| The Qinghai-Tibet Plateau is the largest copper resource base in China,where three giant porphyry copper belts,i.e.Bangong-Nujiang Cu belt,Yulong Cu belt and Gangdese Cu belt)have been discovered.The traditional Gangdese porphyry Cu belt starts from Gongbujiangda County in the east and ends at Ngamring County in the west,and stretches for nearly 600km(east of 87°E).Many superlarge porphyry Cu deposits,such as Qulong,Xiongcun and Zhunuo,are distributed in the metallogenic belt.However,the western part(west of 87°E)of the Gangdese metallogenic belt has been poorly explored and studied.In recent years,a number of porphyry Cu polymetallic deposits(such as Luerma,Bolazha,Daruo,Luobuzhen and Hongshan,etc.)have been discovered.In this paper,we take the newly discovered Cu polymetallic deposits(i.e.Luerma,Balazha,Daruo,Luobuzhen and Hongshan,etc.)as the research objects,detailed research work has been carried out on the deposit characteristics,alteration zoning,metallogenic fluid,metallogenic epoch and genesis of each deposit,and we summarized the genesis mechanism,metallogenic law and metallogenic series of typical deposits.From the scale of prospecting and exploration,this paper systematically summarized the prospecting indicators,geophysics,geochemistry and remote sensing information,and on this basis,the genetic model of porphyry Cu deposits in the west part of the Gangdese metallogenic belt has established.Combined with the comprehensive information of geophysical prospecting,geochemical prospecting and remote sensing,we established the comprehensive prospecting model consists of geological,geophysical,geochemical and remote sensing information,and finally carry out the metallogenic prediction in the study area using the random forest algorithm.The main research contents and innovative achievements are as follows:1.The characteristics,alteration zones and genetic types of typical deposits are summarized.Late Triassic Luerma porphyry Cu(-Au)deposit: It is located in the Gangdese-Xiachayu volcanic magmatic arc belt on the southern margin of the Lhasa Terrane,is a newly discovered typical porphyry Cu deposit in the west part of the Gangdese metallogenic belt.The ore body consists of a porphyry Cu ore body(hosted in the Late Triassic quartz monzonite),a hydrothermal vein Au(Cu)ore body(hosted in structural fracture zone)and hydrothermal vein Cu ore body.With ore-bearing porphyry as the center,it has the alteration characteristics of typical porphyry deposits such as K-silicate alteration,beresitization and propylitic alteration.The hydrothermal veins develop from early to late: quartz-K-feldspar veins(A veins),quartz-metal sulfide veins(B veins),quartz-epidenite-carbonate veins(D veins).The results of fluid inclusions show that the ore-forming fluid belongs to the high-temperature and high-salinity H2O-Na Cl system,which is a typical magmatic high-temperature hydrothermal ore-forming fluid,and the genetic type is porphyry-type.Late Cretaceous Balazha porphyry-skarn-type Cu-Mo deposit: It is located in the Coqen-Shenza magmatic arc belt on the northern margin of the Lhasa Terrane.Ore bodies mainly occur in the Late Cretaceous biotite granite porphyry,and few ore bodies occur in the contact zone between granite porphyry and limestone(skarn-type ore bodies).Typical K-silicate alteration and beresitization zone are developed in the center of porphyry,and skarn zone is developed in the contact zone between porphyry and peripheral carbonate,which is the result of porphyry mineralization.Paleocene Daruo porphyry Cu polymetallic deposit: It is located in the Gangdese-Xiachayu volcanic magmatic arc belt on the southern margin of the Lhasa Terrane.Cu orebodies occur in the Paleocene granite porphyry and breccia tuff of the Dianzhong Formation.The geological characteristics show that the formation of Cu ore bodies is closely related to the Miocene granite porphyry.Oligocene-Miocene Hongshan-Luobuzhen porphyry-epithermal metallogenic system: It is located in the Gangdese-Xiachayu volcanic magmatic arc belt on the southern margin of the Lhasa Terrane.Oligocene granite porphyry is the ore-bearing porphyry of the Hongshan porphyry Cu deposit,showing typical porphyry mineralization and alteration characteristics.Luobuzhen epithermal Ag-Au deposit occurs in the secondary structural fracture at the far end of the porphyry,and geological characteristics show that its heat source and metallogenic material source are the Oligocene Hongshan granite porphyry.The spatial distance between the Hongshan deposit and Luobuzhen deposit is about 2km,forming an Oligocene-Miocene porphyry-epithermal metallogenic system.2.Determine the metallogenic epoch and summarize the spatial and temporal distribution of porphyry deposit for the western part of the Gangdese metallogenic belt.The zircon geochronology of Luerma ore-bearing porphyry shows that the mineralization occurred in the Late Triassic(?213 Ma),which successfully advanced the metallogenic time of porphyry deposits in the Gangdese metallogenic belt to the Late Triassic and extended the Gangdese porphyry copper belt to the west for nearly 200 km.The zircon geochronology of Balazha ore-bearing porphyry shows that the mineralization occured in the Late Cretaceous(?90 Ma).The Zircon geochronology of the Daruo ore-bearing porphyry shows that the mineralization occurred in the Paleocene(?60 Ma),which is the first Paleocene porphyry Cu mineralization in the metallogenic belt.The zircon geochronology of the Hongshan-Luobuzhen ore-bearing porphyries show that the mineralization occured in the Late Oligocene-Miocene(25?12Ma).3.The metallogenic model and comprehensive prospecting model are established,and the metallogenic prediction of the western part of Gangdese metallogenic belt is made by using the comprehensive prospecting model,and a number of metallogenic prospective areas with prospecting value are delineated.We have established the metallogenic model maps for typical deposits in the western part of metallogenic belt respectively,and built the comprehensive prospecting model according to the geophysical,geochemical and remote sensing information of each research area.Based on the comprehensive prospecting model,combined with the random forest algorithm,the metallogenic prediction of the study area was carried out,and 11 prospecting area of porphyry Cu polymetallic deposits were delineated: 2 grade I prospective area,3 grade II prospective area,and 6 grade III prospective area.Among which,Luobuzhen,Dajiacuo,Daruo,Balaza,Gaerqiong and Budongla prospects have great prospecting potential and are expected to discover new deposits(ore spot),which opens up a new perspective for prospecting and exploration in the Gangdese metallogenic belt. |
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