二连盆地乔尔古-齐哈地区赛汉组上段砂体成因分析及找矿意义

Genesis Analysis of Sandstone of the Upper Member of Saihan Formation and Its Prospecting Significance in the Qiaoergu-Qiha Area of Erlian Basin

二连盆地乔尔古-齐哈地区研究和勘探控制程度较低,而砂体结构、规模及成因分析是砂岩型铀矿找矿预测的首要任务。通过露头调查、钻孔岩心观察、砂岩粒度分析及砂体展布特征,对研究区砂岩型铀矿目的层赛汉组上段沉积体系进行恢复。研究发现,赛汉组上段砂体呈条带状,总体呈南西-北东向展布,沉积环境为河流体系,中下部(Ⅰ、Ⅱ旋回)为辫状河沉积,可识别出心滩沉积、河道滞留沉积及泛滥平原沉积等沉积微相,砂体规模大,连通性好;顶部(Ⅲ旋回)为曲流河沉积,可识别出边滩沉积、河道滞留沉积及泛滥平原沉积等沉积微相,砂体规模小,非均质性增强,连通性差。辫状河相为研究区砂岩型铀矿有利沉积相带,铀矿化垂向上分布于赛汉组上段中下部(Ⅰ、Ⅱ旋回)辫状河心滩及河道滞留沉积砂体中,其中Ⅱ旋回铀矿化最为发育,平面上分布于辫状河道拐弯、交汇、心滩短轴两侧向泛滥平原过渡部位。目的层沉积体系分析,对铀成矿空间定位及指导勘探部署具有重要意义。

The study and exploration level is relatively low in the Qiaoergu-Qiha area of Erlian Basin. In order to prospecting and predicting sandstone type uranium mineralization, the sand body structure, scale and genesis should be studied first. In this paper, the genesis of target bed for sandstone type uranium deposits in the Upper Member of Saihan Formation was analyzed in detail by outcrop investigation, core observation, sandstone grain size analysis and sand distribution system mapping. It was found that the sand body in the Upper Member of Saihan Formation was banded and generally distributed from southwest to northeast. The sedimentary environment was river sedimentary system and the middle and lower part(Depositional cycle Ⅰ and Ⅱ) of the Upper Member was braided river deposit with large scale sand body and good connectivity, while the meandering stream system developed in the upper part with small scale sand body and poor connectivity. Braided river facies is the favorable sedimentary facies for sandstone type uranium mineralization in the study area. Uranium mineralization is vertically distributed in the braided river sand body in the middle and lower part( Depositional cycles Ⅰ and Ⅱ) of the Upper Member of Saihan Formation, and distributed in the places where the braided river turns, intersects and the transition zone from both sides of the short axis of the heart beach to the flood plain.