The geological and geochemical characteristcs of the mixed crust-mantle derivation type uranium-bearing granitoids in the lower Yangzi fault depression zone

On the basis of study on the geology, petrology, mineralogy, petrochemistry, geochemistry, REE, Sr, Pb, and O isotope compositions in Anlu quartz syenite belt (AL) and Yaocun potash feldspar granite massive rock, it is shown that the initial rock-forming material derived from more depth and the magmas, which were rich in alkaliand poor in water, were derived from the mantle through partial melting and contaminated by the crustal materials in the process of movement upward and emplacement along the deep faults. According to the crust-mantle mixing model for Sr and Pb isotopes, it is calculated that 57% and 52.8% of the materials were derived from the mantle for Yaocun massive rock and Anlu rock-belt respectively, i.e., 43% and 47.2% of materials from the crust respectively. The genetic series of these granitic rocks may belong to that of mixed crust-mantle derivation