Geochemical Studies On Zoujiashan Deposit In Xiangshan Uranium Ore Field

Zoujiashan uranium deposit is the largest deposit located in the northwest of the Xiangshan Caldera in Xiangshan uranium ore field. As the typical hydrothermal deposit, Zoujiashan deposit is controlled by structure. It is still under debate about the genesis of the deposit, such as the controversy on the source of hydrothermal fluid and the source of uranium. The structure framework, characteristic of alteration and characteristic of uranium ores in drilling cores were investigated by geological survey in the field. Meanwhile, the micro-characteristics of uranium ore, alteration patterns,geochemical characteristics of main elements, trace element and REE in uranium ore and in altered wall rock were studied by microscopic, SEM analysis, electron microprobe analysis. Based on the above research, the following summary on mineralization characteristics and geochemical characteristics have been obtained.（1） The mineralization of Zoujiashan deposit is strictly controlled by the structural fracture with the zoning of hydrothermal alteration. There are various types of alteration and frequently hydrothermal activity. The main alterations relate to uranium mineralization are hydromicazation, fluoritization, chloritization and pyritization. Acid alteration period is the main mineralization stage.（2） Uranium minerals mainly include pitchblende, brannerite and uranothorite.Some secondary uranium minerals are visible in field. There are some other minerals coexist with uranium such as apatite, xenotim, pyrite and fluorite. Uranium can be adsorbed by melanocratic minerals, mainly exist on the surface and edge of melanocratic minerals.（3） From altered wall rock to uranium ores, U、Al₂O₃、MgO、CaO、P₂O₅concentration are increased corresponding to the increase of loss of ignition. From unaltered rock to uranium ore SiO₂ is descending, while with the increase of depth,the average content of MgO is increased. Although the overall content of the sample K₂O is higher than Na₂O, the mineralization may be more closely to the sodium metasomatism through that in uranium ore Na₂ O is higher than K₂O.（4） From altered wall rock to uranium ore the concentration of U and Th increased. The content of Th increased with the increasing of U content indicated the positive correlation between them. And the concentrations of Rb,Ba,Sr,P,Ti changed in wide range. Comparison with altered wall rock, the Th/U ratio in uranium ores is lower, which imply the differentiation between U and Th in the mineralization process and the remobilization of U.（5） From altered wall rock to uranium ore, Σ REE is increased, Comparison with altered wall rock the HREE are more enriched in uranium ores, and with the increase of depth the HREE are more enriched. LREE/HREE in uranium ore ranges from 1.03 to 6.21 with the meanvalue of 3.20. The ratio in altered wall rock is of 1.17 to 8.99 with the meanvalue of 5.18, while the LREE/HREE in fresh rock is of 4.60 to8.34 with the average value of 5.588. The change pattern of LREE/HREE ratio show that there is a close relationship of the evolution degree of hydrothermal to uranium mineralization. The negative Eu pattern also implied the deep source of hydrothermal solution.