Genesis of ankerite and its relationship with uranium mineralization in the Hailijin uranium deposit, southern Songliao Basin, China

Ankerite forms in hydrothermal fluids derived from basic dikes, and as temperature decreases, ankerite and uranium minerals precipitate in sequence. • Ankerite forms in hydrothermal fluids derived from basic dikes. • Ankerite is genetically related to uranium mineralization. • Ankerite and uranium minerals precipitate in sequence as temperature decreases. Ankerite cements in the Hailijin uranium deposit of the southern Songliao Basin serve as an excellent carrier for uranium mineralization. This study aims to characterize the morphology, contents, fluid inclusions, and elemental-isotopic compositions of the ankerite cements within the uranium reservoirs, and then reveals genesis of the ankerite and its relationship with uranium mineralization. In red sandstone, the ankerite is predominantly euhedral granular with an average content of 0.92 %. In yellow sandstone, it occurs as euhedral to subhedral crystals (average content: 0.62 %). In gray-white barren sandstone, it is mainly colloidal or granular, with an average content of 0.97 %. In mineralized sandstone, the ankerite exists in colloidal or granular form and has the highest average content (1.61 %). In primary gray sandstone, it appears as euhedral to subhedral crystals (average content: 0.94 %). Fluid inclusions in the ankerite yield homogenization temperatures of 140–180 °C (Th) and salinities of 8–12 wt% NaCl equiv. Sc, V, U, Zn, and Y exhibit remarkable enrichment in the ankerite, while Li, Cu, Rb, Ga, Zr, Nb, Ba, and Hf display systematic depletion patterns. The rare earth elements of ankerite generally exhibit the characteristics of light rare earth element depletion and heavy rare earth element enrichment. Ce/La ranges from 1.3 to 2.645, with an average value of 1.816, and Eu anomaly value (δEu) fluctuates between 0.881 and 1.093, with an average of 1.014. 87 Sr/ 86 Sr values of the ankerite range from 0.70598 to 0.70779, with an average value of 0.70748. The study indicates that the ankerite likely forms in hydrothermal fluids associated with basic dike intrusion. As temperature decreases, the ankerite and uranium minerals sequentially precipitate from these hydrothermal fluids. This study reveals the mechanism of hydrothermal fluids participating in mineralization of sandstone-hosted uranium deposits.