贵州云峰铝土矿中铀矿物的发现

有关铝土矿中铀富集的报道很多,但至今未见独立铀矿物存在的相关文献。本次研究采用岩相学观察、X衍射(XRD)、ICP-MS、电子探针(EPMA)、拉曼光谱分析等手段,对黔中典型的铝土矿——云峰铝土矿中的晶质铀矿进行了研究。研究发现该铝土矿床中,铀富集明显(w(U)(18×10~(-6)～62×10~(-6)),平均值35×10~(-6)),铀矿物大小呈微米至亚微米级,围绕锐钛矿边缘生长、或充填于高岭石微裂隙中、或散布于与黄铁矿密切相关的高岭石或硬水铝石中。铀矿物的主要组分为UO_2(w(UO_2)为52.2%～80.88%)和TiO_2(w(TiO_2)为1.85%～14.98%);电子探针面扫描显示铀矿物中钛分布不均匀;铀矿物的拉曼特征波长为442 cm~(-1)和454 cm~(-1),因此,初步推测铀矿物为晶质铀矿和含钛晶质铀矿。其形成过程大致如下,来源于下寒武统牛蹄塘组黑色岩系中的铀(U~(4+))在风化过程中氧化为U~(6+)、析出、被Al~-, Fe~-氧化物/氢氧化物吸附;在沉积和成岩过程中,随着三水铝石转变为勃姆石和硬水铝石、铁氧化/氢氧化物转变为黄铁矿,吸附的铀解吸、还原(U~(6+)至U~(4+))、最后形成铀矿物。

Discovery of uranium minerals in Yunfeng bauxite deposit, Guizhou Province

Elevated concentrations of uranium have been found in many bauxite deposits, however, occurrence of separate U-minerals in the bauxite deposits has not yet been reported. In this paper, the authors carried out petrographic, XRD, ICP-MS, electron probe micro-analyzer (EPMA) and Raman spectroscopic studies of bauxite ores from the Yunfeng deposit, one of typical bauxite deposits in central Guizhou. The results show that the bauxite ores are characterized by high content of uranium (18×10^-6 to 62×10^-6, averagely 35×10^-6). Micron-to submicron-sized grains uraninite occurs as rims of Ti-oxides, fillings of micro-fractures in kaolinite, and disseminated grains in association with sulfides in the matrix of diaspore and kaolinite. EPMA analysis indicates that the U-minerals are mainly composed of UO₂(w(UO₂) 52.2% to 80.88%) and TiO₂(w(TiO₂) 1.85% to 14.98%) which are unevenly distributed in the U-minerals. Raman spectroscopic analyses show that the Raman peaks appear at around 442 cm^-1 and 454 cm^-1 for the U-minerals. The U-mine rals are suggested to be uraninite and Ti-bearing uraninite. The formation of uraninite is inferred as fol-lowing stages, during weathering stage, uranium was liberated from the source rock (the Lower Cambrian black shales of the Niutitang Formation) due to oxidation uranium from UU⁴⁺ to U⁶⁺, subsequently, most of the U⁶⁺ was absorbed by Al^-, Fe-Oxide/hydroxide. During deposition and diagenesis stages, the majority of U⁶⁺ was liberated from the Al-, Fe-Oxide/hydroxide, reduced to UU⁴⁺ again and finally converted to uraninite, together with the convention of gibbsite to boehmite and diaspore as well as the Fe-Oxide/hydroxide to pyrite.