Research On The Ore-controlling Structure And Genesis Of The Matigou Gold Deposit In West Oinling

West Qinling is an important area of lead-zinc(copper)-gold deposits in China.Matigou gold deposit is located in west Shangdan Fault Belt of West Qinling,which is in northwest part of Fengxian-Taibai ore concentration area.Folds and Faults are well developed in study area.The fact that gold deposit in Fengxian-Taibai area is controlled by structure has reached agreement.However,the metallogenic conditions,characteristic of ore-controlling structure and genesis of the Matigou gold deposit are lack of research.Therefore,combined with the regional geological background and previous research results,This paper preliminarily studies the geological characteristics,magma and tectonic mineralization of the Matigou gold deposit,through field investigation and indoor data analysis.The following main achievements have been achieved:(1)The ore-bearing stratum of Matigou gold deposit is Luohansi Rock Group.Luohansi Rock Group underwent early north-south shear deformation,mid-term dextral shear deformation and late recumbent fold deformation.Ore-controlling structure of Matigou gold deposit is composed of a set of fissures,which is 300° strike,NWW dip,dip angle 30°.The fracture zone consists of a series of irregular micro-fracture and tensile fissures,which is 350° strike,dipping to E,dip angle 50°-60°.The kinematics characteristics of the ore-bearing structure belt in the space is dextral and normal slip.According to characteristics of the structure,We deduced that this area is in extensional tectonic setting when the mineralization occurs.(2)Pangjiahe,Laowangou,Zuojiazhuang,Wenjiazhuang gold deposits in Fengxian area are obviously controlled by structure.The strike of ore-bearing faults and gold ore body in these gold deposits are East-West or North-West directions.The structural styles of gold deposits are affected by the subduction,collision and closure of the Qinling ocean.The Pangjiahe,Zuojiazhuang and Wen Jiazhuang gold deposits have similar structural characteristics.It is deduced that the tectonic setting of them is similar when the mineralization occurred in syn-collision or later period(240?220Ma).(3)Granodiorite which is in west side of mining area,belongs to HeJiazhuang pluton,monzonitic granite and HeJiazhuang pluton are products of the same magmatism.Mineralized granite porphyry is closely related to gold deposit.The main source of metallogenic fluid in Matigou gold deposit is magmatic water.It is possible that gold mineralization may be related to magmatic activity or deep neutral-acid intrusive rocks and their related hydrothermal activities.Magmatic hydrothermal fluids are the main ore forming fluids of gold deposits in Fengxian area,with a mixture of small amount of atmospheric water in the later period.(4)In West Qinling,time of the transition period from collision to post-collision extensional environment is about 220-205Ma.The mineralization age of this gold deposit should be later than that of granite porphyry.According to the tectonic setting and time of the granitic porphyry crystallization,we inferred that the minerlization occurred during the 220-190Ma period.(5)In combination with the above research,we can see that the genesis of Matigou gold deposit is related to structure and magmatic activities.In the end of collision orogenic stage,the northwest trend tensile torsional fractural structural zone provided channel and space for the hydrothermal fluid under extensional tectonic environment.The magmatic hydrothermal is the heat source and provided the ore forming fluid.Then hydrothermal fluid precipitated and formed ore body in the micro fissures of structural belt.Thus Matigou gold deposit is a structural altered rock type gold deposit which is affected by mid-low temperature hydrothermal activities.