LIU Xu1, XIA Fei1*, ZHANG Cheng-yong1, ZHANG Qun-xi1, LIU Bo2, HOU Shu-ren2

(1. State Key Laboratory of Nuclear Resources and Environment, East China University of Technology, Nanchang 330013, China;
2. Geological Party No.208, China National Nuclear Corporation, Baotou 014010, China)

Abstract: The Tamusu uranium deposit in the Bayan Gobi Basin is a super-large sandstone-type uranium deposit in northern China. However, it has special mineralization characteristics, with high grade and many ore layers. Its genesis has been controversial. New evidences are urgently needed to solve its mechanism of uranium mineralization. In the field geological survey of the project team, it was found that the purplish red uranium ore occurred in the oxidation zone had obvious reworking traces of hydrothermal fluid. This is a new type of uranium mineralization. Through rock and mineral identification, etching track, electron probe and other experiments, we have systematically analyzed mineral alteration characteristics of the purple uranium ore in this area, and discussed the genesis of uranium enrichment of the deposit. It is believed that the purple-red uranium ore of the Tamusu deposit is closely related to the hydrothermal alteration, and its alteration zone can be classified into fluorite vein subzone, purple-red fluorite cement subzone and grayish white kaolinite subzone. Uranium minerals occurred mainly in dispersed and adsorbed states whose distribution is consistent with that of collophane. This type of uranium ore is the product of the interaction between the deep reductive U- and P-rich hydrothermal fluid moved into the ore-targeting layer and the weak alkaline fluid in the oxidation zone. The change of pH and Eh conditions caused the simultaneous precipitation and enrichment of U and P. Combined with the analysis of geological characteristics of the ore body, it is considered that the Tamusu deposit is a sandstone-type uranium deposit with composite genesis formed by the interaction of supergene oxidation fluid and deep hydrothermal fluid. The supergene oxidation fluid caused the migration of uranium from the erosion source area and the stratum, and the enrichment and precipitation of uranium at the redox transition interface, while the hydrothermal fluid which carried the deep sourced uranium into the oxidation zone had formed the phosphorus-rich uranium ore. They are main reasons resulted in the formation of high uranium grade multi-layer ore bodies in the Tamusu deposit.

Keywords: sandstone type uranium deposit; uranium phosphorus mineralization; hydrothermal fluid activity; interlayer oxidation; Tamusu

ACTA MINERALOGICA SINICA Vol. 43, No. 3, 2023, Page 325