Study On The Jinding Super-large Lead-zinc Deposit In Sanjiang Area,Southwest China

As one of the world-class super-large deposits,the Jinding Zn-Pb deposit has been widely concerned by scholars.The samples we collected in this work are the ore minerals and gangue minerals in the main metallogenic period.The sulfur-lead isotopes,hydrogen-oxygen isotopes,carbon-oxygen isotopes and fluid inclusions have been analyzed.We discuss the material sources,fluid sources,and lower limit of temperature-pressure conditions about the mineralization.The results are as follows:The δ³⁴S of the sulfides in the Jinding deposit ranges from-13.4‰to-26.8‰.The sulfur mainly comes from the crust and is mainly produced by bacterial sulfate reduction（BSR）.The data points of lead isotope in the composition diagram(²⁰⁶Pb/²⁰⁴Pb 18.438¹8.511,²⁰⁷Pb/²⁰⁴Pb15.642¹5.669,²⁰⁸Pb/²⁰⁴Pb 38.636³8.736)are in the upper crust of the Lanping Basin,indicating the source of crust and the sedimentary layers.TheδD_H2O of fluid inclusions in sulfides is-59.5‰^-43.3‰,andδ¹⁸O_H2O is-6.4‰^-3.7‰.In the plot ofδD-δ¹⁸O,the data points are close to the meteoric waterline with significant drift,which indicates that the ore-forming fluid mainly originates from meteoric water and reacts with wall rocks.The calcite show a large variation ofδ¹³C_PDB（-22.6‰^-3.4‰）,indicating the mixed carbon source of sedimentary organics and marine carbonates.Theδ¹⁸O_SMOW（19.5‰²3.4‰）are similar to those of the sediments.In the plot ofδ¹³C_-δ¹⁸O,the data points are distributed in marine carbonates and sedimentary organics.Microthermometric measurements of the fluid inclusions indicate that the homogenization temperatures are 60²84°C,mainly in the range of 50¹40°C,which are the medium-low temperatures.The salinities are 8²4 wt%NaCl.eqv,and mainly concentrates in the two intervals:9¹6 wt%NaCl.eqv and 18²4 wt%NaCl.eqv.Homogenization pressures are not high（0.02³.86MPa）.Densities are in the range of0.98¹.15g/cm³.Combining previous studies and this work indicates that the ore-forming materials of the Jinding deposit originate from the crust,and are related to the sedimentary layers of the Lanping Basin,especially the Upper Triassic Sanhedong Formation.The ore-forming fluids mainly come from meteoric water reacted with the wall rocks,which represents the brine system.The Jinding deposit is a typical epigenetic deposit and it is irrelevant to the magmation.Under the special tectonic setting,the metal-bearing fluids in the basin were injected into the dome reservoir with reduced sulfur,resulting a large amount of precipitated ores.