Study On The Mineralization Tectonic Setting And Genesis Of Naozhi Gold Deposit, Eastern Jilin Province

Naozhi Gold Deposit is a significant gold production base in Jilin Province.Since1990, the mine put into operation and has produced approximately1900kg Autill2009. The main gold veins are number9-2and10-5, which providing ore266720t,gold metal1517.3kg. In this thesis, we have done the research of the mines’geological features, the geochemistry of host rock and veins, the geochronology ofU-Pb isotope and the genesis of this gold deposit.The study shows that the region have three major NS trending fault zones,including Jiqingling NS fault zone, Antian-Miantian NS trending fault zone,Ludi-Changde NS trending fault zone, the faults towards160~180, and length of16~20km. The orebody are strictly controlled by NW, NWW tensile structures, andclosely related to the volcanic rock and ultra-shallow intrusive rocks which weregenerated by the late Cretaceous volcanic activity. In which the Ludi-Changde NStrending fault zone complexes with the NW structure, is a favorable location of gold,polymetallic mineralization area. The major types of wall rock alterations arepropylitic, K-feldspar, adularia, argillic, pyrite-phyllic, carbonate, silicification, etc,mainly in the low-temperature alteration minerals. The orebody exists in the crushingalteration zones, and strictly controlled by the broken alteration zones. The mainorebody of Naozhi gold deposit’s metallic minerals are mostly low-temperatureminerals assemblages, such as gold, electrum, chalcopyrite, galena, sphalerite,bornite.Mainly non-metallic minerals are quartz, sericite, calcite and adularia.Through the identification of the flakes, we found the presence of adularia in thegangue minerals, the contact surface of granodiorite and diorite inclusions. Throughthe identification, we believe that the igneous rock’s petrogenesis belongs to themagma mixing. The volcanic rocks are hornblende andesite and pyroxene andesite.Through the identification of polishedsection, we found that the sulphides content ofabout30%~50%, mainly pyrite, chalcopyrite, galena, sphalerite, in which, the pyriteis divided into three generations.The Electron Microprobe analysis obtained that the pyrite content a low grade ofCo, Ni elements, which reaction out a characteristic of epithermal gold deposit. Thesphalerite contains less Fe, comparative the results of previous studies, we found that,in Naozhi gold deposit, the mineralization temperature of the sphalerite is about100℃~200℃.Through the study of geochemical and U-Pb dating of the granodiorite, we foundthat the age of this set of magmatic rock is about166Ma±, the Middle Jurassic. The magma sources is a Crust-mantle mixed type, and dominated by crustal magma. TheDiagenetic tectonic background is that, in this region, the subduction of the Pacificplate led the crust a strong extension, then the lithospheric thinning, which triggered amassive underplating, and later formed a granite system.The diagenetic age of this set of hornblende andesite is about130Ma, the age ofthe Ultra-shallow intrusive rocks is between the age of mineralization and hornblendeandesite. The rock composition is calc-alkaline series, characterized by arc-islandfeature, magma source is a Crust-mantle mixed type. The diagenetic andmineralization tectonic background is that, after the Mesozoic, the eastern region ofYanbian got into the circum-pacific continental margin activation phase, thesubduction exacerbate the stretching activities of this area, thus forming a set ofmagma eruption and intrusion from lower crust to upper mantle, and the mainactivities of late magmatic activity is the ultra-shallow intrusive dike’s intrusion. Thisset of volcanic rocks’ diagenetic is slightly earlier than the age of mineralization, andinseparable with the genesis of the gold deposit.The mineralization of Naozhi gold deposit is very closely related to the LateJurassic-Early Cretaceous cycle’s ultra-shallow intrusive rocks. The ore bodies of thedeposit formed in the Early Cretaceous’ final volcanic eruption-intrusion cycles,named Jingouling(127Ma). The mine is located in the interchange ofDunhua-Duhuangling EW trending deep fault and Gaya river NW trending deep fault,Tumen-Wangqing NS trending deep fault is also across throuth this region. Thetectonic factors are developed in this region, such as the cross-cutting activities of theEW trending compressive shear fissures and NW trending shear fissures pressure witha same distance (200m). The main ore body mainly related with the thirdmineralization stage transtensional fractures.Through the study of fluid inclusions of the ore body of Naozhi gold deposit, weobtained important physical-chemical parameters. The main types of fluid inclusionsare gas-liquid two-phase type, gas rich type and a small amount of mineral inclusions.Because of the joining of magmatic hydrothermal in early mineralization time,leading to its high temperature of mineralizing fluid and high salinity. Thehomogenization temperature of main mineralization is about193.5℃~283.6℃. Thesalinity is in the average of8.42wt%NaCl, low density0.64~0.96g/cm3.Consolidated the ore features, gangue characteristics, wall-rock alteration and orestructure, we believe that Naozhi gold deposit belongs to the low sulphidationepithermal gold deposit.