Genesis and Chronology of Baiganhu-Jialesai W-Sn Mineralization Belt, Qimantage, East Kunlun Mountain, NW China

The small intrusions consist of oligoclase granites are closely related with W-Sn mineralization in Baiganhu-Jialesai mineralization belt.The results of LA-ICP-MS U-Pb isotope dating show that oligoclase granite containing tungsten and tin ores was formed in 429.5±3.3 Ma.The εHf_(t) values of oligoclase granite vary from -11.05 to 7.40 with average of -1.26,and the peak value of T2DM vary from 944 Ma to 2 111 Ma with average of 1 492 Ma.Because of crystal fractionation and fluid activity during the latest stage of magma evolution,geochemical data of oligoclase granite are characterized with rich Rb,Cs,Nb and Sn,depleted Ba,Zr,Hf,Th,Sr,Ti,V and La.The granites in Baiganhu-Jialesai mineralization belt were derived from the melting of ancient felsic crust because of mantle underplating during the extension environment,and oligoclase granite was formed in the latest stage of magma evolution.There are two ore-forming stages in Baiganhu W-Sn deposit.In the first stage,during the intruding process of magmas containing tungsten and tin into wall rocks in early Silurian period,the batholith consist of monzonite granite was formed in deep,and small intrusions consist of oligoclase granites were formed in shallow.Then,the skarn-type and greisen-type tungsten ore bodies were formed in the top and contact belt of the small intrusions.In the second stage,after the fluid of latest magma evolution leaching metals from wall rocks,such as W and Sn,the quartz-veined tungsten ore bodies were formed along the fissures.