鄂尔多斯盆地延长组长7段富铀烃源岩的铀赋存状态与富集机理  

Occurrence and concentration of uranium in the hydrocarbon source rocks of Chang 7 member of Yanchang Formation, Ordos basin.

作　　者：秦艳[1] 张文正[2] 彭平安[3] 周振菊[1,4] 

机构地区：[1]中国科学院广州地球化学研究所,成矿动力学重点实验室,广州510640 [2]中国石油长庆油田分公司勘探开发研究院,西安710018 [3]中国科学院有机地球化学国家重点实验室,广州510640 [4]中国科学院研究生院,北京100049

出　　处：《岩石学报》2009年第10期2469-2476,共8页Acta Petrologica Sinica

基　　金：国家基础研究发展计划(973)项目(2003CB214600, 2006CB403500);国家自然科学基金(40773028)资助.

摘　　要：鄂尔多斯盆地晚三叠世延长组长7段是一套深湖相富铀烃源岩,岩石富含草莓状黄铁矿、有机质纹层、胶磷矿等。本文通过电子探针、LA-ICPMS、逐级化学提取、α径迹蚀刻等方法研究了长7段烃源岩中铀的赋存状态,发现烃源岩中约50%以上的铀赋存于胶磷矿中,20%以上的铀以吸附形式赋存于有机质中。因此,胶磷矿在铀的富集过程中起了重要作用。岩石地球化学参数表明长7段烃源岩沉积于缺氧环境,频繁的火山喷发活动为长7段富铀烃源岩层提供了丰富的铀源。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铀从凝灰岩中向长7段黑色页岩中迁移,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、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段富铀烃源岩中的形成。The Seventh Member (abbreviated to Chang-7) of the Yanchang Formation of I,ate Triassic in the Ordos Basin is a lacustrume suite of U-rich hydrocarbon source rocks. These rocks within the Chang-7 Member are rich in frambodial pyrite, organic matter laminas and collophane. In this paper the uranium occurrence in the rocks of the Chang-7 Member were studied using electron microscopy, LA-ICPMS, sequential extraction procedure and a-track etching. The results show that in the source rocks more than 50% uranium occurs in collophane, and more than 20% uranium is absorbed in organic matter. Collophane plays an important role in the enrichment of uranium. The petrochemical parameters show that the rocks of the Chang-7 Member were formed in anoxic sedimentary environment. Frequent volcanic eruption in the early deposition of the Chang-7 Member provided abundant uranium for the U-rich hydrocarbon source rocks. In the anoxic sedimentary environment during the early diagenetic stage, uranium migrated from tuffs to black shale of the Chang-7 Member and enriched in collophanes and organic matter laminas as a result of exchange between bottom and interstitial waters. In a word, the anoxic deposition environment, the U-abundant tuffs, and the high contents of organic matter and collophane led to the enrichment of uranium in the U-rich hydrocarbon source rocks of the Chang-7 Member in the Ordos basin.

关 键 词：鄂尔多斯盆地 延长组长 烃源岩层 铀赋存状态 富集机理 胶磷矿 有机质 沉积环境 逐级化学提取 岩石地球化学 缺氧环境 源岩沉积 吸附形式 晚三叠世 上三叠统 喷发活动 径迹蚀刻 交换作用 黑色页岩 富集过程 

分 类 号：P58[天文地球—岩石学]