CSAMT在松辽盆地梅里斯地区铀矿勘查中的应用

The application of CSAMT in uranium exploration in Meilisi area of Songliao basin

上白垩统四方台组是松辽盆地北部铀矿找矿的主要层位之一,其铀矿化主要受控于上白垩纪曲流河三角洲沉积体系,工业铀矿体主要在底部砂岩层富集,多呈板状、透镜状,矿体规模与砂体规模、层数等密切相关,砂体规模越大,矿化层越多,矿体规模越大,反之则规模越小。但是上白垩统四方台组底部砂体在松辽盆地西部超覆带内梅里斯地区发育情况尚不明确。以可控源音频大地电磁测深(CSAMT)为手段,利用Occam算法反演得到研究区电阻率断面,结合研究区内各地层岩石电阻率特征,分析了研究区内盖层结构,尤其是找矿目的层上白垩统四方台组的空间分布特征,同时还推断了基底起伏特征以及断裂走向、倾向及其延深情况。研究结果显示:研究区内四方台组河流相砂体主要分布于研究区的东南部,多呈透镜状,整体表现为自南东向北西呈逐渐尖灭的特征,厚度一般不超过180 m。研究成果为钻探工程的部署提供了依据。

Sifangtai formation of the Upper Cretaceous is one of the main horizons for uranium exploration in the northern part of Songliao basin.The uranium mineralization is mainly controlled by the sedimentary system of the Upper Cretaceous meandering river delta.Uranium deposits are mainly enriched in the bottom sandstone layer,mostly in plate-like and lens shaped shapes.The size of the ore body is closely related to the size and number of layers of the sand body,the larger the sand body size is,the larger the ore body size is.Conversely,the smaller the size of ore body is.However,the development of sand bodies at the bottom of the Upper Cretaceous Sifangtai formation in Meilisi area of the western overlying zone of Songliao basin is not yet clear,in this article controlled source audio-frequency magnetotelluric(CSAMT)was used to invert the resistivity section of the study area with the Occam algorithm.Combined with the resistivity characteristics of rocks in various layers of the study area,the structure of the cap rock was analyzed,especially the spatial distribution characteristics of the Cretaceous Sifangtai formation in the target layer for ore exploration.At the same time,the characteristics of basement undulation,as well as strike,dip,and depth of the fault were also inferred.The research showed that the river facies sand bodies of the Sifangtai formation in the study area are mainly distributed in the southeastern part of the study area,mostly in a lens shape,showing a gradually pinching feature from southeast to northwest,with a thickness generally not exceeding 180 meters.The achievements of this measurement provided a basis for the deployment of featured drilling engineering.