Objective The characteristics of interlayer oxidation zone restrict sandstone−type uranium mineralization. Therefore, it is of great significance to study the geochemical characteristics and genesis of interlayer oxidation zone for evaluating the potential of sandstone−type uranium mineralization.

Methods According to the drilling information, combined with sand dispersion system mapping, sediment debris composition, environmental sensitive parameters and elemental geochemical characteristics, the key information of interlayer oxidation zone was analyzed.

Results The research reveals that the sand bodies in the study area are mainly composed of red sandstone, yellow sandstone, grey ore−bearing sandstone and primary grey sandstone, which correspond to the strongly oxidized zone, weakly oxidized zone, transitional zone and reducing zone, respectively. The average values of environmentally sensitive parameters including Th/U, TOC, Fe²⁺/Fe³⁺, S²⁻ and total sulfur content are as follows: 2.56, 0.1%, 0.35, 4.62×10⁻⁶ and 0.03% for the strongly oxidized zone; 1.89, 0.1%, 0.15, 5.68×10⁻⁶ and 0.03% for the weakly oxidized zone; 1.05, 0.17%, 0.42, 6.03×10⁻⁶ and 0.04% for the transitional zone; 1.02, 0.2%, 0.72, 16.49×10⁻⁶ and 0.09% for the reducing zone; and 0.03, 0.58%, 0.93, 29.22×10⁻⁶ and 0.41% for the ore−bearing zone. Trace elements including Y, Co, Ni, Zn, Sm, Gd, Dy and Er exhibit the highest average contents in the ore−bearing zone, with the respective values of 21.67×10⁻⁶, 32.72×10⁻⁶, 20.84×10⁻⁶, 47.63×10⁻⁶, 3.95×10⁻⁶, 3.11×10⁻⁶, 3.12×10⁻⁶ and 1.81×10⁻⁶.

Conclusions The results indicate that all environmentally sensitive parameters show a gradually increasing trend from the strongly oxidized zone to the ore−bearing zone. Elements including Y, Co, Ni, Zn, Sm, Gd, Dy and Er are enriched in the mineralization areas of the transitional zone. When the oxygen−containing uranium−containing fluid enters the uranium reservoir, the oxygen in the fluid reacts with the reducing substances in the sand body, Fe²⁺ is oxidized to Fe³⁺, U(Ⅳ) is oxidized to U(Ⅵ), and migrates with the fluid in the form of uranyl complex ions. When the oxygen in the fluid is gradually depleted, Fe³⁺ is reduced to Fe²⁺ and combined with S²⁻ to form pyrite. Uranyl complex ions are reduced to form pitchblende and precipitated, and some U(Ⅳ) reacts with SiO₄²⁻ to form uraninite. When the mineralization occurs, the complexation degree of different complex anions in the fluid with trace elements and rare earth elements is different, which makes the four trace elements such as Y, Co, Ni and Zn and the four rare earth elements such as Sm, Gd, Dy and Er enriched at the same time. Uranium mineralization is mainly developed in the transition zone near the weak oxidation zone, indicating that the transition zone and near the oxidation zone is a favorable uranium prospecting area in the study area.