Reserach On The Mineralogy And Fluid Inclusions Of The Miaoliang Gold Deposit In Shanyang County,Shaanxi Province

Miaoliang gold deposit is located 35km northwest of Shanyang County,Shaanxi Province.The geotectonic position is located in the center of Zhashui—Shanyang polymetallic ore concentration area in the east part of the Indosinian fold belt of South Qinling.There are many metal deposits in the ore concentration area,but the scale is not large.In contrast,the metallogenic characteristics of Miaoliang gold deposit are special,but the research level is very low.Taking Miaoliang gold deposit as the research object,through detailed field geological investigation and indoor comprehensive research,this paper mainly discusses the formation conditions and genesis of rock mass,the characteristics of ore-forming fluid,the source of ore-forming materials,and ore-forming mechanism of the deposit,and mainly makes the following progress and understanding:(1)Miaoliang gold deposit occurs in qingshiya formation of Middle Devonian.The gold ore body is controlled by NWW trending faults in the mining area,mostly in lenticular and vein shape in breccia and strata.The ore minerals are mainly pyrite and chalcopyrite,followed by pyrrhotite,galena,arsenopyrite and trace sphalerite,porphyry,limonite etc.the precious metal minerals can be found in natural gold,silver gold,etc;gangue They are mainly quartz,sericite,chlorite,carbonate minerals,etc.the wall rock alteration is mainly sericitization and silicification,followed by potassization,chloritization,carbonation and ferritization.(2)A systematic mineralogical study of the main ore-forming minerals in the granitic porphyry and granodiorite porphyrite related to mineralization in the mining area is carried out.The results show that the granite in the area belongs to the calc-alkaline series and type I granite;it is formed in the water-rich and high-oxygen fugacity orogenic belt environment,and the diagenetic material source has the characteristics of crust-mantle mixing mainly in the lower crust;the formation temperature is between 710?760?,the pressure is between105Mpa?162Mpa,and the emplacement depth is about 3.96?6.11Km.(3)The geological characteristics,mineral composition,structure and structure of ore bodies are summarized,and the metallogenic periods and stages are divided.The study of the main ore minerals in the ore body shows that there are inclusions gold,intergranular gold,and lattice gold in the ore field,and the fineness of gold is between 783.51?841.24.Pyrite electron probe in different types of ores and granites shows that the S/Fe ratio,?Fe and?S value,Co/Ni ratio,Au/Ag value,Co-Ni-As diagram of pyrite indicate that pyrite in Miaoliang gold deposit show that the pyrite in Miaoliang gold deposit is of magmatic hydrothermal origin;The ore deposit is formed in the medium-temperature and medium-shallow environments.The p H value of ore-forming fluid is about 7.3,and the Eh value is slightly lower than-0.37.(4)The fluid inclusions in Miaoliang gold deposit are H₂O-NaCl gas-liquid two-phase type,some H₂O-NaCl-CO₂ gas-liquid three-phase type,a small amount of pure CO₂ type and daughter bearing multiphase inclusions;the homogenization temperature of the main mineralization stage is 172.1?345.2?,mainly concentrated in 200?300?,the salinity is between 0.6%?13.4%,the density is 0.75?0.95g/cm³,and the mineralization pressure is14.60?37.15Mpa.The average is 25.82Mpa,with a depth of 1.46?3.72Km,with an average of2.58Km;From the early stage to the late stage of mineralization,the fluid properties evolved from medium high temperature,medium salinity,low density,CO₂ rich fluid to medium low temperature,medium low salinity,medium density,CO₂ poor fluid,fluid boiling and pressure reduction are the main reasons for gold enrichment.(5)The S and P isotopes of pyrite in different types of ores show that the sulfur in pyrite is the sulfur in deep mantle mixed with part of the sulfur in the crust;the lead comes from the orogenic belt formed by crust and mantle activities,with the characteristics of crust mantle mixed source,which is basically consistent with the lead isotopic source of Yanshanian granites in South Qinling.(6)According to the structural background,geological characteristics,ore controlling factors,diagenetic age,mineralogy,fluid inclusions,isotopes and other characteristics of the deposit,it is considered that the meso low temperature meso epithermal magmatic gold deposit is controlled by the structure.