Abstract:Based on analysis of petrography, petrochemistry, trace elements and rare earth elements of Sujiazhuangzi ultrabasic rocks in Zhaoyuan city, it is regarded that Sujiazhuangzi ultrabasic rocks in Jiaobei terrane are the products of mantle derived magma emplaced by the immature continental crust of Archean in the extensional environment. The original rocks are olivine-pyroxeniteor augite, and serpentinite is formed by strong hydrothermal metasomatism or alteration in the late stage. The main mineral composition is serpentine, which has a typical serpentine reticulate structure. As showed by trace elements, the lithophile elements, such as Ba, Sr and V are high, while Cr and Zr are low. Chalcophile elements, such as Cu, Pb, Zn and As are obviously high, while Ag, Au and W are low.Siderophile elements, such as Co and Ni are high, while Mo is low, which is characterized by rich lithophile and sulfophilic elements. The normalized REE distribution pattern of chondrite is LREE enrichment with right wing type, and ∑REE is lower than that of ridge basalt, and similar to that of island arc basalt. The fractionation degree of light and heavy REE is relatively low, which records that the secondary metasomatism of fluid undergoes certain oxidation in the process of serpentinization. The ultrabasic rocks in Jiaobei terrane participate in the evolution from immature to mature continental crust in the Archean period. It has formed the initial source bed of Jiaodong gold deposit in the granitic greenstone terrane together with the Archean basement rock series, and participate the mineralization process.
