Geology,Ore-forming Fluid And Material Sources Of The Fangyangshan Cu-Pb-Zn Poly-Metallic Deposit In Zhenkang County,West Yunnan Province,SW China

The Fangyangshan Cu-Pb-Zn poly-metallic deposit in Zhenkang County,west Yunnan province,is the only copper-rich deposit recently discovered in the south of Baoshan block for“Sanjiang metallogenic belt”,and has some differences in geological characteristics with two typical lead-zinc deposits in the Baoshan block.In this paper,we systematically studied the geology,geochemical characteristics of C-O-S-Pb isotopes and fluid inclusion of the Fangyangshan deposit for the first time,integrated with the previous study of Baoshan block,in order to revealing the sources of ore-froming fluids and materials,and discussing its ore genesis and metallogenic mechanism.The geological characteristics of the Fangyangshan deposit shows that the ore bodies occurred as veined and lenticular in the interlayer fracture zone of carbonate and calcareous salte in the Shahechang formation,the upper Cambrian.The mineralization preriod can be divided into the hydrothermal stage dominated by ores of Fe-Zn and the superposition stage dominated by ores of Cu,Pb and Zn.Ore minerals are dominated by pyrite,sphalerite,chalcopyrite,galena,quartz and carbonate minerals.In the early stage,ore textures and structures are characterized by euhedral-subhedral granular texture,crushed and vein structure.However heterogeneous granular,metasomatic dissolution-residual structure and vein-reticular structure are widely developed in the late stage.The study of fluid inclusions show that hydrothermal stage is dominated by liquid-and gas-rich inclusions and bits of inclusions containing NaCl and KCl.Their homogenization temperatures range from 240 to 280?and salinities from 10.0 to18.0 wt.%NaCl equiv,charactrized as H₂O-KCl-NaCl system.The early stage surposition is characterized by CO₂-rich and a daughter minerals-bearing fluid inclusions.Their homogenization temperature and salinity both shows two peaks of concentration,the homogenization temperature concentrate in 360-400?and 240-320?,meanwhile the salinity concentrate in 4.0-14.0 wt.%NaCl equiv and 16.0-24.0 wt.%NaCl equiv,mainly reflected as H₂O-CO₂-KCl-NaCl system.The late surposition stage are mainly characterized by liquid-riched and pure-liquid inclusions,with homogenization temperature ranging from 220.0 to 340.0?and salinity ranging from 8.0%to 14.0 wt.%NaCl equiv respectively,the ore-forming fluids belonged to the H₂O-NaCl system.These results show that the ore-forming fluids mainly came from the medium-high temperature and salinity magmatic hydrothermal,which formed by continental collision,and have been influenced by medium-low temperature and low salinity meteoric water in the late stage.Isotopic geochemical characteristics show that the value of?¹³C_PDB and value of?¹⁸O_SNOW in different stages in the range of-5.88 to-2.29‰and 8.18 to 12.79‰respectively,indicating that the Fangyangshan ore-forming fluid is sourced from magmatic hydrothermal,and were influenced by the carbonate dissolution of surrounding rocks and effect of sedimentary mixing or high temperature in the later stage.The research result indicates that?³⁴S_CDT values of the sulfides are characterized by the enrichment of?³⁴S,ranging from 8.24 to 14.91‰with average of11.51‰,which are very close to the composition of barite in the region,indicating that the sulfur mainly from the evaporation cream rock in the marine carbonatite,by Thermal-chemical Sulfate Reduction.The Pb isotope compositions of the sulfides shows ²⁰⁶Pb/²⁰⁴Pb,²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ranges of 18.2984 to 19.0819,15.7731to 15.8103 and 38.6550 to 39.3092,demonstrating that crust-derived nature obviously,and the result of research is consistent with skarn Pb-Zn deposit in the Baoshan Block,and it is shown that the sources of ore-froming materials for the Fangyangshan deposit main come from the upper crust.Comprehensive studies suggest that the fangyangshan deposit is similar to the Luziyuan and the Jinchanghe skarn deposits,its the product of the coupling action between magmatic hydrothermal produced by crustal shortening and thickening melting and the metallogenic materials from the upper crust.We propose that the Fangyangshan poly-metallic deposit is a mesothermal hypothermal deposit which is related to the continental collision orogeny,and obviously cotrolled by the struture.