Sulfur isotopic study of vein deposits in the Kinki district, Inner Zone of Southwest Japan

Abstract

Sulfur isotopic compositions of sulfide minerals (sphalerite, chalcopyrite, pyrite, pyrrhotite, etc.) from plutonic and subvolcanic vein deposits of the Kinki district in Inner Zone of Southwest Japan are examined in relation to regional metallogeny with special reference to sulfur isotopic variations among mineralization stages of individual vein deposits. The δ³⁴S values of sulfide minerals from plutonic vein deposits are in the range from -10.5 to +1.8‰. Plutonic vein deposits genetically related to Cretaceous granitoids in San'yo belt are characterized by larger negative δ³⁴S values (-10.5 to -5.7‰), while those related to Palaeogene granitoids in San'in belt are characterized by higher values (-0.4 to +1.8‰). On the other hand, δ³⁴S values of subvolcanic vein deposits are in the range from -6.2 to +5.0‰.
The δ³⁴S values in plutonic W-Sn-Cu vein deposits at the Otani mine are characterized by relatively larger negative values, but sulfide minerals formed in the latest stage tend to show higher δ³⁴S values than earlier stage ones.
In representative subvolcanic polymetallic (Cu, Zn, Pb, Sn, W) vein deposits at Akenobe mine, three major mineralization stages, called Pb-Zn stage, Cu-Zn stage and Sn-W stage, are distinguished from area to latest by major tectonic breaks. It is inferred that δ³⁴S values of sulfide minerals decrease from Pb-Zn stage (-1.8 to -1.40‰) to Cu-Zn stage (-3.5 to -0.6‰) and increase from Cu-Zn stage to Sn-W stage (-2.4 to +1.0‰).
In general, δ³⁴S values may have increased from early to later stage of mineralization in both plutonic and sub-volcanic vein deposits in the district.
The δ³⁴S value of polymetallic vein deposit transecting Kieslager deposit at the Akenobe-minamidani deposit is -4.1‰ which is similar to those of Cu-Zn stage at the Akenobe mine.