LA-ICP-MS Dating of the Aegirine-Augite Syenite of Yushishan Nb-Ta Deposit in Eastern Altun and Its Constraints on the Metallogenetic Age

Lying in the joint of Hongliugou-Lapeiquan ophiolitic melange zone (eastern part of the Altun Mountains), Qilian orogenic belt and Oulongbuluke microcontinent, Yushishan Nb-Ta Deposit is a large-size deposit recently discovered. Based on the study of its metallogenic background, the major ore-bearing strata is found to be Ao'yougou Formation of Changchengian Period. The lithological association includes metamorphic volcanic rock and marble, mixed with aegirine-augite syenite, where develop minerals rich in Nb-Ta such as fine-grain pyrochlore and aegirine-augite. The LA-ICP-MS dating for zircons from an aegirine-augite syenite sample yields the diagenetic age of 776.8±2.5 Ma, indicating that the metallogenic age is similar or slightly later than the mineralization of the rock. Combined with petrological-mineralogical characteristic under the microscope and metallogenic age, the aegirine-augite syenite and Nb-Ta deposit were probably formed in continental rift tectonic background induced by the breakup of Rodinia supercontinent in Nanhua Period.