The Characteristics And Geological Meaning Of Copper Isotopesin South Tiegelong(Rongna Section)Copper-gold Deposit,Duolong,Tibet

High-sulphidation(HS)copper deposit represents an important type of deposits that were formed under highly oxidized conditions and related to acidic fluids.Here we report the first study of copper isotopes for sulfides sampled from the South Tiegelong HS copper deposit,Tibet,to investigate Cu isotopic signature of the HS deposit and to evalute the possible application of Cu isotopes as a tool for exploring.Copper isotopic ratios of samples from all four drill holes display consistent progressive increase with depth,with an overall variation of 865Cu up to 7.60‰.Such a large range of Cu isotopic compositions is dramatically different from that observed in porphyry magmatic-hydrothermal deposits,the latter of which commonly displays a small ? 65Cu range with decreasing values with depth.The large 865Cu variation thus must be supergene origin and reflect strong leaching at oxidized conditions in the HS deposit.The systematic increase of 865Cu with depth can be explained by the release of isotopically heavy Cu at the top and its transport downward,supported by the coupling of positive 865Cu values with high Cu grade and the occurrence of both negative and positive ?65Cu values in two drill holes.Nevertheless,samples from other two drill holes sampled at similar depths missed isotopically heavy or light zones,respectively.Mass-balance consideration must indicate the existence of such zones which had been eroded or have not been found yet.We speculate that such mineralized targets,if being buried in depth,may be further explored by ascertaining the pathways through which the ore-forming metals migrated using Cu isotopes.Collectively,our results indicate that the large Cu isotope variations in HS deposits may have a great potential for exploring.