Geochemical Characteristics and Petrogenesis of the Early Cretaceous Mafic–Felsic Dykes in the Shijia Gold Deposit, Penglai, Shandong Province

The Shijia gold deposit is situated in the north of the Penglai–Qixia gold belt in the Jiaodong Peninsula. Different types of early Cretaceous mafic–felsic dykes, mainly including lamprophyre, diabase, and granite porphyry dykes, are closed associated with gold mineralization in space at Shijia. Based on the study of geochemical characteristics of vein rocks, it is concluded that lamprophyre and diabase dykes are characterized by low contents of SiO₂, TFe₂O₃ and high MgO, they are enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs; Such as Ba, Sr, and Pb), but depleted in high field strength elements (HFSEs; Such as Nb, Ta, Zr, Hf, and Ti). It is considered that lamprophyre and diabase dykes with arc–like trace element patterns are originated from partial melting of the enriched lithospheric mantle. Granite porphyry dykes are peraluminous, high potassium calc–alkaline rocks which are characterized by high concentrations of SiO₂, K₂O and Al₂O₃, with enrichment in LREEs and LILEs (Th, U, Rb, Ba, and Pb) and depletion in HFSEs (Ta, Nb, Ti, Zr, and Hf). They were formed by partial melting of greywacks under the background of asthenosphere upwelling and mantle–derived magma underplating. Although some researchers suggest that these dykes can be used as effective ore prospecting indicators, chronological studies show that there is no direct genetic relationship between the dykes and gold mineralization.