The genesis of the Shaping carbonate-hosted uranium deposit, South China: Constraints from in situ calcite U-Pb dating and Sr isotopes

• Late Cretaceous metallogenic episode (80.5–83.0 Ma) identified in South China. • Uranium mobilized from marine carbonate. • Mineralization related to Paleo-Pacific slab rollback. The South China host various types of uranium deposits, including granite-hosted, volcanic-hosted, and sedimentary rock-hosted (carbonaceous-siliceous-pelitic rocks) uranium deposits. However, the genesis of carbonate-hosted uranium deposits, an important subtype of the sedimentary rock-hosted uranium deposit, remains insufficiently investigated. Here, we conducted in situ U-Pb dating, Sr isotopes analysis, trace elements and fluid inclusion on the Shaping uranium deposit hosted in the Ordovician dolostone in Guizhou Province. The calcite U-Pb age of 80.5–83.0 Ma indicates Late Cretaceous mineralization, classifying the deposit as epigenetic. The ore-stage calcite exhibits 87 Sr/ 86 Sr ratios ranging from 0.70851 to 0.70888, comparable to unaltered host rocks (0.70910–0.70948). The coupled relationship between high U contents in unaltered host rocks and Sr isotopic signatures indicates that uranium mineralization originated from fluid extraction of U from the carbonate rocks. Ore-stage calcite exhibiting low Fe concentrations (288–348 ppm) and strong negative Eu anomaly, which suggests an oxidizing fluid environment. Simultaneously, low-salinity fluid inclusions (<4.6 wt% equiv. NaCl) demonstrate meteoric water-dominated ore-forming fluids. Based on our study and integrating previous research, we present a revised metallogenic model for the Shaping deposit. During the late Cretaceous (∼80 Ma), the study area experienced lithospheric extension induced by the rollback of the Paleo-Pacific Plate (or Neo-Tethyan slab), resulting in regional thermal anomalies. The high heat flow heats meteoric water infiltrating along shallow crustal fault systems, forming a deep-circulation hydrothermal system. These oxided (high f O 2 ) fluids leached U from marine carbonates strata and subsequently migrated upward along fault systems, where they interacted with reducing agents (e.g., organic matter) in the host strata to induce U mineralization.