关键词: 三江口东岩体, 锆石U-Pb定年, S型花岗岩, 铀成矿潜力

Abstract: The southern Zhuguangshan composite pluton (SZCP) is one of the important uranium resource bases of China. The S-type
granites in SZCP have a close relationship with uranium ore deposits, while the I-type granites in SZCP possess no uranium
metallogenic potential. The Sanjiangkou granitic pluton in the western part of SZCP has similar lithology to the adjacent
Yanshanian Changjiang granite which is a S-type granite and hosts uranium ore deposits. Till present, the Sanjiangkou granite has
rarely been studied, its precise chronology is lacked and its genetic type needs to be determined. In this paper, an integrated study
including geochronology, petrogeochemistry and Sr-Nd isotopic geochemistry of eastern Sanjiangkou granite and comparison with
uranium-bearing Changjiang granite has been conducted. LA-ICP-MS zircon U-Pb dating for the eastern Sanjiangkou granite yields an
age of 161.9±2.1 Ma, suggesting its emplacement in the early Yanshanian period. Chemically, the granite has high SiO2 contents (73.5%~76.1%) and low FeOT (1.12%~3.25%), MgO (0.07%~0.83%) and CaO (0.64%~1.27%) contents, thus is highly fractionated with high
differentiation index (DI) values (86.4~93.6). A/CNK values of the granite vary from 1.00 to 1.35, indicating that it is a peraluminous to
strongly peraluminous granite. The granite is depleted in Ba, Sr, Nb, Eu and Ti, but enriched in Rb, Th and U, showing characteristics
of a typical low Ba and Sr granite. The rock samples display medium total REE contents (ΣREE = 119 × 10-6~268 × 10-6), and their REE
distribution patterns are right-inclined. Isotopic geochemical analysis results reveal variable initial 87Sr/86Sr ratios (0.70789~0.71488),
yet low and constant εNd(t ) values (-10.8~-9.6) with two stage model ages of 1.73~1.83 Ga. The geochemical and geochronological
characteristics of the eastern Sanjiangkou granite are similar to those of the Changjiang granite. Both of them are believed to be S-type
granitoids. Combining zircon U-Pb dating and regional tectonic setting, we suggest that the genesis of these granites were likely related
to the crustal extension during the early Yanshanian in South China, and they were generated through partial melting of the Mayuan
Group para-metamorphic rocks, with possibly minor involvement of mantle materials. Compared with the Changjiang granite, the
eastern Sanjiangkou granite is believed to possess prosperous uranium mineralization potential.

Key words: eastern Sanjiangkou granite, Zircon U-Pb dating, S-type granite, uranium mineralization potential