豫西卢氏县柳树湾伟晶岩型铀矿床岩石地球化学特征及其成矿意义

Petrogeochemical Characteristics and Metallogenic Significance of Liushuwan Pegmatite-type Uranium Deposit in Lushi County,Western Henan Province

伟晶岩型铀矿床由于其易规模化和便于开采的特点成为非常重要的铀矿床类型。该矿床类型在我国以商-丹地区最具有代表性。经过近几年的铀矿勘测,在豫西柳树湾地区发现了一定规模的铀矿床,通过详细的野外勘测以及岩石学和地球化学分析,显示豫西柳树湾矿体的形态为脉状或透镜状;赋矿层段由于强烈的钾化作用而表现出肉红色,具发育烟灰色石英以及矿物颗粒明显增大等特征;主量元素显示研究区整体具有富Si、K和Al过饱和以及低氧逸度等特征,含矿伟晶岩段稀土元素的配分模式呈现右倾型、强烈Eu亏损的特征,且∑REE、δEu、Th、Ti、V、Zn、Pb等特征元素含量与U关系密切。通过对研究区与光石沟铀矿床和小花岔铀矿床进行对比显示,发现这3个地区在矿体形态、矿物组成和岩石学特征方面极为相似,但在副矿物类型上柳树湾地区出现铀钍石;柳树湾与小花岔铀矿床的SiO_(2)含量与U呈现正向相关关系,但光石沟铀矿床呈现负向相关关系;柳树湾与小花岔铀矿床非含矿层段的稀土元素配分模式图均呈现平滑特征,但光石沟铀矿床呈右倾特征。由于小花岔铀矿床形成的时间最早,且光石沟与小花岔铀矿床更靠构造中心,使其在时间尺度、岩浆侵入和构造作用的联合控制下造成了柳树湾、小花岔和光石沟赋矿围岩的地球化学特征的差异。

Pegmatite-type uranium deposits become a very important uranium deposits type due to their large scale and easy mining.Typical pegmatite-type uranium deposits in China are produced in Shang-Dan area of Lushi country.After recent years’exploration,uranium deposits have been discovered in Liushuiwan area,western Henan.Detailed field surveys and petrological and geochemical analyses found that the ore bodies are in shape of vein-like or lens,the ore hosting rocks are of fleshy red color due to strong the potassium-metasomatism,and the quartz is smoky gray with enlarged grain.The host rocks are rich in Si,K,and oversaturated in Al,low in oxygen fugacity,the uranous pegmatite is of right inclined REE pattern with strong Eu depletion,and the∑REE,δEu,Th,Ti,V,Zn,Pb are closely related to U.Comparison between the uranium deposit in Lushuiwan,Guangshigou and Xiaohuacha showed that they are similar in ore body morphology,main mineral composition and petrological characteristics,but there are some other differences.In Liushuwan,there occurred the uranthorite;in Liushuwan and Xiaohuacha the SiO_(2) is positively correlated with uranium,while in Guangshigou SiO_(2) is negatively correlated with uranium;REE patterns of host rocks in the Liushuwan and Xiaohuacha are nearly horizontal,while in Guangshigou REE pattern is right-inclined.The reason cause the difference may rise from the difference of forming age and the structural location between Liushuwan,Xiaohuacha and Guangshigou,deposit in Liushuwan area formed earlier and located farther from the structure-magmatism center,which comprehensively control of metallogenic scale,magmatic intrusion and tectonic processes and resulted in the difference.