A reconnaissance of Cu isotopic compositions of hydrothermal vein-type copper deposit, Jinman, Yunnan, China

The Jinman deposit is a low-temperature hydrothermal vein-type copper deposit, which occurs along faults and fractures within Middle Jurassic sandstone and mudstone units of the Lanping-Shnao Mesozoic-Cenozoic basin of Yunnan Province. In this note, we report for the first time the Cu isotopic compositions of Cu-sulfides from the Jinman deposit. The data show large variations and low delta(65)Cu values of -3.70parts per thousand to +0.30parts per thousand, which are in sharp contrast to the delta(65)Cu values of high-temperature magmatic-hydrothermal copper deposits (-0.62parts per thousand to +0.40parts per thousand) and the modern ocean-floor massive sulfide deposits (-0.48parts per thousand +1.15parts per thousand). It is suggested that the Cu Isotope fractionation at Jinman is affected mainly by the following factors, i.e. a low temperature of ore formation (150-286degreesC); a sedimentary source for ore materials; various stages of ore deposition; and involvement of organic matter in the ore-forming processes.