Metallogenic epoch and regional crust evolution in the Jiaodong gold deposit, Shandong Province: Evidence from SHRIMP zircon U-Pb ages of mafic dykes

Although mineralogenetic epoch of the Jiaodong gold deposit in Shandong Province has been studied by many previous researchers, the accurate time frame of mineralization remains undecided. This paper reports SHRIMP zircon ages and oxygen isotopic values for pre-metallogenic and post-metallogenic mafic dykes in the Jiaojia gold deposit of Jiaodong Peninsula. In CL photos, the igneous zircons show good crystal form and clear zoning. Two samples from pre-metallogenic mafic dykes have recorded concordant ages of 124.9±1.8Ma (n=2, MSWD=2.2)and 124.2±1.1Ma (n=2, MSWD=0.50). A sample from post-mineralization lamprophyre yielded a concordant age of 112.2±0.7Ma (n=1), and therefore the emplacement age of the pre-metallogenetic mafic dykes is ≤ 124.9Ma and ≤ 124.2Ma. The emplacement age of the post-mineralization lamprophyre is ≤ 112.2Ma. The metallogenic age of the Jiaojia gold deposit is ≤ 124.2Ma. These data indicate that time limitation of mineralization of the Jiaojia gold deposit should be from 124Ma to 112Ma. Besides, the obtained multiple stages of inherited zircon ages from the samples have recorded the magmatic and/or metamorphic events of Jurassic, Triassic, Paleozoic, Neoproterozoic, Mesoproterozoic and Neoarchean. This suggests that, in addition to Neoarchean, Mesoproterozoic and Neoproterozoic geological bodies in North China Craton, there are also Paleozoic and Triassic geological bodies from Sulu orogenic belt in the depth of the Jiaobei uplift. These data suggest that the materials of the Sulu ultrahigh-pressure metamorphic belt was thrusting under the Jiaobei uplift. The δ¹⁸O values of zircons vary from 3.86‰ to 11.37‰, and this indicates that different stages of zircons have diverse oxygen isotope compositions and diversified material sources.