values are highest in molybdenite deposits, as -0.5 to +3.6 ‰δ34S. The δ34S values of base metal deposits, which are mostly skarn type, vary more widely than those of the molybdnite deposits, ranging from -3.4 to +5.5 ‰δ34S. Tungsten and gold deposits, mostly of vein type, are hosted in the intruded sedimentary rocks and have low and widely varying δ34S values (+2.8～-16.7 ‰). Influence of biogenic sulfur from the Permian host pelitic rocks is considered for the low values of the Higashi-iwai (Au-W) and Masunai (Au) deposits. The δ34S values of the granitoid-hosted molybdenite are averaged as +0.7 ‰, which is similar to +1.5 ‰δ34S of the averaged rock sulfur value of the Tono and Miyako plutons. This and lower δ34S values of the Kitakami sulfides, as compared with those of the Mo Province of Southwest Japan, may be correlated to a low fO2 magnetite-series character in the Kitakami Mountains. The intrusion-related gold deposits are divided into high-Au/Ag type with low contents of associated sulfides and low Au/Ag type with high contents of the associated sulfides. The former has -13.8～+2.8 ‰δ34S, indicating biogenic sulfur from the host sediments in some ore deposits, while the latter values, being -0.8～+5.5 ‰δ34S, are more close to δ34S value of granitoid sulfur, implying higher contribution of magmatic sulfur for the low Au/Ag type.
