The Ar-Ar Geochronology of Sericite from the Cryptoexplosive Breccia Type Pb-Zn Deposit in Narusongduo,Tibet and its Geological Significance

The Narusongduo Pb-Zn deposit,located in the Longgeer-Gongbujiangda fault-block uplift belt in the center of Lhasa Terrane,Tibet,is one of the representative ore deposits in the Pb-Zn-Ag polymentallic ore belt in the northern side of the Gandese copper ore zone. This deposit is characterized by two types of mineralization,namely cryptoexplosive breccia type in the eastern part and skarn type in the western part. Sericite from the Pb-Zn main orebody of the cryptoexplosive breccia type in Narusongduo was measured by40Ar-39Ar dating. The results show the40Ar-39Ar plateau age of57. 81 ± 0. 66Ma,while the isochronal age of 57. 90 ± 1. 70Ma and the inverse isochronal age of 57. 70 ± 0. 77Ma. The40Ar-39Ar plateau age is in agreement with the isochronal age and the inverse isochronal age within a reasonable error range,which can be regarded as the ore-forming age of the cryptoexplosive breccia type Pb-Zn orebody. Considering the regional geological background,this study suggests that the cryptoexplosive breccia type Pb-Zn deposit in Narusongduo formed during the main Indian-Asian collisional period.