摘要
赣南白面石铀矿区是华南重要的火山岩型铀矿区,矿体产在白面石火山盆地的玄武岩和砂岩中。该火山盆地基底为白面石花岗岩,以前的研究表明是白面石花岗岩为铀矿化提供了成矿所需的铀。锆石LA-ICP-MSU-Pb同位素定年研究表明白面石花岗岩形成于(241±7)Ma,为印支期花岗岩。白面石花岗岩主要岩性为中细粒二云母花岗岩,岩石具有高硅(SiO2含量为71.99%～73.82%)、高铝(Al2O3含量13.26%～14.57%)的特点,铝饱和指数A/CNK为1.15～1.28,属于强过铝花岗岩。微量元素组成特征表现为富集Rb,Th,Ta和亏损Sr,Ba,Ti和Eu。稀土元素显示轻稀土富集和Eu负异常的特点。白面石岩体具有较高的(87Sr/86Sr)i比值(0.71162～0.71613)和较低的εNd(t)值(-13.9～-12.2),两阶段Nd同位素模式年龄变化为2.01Ga～2.15Ga。岩浆期锆石具有较低的εHf(t)值,变化为-15.1～-11.9,两阶段Hf模式年龄计算为2.01Ga～2.21Ga,与Nd模式年龄一致。岩相学和地球化学特征均表明白面石花岗岩属于典型的强过铝S型花岗岩,结合年代学和同位素特征,推测其源区可能是类似于桃溪群的变质沉积岩。白面石花岗岩的地球化学特征类似于华南许多的产铀花岗岩,可能是多期变质和重熔事件使其成为富铀花岗岩,随后在后期的地壳拉张导致的热液活动中转移铀,为铀矿化提供铀源。
The Baimianshi uranium ore district is an important volcanic-hosted uranium district in South China.The uranium ore bodies occur in basalts and sandstones in the Baimianshi volcanic-sedimentary basin.The basement of the basin is composed of the Baimianshi granite and the Xunwu metamorphic rocks.Previous studies indicated that the Baimianshi granite provided uranium for the mineralization.In this study,LA-ICP-MS U-Pb dating of zircons from the Baimianshi granite was made showing an emplacement age of（241±7）Ma.The Baimianshi granite is a medium-fine grained two-mica granite,characterized by high SiO2 contents（71.99%-73.82%）,with high A/CNK ratios（1.15-1.28）.It is enriched in Rb,Th,Ta and depleted in Sr,Ba,Ti and Eu,and characterized by variable REE contents with LREE enrichment and obvious Eu depletion.The Baimianshi granite has relatively high initial 87 Sr/ 86 Sr ratios（0.71162-0.71613）and low εNd（t）values（-13.9--12.2）.Two-stage Nd isotopic model ages vary from 2.01 Ga to 2.15 Ga.Its magmatic zircons have low εHf（t）values（-15.1--11.9）,with Hf model ages of from 2.01 Ga to 2.21 Ga,which are similar to the Nd model ages.Petrography and geochemistry indicate that the Baimianshi granite belongs to strongly peraluminous S-type.Combined with geochronology and isotope compositions,it is thus considered that the Baimianshi granite might be derived from partial melting of the metamorphic rocks similar to the Taoxi Group.The geochemical characteristics of the Baimianshi granite are similar to those of other uranium-bearing granites in South China.Multi-stage metamorphism and remelting resulted in uranium enrichment in granites.Later hydrothermal fluid activity associated with crustal extension might have leached U from the granite to form the Baimianshi U deposit.
出处
《高校地质学报》
CAS
CSCD
北大核心
2010年第2期149-160,共12页
Geological Journal of China Universities
基金
教育部科学研究重大项目(306007)
中国核工业地质局十一五基础科研项目(YK08)
内生金属矿床成矿机制研究国家重点实验室自主研究项目(2008-I-04和2008-III-02)资助
关键词
产铀花岗岩
地球化学
岩石成因
白面石花岗岩
赣南
uranium-bearing granite
geochemistry
petrogenesis
Baimianshi U deposit
southern Jiangxi Province
