Abstract:

The Daqiaowu uranium deposit is a volcanic-intrusive rock-hosted uranium deposit, where zircon ε Hf(t) values of the
volcanic-intrusive complex (dated at 138~125 Ma) exhibit a remarkable rise from approximately -13.0 to -3.0 through time. Zircon
saturation temperatures of these rocks also show an increase from ~749℃ to ~846℃. These characteristics suggest that volcanicintrusive
rocks in the Daqiaowu were generated by mixing of magmas derived from mantle and crust, and that more inputs of
mantle-derived materials were added to younger rocks. Together with a compilation of granitic intrusive rocks associated with magma
mixing in Xiangshan, Furongshan and Muchen, we found that whole-rock εNd(t) and zircon εHf(t) values of these granitic rocks increased

from -9.0 to -2.0 and -10.0 to 2.0 during 135~112 Ma, respectively, suggesting more contributions of mantle-derived magma through
time in the eastern part of Gan-Hang Tectonic Belt (GHTB) than in the western part. Sr-Nd isotopic modelling results indicate that the
percentage of mantle-derived magma has increased from 0% to ~60% during 135~112 Ma. Generally, mantle-derived magma has lower
uranium contents than does the derived magma. The magma mixing/mingling between them would be expected to dilute the uranium
contents of the crust-derived magma and lower its uranium metallogenic potentials. More mantle-derived materials in the commingled
magmas would lead to much lower uranium metallogenic potential. The fact that magma mixing is more intense in the eastern part of the
GHTB than in the western part probably is one of the reasons for the emplacement of larger uranium deposits in the western GHTB.
Thus, in order to find larger uranium deposits in the eastern part of the GHTB, more attention should be paid to such areas with both
uranium-rich basement (granites or felsic metamorphic rocks) and the overlying Early Cretaceous volcanic rocks.

Key words: volcanic-intrusive complex, Hf isotope, crust-mantle magma mixing, uranium metallogenic potential, Gan-Hang Tectonic Belt