Thermochronological Constrains On The Exhumation History Of Porphyry-type Deposit In Gangdese Metallogenic Belt,Tibet

Uplift and exhumation in arc area may control the spatial and temporal distribution and affect the preservation potential of porphyry-type and epithermal deposits.Gangdese arc is a polymetallic metallogenic belt.Current research show that porphyry deposit is the most typical metallogenic type in this belt and most of the large and giant deposits are distributed in the eastern part of it,however,rare deposits located in the central and western part.As the geological background is similar along the Gangdese arc,the metallogenic background and mechanism may not be the main factor that control the deposit distribution.However,burial,uplifting and exhumation after mineralization may have certain relationship with the deposit distribution in the arc area.This study conducted low-temperature thermochronological research on Xiongcun,Jiru and Zhunuo deposits from central and Qulong,Chongjiang and Tinggong deposits of eastern Gangdese,analyzed the magmatic-hydrothermal evolution and exhumation history of deposits,and discussed the connection between distinct exhumation and deposit distribution in the arc area.Thermochronological results review that Qulong deposit occurred rapid exhumation between 12.6?10.0Ma,and the total exhumation amount are about 1.7?2.9km so far.The rapid exhumation period and amount in Tinggong deposit are 8.5?7.0Ma and >2km,separately.Two periods of rapid exhumation occurred at 22?18 and 15?8Ma,respectively,in Xiongcun area,and obtained total exhumation about 7.5?8.5km.The mineralization depth of Chongjiang deposit was about 2.0?2.5km,and suffered exhumation after 8Ma.However,thermal data suggest that the mineralization depth were very shallow at Jiru and Zhunuo deposits(<1km),indicating the total exhumation amount of this two deposits are <1km.Combined with previous data,this study found that the total exhumation amount in northern belt of eastern Gangdese are <2km since Eocene,however,up to 4km in northern belt of central Gangdese;The exhumation amount since Oligocene-Miocene in most part of the southern belt of central and eastern Gangdese arc are up to 6?8km except the northern part of central Gangdese and Lhasa-Zedang district in eastern Gangdese have been weakly exhumed(<3km).The spatial and temporal distribution of deposits and exhumation in Gangdese area reviews that the spatial distribution of Paleocene – Eocene,Miocene and Oligocene deposits are consistent with the weak exhumed northern Gangdese belt,strong exhumed southern Gangdese belt and medium exhumed Lhasa-Zedang district in southern Gangdese belt,respectively.According to the exhumation characteristic in the region,this study argues that Paleocene-Eocene deposits have more prospecting significance in northern Gangdese area,Miocence deposits have resource potential in northern part of southern belt in central Gangdese and Lhasa-Zedang district in eastern Gangdese,and the latter is also the most favorable area for Oligocene deposits.Due to the deposits may have been buried by volcanic-sedimentary strata after mineralization,the Pre-Cenozoic deposits have more prospecting significance in the strongly exhumed area.