Abstract:

There are three episodes volcanic eruptions in the North China at Meso-Neoproterozic,the volcanic rocks named Dahongyu Group,Chuanlinggou Group and Tuanshanzi Group.They are mostly alkahne basic rocks except for some dykes.The main rocks consist of phonotephrite,tephriphonohte,phonolite，foidite，trachyte，trachyandesite．The geochemical characteristic of the Volcanic rocks indicate the major contents are very rich for alkaline especially in K₂0 and TiO₂;the trace elements are rich in LILE,but they are depleted in HFSE,especially in Yb and Y.It is usually interpreted that these volcanic rocks were formed in the expand rift,since the incompatible element ratios such as Ba／Nb，Th／Nb，Ba／La，Zr／Hf，Nb／Ta and Sm-Nd.Rb-Sr isotopic data showed that magma may be from the mantle.However,they also were influenced by the continental crust.Therefore,it is implicated the volcanic rocks were formed in a continental rift.There also distributed many silver-polymetal deposits such as Dongzigou,Jiangjunguan,Yinyeling,Louxuanchang and Zhaizhuang deposits along the volcanic rocks.The mineralization epoch of these deposits and forming ages of the volcanic rocks are both about1,521Ma to 1,700Ma. Most ore bodies are distributed with in the volcanic rocks,sometimes volcanic rocks are the wall rocks of the ore bodies,and sometimes ore bodies are occurred in volcanic edifice.The dominant ore mineral assemblages are tetrahedrite，nativecopper,hessite and other sulfides,which implicated that they formed on low-middle temperature with volcanism.Therefore,it can be proved that the volcanism have taken a pivotal action for the forming of deposits in the Meso-Neoproterozic.

Key words: Meso-Neoproterozic volcanic rock, continental rift, silver-polymetal deposit, mineralization, the Dongzigou district of Hebei