A sulfur isotopic study of alabandites from some manganese ore deposits in Japan
Alabandites from Pretertiary beddedand Tertiary vein-type manganese deposits in Japan have been examined for their sulfur isotopic composition. ƒÂ34S (CDT) value ranges widely from -31 to +1.1•ñ in 12 specimens taken from 10 bedded type deposits. While the mineral is no more than a minor constituent in most of the deposits, the isotopic features clearly indicate that these alabandites are of bacteriogenic sedimentary origin, thus raising an important constraint for the genesis of this group of deposits. A cluster of ƒÂ34S around -30•ñ implies an open-system, steady-state reduction (SCHWARCZ and BURNIE, 1973) from a source SO42with the isotopic level of ca. +20•ñ. The inferred source is likely to have been in the Triassic sea. Current conjectures upon the age of host sedimentary rocks of the deposits concerned are in favor of this view. Alabandites from the Tertiary (Miocene) vein type deposits show only a minor variation in ƒÂ34S, +4 to +5•ñ. The data are very similar to the average isotopic composition of sulfides of the Miocene, "Green Tuff", mineralization represented by the kuroko type deposits. The remarkable consistency in sulfur isotopic composi tion of the Green Tuff mineralization over an extensive area may require a huge, common reservoir of sulfur in some form, which still remains an enigma.