湖南仁里铌钽矿床辉钼矿Re-Os同位素年龄及其地质意义

Re-Os Dating of Molybdenite from the Renli Nb-Ta Deposit,Hunan Province,and its Geological Significance

仁里铌钽矿床是我国东部近年来新发现的超大型高品位花岗伟晶岩型铌钽矿,已探明的Ta2O5资源量10791 t,Nb2O5资源量14057 t,Ta2O5平均品位0.036%,Nb2O5平均品位0.047%,矿床仍具有较大的找矿潜力。为了厘定铌钽等稀有金属矿的成矿年龄,研究其成矿物质来源,为下一步勘查及成矿预测指明方向,本次对5号主矿脉钻孔ZK1616中的4件辉钼矿样品进行了Re-Os同位素年龄测试,获得的4件辉钼矿Re-Os平均模式年龄为130.5±1.1 Ma(MSWD=0.17),4件辉钼矿中Re含量为76.59~106.33μg/g,平均值为96.81μg/g。综合研究表明稀有金属成矿作用发生在中生代早白垩世,成矿年龄为130.5 Ma左右,成矿物质来源于壳幔混合源,以及岩浆演化晚期富F、Cl热液流体对冷家溪群地层稀有金属元素的释出、迁移和叠加。

The Renli is a super-large Nb-Ta deposit of high-grade granitic pegmatite-type newly discovered in the eastern part of China.The deposit has proved reserves of 10791 t Ta2O5 and 140571 t Nb2O5,and there is still a large potential for prospecting.The average grade of Ta2O5 and Nb2O5 is 0.036%and 0.047%respectively.In order to determine the ore-forming age of the rare metal deposit,molybdenite Re-Os isotope dating was carried out on four molybdenum samples from the No.5 main vein borehole ZK1616.Molybdenum Re-Os dating yield a mean model age of 130.5±1.1 Ma(MSWD=0.17)and isochronal age of 131.2±6.0 Ma(MSWD=0.31).The Re contents of the four molybdenite samples vary from 76.59 to 106.33μg/g,with an average of 96.81μg/g.The results show that the rare metal mineralization occurred in the Early Cretaceous.The ore metals were likely derived from a mixed source of crust and mantle,moreover,the fluorine-rich hydrothermal fluids released from the granite during the late stage magmatic evolution might have interacted with the Lenjiaxi group and released the ore metals within the strata and thus contributed to the rare metal mineralization.