【摘要】 冀北窟窿山流纹斑岩位于赤峰—开原断裂以南、尚义—平泉断裂带以北的华北克拉通北缘隆起带和沽源—红山子铀成矿带的西南段,主要分布于窟窿山北西部,出露面积约25 km²。本文通过SHRIMP锆石U-Pb定年和主量元素、微量元素、稀土元素、Sr—Nd—Pb—O同位素组成测试,查明流纹斑岩形成的地质时代,探讨流纹斑岩的物质来源和形成的构造背景,分析流纹斑岩与铀矿化的关系。分析结果显示:流纹斑岩SHRIMP锆石n(²⁰⁶Pb)/n(²³⁸U)年龄为138.4±1.3 Ma（n=12,MSWD=0.25）,属早白垩世早期;流纹斑岩具有高硅、富钾、钠,高FeO^T/MgO值,贫Al、Mg、Ca、P的高分异特征,属准铝质—弱过铝质高钾钙碱性系列岩石,在SiO₂—[（Na₂O+K₂O）—CaO]和SiO₂—FeO^T/（FeO^T+MgO）图解中落于A型花岗岩区;∑REE含量较低,Eu负异常明显,具轻稀土富集型稀土配分曲线特征,富集Rb、Th、U、Nb、Ta、Zr、Hf、Y等元素,亏损Sr、Ba、P、Ti等元素,10000Ga/Al=3.74～4.29（>2.6）,Zr+Nb+Ce+Y=374×10^-6～402×10^-6(>350×10^-6),显示A型花岗岩微量元素的特征。流纹斑岩的[n(⁸⁷Sr)/n(⁸⁶Sr)]_i值变化范围较大（=0.690385～0.724000）,ε_Nd（t）值较低（=-16.2～-14.9）、T_DM2较大（=2163～2244 Ma）,Pb同位素比值较低{[n(²⁰⁶Pb)/n(²⁰⁴Pb)]_i=16.893～16.922、[n(²⁰⁷Pb)/n(²⁰⁴Pb)]_i=15.393～15.424、[n(²⁰⁸Pb)/n(²⁰⁴Pb)]_i=37.716～37.771},在铅同位素图解中窟窿山流纹斑岩同时带有下地壳物质和富集地幔印记;δ¹⁸O_V-SMOW=3.5‰～4.9‰,低于正常地幔的δ¹⁸O_V-SMOW值（=5.3‰±0.3‰）,具低氧流纹岩特征。Sr—Nd—Pb—O同位素特征显示,流纹斑岩可能是源于DMM型、EMI型地幔和少量古老下地壳混合形成的年轻下地壳部分熔融的产物,而且与高温热液蚀变有关。对比表明,窟窿山流纹斑岩与中国东部绝大多数与火山岩有关的热液型铀矿的赋矿围岩时代一致,特别是与沽源—红山子铀成矿带西南段张麻井铀矿的赋矿流纹斑岩特征一致,而且在流纹斑岩的接触带内已揭露到铀矿化,指示窟窿山流纹斑岩的内、外接触带具有良好的找矿前景。更多还原

【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 km². SHRIMP zircon U-Pb dating indicate that the zircon of rhyolite porphyries n(²⁰⁶Pb)/n(²³⁸U) age was 138.4 Ma±1.3 Ma（N=12,MSWD=0.25）, which belongs to the early stage of Early Cretaceous. Kulonghsan rhyolite porphyries have high SiO₂, K₂O, Na₂O, high ratio of FeO^T/MgO, poor Al₂O₃, MgO, CaO, P₂O₅. A/CNK=0.94～1.09, K₂O/Na₂O=1.03～1.30, which belong to the Peraluminous—weakly peraluminous high potassium calcium alkaline series rock. In the SiO₂ vs（Na₂O+K₂O）—CaO and SiO₂ 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), 10000 Ga/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(⁸⁷Sr)/n(⁸⁶Sr)]_i=0.690385～0.724000, relative low Nd(ε_Nd（t）=-16.2～-14.9) and young Nd modle age(t_DM2=2163～2244 Ma), they exhibit low radiogenic Pb istopic compositions, [n(²⁰⁶Pb)/n(²⁰⁴Pb)]_i=16.893～16.922, [n(²⁰⁷Pb)/n(²⁰⁴Pb)]_i =15.393～15.424, [n(²⁰⁸Pb)/n(²⁰⁴Pb)]_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. δ¹⁸O_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.更多还原