伊犁盆地郎卡地区铀矿目的层砂岩特征及成矿意义

摘要

郎卡地区是在伊犁盆地南缘近年发现的又一砂岩型铀矿有利成矿地段.通过野外露头岩石、钻孔岩心观察和系统取样,对郎卡地区盆缘和盆内目的层砂岩进行了详细的显微镜下鉴定,以及和蒙其古尔地区岩石学特征进行了对比,并对郎卡地区铀矿石进行了电子探针分析.研究结果表明,研究区目的层砂岩有着较低的成分成熟度和结构成熟度,为近源沉积产物;成岩作用过程中碎屑颗粒普遍发育溶蚀作用,形成许多溶蚀孔,这些次生孔隙是氧化流体及铀运移的有利通道;岩石中较多的碳酸盐化为该区的显著特点,有别于相邻的蒙其古尔地区岩石特征,郎卡盆缘露头砂岩具有基底式胶结的碳酸盐化,使后期的地表氧化流体很难进入地层形成大规模的氧化带进而成矿;电子探针分析结果表明,朗卡地区铀的主要存在形式为沥青铀矿,还有少量的铀石、钛铀矿以及显微吸附态铀,这与蒙其古尔矿床基本相同.综合郎卡地区的岩石学和铀的存在形式等特征,认为郎卡地区和蒙其古尔矿床可能有着相似的铀成矿作用,但成矿阶段中缺少晚期地表流体对矿床的叠加改造作用而区别于蒙其古尔矿床.%Langka is another metallogenic potential area of the interlayer oxidation zone sandstone-type uranium that was found in the southern margin of the Yili Basin in recent years.Based on the observation and systematic sampling for the rocks from field outcrop and drilling cores, the microscopy identification of the target layer sand-stones from both margin and inner of the basin was performed,and a comparison of the petrographic characteristics between the sandstones from Langka and Mengqiguer was made,and the electron microprobe analysis was also per-formed on the ore samples.The results show that the sandstones are sedimentary products adjacent to the sources due to the low compositional maturity and textural maturity.The dissolution occurs widespreadly on the clastic parti-cles in the process of the diagenesis,and produces a lot of dissolved pores which are the favorale migration channels for the oxidized fluid and uranium.Differing from the petrologic characteristics of Mengqiguer,the major carbonate in the rocks is a distinctive characteristic in Langka,while the basal carbonate cement of the rocks from basin mar-gin in Langka makes it difficult for the later oxidized surface water to enter the layer and form large -scale interlayer oxidation and ore.The results of the EMPA show that the main existing forms of the uranium in Langka are pit-blende and a small number of coffinite,brannerite and micro uranium with absorption state,which is basically same to Mengqiguer Deposit.Combined petrologic characteristics,uranium existing form and so on,the mineralization in Langka is similar to Mengqiguer Deposit,but the stage of mineralization is different from Mengqiguer Deposit due to a lack of the superposition and transformation of the deposit by the later surface water.