Geochemical Characteristics And Genesis Of Vein Rich Copper Deposit In Yongping Qingyang Plant,West Yunnan

The newly-discovered Qingyangchang Cu-Co poly-metallic deposit is located in the southern Lanping basin,West Yunnan?SW China?.It hosts high-grade Cu ore,and associated with Co.The deposit shows distinct geological differences from sandstone-hosted Cu deposit and bears highly value of research.This paper focuses on a systematic study of the tectonic stages division,ore mineralogy,fluid inclusions and deposit geochemistry.Based on the coupled relationship among tectonics,ore-fluids and mineralization,this study discusses the ore-forming fluid and metal source?s?,as well as key mechanisms for ore precipitation.The major results are as follows:?1?The ore-bodies occur mainly as vein/lenticular in the NE-trending extensional faults,with brecciated,massive,veined/stockwork,banded and miarolitic ore types.Three mineralization stages can be recognized as sedimentary diagenetic,hydrothermal mineralization and supergene,in which the second stage can be further divided into four?I–IV?sub-stages,and the main Cu mineralization formed in II and III stages;?2?The petrography and microthermometry of fluid inclusions in barite of stages I–IV show that the initial ore-forming fluids have high-temperature?280.8?364.4°C?,high-salinity?2?16%Na Cleqv?and volatile-rich characteristics,while temperature?120?183°C?and salinity?2?10%Na Cleqv?of the late-stage significantly decrease.The inclusions in the initial fluids are complex,small and have obvious characteristics of fluid boiling.Therefore,the mechanism of ore precipitation is mainly cooling and boiling of fluid.?3?The sulfides at Qingyangchang have?³⁴S values of tennantite?3.13?6.47‰?,chalcopyrite?3.00?6.24‰?and pyrite?3.83?4.03‰?,respectively,and the S isotope fractionation equilibrium was not reached.Considering the extensive development of barite in the Qingyangchang mining area,and taking barite?³⁴S?16‰?in the adjacent mining area as a reference,it is estimated that?³⁴S is about 15‰according to the big-book model,which is close to that of gypsum of evaporite sequence in the basin.?4?Studies on trace elements show that the contents of In,Se and Te in sulfides are very low or below the detection limit,and the ratio of Sb/Bi is relatively large,indicative of low temperature of ore formation;The barites at different stages are characterized by low REEs(?REE=3.94×10^-6),MREEenrichments and obvious Ce-negative and Eu-positive anomalies,which indicate that the ore-forming fluids were mainly sourced from the hot basinal brines,and the ore-forming materials mainly from the sedimentary wallrocks?especially the salt-bearing sequence?.In summary,the Qingyangchang deposit is closely related to the thrust nappe structure in the Cenozoic tectonic evolution of Lanping basin,and is the product of large-scale mineralization triggered by continental collision.The ore fluid is mainly derived from hot brine in the basin,the ore material is mainly derived from the?especially the salt-bearing?strata,and the metallogenic mechanism is mainly related to cooling and boiling of the fluid,suggestive of low-temperature hydrothermal type.