松辽盆地协尔苏地区泉头组一段砂体及铀矿化特征分析

CHARACTERISTICS OF URANIUM MINERALIZATION OF THE SANDSTONE OF THE FIRST MEMBER,QUANTOU FORMATION,IN XIERSU DEPRESSION,SONGLIAO BASIN

松辽盆地南部协尔苏凹陷泉头组一段分为上、下两部分，下部为以泥石流为主的冲积扇相沉积，上部为冲积扇-辫状河相沉积．分析表明：下部砂体泥砾混杂、粒度较粗，不利成矿；上部主要发育两层砂体，砂体厚5～40m，延伸稳定，有利于砂岩型铀矿化的形成．根据泉一段砂体的岩石学特征、岩石化学特征、后生氧化-还原特征认为，由于深部有机流体的后生还原作用及基底-盖层贯通断裂继承性活动对下部层位煤层气进行纵向疏导，泉一段砂体后生地球化学环境改变为还原环境，主要表现为发育煤成烃油浸砂岩及烃类质量分数很高，砂岩由原生红色褪色化成灰色、灰绿色；在此基础上，后期叠加层间氧化作用，但由于下部层位煤层气持续作用，本区氧化特征不明显，氧化砂岩以浸染状、斑点状、团块状和条带状残留于还原砂岩中．通过分析协尔苏凹陷钻孔岩心铀钍含量及铀矿化特征，认为达官五家子地段、塔林布敦吐地段泉一段砂体铀含量高，铀的活化迁移作用明显，砂体存在铀的后生富集；铀的存在形式主要为吸附铀，为黏土矿物及有机质，铀矿物主要为沥青铀矿．分析认为研究区具有较好的铀成矿潜力．

The first member of Quantou Formation in Xiersu Depression, Songliao Basin, is divided into two parts. The lower part is dominated by alluvial fan facies; while the upper consists of alluvial fan-braided river facies. Analysis shows that the lower part is composed of mixed mud and gravels with coarse grains, which is adverse to mineralization. The upper part contains two layers of sandstone extending stably, with thickness ranging from 5 to 40 m, which is favorable for uranium mineralization. Because of the epigenetic reduction in deep organic fluid and the guidance of base-cap linked faults, the CBM in the lower layer moved upward, making the Quantou Formation changed to a reducing geochemical environment. By analysis of the contents of uranium and thorium and the characters of uranium mineralization, it is suggested that the amount of uranium is high in the sandstone of the first member of Quantou Formation in Daguanwujiazi and Talinbuduntu, with obvious activation and migration of uranium and epigenetic enrichment. The uranium exists mainly in adsorbent as clay minerals and organic matter. The main uranium mineral is pitchblende. It is concluded that the study area has a good potential for uranium mineralization.