鄂尔多斯盆地三叠系延长组油页岩中铀的富集机理研究

The oil shales of the Chang 7 member of the Yanchang Formation in the Erdos Basin were deposited during maximum lake extension during the Late Triassic. The Chang 7 oil shales are rich in organic carbon, pyrite and collophane, and show a remarkable positive uranium anomaly. The sources of uranium in the oil shale were argumentative. It is vague about the modes of occurrence of uranium and the factors which affect the enrichment of uranium. The roles of organic matter and collophane are unclear. Therefore, it is significant to find out the occurrence and the source of uranium in the chang 7 oil shales and discuss the factors of the enrichment of uranium in the chang 7 oil shales, it is important to study the enrichment mechanism of uranium in the black shale. This project will confirm the modes of occurrence of uranium and discuss the factors affecting uranium enrichment in the chang 7 oil shales by petrology, phase analysis, the mineral composition, sequential extraction procedure and radiography. Find out the source of uranium in the chang 7 oil shales by major and trace element analysis, radio isotope analysis, in situ trace element and isotope. Study the process of migration and enrichment of uranium and discuss the roles of organic matter and collophane in the concentration of uranium combind with simulation experiment. This study should help to identify the mechanism of uranium enrichment in lacustrine sediment and shed light on the possible origin of these oil source rocks.

在鄂尔多斯盆地三叠系延长组长7段油层组中广泛分布着数米到数十米的油页岩，该油页岩富含有机碳、黄铁矿和胶磷矿，而且异常富集放射性铀元素。该油页岩中铀的物质来源存在争议，铀的的赋存状态、铀异常富集的原因还不明确，有机质和胶磷矿在铀富集过程中的作用也不清楚。因此，查明长7油页岩中铀的赋存状态、铀的物质来源，探讨长7油页岩的铀富集的影响因素，对于研究黑色页岩中铀的富集机理具有重要的意义。本项目拟通过岩石学特征观察、化学物相分析、矿物组成分析、逐级化学提取实验，结合放射性照相等方法查明油页岩中铀的赋存状态和富集因素，通过主、微量元素分析、同位素分析以及微区微量元素和同位素分析明确铀的来源，结合模拟实验研究铀的运移、富集过程，探讨有机质、胶磷矿等在铀富集过程中的作用，综合前人资料总结黑色页岩中铀的富集机理。

对鄂尔多斯盆地上三叠统长7段油页岩进行系统观察与采样，并进行岩石矿物学、 元素地球化学、有机地球化学、同位素地球化学等系统分析测试，开展了油页岩中铀的富集机理研究。有机地球化学参数和岩石地球化学参数表明长7优质烃源岩形成于缺氧的沉积环境，而延长组其它层段泥岩形成于相对氧化的沉积环境。长7早期频繁的火山喷发活动为长7油页岩提供了丰富的铀源。通过电子探针、LA-ICPMS、逐级化学提取、α径迹蚀刻等方法研究了长7优质烃源岩中铀的赋存状态，实验结果表明在长7油页岩中铀以类质同象赋存于胶磷矿中、以吸附态和有机质中。在缺氧的沉积环境下，成岩作用早期底层水和裂隙水的交换作用使得铀从凝灰岩中向延长组长7黑色页岩中扩散，赋存于胶磷矿和有机质纹层中。总之，缺氧的沉积环境、丰富的铀源、高含量的有机质及胶磷矿共同促进了铀在鄂尔多斯盆地上三叠统延长组长7优质烃源岩中的富集。