藏南柯月铅锌矿床辉绿岩年代学及地球化学特征研究

STUDY OF ZIRCON U-Pb CHRONOLOGY AND GEOCHEMISTRY OF DIABASE IN THE KEYUE Pb-Zn DEPOSIT,SOUTHERN TIBET

柯月铅锌矿床是藏南特提斯喜马拉雅锑金多金属成矿带内重要的铅锌矿床之一,针对区内唯一发育的岩浆活动产物-辉绿岩进行年代学测定,以明确与成矿作用之间的关系。本次研究在详细的大比例尺地质填图基础上,对区内1个辉绿岩样品进行了年代学及3个样品地球化学特征研究。测试结果表明,区内辉绿岩锆石U-Pb年龄为138.1Ma±4.5 Ma(MSWD=2.10),侵位于早白垩世。岩石地球化学特征体现出相对亏损Sr,Ba,U等大离子亲石元素,而相对富集Nb,Th,Ti等高场强元素特点,Th/Ta比值显示出亏损地幔特征,Nb/Ta比值及Zr/Hf比值均靠近原始地幔,表明柯月矿区辉绿岩岩浆源区为较纯的幔源,较少受到地壳混染。通过与区域早白垩世岩浆活动对比研究,认为柯月矿区辉绿岩与区内铅锌成矿作用并无成因联系,其仅仅属于Comei-Bunbury大火成岩省的一部分,是Kerguelen地幔柱岩浆活动早期产物,柯月铅锌矿床的形成可能与中新世淡色花岗岩浆活动相关。

The relationship between diabase and mineralization in the Keyue Pb-Zn deposit along the Tethyan Himalaya Sb-Au polymetallic metallogenic belt, southern Tibet, is not clear duo to previous poor investigation and study. Detailed large scale geological mapping in the field has made it available for the study of geochronology （one sample） and petrogechemistry （three sam- ples） of diabase in Keyue deposit. Zircon U-Pb dating of the dabase yields a 138.1 Ma±4.5 Ma age （MSWD-= 2.10）, indicating that the diabase was formed in Early Cretaceous. Geochemical characteristics reveal that the dabase lacks LILE, e. g. Sr, Ba, U and others, but enriches in Th, Nb,Ti and other HFSE, indicating that the diabase is originated from relatively pure mantle source and less contaminated by crust. Through comparative study on regional magmatism in early Cretaceous,it is considered that there is no genetic relation between diabase and lead-zinc mineral- ization,and the diabase in the Keyue deposit belongs to part of the Comei-Bunbury large igneous province,which was the early product of the Kerguelen mantle plume magmatism, while the for- mation of the Keyue lead-zinc deposit is related to the Miocene magma activities.