Geological Characteristics Of Xiangluwanzi Gold Deposit In Meihekou City,Jilin Province,and Its Prospecting Direction

Xiangluwanzi gold deposit is situated Meihekou City in the central of Jilin Province,Northeast of China.The study area tectonically lies in the intersection between the east section of the Central Asian Orogenic Belt and the north margin of the North China Craton with the Dunhua-Mishan deep fault belt as the boundary.The north part of the study area belongs to Jilin-Heilongjiang orogenic belt,the east extension of the central Asian orogenic belt,while the south part of the study area belongs to the Longgang block,the east part of the northern margin of the North China craton.The Xiangluwanzi gold deposit is located on the northern margin of the Longgang block,occurred in a trianglar zone sandwished between the Dunhua-Mishan fault and Liuhe Mesozoic graben.The main exposed strata in the study area are:Neoarchean Jiapigou group and Longgang group,Proterozoic,Paleozoic,Mesozoic,Jurassic and Cretaceous,and Cenozoic.The Jiapigou Group includes the Laoniugou Formation and Sandaogou Formation,while the Longgang Group includes the Yangjiadian Formation and Sidaolazihe Formation.The tectonic-magmatic activities in the study area are frequents,those them can be dedivied into five epsodes.Among them Yanshanian magmatic activity is closely related to the regional gold mineralization.The regional structures are main composed by deep faults such as NE-striking Dunhua-Mishan fault and Yalujiang fault,and NW-striking Fuerhe-Gudunhe fault,those faults controlled the spatial distribution of hypabyssal-ultrahypabyssal magmatic rocks and gold deposits.Xiangluwanzi gold deposit is controlled by the EW trending Yancongqiaozi-Longtou brittle-ductile shear zone,which also controls the distribution of cryptoexplosive breccia.NE trending faults and EW trending brittle ductile shear zones control the location,scale and occurrence of Dongshan and Xishan volcanic cryptoexplosion breccia.The ore body in Xiangluwanzi gold deposit mainly occurs in the cryptoexplosive breccia body,within the fracture of cryptoexplosive breccia and Archean Yangjiadian Formation,in the felsite dike or on the hanging wall and foot walls of the dike.The dikes in the gold mine area are distributed in NE direction,and mainly include diabase,diorite,lamprophyre,and felsite,of which felsite is closely related to gold mineralization.The wall rock alteration of the deposit is strong,including mainly the pyritization,silicification,sericite,chloritization,carbonation,etc.,of which silicification and pyrite sericite are closely related to gold mineralization.LA-ICP-MS zircon U-Pb dating and petrochemical composition testing were carried out for cryptoexplosive breccia,cryptoexplosive breccia tuff and felsite in Xiangluwanzi gold deposit.The ²⁰⁷Pb/²⁰⁶Pb weighted average age of zircons in cryptoexplosive breccia is 2541±34Ma,the ²⁰⁷Pb/²⁰⁶Pb weighted average age of zircons in cryptoexplosive tuff is 2521±16Ma,and the ²⁰⁶Pb/²³⁸U weighted average age of zircons in felsite is 161.4±1.1Ma.The original rocks of cryptoexplosive breccia are mainly Neoarchean granitic gneiss and plagioclase amphibolite gneiss,and the rock-forming age of felsite is Late Jurassic.The mineralization of the gold deposit is divided into three metallogenic periods:the pre-period of mineralization,the hydrothermal period and the epigenetic period,among which hydrothermal period is also divided into four stages:（Ⅰ）gold-pyrite-quartz stage,（Ⅱ）gold-pyrite-sulfide-quartz stage,（Ⅲ）gold-pyrite-sulfide-quartz-carbonate stage,（Ⅳ）quartz-carbonate stage;among them the（I）and（II）are the main mineralization stages of gold.In the fluid in inclusions of quartz in the Xiangluwanzi gold deposit,there are four types of primary fluid inclusions:pure CO₂（C）,CO₂ containing inclusions（CL）,CO₂-rich inclusions（LC type）,and gas-liquid two-phase（VL）.The ore-forming fluid is a medium to low temperature and low salinity fluid,with temperatures ranging from 153.5°C-238°C,peak temperatures ranging from 156°C-210°C,and salinity ranging from 5.09 to 9.34 wt%Na Cleqv.The mineralization pressure is 128-240Mpa,and the mineralization depth of the deposit is 1.28 km-2.4 km.The ore-forming fluid of the Xiangluwanzi gold deposit mainly comes from magma,and atmospheric precipitation is added during the ore-forming process.The genesis of Xiangluwanzi gold deposit is a medium low temperature hydrothermal type occurring in cryptoexplosive breccia.The Xiangluwanzi gold deposit is closely related to cryptoexplosive breccia and felsite dike.Regionally,some gold deposits occur near or within the Dunhua-Mishan deep fault zone,where secondary fault structures are developed and magmatic activity is frequent,providing a good prerequisite for gold mineralization.There is a difference in the polarizability between gold ore and surrounding rock,and the average resistivity of gold ore is slightly lower than that of surrounding rock.The polarizability can be used as a prospecting index for gold ore.The gold content in cryptoexplosive breccia and felsite veins is generally higher than that in surrounding rocks.The combination of Au,Ag,Cu,Pb,Zn,As,Sb,and Hg elements in stream sediment,soils,and rocks in the gold mine area can be used as a prospecting index for gold deposits.The low and gentle magnetic anomaly areas on both sides of the Dunhua-Mishan deep fault zone,and the annular structural area delineated by remote sensing are favorable locations for regional prospecting of the cryptoexplosive breccia type gold deposits.The cryptoexplosive breccia body in the Xiangluwanzi Xishan ore section still extends from500m to 900m below the earth surface,so the deep gold prospecting in the Xiangluwanzi Xishan ore section should be enhanced.