Study On Material Composition And Genesis Of The Laodou Gold Deposit In West Qinling

The Laodou gold deposit is located in the northeast margin of the Dewulu pluton in the middle of the Xiahe-Hezuo ore cluster in the western Qinling Mountains.It is produced in the contact zone between the Dewulu quartz diorite and Laodoucun quartz diorite porphyry.In the Daguanshan group of the lower Permian,the ore body is controlled by near-north-south faults,and the ore-forming surrounding rocks are mainly Laduocun quartz diorite porphyry.Mineralogy studies have shown that the ore mineral composition of the Laodou gold deposit is mainly pyrite,arsenopyrite,galena,sphalerite,antimony ore,chalcopyrite,etc.,followed by a small amount of hafnium copper ore,antimony lead ores,brittle sulfur-antimony lead ores,lump sulfur-antimony copper ores,fangyan tin ores,etc.Non-metallic minerals are mainly quartz and tourmaline,followed by plagioclase,sericite and chlorite.According to the characteristics of the ore structure and mineral symbiosis combination,the mineralization process is divided into hydrothermal period and superficial period,and the hydrothermal mineralization period can be divided into three mineralization stages:(?)quartz-tourmaline-less sulfide Stage;(II)quartz-tourmaline-polymetal sulfide stage;(?)carbonate stage.Types of fluid inclusions include CO2-H2O inclusions(C-type),aqueous inclusions(W-type),and multiphase inclusions with sub-crystals(S-type).The uniform temperature of:fluid inclusions in the early,middle and late stages is concentrated at 250?350?,220?320? and 160?260?.The salinity of the fluid in the early stage has two terminal elements:4.67?13.98%NaCleqv and 31.8-40.5%NaCleqv.There are also two terminal elements of 0.88?18.04%NaCleqv and 30.3?47.1%NaCleqv in the middle stage fluid salinity,while the late stage fluid salinity is concentrated in 0.53?6.63%NaCleqv.The ore-forming fluids evolved from fluids with medium temperature,medium and high salinity in the early stage to fluids with low temperature and low salinity in the late stage.The inclusion characteristics reflect the characteristics of the fluid as magmatic fluids,and there is a boiling phenomenon during migration and evolution.Sulfur and lead isotope analysis data show that the total sulfur isotope value ?34S?s in the hydrothermal mineralization period is between-13.2‰ and 8.9‰;206Pb/204Pb,207Pb/204Pb,and 208Pb/204Pb values range from 18.023?18.248,15.571?15.630 and 38.205?38.508,analysis shows that the ore-forming materials mainly come from deep magma;carbon,hydrogen,and oxygen isotope analysis data show that the ?OH2O value of each metallogenic stage varies from-91.2%o?-60.1‰,and the ?18Oh2o value varies from-1.45‰-12‰,?13CPDB value varies from-2.6?-5.1‰,analysis shows that the ore-forming fluid was dominated by magmatic water in the early stage,and atmospheric precipitation was mixed in the fluid in the middle and late stages.Comprehensive studies have shown that fluid boiling and mixing are important mechanisms leading to the enrichment and precipitation of ore-forming elements.The type of the Laodou gold deposit is a magmatic hydrothermal gold deposit controlled by fracture structures.