Primary uranium sources for sedimentary-hosted uranium deposits in NE China: insight from basement igneous rocks of the Erlian Basin

International audienceCarboniferous–Permian, Triassic and Jurassic igneousbasement rocks around the Erlian Basin in northeastChina have been investigated through detailed mineralogical,whole-rock geochemistry, geochronological data and Sm–Ndisotope studies. Carboniferous–Permian biotite granites andvolcanic rocks belong to a calc-alkaline association and wereemplaced during the Late Carboniferous–Early Permian (313±1–286 ± 2 Ma). These rocks are characterised by positiveεNd(t) (3.3–5.3) and fairly young TDM model ages (485–726 Ma), suggesting a dominant derivation from partial meltingof earlier emplaced juvenile source rocks. Triassic biotitegranites belong to a high-K calc-alkaline association and wereemplaced during the Middle Triassic (243 ± 3–233± 2 Ma).Their negative εNd(t) (−2 to −0.1) and higher TDM model ages(703–893 Ma) suggest a contribution from Precambrian crustduring the magma generation processes, leading to a strongenrichment in K and incompatible elements such as Th and U.Highly fractionated magmas crystallised in U-rich biotite (upto 21 ppm U) and two-mica granites. In biotite granite, themajor U-bearing minerals are uranothorite and allanite. Theyare strongly metamict and the major part of their uranium(90 %) has been released from the mineral structure and wasavailable for leaching. Mass balance calculations show thatthe Triassic biotite granites may have, at least, liberated ∼14,000 t U/km3 and thus correspond to a major primary uraniumsource for the U deposits hosted in the Erlian Basin