Research On Mineralization Of The Lengshuikeng Porphyry Silver-lead-zinc Deposit In Jiangxi Province, China

The Lengshuikeng porphyry silver-lead-zinc deposit in Jiangxi province is the most representative one which is very rare in world wide. It is different from the porphyry copper(molybdenum) deposits for that the porphyry silver-lead-zinc deposit is not a common recognition one. Research on the porphyry copper(molybdenum) deposit is very matured, but it is quite weak regarding to research on the porphyry silver-lead-zinc deposits. The key problem is that the reasons for different mineralization between Ag-Pb-Zn and Cu-Mo elements, which remain unknown until now.Based on previously published data on the Lengshuikeng deposit, the author carried on field investigation and studies on deposit geochronology, lithogeochemistry, isotopic geochemistry and inclusion geochemistry of the deposit. The dissertation discusses aspect of structure control on the Lengshuikeng porphyry deposits, the origin of Cu-beared magmas and mechanism of ore-forming materials and evolution of the ore forming.The porphyry silver, lead, zinc deposit in Lengshuikeng is located in southern of splicing belt of the Yangtz and the South China tectonic plate, where suited in Langgang-Yuefengshan volcanic basin of northwest Wuyi upwelling area in south of China. The district were controlled by compound fault that Northeast big fault of Yingtan-Anyuan and East to west deep fault of Guangfeng-Pingxiang in Caledonian epoch. Distribution of ore-bearing granite-porphyry were strictly controlled by Erkou-Hushi fault, which is a big Northeast strike-slip fault in the district, and the granite-porphyry were emplaced in volcanic rocks which was located in bottom member of Daguling group and Erhuling group in Jurassic system. The chronology study of zircon U-Pb by SHRIMP to ore-bearing granite-porphyry show that the diagenetic age was 162Ma, in middle of Yanshan epoch of Jurassic system, when was in late of collision to orogenic tectonic surrounding. The ore-bearing porphyry is alkali-feldspar granite-porphyry, which belong to calc-alkalic rock. The research on trace elements and rare earth elements show that the ore-bearing granite-porphyry, intrusive vein rock and the surrounding rock-volcanic rocks of late Jurassic system, all of them origin from remelting of crustal rocks, so they were granite of sedimentary style, it is obvious different from typical ore-bearing granite of the porphyry copper. Research on characteristics of isotope of Pb, Sr, Nd, O, Hf system of ore-bearing granite-porphyry show that rocks origin from metamorphic rocks in basement of Wuyi district, which formed by remelting of upper crustal material. Difference from typical porphyry copper(Molybdenum) deposit, the ore field have much alteration of hydrogen metasomatism which relative to mineralization and carbonation alteration, the mineralization mainly occured in middle-low temperature stage.The mineralizing fluid of porphyry silver, lead, zinc deposit in Lengshuikeng belong to CaSO₄ (MgCl₂) -NaCl-KCl-H₂O magmatic hydrothermal system, the fluid system have characteristics of middle-low temperature and middle-low salinity. The mineralizing fluid composition of isotope of hydrogen oxygen, carbon oxygen, sulfur and lead show that the fluid origin from magmas of granite-porphyry, there are meteoric water mixed during the mineralization, the ore-forming material mainly came from magmas system of porphyry rocks.Study on chronology of sericite by Ar-Ar method show that the metallogenetic epoch of the deposits was 162Ma, it is same as the chronology of ore-bearing porphyry rocks and the time of mineralization maybe continued limit to 27Ma. By analysis the characteristics of mineralization, ore-control factor, geophysical and geochemical prospecting index, the author primary summarized the prospecting model of porphyry silver, lead, zinc deposit in Lengshuikeng mine field.Synthesis contrast to the porphyry silver, lead, zinc deposit in Lengshuikeng with the most of porphyry copper(Molybdenum) deposit in the world, the author think that the reason for occurring different mineralization of porphyry ore deposit is that the source of porphyry magma and character of the source is different, which is also the key factor for the difference of character of ore-bearing porphyry rocks, alteration system of surrounding rocks and mineralizing fluid of two kind porphyry ore deposit.