松辽盆地西南部上白垩统姚家组原生黏土矿物组合特征及其找铀意义

Characteristics of Primary Clay Minerals in the Upper Cretaceous Yaojia Formation of Southwest Songliao Basin and Their Significance

黏土矿物是砂岩型铀矿表生成矿流体水-岩作用的重要产物。本文以岩心光谱扫描为主要技术手段,结合野外地质编录、偏光显微镜、扫描电镜等方法,首次对松辽盆地西南部钱家店铀矿床及远离矿区的88个钻孔超过9 000 m岩心进行了系统的蚀变矿物填图,提取了主要黏土矿物和Fe^(3+)氧化物信息。结果表明,主要产铀层位姚家组原生黏土矿物组合主要是"伊利石+(蒙脱石)伊蒙混层",仅有少量的高岭石、绿泥石,它们与松辽盆地北部具有相似特征,是沉积期古气候的响应。而成矿段中,高岭石含量与铀矿物具有明显正相关性,是成矿流体轨迹的重要指标。原生砂岩的黏土矿物、Fe^(3+)氧化物矿物(化)信息往往呈现成层性或韵律式变化,而经过成矿流体改造的砂岩,其黏土矿物、Fe^(3+)氧化物信息往往呈现"舌状"或"正态曲线状"的突然变化,这些特征可以成为原生砂岩颜色判别和后生成矿流体追踪的重要指标,它们对砂岩型铀矿成矿规律研究与找矿具有重要意义。

Clay minerals are important products of the epigenetic ore-forming fluid＇s water-rock reaction in sandstone type uranium deposits. In this paper, using the core spectrum scanning technique as the main research method in combination with such means as field geological logging, polarizing microscope and scanning electron microscopy（SEM）, the authors conducted for the first time systematic alteration mineral mapping of 88 drill holes in the Qianjiadian uranium deposit as well as the neighboring areas and extracted information of the main clay minerals and ferric iron oxides. The result shows that the primary clay mineral assemblage of Yaojia Formation, which is the main uranium-producing layer, is ＂illite＋illite and montmorillonite immiscible layer（or montmorillonite）＂, with only a small amount of kaolinite and chlorite. These features are similar to characteristics of clay minerals in northern Songliao Basin, being the palaeoclimate response in the sedimentary period. However, the content of kaolinite has an obvious positive correlation with that of uranium minerals in the ore section, which is an important indicator of the locus of the ore-forming fluid. The ore-forming information of clay minerals and ferric iron oxides of primary sandstone tends to exhibit stratified or rhythmic variation, whereas the information of clay minerals and trivalent iron oxides often exhibit ＂ongue shape＂ or ＂normal curve＂ features. These characteristics serve as important criteria to judge the color of the original sandstone and trace the epigenetic metallogeny, thus having great significance for the study and prospecting of sandstone type uranium deposits.