Jiangxi Province The Pengshan 18 Orefield Zhang Pb-zn Geological Features Forming Material Source

The Pengshan orefield is a huge orefield predominated by Sn,Pb and Zn deposits.These are distributed as a halo pattern with transition from a high-temperature mineral assemblage in inner zone to a low-temperature mineral assemblage in outer zone.The Zhangshiba Pb-Zn deposit is located in the middle zone of pattern with a middle-low temperature mineral assemblage.This paper presents some new geochemical analyses and fluid inclusion measurements,and provides some new insights into geochemical characteristics,ore-forming fluid source,and metallogenic mechanism of the deposits.A suitable regional metallogenic background is an important precondition for formation of the Zhangshiba Pb-Zn deposit.It is shown that the activation of deep basement faults in Mesozoic Era is responsible for formation of pathways for magma uplifting along some cross zones of the faults,and the dome tectonic system resulted from magma emplacement acts as important locations for migration of ore-forming hydrothermal fluids.The Zhangshiba Pb-Zn deposit is obviously controlled by the dome tectonic system.The orebodies are found mainly in the sliding fault system deposit possibly formed in the late Yanshanian period belongs to a type of middle-low temperature hydrothermal deposit.The formation process of the deposit can be divided into three stages including quartz-pyrite,quartz-sphalerite/galena(multi-sulfide),and quartz-carbonate(little sulfide)stages.The fluid inclusion measurements as well as hydrogen and oxygen isotope analyses indicate that ore-forming fluids with middle temperature and low salinity were not homogeneous when ore minerals crystallied from them.It is shown that evident addition of some introduced fluids possibly from infiltating atmospheric water into the ore-forming fluids and their ebullition occur during the metallogenic process.The hydrogen and oxygen data support deriation of the ore-forming fluids at the major metallogenic stage from mixture of magmatic water with atmospheric water,and are consistent with increasing of atmospheric water with decreasing of temperature rom 35℃ to 150 ℃ and its final predomination in the ore-forming fluids.The trace element as well as lead and sulfur isotope analyses on the samples collected from various geological bodies of the mine provide evidence for derivation of lead in ores not from a single normal source ,but from abnormal multi-source with mixture of much upper crust component with less mantle component.Meanwhile,the sulfur isotope and rare earth element analyses support evident concordance in material source of crust composition between the orebodies and Pengshan pluton and close relation of metallogeny to Yanshanian granite magmatism,which leads to inference that the ore-forming materials are mainly from Pengshan pluton.An analysis has been also carried out on the factors of influence on metallogeny such as magmatic rocks,wall rocks and structures,and a discussion had on metallogenic dynamic system,pathways for ore-forming fluid migration ,and metallogenic process.