【作者】 张本浩；

【导师】 吴柏林；

【作者基本信息】 西北大学 ， 矿物学、岩石学、矿床学， 2011， 硕士

【摘要】 鄂尔多斯盆地晚三叠世延长组长7段底部的烃源岩中,存在着明显的放射性异常现象,研究表明,这种放射性异常主要是由放射性铀元素引起的。该层段主要是一套深湖相的富铀烃源岩,其矿物学特点是富含有胶磷矿、草莓状黄铁矿、有机质等。综合运用薄片鉴定、光片观察,扫描电镜、电子探针、能谱分析、主量与微量元素测试分析、逐级化学提取以及α放射性照相等多项现代分析测试技术,详细研究了长7段底部富铀烃源岩的地质地球化学特征、铀的赋存状态,明确了其中主量、微量元素与U的相关性,分析了烃源岩中铀富集的形成环境,探讨了铀的来源及富集机制。在铀的赋存状态研究中首次发现了独立铀矿物类型。铀除了以类质同象赋存于胶磷矿中,以及以吸附态赋存于黄铁矿和有机质中外,尚发现以独立铀矿物形式存在于胶磷矿中,铀矿物颗粒大小在2-14μm之间,矿物类型为铀石、含钛铀矿物。这表明其形成于中低温、还原-强还原环境,因而认为长7富铀烃源岩曾经历低温热液作用。进一步研究表明,胶磷矿中所占铀的总比例可达50%,黄铁矿中吸附的铀含量可占20%,另外铀尚有少量被吸附在有机质及粘土矿物中,比例应在10%以下。综合长7烃源岩存在大量薄层火山凝灰岩、大量微生物活动及遭受过热液作用的认识,认为长7烃源岩中铀的来源及大量富集是生物作用、火山喷发活动及湖底热液活动等共同作用的结果。更多还原

【Abstract】 At the bottom of the Chang7 member of Yan Chang Formation in Ordos basin,the source rocks, show obviours radioactive abnormal phenomenon which mainly caused by radioactive uranium element based on study. The U-rich source rocks developed in the deep lake that charactered by concentrating on collophane, frambodial pyrite, organic matter and so on in mineralogy.With the help of synthesis using many modern analysis and test technologies, including thin slice identification, scanning electron microscope, electron probe,energy spectrum analysis, elements geochemistry analysis, sequential chemical extraction,α-radiography photo and so on,we studied the geochemical characteristics of the source rocks at the bottom of Chang7 formation and the occurrence of uranium element detailedly.At the same time,we found the relationship between major and trace elements and uranium element.What is more,we always analyzed the occurrence condition of U-rich source rocks, the origin of uranium in the source rocks and the mechanism of its occurrence.We,firstly, found the independent uranium mineral in the U-rich source rocks in Chang7 member.Uranium can occurrent in collophane as independent mineral more than allomerism in collophane or absorbing in pyrite and organic matters.The independent mineral can divided into uranium stone,and titanium with their particle size between 2μm-14μm.The evidence indicates that it developed in the low to moderate temperature and reduced to strong reduced environment and the U-rich source rocks in Chang7 formation had influend by epithermal action. For the further study,the highest proportion of uranium in the collophane is 50%,the proportion of absorbing uranium in pyrite is nearly 20%.There is less than 10% uranium absorbing in organic matters and clay mineral by supposed.Integrating the recognition that there is the thin bed of ash tuff,evidences of activities of lots microbe and epithermal action in Chang7 formation,we hold that the origin and the occurrence of urament in Chang7 source rocks is the synthetical result of biogenicagency, volcanic action, hydrothermal fluid action at the bottom of the deep lake and so on.更多还原