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产于北大河群的早元古代火山岩是北祁连山西段最主要的三期火山岩之一。其地球化学特征表明，该期火山岩的原岩为具有双峰式组合的拉斑玄武岩和中酸性凝灰岩。两者具有完全不同的稀土分布型式，前者以极低的富集轻稀土为特征，而后者则以强烈富集轻稀土为特征：基性火山岩的微量元素分布曲线指示了其形成于裂陷槽环境。结合Ｎｄ同位素特征以及区域背景得出本区早元古代变质火山岩形成于裂陷槽环境。
The Early Proterozoic volcanic rocks that originated in the Beidahe Group are one of the three major volcanic rocks in the western part of the northern Qilian Mountains. Its geochemical characteristics show that the protoliths of the volcanic rocks of this period are tholeiite basalt and intermediate-acid tuff with bimodal assemblage. Both have completely different RE patterns, the former characterized by very low enrichment of LREE while the latter are characterized by intensive enrichment of LREE: The trace element distribution curve of the basic volcanic rocks indicates that it forms in the fissure trough surroundings. Combined with the characteristics of Nd isotopes and the regional background, it is concluded that the Early Proterozoic metamorphic volcanics formed in the rift trough environment.