藏南扎西康Sb-Pb-Zn-Ag矿床Sm-Nd、Rb-Sr成矿年龄

Sm-Nd and Rb-Sr metallogenic ages of Zhaxikang Sb-Pb-Zn-Ag deposit,South Tibet

由于成矿作用的多期性与复杂性,如何精确获取铅锌矿床成矿年龄一直是成矿年代学研究的难点之一。近年来,随着矿物提纯技术及分析测试手段不断完善,基于Sm-Nd及Rb-Sr体系测定热液矿物年龄逐渐成为一种有效的定年方法。通过测定西藏南部扎西康超大型Sb-Pb-Zn-Ag矿床中热液成因菱锰矿Sm-Nd与黄铁矿Rb-Sr同位素组成,获得菱锰矿和黄铁矿对应等时线年龄分别为(99.1±0.9)Ma和(98.0±1.8)Ma,记录了一次重要的热液成矿事件。此外,菱锰矿初始143Nd/144Nd值在0.512301~0.512849之间,经99 Ma球粒陨石CHUR计算出εNd值在-6.57384~4.115965之间,黄铁矿87Sr/86Sr值在0.714021~0.719708之间。这2种矿物均具有盆地流体同位素组成特征。结合前人对成矿物质和成矿流体特征的研究,笔者认为:扎西康矿床主成矿期形成于印度板块向北偏移过程中产生的张性构造系中,矿床属于盆地构造环境控制的铅锌矿床。

How to accurately obtain the metallogenic age of lead-zinc deposit is a difficult point of geochronology due to the multistage and complexity of mineralization.In recent years,with the continuous improvement of mineral purification and testing methods,determination of the age of hydrothermal mineral based on Sm-Nd and Rb-Sr isotope system has gradually become an effective way of dating.The authors presented the Rb-Sr and Sm-Nd isotopic composition of hydrothermal genesis and pyrite from Zhaxikang superlarge Sb-Pb-Zn-Ag deposit in south Tibet,and obtained the corresponding isochron ages of rhodochrosite and pyrite,which are(99.1±0.9)Ma and(98.0±1.8)Ma respectively.These data have recorded an important hydrothermal mineralization event.Furthermore,The 143Nd/144Nd ratios of rhodochrosite are between 0.512301 and 0.512849,and calculation of theεNd values with chondrites CHUR at 99 Ma yielded the ages between-6.57384 to 4.115965.The 87Sr/86Sr ratios of pyrite are between 0.714021 to 0.719708.The two minerals have the characteristics of basin fluid isotopic composition.Combined with early research results,the authors point out that the main mineralization of the Zhaxikang deposit took place in the extensional structure system associated with basin environment during the northward migration of the Indian plate.