Metallogenic Model And Prospecting Direction Of Matigou-Miaogou Gold Deposits In Fengxian County?Qinling

A series of ductile-brittle fault belts,mylonites and cataclastic rocks with different layers and different properties due to shear nappe,translation and strike-slip have been formed in Shangdan tectonic melange belt due to plate subduction and collision.With the participation of gold-bearing hydrothermal fluid,a gold-bearing tectonic belt with very important prospects has been formed in central Shaanxi.The Matigou-Miaogou gold deposit is located in this zone,where faults and folds are well developed,and the relationship between regional tectonic evolution and mineralization has been established and perfected.However,there is still a big gap in this area,especially in the study area,the characteristics of structural elements and the occurrence of metallogenic process are not clear and precise,and the metallogenic model has not been established.Therefore,this paper is carried out through field investigation.Based on the geological structure and characteristics of the deposit,combined with the regional geological background and the previous research data and results,the special study of ore-controlling structure,the occurrence and evolution of ore-controlling structure,the genesis of ore-forming process and so on are discussed,and the metallogenic model is established for ore prospecting and prediction.The following results have been achieved:1.The gold mineralization alteration zone in Matigou-Miaogou gold mining area mainly occurs in clastic rock section of the Luohansi Group?Pz₁L?.Its lithology is grey-green metamorphic siltstone and silty phyllite.Silicification,sericite fading alteration and pyritization are important prospecting indicators for gold deposits.The main tectonic deformation period is early Indosinian regional foliation,shallow tectonic foliation and mylonitic foliation fold,accompanied by cleavage and parasitic fold development,Yanshanian superimposed anti-S-type structure.2.The main ore-controlling structures of Matigou-Miaogou gold deposit are faults and folds,in which the East-West ductile-brittle shear zone and its secondary brittle faults are the main ore-controlling structures.The faults including the main ore-controlling faults in the mining area are divided according to different scales and tectonic stages,and the control of different faults on the orebody is also different.The ore-controlling structures in the mining area are the Tangzang-Shangdan structural mixed zone,the Luohansi-Wayao upper brittle-ductile Composite Fault Zone?F9?,the brittle-ductile shear zone RF1 and RE2,and the Jingshaowan composite back and shear zone occurrence change and dilatation.Gold orebodies are mainly controlled by secondary and tertiary structures,namely regional composite fracture F9 and its subordinate brittle-ductile shear zone.Fracture F9 of Luohansi-Wayao is nearly EW-NW,and tends to be over 2 km apart.It is characterized by superimposition of ductile shear deformation and brittle fracture fragmentation.3.The gold grade chemical analysis of different types of rocks?ores?and their fabrics in the study area shows that the mineralization occurs in the vicinity of altered mylonite zone,altered fractured zone and granite vein.The ore types are mylonitic altered rock,cataclastic altered rock and quartz vein type.The trace and rare earth elements of rock mass and ore show that granite is closely related to gold mineralization and has similar source.The pyrite sulfur isotope tracer shows that the source of ore-forming fluid is the mixture of metamorphic strata and magmatic water.Different rock?body?veins may be the products of homologous magmatism and its evolution,and at least participate in the Gold Metallogenetic process.The ore-forming fluid medium is mixed source water,which has the characteristics of magma and stratum metamorphic water and a small amount of meteoric water.Gold mineralization is related to deep intermediate-acid intrusive rocks and their hydrothermal activities.The metallogenic hydrothermal fluid of Matigou-Miaogou gold deposit is mainly metamorphic hydrothermal fluid.4.The three gold mineralization alteration zones delineated include two main brittle-ductile shear zones?RF1 and RE2?.RF1 is located in the north-central part of the mining area,with NW-trending distribution,30-60 degrees dip angle,Tuguanpugou in the west,and Lingshanggou in the east,with a width of about 0.5-1 km.It is involved in the clastic rock section of Luohansi Group?Pz₁L^c?.RF2 is located in the southern part of the mining area,which is generally NWW-oriented and inclined at 30 degrees.From Qiaojiashan Valley in the west to Jiangjiashan Valley in the east,the width is about 0.3-0.8 km.Involved in the quartzite section of Luohansi Group?Pz₁L^b?;the two deformation zones underwent compressive shearing to extensional action,forming the evolution and superposition of ductile to brittle structures.The alteration mineralization is very concentrated.The intensive silicification zones are mainly distributed in and around the two strong deformation zones,and the later quartz veins develop along the brittle structures.The dense zones of pyritization and limonite mineralization are also closely related to the spatial distribution of two brittle-ductile deformation zones and strong silicification zones.Strong deformed structures,mylonitization,cleavage?sheet?physical and chemical zones and synclinal tight folds can be seen in the shear zone.The orebody dips northward gently and steeply locally,and is controlled by the upright schistosome belt of northward dip.The space may be in the form of multiple folds or fold stacks.The intrusive rocks closely related to the gold orebody are mainly Late Triassic granite porphyry veins,which are spatially distributed in the upper and lower walls of the gold orebody and extend along the complex dorsal core and the nearly EW-trending brittle-ductile shear zone.5.The metallogenic stages of Matigou-Miaogou gold deposit are as follows:the post-collision orogeny of the late Warwick-Indosinian period formed both extensional and compressive-shear nappe structures.The stripping faults and F9 and its secondary structures in the EW region between the interfaces of various segments of the Lohansi Group before the metallogenic stage of the study area,and the transformation of the Compressional-Extensional structural system from the Late Indosinian period formed NW and NWW brittle-ductile structures.Seismic shear zones and brittle superimposed structures.The main ore-forming body is hydrothermal alteration and enrichment during brittle-ductile shear deformation in Late Indosinian period,while magmatic hydrothermal mineralization and gold-bearing quartz veins in fracture zone superimposed in brittle period.Its genesis is related to tectonics and magmatic activity,and is obviously controlled by tectonics,especially mylonite and structural schistosomiasis belt.The deposit types are altered mylonite type,structural altered rock type and quartz vein type.Its genesis is a multi-stage hydrothermal superimposed gold deposit controlled by brittle-ductile shear zone type.Based on the comprehensive study of understanding and geological characteristics of the mining area,the prospecting indicators of the study area are structure,alteration,lithologic association and dike,and three target areas are delineated in the study area.