Study On The Geological Characteristics And Genesis Of Songshunangou Au Deposit In Menyuan County,Qinghai Province

Shongshunangou gold deposit is located in Menyuan county,Qinghai Province.The tectonic position is located in the middle of the Mesoproterozoic-Early Paleozoic belt in the northern Qilian.The southern margin of the North Qilian's fault is in the south of the deposit and the basemental uplift of Middle Qilian is close to the deposit.It is an important deposit located in copper,gold,zinc and lead metallogenic belt of Tuolai Mountain-Daban Mountain in North Qilian,which is formed during Caledonian.The exposed strata in the area is mainly Upper Ordovician marine volcanic rocks,including volcanic breccia,basaltic andesite,andesite crystal tuff and basaltic andesite crystal tuff.There are many fracture structures in this area.Most of them are NWW~SEE reverse fault and some are SN translate the fault.Magmatic activity in the deposit area is frequent.The main types of rock quartz diorite formed in early Caledonian,flesh red granite diorite porphyry and diorite porphyrite formed in late Caledonian.Gold mineralization has relation to flesh red granite diorite porphyry.Shongshunangou gold deposit can be devided into East part and West part.West part is located in the contact zone between granite diorite porphyry and basaltic andesite where two industrial ore bodies have been found.The main ore body presents spindle shape and wedge shape larger in the shallow when looked through profile.The main matal minerals are magnetite,chalcopyrite and pyrite,with a small amount of bornite,galena and sphalerite.Ore stuctures contain sparsely disseminated,stringer disseminated and veinlet structure.Alteration shows typical surface-type characteristic and is devided into different parts with different mineralization.Alteration from inside to outside consists of potassic alteration+silicide+magnetite(potassic zone)+silicide+epidote+chalcopyrite(silicide and epidote zone)+epidote+ chlorite+carbonate+pyrite(propylitization zone).Gold mineralization has close relationship with silicide,epidotization and chalcopyrite.East part is located in NW~SE ductile shear zone and the surrounding rock includes sericite quartz schist and sericite chlorite schist.The ore body is strictly controlled by structures and 24 industrial ore bodies have been found.The occurrence of ore bodies are almost the same as that of rock schistosity.The main matal minerals are pyrite,sphalerite,galena and chalcopyrite.The type of ore is quartz and carbonate vein which contain gold and alteration in surrounding rock include silicide,carbonatization and sericitization.The ore-forming fluid in Songshunangou gold deposit is characterized by middle ore-forming depth,middle temperature and middle-low salinities.Ore-forming temperature is 260?~300?,Ore-forming salinities is 2.3~12.4wt%,Ore-forming pressure is 19.5~26.6MPa,Ore-forming depth is 2.0~2.64 km.Main mineralization stage ore-forming temperature in East part is 140?~210?,The study of hydrogen and oxygen isotope indicates that the ore-forming fluid in Shongshunancha gold deposit is primary magma water,mixed with atmospheric precipitation during late stage.The study of sulfur and lead idotope indicates that the source mineralization material is the hybrid of crustal and mentle material.This research conduct rock geochemical study in granite diorite porphyry which has close relation to mineralization in West part.The study finds that the rock belongs to high potassium Ca-alkaline series,showing the feature of I-typed granite.The rock concentrate large ion lithophile elements and relatively lost high field-strength element.Combined with the existing chronology data and evolution and analysis of regional tectonic,the research found that the deposit is formed in continental margin techtonic setting,where North Qilian ocean has subduction to Middle Qilian continent in the south.Compared wih typical porphyry copper(gold)deposit,The Weat part has the characteristics of porphyry deposits,but it has its particularity.So the deposit is defined as porphyroblastic deposit.The Esat part is located in the south contact zone,obviously controlled by fracture stuctures,and it is defined as middle-low temperature hydrothermal vein deposit.The two parts of the deposit have closely related to time,space and cause of formation.The study tentatively suggest that the two parts belong to the same metallogenic system.Through comprehensive analysis,the Songshunangou gold deposit was formed in active continental margin setting in late Caledonian.The West part is controlled by rock and structures and most of ore bodies is located in the inside and outside contact alteration zone between granite diorite porphyry and basaltic andesite.Basaltic andesite is the main ore-bearing rock and large ore body is always formed in the intersection of structure and rock joints.The core part concentrates magnetite and chalcopyrite.Middle part concentrates pyrite,where a shell of pyrite is formed.Sphalerite and galena is concentrated outside.Gold mineralization has close relation to magnetite and chalcopyrite.Silicide,epidotization,magnetite,chalcopyrite are the important alteration and mineralization marks in West part.On the other hand,the pitch of East part is in the southwest.The deposit has good metallogenetic potentiality.The study focuses on magma intrusion into chlorite silk mica schist in the area,which cause physical and chemical alteration mineralization marks.In a word,the study indicates that copper,gold,zinc and lead metallogenic belt of Tuolai Mountain-Daban Mountain in North Qilian where the deposit is located is a potential mineralization in Qilian orogenic belt.The prospecting work in this area is expected to make greater breakthrough by finding new mineralization,accumulating experience and summarizing the metallogenic regularities and prospecting indicators.