Metallogenic Mechanism Of Jinjingzui Porphyry Gold Deposit,Edong Ore Cluster

Jinjingzui gold deposit is located in the Edong ore cluster,Middle-Lower Yangtze River Belt.The ore bodies are produced within the Jinjingzui small intrusion and the deposit is a representative of gold only deposits.This study,based on field study of vein type classification,vein cutting,observation of alteration characteristics,used EPMA,SEM image observation,fluid inclusion thermometry,cathodoluminescence image observation,single mineral isotope analysis,and micromineralogy observation to study the hydrothermal mineralization stage;this study used zircon SHRIMP U-Pb dating,whole rock composition analysis,and isotope analysis to study the intrusion.The main achievements are as follows:The age of the dioritic intrusion is 139.6±0.8Ma.Trace element composition characteristics suggest that the origin of the intrusion is closely related to the subduction environment.Potassic alterarion,chlorite-actinolite alterarion and phyllic alteration occur in the intrusion,while skarn alterarion occurs at the boundary between the intrusion and carbonate host rock.In this study,the veins are divided into three main types,with the early sulfide lacking X type,the second stage quartz-sulfide-calcite L type,and the late stage calcite sulfide H type;gold mineralization occurs in the first two types of veins.Abundant bismuth-tellurium minerals occur in the deposit with conspicuous spatial relation with native gold and gold minerals.Microscopic mineralogy shows that the mineral assemblage of gold and bismuth-tellurium minerals often coexist with the coarse grained Q1 quartz and hydrothermal K-feldspar,and fluid inclusion thermometry shows that Q1 quartz has high homogenization temperature?⁶00??and with substantial quantity of high salinity crystalline inclusions.Fine grained pyrrhotite included in Q1 quartz widely occur,suggesting that the sulfidation state and oxidation state in Q1 quartz stage is below the pyrite-pyrrhotite buffer.Thereafter,the oxidation and sulfidation state of the veins composed of large amounts of pyrite and calcite formed above the pyrite-pyrrhotite buffer.Previous thermodynamic simulations and experiments show that Bi³⁺in hydrothermal fluids can be reduced to native Bi at low oxidation and sulfidation states,and it becomes an immiscible face with the fluid as melt when the temperature is greater than the melting point of native Bi.In this case,the Au in the fluid will strongly partition into the Bi melt phase,therefore Bi melt can collect Au from the fluid.The role of Tellurium in this process still remain enigmatic,but experiments show that Bi-Te melts with a certain proportion has stronger capacity to coexist with gold than solely Bi melt.