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-Simao 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 δ⁶⁵Cu values of −3.70‰to +0.30‰, which are in sharp contrast to the δ⁶⁵Cu values of high-temperature magmatic-hydrothermal copper deposits (−0.62‰to +0.40‰) and the modern ocean-floor massive sulfide deposits (−0.48‰ to +1.15‰). 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 (150–286°C); a sedimentary source for ore materials; various stages of ore deposition; and involvement of organic matter in the ore-forming processes.