Geological And Geophysical Characteristics Of The Iron-copper Ore Field And Prognosis Of Prospect Area In Gunjiu To R A Region,Tibet

The ore field in GunJiu-R A area,Tibet,is an iron-copper ore field.The studied area is located at the north edge of Gangdisi mountain range,Longer-Gongbujiang uplift.This paper analyzes the geological features and geophysical characteristics of the deposits,studies the genesis of ore deposit and ore-controlling factors,puts forward six potential prospecting areas,which provides a theoretical basis for the next phase exploration.The exposed strata in this area mainly are the Permian marine clastic and carbonate,and the main magmatic rock is late Yanshan Nixiong gabbro-granite body,and intermediate-acid dykes and intermediate-mafic dykes.The Longer-Gongbujiang uplift belt consists of two big regional boundary fault with multi-stage activities.The two faults experienced multi-stage tectonic movement with Mesozosic shear-zone rocks,Mesozosic basin-controlling and Cenozoic basin-controlling properties.They are the main structure controlling rocks and ores deposits.The iron and copper deposits(point)are distributed around the Nixiong gabbro-granite body.The ore bodies occur in the inside and outside contact zone between the intrusive body and the Permian marine carbonate and clastic strata.Type of deposit include skarn deposit,contact metasomatic-hydrothemal deposit and magmatic hydrothermal deposit.The wall rock alteration mainly include hornfels,skarnization,epidotization,silicification,chloritization,potassium and carbonatization.The magnetic susceptibility and remanent value of magnetite ore is the highest,and shows priority of remanent,belonging to stronger magnetism.The average value of remanence angle is 50.8°,and the geomagnitic field angle of the total base station in the research area is 46.5°,belonging to the normal oblique magnetization characteristics.Both the magnetic susceptibility and remanent value of granodiorite are far less than the magnetite ore,but much higher than hornfels lithic quartz sandstone,marble,quartz porphyry and tufflava.The anomalies cuased by shallow buried magnetite have characteristics of high strength,steep gradient,small width,and accompanying of highly positive and highly negative values.The geologic cause for the magnetic anomalies is closely related to the magnetite ore body,it is also the basis of magnetic prospecting and prognosis for prospect area in the study region.By measuring electrical parameters of the different rock outcrops in the study area,it is showed that the volcanic rocks have the lowest resistivity with average of 302?m and the lowest polarization layers with average of 1.13 percent.Marble,fine-grained biotite granite,and fine-grained biotite granite have medium polarization layers,generally,with polarization rate<2%and resistivity between 434?mand 2646?m.Chalcopyrite mineralized skarn and biotite granite are the ore-bearing layer,which has polarization generally greater than 2%,with a maximum of 4.65%,and resistivity varying between 238?1623?m.It is indicated that the mineralized bodies have the highest polarization,providing the physical prerequisite for application of the induced polarization method in the survey area.Iron ore bodies have characteristics of strong magnetic,and copper ore bodies have low resistivity with high polarization.The high precision magnetic method and dual-frequency IP method can well reflect the mineralization information and positioning of ore bodies.Through analysis and research of the metallogenic background,genesis of ore deposit,ore-controlling factors and metallogenic rules,the GunJiu-R A area has a good prospecting potential.Especially in the middle and the south-east of the area,we suggest three potential high-grade ore places,Muzhiding,Shasongnan and Maojialai,which can be carried out gross exploration.And in R A area,we located eight potential copper ore places,including six sharnore body,two magmatic hydrothermal type copper deposit.These are the most important places of prospecting in this area.Based on our comprehensive study on the geological characteristics,ore-controlling factors,the rules of mineralization of iron,copper deposit,and geophysical measurements in GunJiu-R A region,we have conducted metallogenic prognosis,and delineated six prospecting areas,including two Grade A prospecting areas(Zhongqongle and Xurijiamu),three Grade B prospecting areas(Zhuoburia,Nagelongba and Dajiaxiama),and one Grade C prospecting area(peripheral zone of Nixiong intrusive body).