ABSTRACT

Sulfur isotope data of sulfide and sulfate minerals from the Kuroko-type deposits of the Miocene age (63 samples of mill concentrates and 48 separate specimens) and from the later Paleozoic so-called Kieslager-type deposits (20 samples of mill concentrates and 11 separate specimens) are reported. The data of sulfides from the Kuroko-type deposits can be divided into two groups, i.e., a lower δ³⁴S group of which deposits in the Ohdate area are representative and a higher δ³⁴S group characterized by deposits in the Kosaka district. A remarkable difference between the Kuroko-type and the Kieslager-type is that the average sulfur isotopic fractionation factor between sulfides and contemporaneous sea-water sulfate is slightly larger in the Kuroko-type deposits than in the Kieslarger-type deposits. Based on the same logic as developed in the previous paper (KAJIWARA, 1971), the difference between the two groups of the Kuroko-type deposits as well as between the Kuroko-type deposits and the Kieslager-type deposits is most likely due to the difference in oxidation state at the time of their deposition, the first mentioned of each pair being higher in oxygen fugacity of ore formation. Similarly, it is also concluded that the “volcanic type” deposits of SANGSTER (1968) are relatively higher in the depositional oxidation state than the “sedimentary type” deposits.