The Langshan-Zhaertai Mesoproterozoic SEDEX metallogenic belt located in the western part of the northern margin of the North China Platform comprises the Hu ogeq i, Dongshengmiao, Tanyaokou Jiashengpan deposits and some occurrences, which ar e different from the middle Proterozoic typical SEDEX deposits in the world in t he fact that the metabasic volcanic rocks in Huogeqi, the metado ub levolcanic rocks in Dongshengmiao and potassic spilite with blastoporphyritic a nd blasticglomeroporphyritic texture in Tanyaokou deposits have been picked ou t from the only orebearing second formation of the Langshan Group in recent ye ars. The metallogenic process of these deposits are closely relevant to the synsedim entary volcanic activities based on the following facts: ① The SmNd isochron a g e of the basic volcanic rocks varies from 1491 Ma to 1824 Ma（more than or close to the model age of the lead isotope of all sulphide minerals）in these deposits , w ithεNd(t) =(3.48～6.4)±0.8，and the REE composition of them is e n riched in ligh t REEs and depleted in heavy REEs, which indicate these volcanic rocks, formed i n the pullapart basins along the north margin of the North China p l atform during the Mesoproterozoic, were derived from the mantle or lower crust. ② The REE composition of some PbZnPyores is also enriched in light REEs a n d d epleted in heavy REEs. The chondritenormalized REE patterns of them are simila r to the patterns for the basicvolcanc rocks. ③ In the lead isotope compositio n diagram of Doe and Zartman (1979), most of sphalerite, galena, pyrite, pyrrhotit e and chalcopyrite are plotted on both sides of the line for the mantle or betwe en the lin es for the mantle and lower crust. ④ The Cobalt content (ppm) of some pyrites i s much higher than the nickel content of them (Co/Ni＝11.91～12.19). ⑤ Some vol canic blocks an d debrises have been picked out from some pyrite and pyrrhotite ores， which sho w the source of ores directly derived from volcanic eruption and the variety and complexity of the metallogenic process. ⑥ All ZnPbCuFe sulfide orebod ies i n t hese deposits occur in the strata overlying the metamorphic volcanic rocks in th e only orebearing second Formation. In the Jiashengpan deposit lacking synsedi mentary volcanic rocks in the host succession only Pb and Zn ores occur without Cu ore, but the D ongshengmiao, Tanyaokou and Huogeqi deposits with synsedimentary volcanic rocks in the host succession contain Cu ore, indicating relatively high oreforming temperatures, besides Pb and Zn ores. The synsedimentary volcanic eruption directly supplied some oreforming metals, and resulted in secular geothermal anomaly which is favorable for the circulation of th e submarine convective hydrothermal system, resulting in the precipitation o f deep mineralizing fluids exhaling into anoxide basins along the synsedimentary fau lt system in the LangshanZhaertai rift.