Sub-types and Their Characteristics of Kuroko-type Deposits

Abstract

The Kuroko-type deposits in the Hanaoka-Kosaka district are divided into three sub-types based on the ratio of major base metals in a single unit deposit. The ratio of copper to lead and zinc increases in order of the "B", "C" and "Y" sub-types. There is the north-southerly lateral zoning of these sub-type deposits in the Hanaoka and Kosaka districts.
δD values are distinctly high in the "B" sub-type deposits.δ34S values are distinctly high in the "C" sub-type deposits and iron contents of sphalerite are low in the "Y" sub-type deposits. The higher δD values of "B" sub-type deposits occurring in the central part of basins may indicate sea-water as the predominant source for ore fluids. Using iron contents of sphalerite and δ³⁴S values of pyrite the possible depositional environments of three sub-type deposits were estimated on fO ₂-pH diagram.
In conclusion, each ascending ore fluid responsible for different sub-type deposits was different in geochemical nature. This suggests that the chemical and physical changes of ore fluid circulating in a hydrothermal system are important for the cause of differences among three sub-types of the Kuroko-type deposits.