纳米比亚欢乐谷地区白岗岩型铀矿成矿物质来源分析  

Ore-Forming Material Sources of the Leucogranite-type Uranium Deposit in the Gaudeanmus area,Namibia

作　　者：陈金勇[1,2] 范洪海 王生云[1,2] 顾大钊[1,2] 陈东欢[1,2] 

机构地区：[1]核工业北京地质研究院,北京100029 [2]中核铀资源勘查与评价技术重点实验室,北京100029 [3]南京大学成矿作用国家重点实验室,南京210093

出　　处：《地质学报》2016年第2期219-230,共12页Acta Geologica Sinica

基　　金：非洲中南部古老地块铀矿综合识别评价技术及应用研究项目的成果

摘　　要：本文对纳米比亚欢乐谷地区与铀成矿关系密切的白岗岩进行了系统的主量元素、微量元素及Sr-Nd同位素研究。结果表明,矿化白岗岩具有较高的SiO_2(68.81%~76.02%,平均值73.11%),富钾,A/CNK为0.96~1.07,平均值1.01,为亚碱性系列的准铝质-弱过铝质岩石。岩石富集轻稀土[LREE/HREE=2.53~7.71;(La/Yb)_N=2.14~10.40],Eu亏损中等,高Rb/Sr比值(2.03~5.50,平均值4.36),岩石同时富集Rb、Th、U、K及Pb等大离子亲石元素,亏损Ba、Nb、Ta及Sr等元素。岩石的初始^(87)Sr/^(86)Sr比值为0.73035~0.79345,ε_(Nd)(t)值为-13.5^-17.4,晶质铀矿的ε_(Nd)(t)值为-14.8^-16.5,两阶段Nd模式年龄为2.43~2.56Ga。元素和Sr-Nd同位素地球化学特征表明矿化白岗岩是在碰撞后的伸展构造环境中形成的,主成矿期的成矿物质来源于富铀的前达马拉基底;热液叠加改造期的铀可能来源于原生铀矿物本身。paper presents a systematic study of major and trace elements, and Sr-Nd isotopes on leucogranites closely related to uranium mineralization in the Gaudeanmus area, Namibia. The results illustrate that uraniferous leucogranites are high in SiO2 （68.81%-76.02%, averagely 73.11%） and K contents, with 0.96-1.07 of A/CNK （averaging 1.01）, suggesting the sub-alkaline metaluminous to weakly peraluminous rocks. The rock is enriched in light rare earth elements, with LREE/HREE - 2.53-7.71, （La/Yb）N= 2.14-10.40, moderate Eu loss and high Rb/Sr ratios （2. 0345.50 with an average of 4. 36）; enriched in LILE, such as Rb, Th, U, K and Pb, and depleted in Ba, Nb, Ta and Sr. The initial 873r/86Sr ratios of the rock range from 0. 73035-0. 79345 with the eNa（t） values of -13. 5--17. 4; the cNa（t） values of uraninites range from -14.8 to -16.5, and two-stage Nd model ages cluster between 2. 43-2. 56Ga. Detailed elemental and Sr-Nd isotopic geochemical characteristics infer that leucogranites were formed in the post-orogenic extensional environment; the U-rich pre-Damara basement dominantly contributed to the ore-forming material during the main mineralization epoch, whereas the additional uranium infilling at the hydrothermal superimposition-reformation epoch possibly came from the primary uranium minerals themselves.

关 键 词：晶质铀矿 成矿物质来源 Sr-Nd同位素示踪 白岗岩型铀矿 纳米比亚欢乐谷地区 

分 类 号：P619.14[天文地球—矿床学]