Study On The Geological Characteristics And Ore Genesis Of Galonggema Cu Polymetallic Deposits, Yushu, Qinghai Province

Gonggema Cu polymetallic deposits is located in Yushu of Qinghai Province.The tectonic position is located on the northern margin of the North Qiangtang Block,between the Jinshajiang suture zone and the Shuanghu-Longmucuo suture zone,which belongs to the Three Rivers polymetallic metallogenic belt.The metallogenic epoch of Gonggema Cu polymetallic deposits is about Late Triassic,same with the host strata.The exposure strata in the mining area is the second lithologic member of Batang formation of the Triassic.The composition of the formation mainly are tuff,volcanic breccia,agglomerate lava,and locally mixed up with pyroclastic sedimentary rock.The mining area is located in the secondary anticline of the Zhiduo multiple syncline.the anticline controls the structural form of Galonggema deposits.And the nucleus strata of the fold is the andesitic tuff,which is the host strata.The intrusive rocks has not been observed in the mining area,but the geochemical study of the andesitic tuff shows the rocks formed in an island-arc setting.The Galonggema deposits were divided into east mining area and west mining area.And between them,the east mining area has the higher degree of exploration.Until now,the east mining area identified six Cu-Pb-Zn ore bodies?four Cu ore bodies and two Pb-Zn(Cu)ore bodies,among which the ? ore body is the emphasis.This work was mainly in the east mining area.Through the field investigation,we find the ore body with double-layer structure.The upper ore bodies which assume layered?stratiform-like and lenticular forms parallelly occur in the andesitic tuff.The ores' occurrence is consistent with the surrounding rock ',and synchronization fold with the strata,indicating syndepositional characteristics.The lower ore bodies which assume vein and veinlet disseminated is below the bedded ore bodies.The characteristics of ore-bearing formation of Galonggema deposits is composed of pyroclastic rocks and chemical sedimentary of hydrothermal exhalation.The carbon argillaceous slate on orebody roof formed after of exhalative sedimentary mineralization is the sign of the end of the orebody.There develops a series of typical hydrothermal-sedimentary rocks,such as baritic rocks,jasper rocks and iron-rich dolomites,etc.Ore structure are massive structure,vein structure and banded structure.Main metal minerals are pyrite,chalcopyrite,galena,sphalerite,tetrahedrite and bornite etc.,mainly secondary minerals are chalcocite,covellite and malachite.Major gangue minerals are barite,calcite,quartz,sericite and so on.Galonggema Cu polymetallic deposits mainly has a mineralization stage,namely hydrothermal deposition epoch.Because the later metamorphism is weak so the depost preserve the characteristics of the original hydrothermal sedimentation.Flow inclusion measured temperature of hydrothermal deposition epoch range of 105.2?-360.8?,fluid salinity range of 0.18 ~ 7.99% Na Cl,and the fluid density of 0.616 to 0.995g/cm3.The characteristics of hydrogen and oxygen isotopes showed that the ore-forming fluid mainly comes from the sea and a small part from magmatic fluids.The characteristics of sulphur isotopes showed that the sulphur of the major ore-forming stage mainly comes from the seawater sulfate reduced by bacteria or the basement rocks.Lead tectonic model graphic shows the lead from the upper crust,and may be leached by ore-forming hydrothermal from the lower basement strata.The genetic type of Galonggema Cu polymetallic deposits is the VMS-type deposit according to tectonic position,ore-controlling structure,wall rock alteration,wall rock characteristics,form of ore body and the geochemical characteristic of deposits.