赣北石门寺钨多金属矿床辉钼矿Re-Os同位素年龄及其地质意义

Re-Os isotopic age of molybdeinte from the Shimensi tungsten polymetallic deposit in northern Jiangxi province and its geological implications

赣北石门寺钨多金属矿床位于下扬子成矿省江南地块中生代铜钼金银铅锌成矿带中，是燕山期花岗岩岩浆期后热液矿床．也是最近查明的中国规模最大的钨矿床大湖塘钨矿北矿段。通过对该矿床成矿期形成的6件辉钼矿样品进行Re—Os同位素定年，获得其等时线年龄149．6Ma±1．2Ma（n=6，MSWD=1．6）和模式年龄加权平均值150．4Ma±1．4Ma（n=6，MSWD=1．3），二者在误差范围内一致，说明该矿床形成于晚侏罗世。石门寺钨多金属矿床的辉钼矿Re元素含量为334．4×10^-9～22600×10^-9，其成矿物质主要来自于壳源或壳幔混合源。结合区域成矿地质背景推测，在晚侏罗世，石门寺矿区可能受古太平洋与欧亚板块聚合发生地球动力学调整的影响，大面积岩浆活动使之与围岩发生碱质交代作用，成矿物质被萃取．在成矿有利地段富集成矿。

The Shimensi tungsten polymetallic deposit lies in the Mesozoic Cu-Mo-Au-Ag-Pb-Zn ore belt of Jiangnan block with- in Lower Yangtze metaUogenic province. The Shimensi W deposit is related with Yanshanian granites, and is the northern ore block of the largest Dahutang W deposit which was recently prospected in China. In this study, six molybdenite samples of the ore-forming stage were collected for Re-Os isotope dating determine the chronology of the ore deposit. The analytical results yield an isochron age of 149.6Ma±l.2Ma （n=6, MSWD=I.6） and weighted average model age of 150.4Ma±l.4Ma （n=6, MSWD=I.3）. This age indicates that the mineralization took place during Late Jurassic. Moreover, the Re contents of molybdenite samples is 334.4×10^-9～22600×10^-9, which indicate that the ore-forming materials are likely to come from the crust-or crust-mantle-derived ones. In combination with metallogenic geological background, we infer that the Shimensi W deposit is associated with the subduction of the Paleo-Pacific ocean plate beneath the Eurasian continent. It is proposed that the ore-forming materials were extracted by alkali metasomatism between the magma and the wall rock and then concentrated in the favourable areas.