Early Jurassic mafic dykes from the Xiazhuang ore district (South China): Implications for tectonic evolution and uranium metallogenesis

Most U deposits of the Xiazhuang area are located at the intersection between the WNW-trending dolerite dykes and the NNE-trending faults within the Triassic granites of eastern Guidong complex, South China. Previous metallogenesis studies assumed that intrusion of the WNW-trending mafic dykes induced upward migration of mantle-derived CO2-rich fluids, which leached U from the Triassic granite and subsequently precipitated at the intersection between mafic dykes and NEE-trending faults. Our new age data for the WNW-trending dolerite dykes reveal an age gap with respect to the associated U deposits (85-135 Ma) of at least 50 Ma, arguing against this model. Here, we propose that the role played by the dolerite dykes for U mineralizations is more likely to provide a favorable physicochemical environment promoting the precipitation of U from oxidized fluids. The fluids themselves, however, are probably related to the NNE-trending fault system and associated lamprophyre dykes rather than to the dolerites.