Study On Process Of Mineralization And Estabilishment Of Metallogenic Model Of The Jinshan Gold Deposit,Jiangxi Province

The Jinshan gold deposit is located in the Neoproterozoic Jiangnan orogen,southeast of the Yangtze Blocks,northwest of the Jiangshan-Shaoxing fault.This paper did carefully researches on geological characteristics,ore field structure,intrusive rocks,strata,genesis of deposit with the ways of fluid inclusions,raman spectroscopy,wall rock alteration,electron microscopy,transmission electron microscope,Zircon U-Pb isotope,lithogeochemical,Sr-Nd-Hf isotope,S-Pb-D-O isotope,Rb-Sr isochrons.In order to get the processes of mineralization and the establishment of metallogenic model.The intrusive rocks in Jinshan area is diabase and granitic porphyry,Zircon U-Pb isotope result is 854?905Ma.With Sr-Nd-Hf isotope data,the granitic porphyry dikes of the Jinshan area is derived from crustal material and partial melting of mantle participation.The diabase is derived from partially melting of mantle material.Tectonic discrimination diagrams showed diabase the characteristics of arc environment.With carefully ore field strcture studies,two episodes of ore formation events took place in the Jinshan deposit were first proposed in this paper.The ultramylonite ores of early ore-forming period are consistent with the regional NW-trending thrusting ductile structures.The quartz vein-type ores of late ore-forming period which is accordance with the regional later NE-trending strike-slide movement.Jinshan gold wall rock alteration is typical horizontal zoned.The alteration of auriferous quartz veins area is strong beresitization-carbonation,with high-grade gold mineralization;weak carbonation and chloritization occured in both sides of ores with weak mineralization;away from gold ore bodies is phyllite strata,with almost no alteration and mineralization showed.The most likely initial fluid at Jinshan is recorded by the numerous pre-ore stage of H2O-CO2 type inclusions.The fluid has higher homogenization temperatures ranging from 285 to 340?,low salinity values of 1.4 to 6.1 wt.%NaCl equivalent and high contents of CO2.Formation of pre-ore,barren veins sealed the fracture systems and lowered the permeability,and hence,led to a renewed pressure increase.In the gold bearing quartz veins,CO2 rich and H2O-NaCl inclusions show homogenization temperatures from 243 to 272? and from 208 to 266?,and salinity values of 0.6 to 3.6 and 3.5 to 8.9 wt.%NaCl equivalent,respectively.The post-ore stage mineralizing fluids are characterized by low temperatures(109 to 201?)and low salinities(1.1 to 6.4 wt.%NaCl equivalent)in fluid inclusions.We conclude that the pre-ore stage initial fluids were characterized by relatively high temperature,CO2-rich fluid.Immiscibility occurred during the main ore stage,and the fluids have medium temperature and different salinities.Gold mainly deposited in this stage.Isochores from H2O-CO2 type fluid inclusions indicate minimum pressures of 105-262 MPa.The end-members of immiscible inclusions in the main ore stage are formed nearest the solvus and can obtain accurate pressures.The estimated trapping pressure is 76-113 MPa for gold bearing quartz veins.Indicating a pressure decrease happened during the gold mineralization process.Hydrogen and oxygen isotope studies have shown that the Jinshan ore-forming fluids were metamorphic hydrothermal.Consistent with REE characteristics ultramylonite ore and ore-wall rock phyllite,demonstrated ultramylonite type ore-forming materials from phyllite.The S-Pb isotope of the ultramylonite and quartz-type ores tested from pyrite and arsenopyrite,and dates from arsenopyrite in phyllite have the same range.Indicating that the the ore-forming material of Jinshan came from the strata.In this study,the Rb-Sr isochron data is 750 Ma.Tells the fact that the Jinshan formed during Neoproterozoic.With geological features,structural characteristics,wall rock alteration,fluid characteristics,sources of ore-forming fluid,and metallogenic epoch results,concluded Jinshan a typical orogenic gold deposit.The Jinshan metallogenic model is as follows:the Jinshan gold mineralization can be divided into two mineralization periods.The early mineralization period formed the NW ultramylonite ore bodies in Wanjiawu area.The late mineralization period(about 760Ma),formed the NE quartz vein type ore bodies in Yangshan area.After the formation of gold mine,the Jinshan had experienced at least two post-mineralization tectonic activities.Early thrusting along F6 fault plane resulted relatively raising of Wanjiawu part of Jinshan,Then Jinshan deposit experienced a regional tectonic uplift event,resulting in denudation and formed the orebody distribution characteristics.