新疆白杨河铍铀矿床萤石Sm-Nd和沥青铀矿U-Pb年代学及其地质意义

白杨河矿床是我国类型独特的一个特大型铍、铀多金属矿床,铍矿物主要确定为羟硅铍石,铀矿物主要发现沥青铀矿和次生的硅钙铀矿以及少量的铌铀矿,伴生矿物主要是萤石。为恢复铀和铍的成矿过程,划分成矿阶段,本次工作通过系统采集钻孔中的萤石样品,进行了Sm-Nd同位素测年研究,获得了三组等时线年龄,分别为291±16Ma、265±33Ma和207±37Ma,代表了成矿前、成矿期和成矿后萤石的形成;采集中心工地、新西工地和九号工地平巷内的沥青铀矿样品,进行了UPb同位素测年研究,获得了~(206)Pb/~(238)U表观年龄237.8±3.3Ma、224±3.1Ma、197.8±2.8Ma、97.8±1.4Ma和30.0±0.4Ma,利用U-Pb表观年龄将铀矿化划分为四个阶段:中三叠世、晚三叠-早侏罗世、晚白垩世和古近纪中期。因此,白杨河矿床具有铍早铀晚的成矿特点,铀成矿经历了四个阶段。

Fluorite Sm-Nd isochron and pitchblende U-Pb dating in the Baiyanghe Be-U deposit, Xinjiang and their geological significances

Baiyanghe deposit, located in the northwestern Xinjiang, is a super-large Be-U deposit. The beryllium ore mineral was defined as bertrandite and the uranium minerals were identified to be pitchblende and uranophane, with minor uranniobite. Fluorites are dominantly closely associated with Be and U mineralization. In order to restore the ore-forming evolution processes and separate the ore-forming stages, this paper systematically sampled various fluorites from bore holes for Sm-Nb isotopic chronology. Three groups of isochronal ages have been obtained, 291±16Ma, 265±33Ma and 207±37Ma which respectively represent the pre-ore, ore-forming and post-ore fluorites. The U-Pb isotopic dating of pitchblende has obtained apparent ages of ²⁰⁶Pb/²³⁸U as 237.8±3.3Ma, 224±3.1Ma, 197.8±2.8Ma, 97.8±1.4Ma and 30.0±0.4Ma, and the uranium ore-forming process could be separated into 4 stages: Middle Triassic, Late Triassic to Early Jurassic, Late Cretaceous and Middle Paleogene. Therefore, in the Baiyanghe deposit, the beryllium mineralization was earlier than the uranium mineralization, and pitchblende has formed for four times at least.