Abstract:Kulongshan rhyolite porphyries lie in the northern margin uplift belt of North China Craton and Southwest section of the Guyuan—Honshanzi uranium belts, which between the Chifeng—Kaiyuan fault zone and Shangyi—Pinquan fault zone. Kulongshan rhyolite porphyries on located at the Kulongshan area, Fengning, northern Hebei, and it exposes 25 km 2 . SHRIMP zircon U- Pb dating indicate that the zircon of rhyolite porphyries n ( 206 Pb)/ n ( 238 U) age was 138.4Ma±1.3 Ma (N=12,MSWD=0.25), which belongs to the early stage of Early Cretaceous. Kulonghsan rhyolite porphyries have high SiO 2 , K 2 O, Na 2 O, high ratio of FeO T /MgO, poor Al 2 O 3 , MgO, CaO, P 2 O 5 . A/CNK=0.94~1.09, K 2 O/Na 2 O=1.03~1.30, which belong to the Peraluminous—weakly peraluminous high potassium calcium alkaline series rock. In the SiO 2 vs (Na 2 O+K 2 O)—CaO and SiO 2 vs FeO T /(FeO T +MgO) diagrams, they all fall into the A type granite area. The total amount of REE is 474×10 -6 ~531×10 -6 , δEu=0.02~0.05, which show that strong negative Eu anomaly, they belong to light REE enrichment type in the standardized REE distribution curve of chondrite. Kulongshan rhyolite porphyries is Enrichment Rb, Th, U, Nb, Ta, Zr, Hf, Y and other elements, loss Sr, Ba, P, Ti and other elements, Z+Nb+Ce+Y=374×10 -6 ~ 402×10 -6 (>350×10 -6 ), 10000Ga/Al=3.74~4.29(>2.6), which are characteristics of trace elements for A type granite. Kulongshan rhyolite porphyries have abnormal initial ratio of Sr, \[ n ( 87 Sr)/ n ( 86 Sr)\] i =0.690385~0.724000, relative low Nd ( ε Nd ( t )=-16.2~-14.9) and young Nd modle age( t DM2 =2163~2244Ma), they exhibit low radiogenic Pb istopic compositions, \[ n ( 206 Pb)/ n ( 204 Pb)\] i =16.893~16.922, \[ n ( 207 Pb)/ n ( 204 Pb)\] i =15.393~15.424, \[ n ( 208 Pb)/ n ( 204 Pb)\] i =37.716~37.771. In the Pb isotope model diagram, they fall into the lower crust region, which above the tropic of cancer. Meanwhile, they also fall in the EM I enriched mantle region. δ 18 O V- SMOW in rhyolite porphyries are 3.5‰~4.9‰, lower than the normal value of mantle(5.3‰±0.3‰), it may be related to water—rock interaction at high temperatures. The characteristics of Sr—Nd—Pb—O isotopes show that Kulongshan rhyolitic porphyries may be products of partial melting of the young lower crust formed by the mixture of the DMM, EMI type mantle and a small amount of ancient lower crust. The comparison shows that Kulongshan rhyolite porphyries ages are consistent with the ore- bearing host rocks of volcanic type hydrothermal uranium deposits in eastern China, especially Zhangmajing uranium deposits in southwest of the Guyuan—Hongshanzi uranium metallogenic belt. And uranium mineralization has been exposed in the contact zone of rhyolite porphyries, which indicated that the internal or external contact zone of Kulongshan rhyolite porphyries has good prospecting prospects.