Ore Genesis And Mineralization Enrichment Regularities Of Cuyu Gold Deposit In Central Jilin Province,NE China

The Cuyu gold deposit is located at the intersection of the eastern part of the Central Asian Orogenic Belt and the northern margin of the North China Plate.Although the deposit was discovered early,its theoretical research is very weak due to its small scale and low degree of exploration and development.On the basis of data collection and field geological investigation,the regional geological background and metallogenic geological conditions of the deposit are analyzed.Studies have been carried out on petrography,mineralography,microthermometry and laser Raman spectroscopy of fluid inclusion,C-H-O and S-Pb isotope as well as isotope dating,etc.Some properities of the Cuyu gold deposit have been determined,including mineralization and alteration characteristics,ore-forming physical and chemical conditions,characteristics and sources of ore-forming fluid and ore source.Combined with comparision with typical gold deposits in the area,The genetic type of Cuyu deposit has been clarified in to the mesothermal gold deposit,and its metallogenic model has been established.The mineralization and enrichment regularities have been summarized,which are very helpful for the theoretical researches and ore-prospecting in the mining area and adjacent area.The main vein-type ore bodies of the Cuyu gold deposit are mainly controlled by the NW-trending fault zone,and hosted in the altered Late Paleozoic granodiorite and monzogranite,and closely associated with the Mesozoic diorite porphyrite.Ore types are divided into two types:gold-bearing quartz-vein type and altered-rock type,the main metallic minerals in the ore include pyrite,galena,chalcopyrite,sphalerite,arsenopyrite and native gold,etc.The main non-metallic mineral are quartz,calcite,sericite,potassium feldspar,plagioclase and chlorite,and so on.The metallic minerals in ores have granular,metasomatic and autochthonous-semiautochthonous textures,and the ore has obvious massive,vein and disseminated structures.The alteration types of surrounding rock are silicification,sericitization,chloritization and carbonation,among which silicification,sericitization and mineralization are closely related.The results show that the mineralization in Cuyu gold deposit can be divided into three metallogenic stages:namely,quartz-arsenopyrite-pyrite,quartz-polymetallic sulfide,and quartz-calcite stage.The homogenization temperatures of the fluid inclusions in the early mineralization stage of the Cuyu gold deposit range from 201?to 355?,and the salinity from 0.4 to11.6 wt%NaCl equiv.The ore-forming fluid belongs to the H₂O-NaCl-CO₂ system with medium temperature and low salinity.The homogenization temperatures and salinities of the inclusions in the major mineralization stage ranged from 113?to 245?,and from to1.9?8.4 wt%NaCl Equiv.The gas phase components are mainly H₂O,indicating that the ore-forming fluid belongs to H₂O-NaCl system with low temperature and low salinity.The homogenization temperatures of fluid inclusions in the late stage range from 102?to181?,and the salinity range from 3.5 to 8.3 wt%NaCl equiv.The fluid in this stage belongs to H₂O-NaCl system with low temperature and low salinity.According to the results of H-O isotope analysis of fluid inclusions and combined with the ore-forming geological conditions,it is considered that the ore-forming fluids in the early stage of ore-forming are mainly magmatic hydrothermal fluids,and at the late stage the ore-forming fluids are obviously mixed with meteoric water.The results of S-Pb isotope test of metal sulfide show that the metallogenic material of this deposit comes from the deep source.Generally,it is considered that the Cuyu gold deposit belongs to the middle and low temperature hydrothermal vein-type gold deposit,and is closely related to diorite porphyrite in space-time and genesis.The LA-ICP-MS zircon U-Pb dating of diorite porphyrite,closely associated with the gold ore body in the Cuyu gold deposit,show that the ages of the zircon grains are between?160±3?Ma and?185±3?Ma,and the weighted average age is 170.4±1.8Ma?MSWD=0.48?.The ⁴⁰Ar-³⁹Ar age of the sericite in gold ore was 168.27±1.96Ma,and the reverse isochron age is 173.5±2.8Ma.These two were basically consistent within the error range,which indicate that both the diorite porphyrite and associated gold mineralization formed at?170Ma.The diagenetic and metallogenic epoch of Cuyu gold deposit is middle Jurassic.The summary of regional metallogenic regularities shows that the Cuyu gold deposit has similar geological background,ore-forming condition,mineralization characteristics and metallogenic ages with some gold deposits in the Jiapigou-Haigou gold deposit zone in central Jilin province,which implies the Cuyu and gold deposits in Jiapigou-Haigou gold deposit zone are commonly the produced bythe Mesozoic large-scale gold mineralization under the tectonic background of Paleo-Pacific Plate subduction,and the northwest extension direction of Jiapigou-Haigou gold deposit zone has the prospecting potential of hydrothermal vein type gold deposits.In the Cuyu gold deposit,the gold ore bodies are obviously controlled by the NW-trending fault zones.Vertically,the size of the ore body gradually increases from 100m below the surface and the grade of the ore increases,indicating that the deep part of the Cuyu gold deposit may have certain ore-prospecting potential.