大厂锡石多金属硫化物矿床铅同位素演化及其矿床成因的意义

大厂锡石多金属硫化物矿床由两类 4形矿化组成 ,一类为层状及似层状矿化 ;另一类为不规则脉状矿化 ,包括大脉状、细网脉状和囊状 (块状 ) 3种不同形态的矿化。这两类矿化在铅同位素的组成上有比较明显的差异 ,而相同形态的矿化之间大致相同。层状矿化2 0 7Pb/ 2 0 4 Pb和2 0 6 Pb/ 2 0 4 Pb的比值较低 ,在同位素比值图上的数据点比较分散 ,且放射性同位素的含量随生成时代的变新而呈规律性的增加。不规则脉状矿化2 0 7Pb/ 2 0 4 Pb和2 0 6Pb/ 2 0 4 Pb的比值较高 ,数据点比较集中 ,不随埋藏深度的增大而改变 ,并大致与矿区花岗岩相当。同位素组成的特征表明 ,层状矿化的成矿作用与泥盆纪海底热水活动有直接的关系 ,成矿作用与地层同期 ,并受到后期岩浆热液的叠加和改造。不规则脉状矿化与燕山期花岗岩的侵入活动直接相关。

Pb ISOTOPIC EVOLUTION AND ITS SIGNIFICANCE IN ORE GENESIS IN THE DACHANG TIN-POLYMETALLIC ORE DEPOSITS

The Dachang tin\|polymetallic ore deposits are composed of 2 mineralization types and 4 subtypes. One type is composed of stratiform and stratoid ore bodies, the other, irregular veins including wider vein, stockwork and chambered mineralizations. The Pb isotopic features show obvious differences between these two types of mineralization, but the Pb isotopic composition is of no difference among distinct species in the same type of mineralization. \{\}\+\{207\}Pb/\+\{204\}Pb and \{\}\+\{206\}Pb/\+\{204\}Pb ratios in stratiform orebodies are higher and the data are more scattered than those of irregular veins. The radiogenic Pb content does not regularly increase with mineralization depth. The Pb isotopic characteristics indicate that the stratiform mineralization is directly related to submarine hydrothermal fluid exhalation during Devonian synsedimentation, and to the superimposition by magmatic hydrothermalism while irregular vein mineralization is directly related to the intrusion of Yenshanian granites.