Geological Characteristics And Genesis Of The Main Gold Vein In Wufeng Gold Deposits Peripheral Area,Yanji City,Jilin Province

The study area is located in the Badao Mining Area,northwest of Yanji City,Jilin Province.It is the outer part of the Wufeng and Wuxingshan Gold Deposit.It belongs to the shallow low temperature hydrothermal gold deposit of the Mesozoic volcanic rocks in Yanbian.Up to now,more than 110 veins of different scales have been found in the Badao Mining Area(including Wufeng and Wuxingshan Gold Ore Sections).This research area mainly focused on the 8 veins ore body of the No.1 vein,No.4 vein,No.33 vein and No.58 vein.The amount of 122 b + 333 ore is 370 kt,and the amount of metal is 1165 kg.The ore bodies of 1-1 and 1-2 are the main ore bodies in the No.1 vein.The tectonic location is in the Tianshan-Xing'an trough fold area,and the Yanbian superior trough fold belt of the Jihei Hualixi fold.The southwest is bounded by the Gudonghe lithospheric fault,the northwest is bounded by the Liangjiang-Haierba ridge crust fault,and the northern side is the Yanji Sag Basin.The study area is located between the Chaoyanghe fault and the Xiaoyanjihe fault,and the tectonic activity of which is very active,and it has the characteristics of multi-period and inheritance.As a result,a good mineral liquid flow channel and a favorable place for mineralization were formed.The fault structures can be divided into two groups of the northeast and the northwest,including the No.1 fault in the northeast,and the No.1 and 2 faults in the northwest.They are the main ore-controlling ore-bearing structures in the area and play a direct role in the formation of gold deposits.The deposit mainly occurs in the Jingouling Formation,which is consisted of a set of neutral volcanic lava and volcanic debris.The rocks are consisting of quartz horned andesite,andesite lava,quartz andesite,horned andesite,andesite volcanic breccia,pyroxene andesite.The gold-bearing veins are mainly controlled by northeast and northwest faults and are produced along the fault structures.The ore veins are produced as single veins,or secondary parallel veins along both sides of the main vein,forming a complex vein and a network vein pattern.The main types of ore-body wall rock alteration are chlorite,chloridite,silicidation,carbonate,sericite,and ice feldspar,etc.which is consistent with characteristics of typical shallow-formed low-temperature hydrothermal gold deposits wall rock alteration.The metal minerals are mainly pyrite,chalcopyrite,hafnium copper ore,sphalerite,galena,magnetite.The precious metal minerals mainly include natural gold,silver-gold ore,natural silver,fluorite,and tellurides of gold and silver and the gangue minerals are mainly quartz,calcite,chalcedony,opal,feldspar,fluorite,zeolite,kaolinite,sericite,chlorite,chlorite,sodium feldspar,etc.,which are consistent with typical low-temperature mineral combinations.The ore mineral structures include self-shaped and semi-self-shaped and other granular structures,metasomatic structures,crushed structures,interstitial structures.And the ore rock structure is dominated by massive,infectious,fine-network vein-like structures,followed by breccia-like,crystal cave-crystal family-like structures.These structures are belonging to the typical ore structure characteristics of shallow-mediumlow-temperature hydrothermal gold deposit.The results of the fluid inclusions in quartz and calcite show that the ore formation temperature range is 187.2~249.9 ?,which is mainly concentrated between 190~210 ?.The ore-forming fluids have low salinity(mainly concentrated in 2–3wt% NaCl)and low density(average value is 0.88 g/cm3).The pressure is mainly concentrated at 14-16 MPa,and the depth is calculated between 1.31 and 2.08 km.The results of the hydrogen and oxygen isotopes indicate that the ore-forming fluid is a mixture of atmospheric water and magmatic hydrothermal fluid.The carbon isotopes have deep source characteristics,which indicates the ore formation process is related to the volcanic-magmatic intrusion.The ?34S is +1.9~+2.9‰,with an average of 2.3 ‰,and the median value is close to 0.00 ‰,which indicates that the sulfur source is single and mainly magma source.The deposit is produced in continental volcanic rocks in the Yanbian area,and the ore body is produced in veins.The combination of calcite,cryolite,chalcedony(or quartz)is developed in the ore,which is consistent with the characteristics of the low sulfide type shallow low temperature hydrothermal deposit.The tellurium gold deposit is developed in the ore rocks.Since tellurium is enriched in the upper mantle but dispersed element in the crust,the high content of Te in the ore rocks shows the mineral was coming from the upper mantle.And Te is closely related to the alkali-rich magma,which indicates it was brought in by the Mantle-derived magma.This paper considers that the genesis of the main veins in the study area is closely related to the magmatic activity.The characteristics of low temperature,low salinity and low density are very similar to the characteristics of fluid inclusions in typical shallow-temperature low-temperature hydrothermal deposits.With the combination of the geological characteristics and isotope testing studies,the genesis type is determined to be a low-sulfurized shallow-generating low-temperature hydrothermal gold deposit.