Copper isotopes trace the evolution of skarn ores: A case study from the Hongshan-Hongniu Cu deposit, southwest China

Abstract

Transition metal isotopes are sensitive geochemical tracers of ore genesis. Here we present MC-ICP-MS analytical data of Cu isotope compositions from the Hongshan-Hongniu Cu deposit in Yunnan province. The δ65Cu values (δ65Cu=[(65Cu/63Cu)sample/(65Cu/63Cu)NIST976−1]×1000) of seven whole-rock quartz monzonite porphyries and twenty-two chalcopyrite samples from the skarn ore-bodies display relatively narrow ranges from −0.15‰ to 0.38‰ and from −0.02‰ to 0.77‰, respectively. The overlap of δ65Cu values indicates a genetic relationship between the quartz monzonite porphyry and skarn ore-bodies. We also evaluate the spatial and temporal variations of Cu isotope compositions in the skarn ore-bodies by comparison with some well-documented porphyry deposits in the world. The quartz monzonite porphyry shows compositional zoning with the inner domain enriched in heavy Cu isotope and the skarn related to the porphyry depleted in heavy Cu isotope. The chalcopyrites that formed during the late stage of mineralization tend to be enriched in heavy Cu isotope, and this feature is analogous to porphyry deposits. The δ65Cu values of the quartz monzonite porphyry show typical features of hypogene mineralization, suggesting a potential scope for deep exploration and development in this deposit.