鄂尔多斯盆地北部纳岭沟铀矿直罗组含铀岩系蚀源区识别

Identification of provenance on uranium-bearing rocks from the Zhiluo Formation in the Nanlinggou uranium deposit,northern Ordos Basin

【研究目的】纳岭沟铀矿是鄂尔多斯盆地北部最重要铀矿床之一,识别其含铀岩系物源区对于深化成矿作用和找矿预测具有实际意义。【研究方法】笔者通过岩石学、重矿物学、地球化学和沉积相分析等方法,识别了纳岭沟铀矿床中侏罗统直罗组含铀岩系的蚀源区。【研究结果】含铀岩系岩石类型主要为中粗长石砂岩,碎屑成分有长石、石英、黑云母和花岗岩岩屑、变质岩岩屑等,分选中等至差;碎屑多呈棱角状、次棱角状,少数为次滚圆状,磨圆度差至中等。重矿物分布极不均匀,呈棱角状、次棱角状、次滚圆状,磨圆度差至中等;ZTR(锆石+电气石+金红石)指数2%~10%。电气石、尖晶石、锐钛矿、角闪石、碳硅石等呈集簇状分布;碎屑锆石延长系数主要为1~2.2,其次2.2~3.2。稀土元素球粒陨石配分曲线形态相似,ΣREE值104.75×10^(-6)~283.86×10^(-6),LREE/HREE值0.13~0.47,La/Yb值9.60~32.66,元素含量变化幅度大。纳岭沟地区含铀岩系砾质、砂质辫状河沉积相由矿区北东方向至南西方向延展,与高厚度砂体、高含砂率砂体分布规律一致。【结论】纳岭沟铀矿直罗组含铀岩系蚀源区为矿区北东缘的晋蒙交界地带的前中侏罗世隆起区的太古代片麻岩、古元古代孔兹岩、二长花岗岩和古生代岩浆岩、沉积岩和中生代沉积岩、火山岩。

This paper is the result of mineral exploration engineering.[Objective]The Nalinggou uranium deposit is one of the most important uranium deposits in northern Ordos Basin.Identification onthe provenance of uranium bearing rocks is of practical significance for deepening mineralization and prospecting prediction.[Methods]By means of petrology,heavy mineralogy,geochemistry and sedimentary facies analysis,the authors have identified the provenance of the uranium bearing rocks from the Middle Jurassic Zhiluo Formation in the Nalinggou uranium deposit.[Results]The uranium-bearing rocks are dominantly composed of medium coarse arkose.The clastic components are feldspar,quartz,biotite,debrises of granite and metamorphic rock,etc.,with medium to poor sorting.The clasts are mostly angular and sub-angular,and a few are sub-rounded,with poor to medium roundness.The distribution of heavy minerals is extremely uneven,in angular,sub angular and sub rounded shapes,with poor to medium roundness.The ZTR(zircon+tourmaline+rutile)index varies of 2%-10%.The tourmaline,spinel,anatase,amphibole and carbosilica are distributed in clusters.The extension coefficient of detrital zircon is mainly in the range of 1-2.2,followed by the range of 2.2-3.2.The rocks exhibit similar chondrite-normalized patterns with great elemental variations among different samples.TheΣREE,LREE/HREE,and La/Yb values are in the range of 104.75×10^(-6)~283.86×10^(-6),0.13-0.47,and 9.60-32.66 respectively.The uranium bearing strata exhibit highly thick sand bodies.In the mining area,the sedimentary facies extend synchronously from the northeast to the southwest.[Conclusions]In conclusion,it is generally considered that the uranium bearing rocks of the Zhiluo Formation in the Nalinggou uranium deposit is mainly proximal provenance,with a small amount of distal provenance.The sourced rocks are the pre-Jurassic bedrock area exposed at the boundary between Shaanxi and Inner Mongolia on the northeast edge of the mining area.The rock types include Archean gneiss,Paleoproterozoic Khondalite,magmatic rocks,Paleozoic magmatic rocks,sedimentary rocks and Mesozoic volcanic rocks,of which the khondalite belt provides the most important materials.