西藏纳如松多隐爆角砾岩型铅锌矿床绢云母Ar-Ar定年及其地质意义

纳如松多铅锌矿床位于拉萨地块中部隆格尔-工布江达断隆带中段,为冈底斯铜矿带北侧铅锌银多金属成矿带的典型矿床之一。纳如松多铅锌矿床以发育隐爆角砾岩型和矽卡岩型铅锌矿化为特征。利用40Ar-39Ar同位素测年方法对纳如松多东矿段隐爆角砾岩型主矿体成矿阶段形成的绢云母进行了年龄测定,获得绢云母Ar-Ar坪年龄为(57.81±0.66)Ma,对应的正、反等时线年龄分别为(57.90±1.70)Ma、(57.70±0.77)Ma。所测坪年龄与正反等时线年龄具有很好的一致性,可以代表隐爆角砾岩型铅锌矿体的形成年龄。结合区域地质构造背景,纳如松多隐爆角砾岩型铅锌矿床形成于印度-亚洲大陆主碰撞时期。

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

Abstract: The Narusongduo Pb-Zn deposit, located in the Longgeer-Gongbujiangda fault-block uplift belt in the centre 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 by 40Ar-39Ar dating. The results show the 40Ar-39Ar plateau age of 57.81±0.66Ma, while the isochronal age of 57.90±1.70Ma and the inverse isochronal age of 57.70±0.77Ma. The 40Ar-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.