Study On The Metallogenesis Of Endogenous Metallic Deposits In Tanjianshan Area In Qinghai Province

The study area(Tanjian Mountain area)is located in the west of the northern margin of Qaidam Basin in the Qinghai-Tibet Plateau.This area is another UHP metamorphic belt as same as the Qinling-Dabie,with its unique geological characteris.At the same time,it is a composite orogenic belt of China.In the long geological evolution period,it formed different deposits assemblage with corresponding geological structure,and had become one of the important metallogenic belt of western China.There are lots of famous deposits(or ore occurrences)in the northern margin of Qaidam Basin metallogenic belt,such as Xitieshan lead-zinc deposit,Jinlonggou and Qinglonggou gold deposits and so on.Based on the comprehensive analysis and research of a large number of geological data and scientific research achievements in the study area,using orogenic belt theory,this paper have made a detailed discussion and re-determination of the geodynamic background and evolution process of different geologic historical periods in the northern margin of Qaidam Basin.Furthermore,we have established the evolution model of the geodynamics of the northern margin of Qaidam Basin.Meanwhile,modern research methods and techniques of geology research are scientific used in this study to carry out detailed field geological investigation and indoor research on the typical deposits in the area under the guidance of modern metallogenic theory.According to the results,the metallogenic characteristics of Qaidam Basin in different geological history periods and different regional dynamics are systematically summarized.The results of this study show that,during the period of Neoproterozoic,there is an ancient ocean in Qaidam Basin(the northern margin of Qaidam Basin Ocean,hereinafter referred to as NMQBO),which is not a continental rift considered by some scholars.The ancient ocean should be part of Proto-Tethys Ocean tectonic domain,located between the Qaidam block and the Oulongbuluke micro-block.The two blocks are the products of the breakup of Rodinian continent,instead of the products of North China craton.By analyzing the existing research data,we believe that the period of the beginning of the expansion of NMQBO is during the Neoproterozoic.According to Murphy's orogenic theory,the NMQBO should have been subduction to the north and south sides at the same time.Confined to the thick sediments of the southern margin of Qaidam Basin,it is temporarily unable to verify the evidence to the southward subduction.Due to the continuous expansion of the Neoproterozoic oceans,the adjacent continent mainly showed up the characteristic just as the passive continental margin.From the late Neoproterozoic to the Caledonian,NMQBO turned into Proto-Tethys Ocean tectonic domain,and the adjacent continent gave way to the active continental margin since the subduction of the oceanic crust,forming a trench-arc-basin system.During the period of the late Caledonian,NMQBO was "scissors-like" closed.Meanwhile,continental-arc collision and continental-continental collision occurred.while the oceanic crust dragged deep crust and began to collision orogeny.It has entered in the stage of intracontinental orogeny in Hercynian,the stage of Zongwulong accreting orogenesis in the middle and late period,the stage of tectonic evolution in Mesozoic-Cenozoic.Based on the study of the typical deposits in Tanjianshan area,we have confirmed the characteristics of ore-controlling role of the metamorphic core complex in detail in the Jinlonggou gold deposit.It was the first time to identify and demonstrate that the metamorphic core complex played an ore-controlling role in Dushugou gold deposit.The understanding of the ore-controlling role of the metamorphic core complex in Jinlonggou gold deposit has changed the view of predecessor's the ore-controlling role of thrust-nappe structure.The age of granite porphyry closely related to the mineralization in the metamorphic core complex is 356 ± 2.8Ma,indicating that late Hercynian metamorphic core complex closely related to the mineralization had been formed under the background of extension structure.The mineralization of Dushugou gold deposit controlled by metamorphic core complex is consistent with Jinlonggou gold deposit.It is clear that Qinglongtan copper-bearing pyrite deposit in the area is a stacking deposit,formed during the early sedex period and late skarn period mineralization.Wandonggou iron deposit is a skarn type deposit,and the LA-ICP-MS zircon U-Pb dating results of the mineralization-related plagiogranite porphyry is 467 ± 3Ma,which is the product of the Caledonian magmatism.The forming of Qinglonggou gold deposit is due to continentalcontinental collision and intra-continent orogeny in late Caledonian and Late Hercynian-Indosinian.It was affected by the multi-period orogenic superimposition,belonging to the shallow orogenic gold deposit.Hongliugou gold deposit has also experienced the influence of the complex orogeny between the Caledonian and Hercynian-Indosinian,belonging to the shallow orogenic gold deposit.Caledonian period and Hercynian period are important metallogenic periods of this study area.The formation of Qinglongtan pyrite deposit,Wandonggou iron deposit and peripheral Xitieshan lead-zinc deposit is related to subduction of Caledonian oceanic crust.Hongliugou gold deposit and Qinglonggou gold deposit are formed in the process of collisional orogeny in the late Caledonian period.Jinlonggou gold deposit and Dushugou gold deposit are formed in the background of the post-orogenic extension of Hercynian period.