U-Pb Dating and Trance Elements Composition of Tadong Group fromJilin Province and Their Geological Implications

Meng Jie; Liu Xiaoyang; Liang Yihong; Qin Ya; Ju Gao; Li Benxian

doi:10.3799/dqkx.2017.040

Abstract：Tadong Group of Jilin Province is known for large-scale magnetite ore deposit, and Tadong iron deposit is the largest submarine volcano plume-metamorphic-reformation iron deposit in the Jilin-Heilongjiang metallogenic province.Complicated of geological characteristics and geological processes made the ownership of Tadong Group long been controversial.In this paper, the U-Pb zircon ages of the biotite plagioclase gneiss and magnetite diopside plagioclase leptynite are obtained by LA-ICP-MS.Zircons that obtained from biotite plagioclase gneiss are prismatic, and Th/U range between 0.17 and 0.65.U-Pb dating of these zircons record 206Pb/ 238U weighted mean age of 517.6±2.7Ma, indicating the formation age of the vocanic.In the magnetite diopside plagioclase leptynite, there are two kinds of zircons with two age groups, respectively.The first kind of zircons are short columns, and Th/U range between 0.78 and 1.00.U-Pb dating of these zircons record 206Pb/ 238U weighted mean age of 249.8±4.0Ma, indicating the age of thermal disturbance.Another kind of zircons are subhedral short prismatic, and have extremely high U, Th contents, the highest Th contents is 17422μg/g, respectively.U-Pb dating of these zircons record 206Pb/ 238U weighted mean age of 518.3±3.8Ma, attributing to the age of hydrothermal event.It is indicated that there is a hydrothermal process at 518.3Ma or so, which might be related to magmatism.Iron mineralization of Tadong iron deposit of Jilin Province is most likely related with this hydrothermal event.Therefore, one of mineralizations happened in the Early Cambrian Period (±520Ma) in Tadong iron deposit.