The Longwan uranium deposit is located in the central part of the Guizhou-Northwest Hunan metallogenic belt. The deposit is mainly hosted in carbonaceous mudstone and siliceous rocks, and is the first large-scale carbonaceous-siliceous-argillaceous rock type uranium deposit prospected in Guizhou province. The siliceous host rocks have Al/(Al+Fe+Mn) ranging from 0.16 to 0.41 with an average of 0.25, Fe/Ti ranging from 33 to 126 with an average of 73, MnO/TiO2 from 0.16 to 0.74, and MgO/Al2O3 from 0.67 to 4.21, with an average of 1.78. It shows that the rocks were formed in the continental and oceanic high-salinity seawater deposits with the characteristic of typical hot water deposition. The LaN/YbN ratios of the siliceous rocks range from 1.27 to 11.7 with an average of 4.99, indicating a continental margin and deep sea basin. The siliceous rocks have LaN/CeN ranging from 1.72 to 2.99 and δCe from 0.41 to 0.74, indicating a sedimentary environment of open basin and continental margin. The V/(V+Ni) ratios (0.88 to 0.98, with an average value of 0.93) of the siliceous rocks indicate a static sea environment. The larger than unit U/Th values (3.58 to 34.4 with an average of 15.1) of the siliceous rocks indicate a hydrothermal sedimentary origin. The zircon grains in the siliceous rocks have obvious oscillating zoning, with Th/U ratios greater than 0.1, positive Ce anomalies, negative Eu anomalies, LREE depletion, HREE enrichment, and low ΣREE, indicating that the zircon grains in the siliceous rocks are of magmatic origin. The U-Pb ages of zircon grains from the siliceous rocks are mainly concentrated in Mesoproterozoic, Late Proterozoic, Ediacaran-Cambrian, indicating that three periods of tectonic activities in the area. The siliceous rocks are U-rich, which have high U contents ranging from 27.0×10−6 to 193×10−6, with an average of 109×10−6, Th contents of 5.30×10−6 to 9.09×10−6, with an average of 7.42×10−6, and U/Th ratios from 3.58 to 34.4, with an average value of 15.1, and may provide uranium for the later period U mineralization. © 2023 Science Press. All rights reserved.
