WEI Jia-lin1,2, TANG Chao1, XU Zeng-lian1,2, CHEN Lu-lu1,2, GUO Hu1,2, MIAO Pei-sen1,GU She-feng3, ZENG Hui1
(1. Tianjin Center, China Geological Survey, Tianjin 300170, China;
2.Key Laboratory of Uranium Geology, China Geological Survey, Tianjin 300170, China;
3.Exploration and Development Research Institute of Daqing Oilfield Co Ltd., Daqing 163712, China)
Abstract: Recently, an important breakthrough has been achieved on the exploration of sandstone-type uranium resource in the Changyuan of Daqing and adjacent areas in the northern Songliao basin. In addition, a significant clue for further uranium exploration has been found in the deep stratum in the Longhupao region. On the basis of field works including the geological logging of cores and systematic sampling, techniques including polarizing microscope, EMPA, and the analysis of uranium valence state were adopted to study the occurrence of uranium minerals in the uraniferous rocks in the Longhupao region in this paper. The study shows that these uraniferous rocks in the Longhupao region are mainly the light grey sandstones, in which pyritization is closely related to uranium mineralization, of the Quliuhe member at the bottom of the Sifangtai Formation. The main uranium-bearing minerals in this area include coffinite, U-rich Fe-Ti oxides, and clastic quartz containing uranium minerals. All of these coffinites and U-rich Fe-Ti oxides are genetically related to colloidal pyrites. The EPMA analytical results of uranium-bearing minerals show that the coffinite is generally rich in P and Y which are extremely poor in the U-rich Fe-Ti oxides. The EDS element mapping of the U-rich Fe-Ti oxides indicates that they could be produced from the altered detrital ilmenite by the late stage U-rich hydrothermal fluid. Moreover, the distribution characteristics of U4+/U6+ ratios and the paragenetic association of pyrite- ilmenite of the U-rich sandstones indicate that the formation environment of these uraniferous rocks in the Longhupao area is a relatively strong reduced one. Characteristics of the uranium mineral occurrence indicate that the uranium minerals of the U-rich sandstone in the Longhupao area are characterized with the formation of multi-periods with the environmental variation in the uranium mineralization process. From the formation of early stage U-rich Fe-Ti oxides to the formation of late stage P-Y-rich coffinite, the U, Si, P and Y contents of the ore-forming fluid are increased but the reductibility is reduced. It is concluded that the fluid coupling changed from the H2S-rich reductive fluid in the early stage to the uranium and oxygen containing fluid in the late stage.
Keywords: coffinite; Fe-Ti oxide; Sifangtai Formation; Longhupao; the northern Songliao Basin
ACTA MINERALOGICA SINICA Vol. 39, No. 6, 2019, page 709-725
