鄂尔多斯盆地南部烃源岩分布与铀成矿关系研究

Study on the Relationship of Hydrocarbon Source Rock Distribution to Uranium Mineralization in the Southern Ordos Basin

鄂尔多斯盆地砂岩型铀矿资源丰富,其成因与深部油气和富铀烃源岩密切相关,因而具有优越的铀成矿条件和找矿前景。文章总结了盆地南部烃源岩分布特征、含铀性和富铀机理,探讨了铀成矿期与深部富铀烃源岩生排烃高峰期的耦合关系。结果表明,三叠系延长组湖相烃源岩具有整体较高的铀含量,其中长7段烃源岩铀含量最高,平均值达32.8×10^(-6),具有较高的深部铀源潜力;上古生界海陆过渡相的煤系烃源岩铀含量次之,二叠系山西组和泥盆纪本溪组铀含量较高,层段内平均含量分别为8.0×10^(-6)和11.9×10^(-6);下古生界海相烃源岩铀含量整体较低,平均值均小于3.0×10^(-6)。古水体环境是控制烃源岩铀元素丰度的重要因素,古氧相指示因子U_(EF)-Mo_(EF)交会图显示延长组沉积时期古水体多呈缺氧—还原环境,因而具有整体较高的铀含量。盆地南部铀主成矿年龄与三叠系延长组烃源岩生排烃高峰期一致,且最大成矿年龄与烃源岩低熟阶段压实作用孔隙水排出阶段相近,表明盆地深部烃源岩成因流体与铀成矿作用关系密切,深部富铀页岩具有一定的铀源潜力。

Ordos basin is rich in sandstone type uranium resources,which is closely related to deep oil and gas and uranium rich source rock.This paper summarized the distribution characteristics,uranium content and uranium rich mechanism of hydrocarbon source rock in the southern part of the basin,and discussed the coupling relationship between uranium mineralization age and the peak period of hydrocarbon generation and expulsion of deep uranium rich source rocks.The results showed that the lacustrine hydrocarbon source rock of the Triassic Yanchang Formation have high uranium content as a whole,and the hydrocarbon source rock of the Chang 7 Member have the highest uranium content with an average of 32.8×10-6,which is of high potential for deep uranium source.The uranium content of coal seam of marine continental transitional facies of Upper Paleozoic ranks the second,among them,Permian Shanxi Formation and Devonian Benxi Formation is relative higher,with an average of 8.0×10-6 and 11.9×10-6 respectively.The lower Paleozoic marine hydrocarbon source rock has a relatively low uranium content,with an average of less than 3.0×10-6.The paleowater environment is an important factor controlling the uranium abundance of the source rock.The UEF-MoEF cross plot of paleooxygen facies indicator showed that the paleowater during the deposition of the Yanchang Formation was mostly in an anoxic reducing environment,so it had a high overall uranium content.The main uranium mineralization age in the southern part of the basin is consistent with the peak period of hydrocarbon generation and expulsion of the Triassic Yanchang Formation source rock,and the maximum mineralization age is similar to the pore water drainage stage of compaction in the low maturity stage of the hydrocarbon source rock,indicating that the genetic fluid of the deep hydrocarbon source rock in the basin is closely related to uranium mineralization,and the deep uranium rich shale has certain uranium source potential.